WorldWideScience

Sample records for random quantum magnets

  1. Quantum random number generators

    Science.gov (United States)

    Herrero-Collantes, Miguel; Garcia-Escartin, Juan Carlos

    2017-01-01

    Random numbers are a fundamental resource in science and engineering with important applications in simulation and cryptography. The inherent randomness at the core of quantum mechanics makes quantum systems a perfect source of entropy. Quantum random number generation is one of the most mature quantum technologies with many alternative generation methods. This review discusses the different technologies in quantum random number generation from the early devices based on radioactive decay to the multiple ways to use the quantum states of light to gather entropy from a quantum origin. Randomness extraction and amplification and the notable possibility of generating trusted random numbers even with untrusted hardware using device-independent generation protocols are also discussed.

  2. Quantum randomness and unpredictability

    Energy Technology Data Exchange (ETDEWEB)

    Jaeger, Gregg [Quantum Communication and Measurement Laboratory, Department of Electrical and Computer Engineering and Division of Natural Science and Mathematics, Boston University, Boston, MA (United States)

    2017-06-15

    Quantum mechanics is a physical theory supplying probabilities corresponding to expectation values for measurement outcomes. Indeed, its formalism can be constructed with measurement as a fundamental process, as was done by Schwinger, provided that individual measurements outcomes occur in a random way. The randomness appearing in quantum mechanics, as with other forms of randomness, has often been considered equivalent to a form of indeterminism. Here, it is argued that quantum randomness should instead be understood as a form of unpredictability because, amongst other things, indeterminism is not a necessary condition for randomness. For concreteness, an explication of the randomness of quantum mechanics as the unpredictability of quantum measurement outcomes is provided. Finally, it is shown how this view can be combined with the recently introduced view that the very appearance of individual quantum measurement outcomes can be grounded in the Plenitude principle of Leibniz, a principle variants of which have been utilized in physics by Dirac and Gell-Mann in relation to the fundamental processes. This move provides further support to Schwinger's ''symbolic'' derivation of quantum mechanics from measurement. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  3. Double-negative multilayer containing an extrinsic random layer thickness magnetized cold plasma photonic quantum-well defect

    Science.gov (United States)

    Nayak, Chittaranjan; Aghajamali, Alireza; Saha, Ardhendu

    2017-11-01

    Theoretically, the transmission properties of a symmetric double-negative metamaterial one-dimensional photonic crystal containing an extrinsic random layer thickness magnetized cold plasma photonic quantum-well defect structure have been investigated. From the numerical results performed by characteristics matrix method, it is found that, such type of structure possesses a transmission peak within the zero-nbar gap. To design a tunable microwave filter, the effects of many parameters such as randomness of layer thickness of the multilayer defect in terms of standard deviation (σ), strength of external magnetic field (B) and electron density of magnetized cold plasma (ne) on transmission peak is discussed. Our findings show that the histogram for the central frequency of the transmission peaks becomes wider with respect to smaller values of σ. In addition, in the case of B, our investigations also reveal that the histogram shifts to the higher frequency range and vice versa while considering the case of ne . These findings help to design a tunable filter for different microwave applications.

  4. Random Quantum Dynamics: From Random Quantum Circuits to Quantum Chaos

    Science.gov (United States)

    Brown, Winton G.

    Quantum circuits consisting of single and two-qubit gates selected at random from a universal gate set are examined. Specifically, the asymptotic rate for large numbers of qubits n and large circuit depth k at which t-order statistical moments of the matrix elements of the resulting random unitary transformation converge to their values with respect to the invariant Haar measure on U(2 n) are determined. The asymptotic convergence rate is obtained from the spectral gap of a superoperator describing the action of the circuit on t-copies of the system Hilbert space. For a class of random quantum circuits that are reversible and invariant under permutation of the qubit labels, the gap and hence the asymptotic convergence rate is shown to scale as ˜ 1/n for sufficiently large n, with a coefficient that may in general depend on t. Bounds are derived between the convergence rates for a broader class of reversible random quantum circuits and the convergence rates of second order moments of irreversible random quantum circuits are examined through a mapping to a Markov chain. Weak constraints are constructed for finite moments of matrix elements of local observables with respect to the eigenvectors of general many-body Hamiltonians in the thermodynamic limit. This is accomplished by means of an expansion in terms of polynomials which are orthogonal with respect to the density of states. The way in which such constraints are satisfied is explored in connection to non-integrability and is argued to provide a general framework for analyzing many-body quantum chaos. Hamiltonians consisting of the XX-interaction between spin-1/2 particles (qubits) which are nearest neighbors on a 3-regular random graph (non-integrable), and an open chain (integrable), are diagonalized numerically to illustrate how the weak constraints can be satisfied. The entanglement content of the eigenvectors of chaotic many-body Hamiltonians is discussed as well as the connection between quantum chaos and

  5. Dissipative random quantum spin chain with boundary-driving and bulk-dephasing: magnetization and current statistics in the non-equilibrium-steady-state

    Science.gov (United States)

    Monthus, Cécile

    2017-04-01

    The Lindblad dynamics with dephasing in the bulk and magnetization-driving at the two boundaries is studied for the quantum spin chain with random fields h j and couplings J j (that can be either uniform or random). In the regime of strong disorder in the random fields, or in the regime of strong bulk-dephasing, the effective dynamics can be mapped onto a classical simple symmetric exclusion process with quenched disorder in the diffusion coefficient associated to each bond. The properties of the corresponding non-equilibrium-steady-state in each disordered sample between the two reservoirs are studied in detail by extending the methods that have been previously developed for the symmetric exclusion process without disorder. Explicit results are given for the magnetization profile, for the two-point correlations, for the mean current and for the current fluctuations, in terms of the random fields and couplings defining the disordered sample.

  6. Quantum Spin Stabilized Magnetic Levitation

    Science.gov (United States)

    Rusconi, C. C.; Pöchhacker, V.; Kustura, K.; Cirac, J. I.; Romero-Isart, O.

    2017-10-01

    We theoretically show that, despite Earnshaw's theorem, a nonrotating single magnetic domain nanoparticle can be stably levitated in an external static magnetic field. The stabilization relies on the quantum spin origin of magnetization, namely, the gyromagnetic effect. We predict the existence of two stable phases related to the Einstein-de Haas effect and the Larmor precession. At a stable point, we derive a quadratic Hamiltonian that describes the quantum fluctuations of the degrees of freedom of the system. We show that, in the absence of thermal fluctuations, the quantum state of the nanomagnet at the equilibrium point contains entanglement and squeezing.

  7. Certified randomness in quantum physics.

    Science.gov (United States)

    Acín, Antonio; Masanes, Lluis

    2016-12-07

    The concept of randomness plays an important part in many disciplines. On the one hand, the question of whether random processes exist is fundamental for our understanding of nature. On the other, randomness is a resource for cryptography, algorithms and simulations. Standard methods for generating randomness rely on assumptions about the devices that are often not valid in practice. However, quantum technologies enable new methods for generating certified randomness, based on the violation of Bell inequalities. These methods are referred to as device-independent because they do not rely on any modelling of the devices. Here we review efforts to design device-independent randomness generators and the associated challenges.

  8. Certified randomness in quantum physics

    Science.gov (United States)

    Acín, Antonio; Masanes, Lluis

    2016-12-01

    The concept of randomness plays an important part in many disciplines. On the one hand, the question of whether random processes exist is fundamental for our understanding of nature. On the other, randomness is a resource for cryptography, algorithms and simulations. Standard methods for generating randomness rely on assumptions about the devices that are often not valid in practice. However, quantum technologies enable new methods for generating certified randomness, based on the violation of Bell inequalities. These methods are referred to as device-independent because they do not rely on any modelling of the devices. Here we review efforts to design device-independent randomness generators and the associated challenges.

  9. Logical independence and quantum randomness

    Energy Technology Data Exchange (ETDEWEB)

    Paterek, T; Kofler, J; Aspelmeyer, M; Zeilinger, A; Brukner, C [Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Vienna (Austria); Prevedel, R; Klimek, P [Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna (Austria)], E-mail: tomasz.paterek@univie.ac.at

    2010-01-15

    We propose a link between logical independence and quantum physics. We demonstrate that quantum systems in the eigenstates of Pauli group operators are capable of encoding mathematical axioms and show that Pauli group quantum measurements are capable of revealing whether or not a given proposition is logically dependent on the axiomatic system. Whenever a mathematical proposition is logically independent of the axioms encoded in the measured state, the measurement associated with the proposition gives random outcomes. This allows for an experimental test of logical independence. Conversely, it also allows for an explanation of the probabilities of random outcomes observed in Pauli group measurements from logical independence without invoking quantum theory. The axiomatic systems we study can be completed and are therefore not subject to Goedel's incompleteness theorem.

  10. Magnetically driven quantum heat engine.

    Science.gov (United States)

    Muñoz, Enrique; Peña, Francisco J

    2014-05-01

    We studied the efficiency of two different schemes for a magnetically driven quantum heat engine, by considering as the "working substance" a single nonrelativistic particle trapped in a cylindrical potential well, in the presence of an external magnetic field. The first scheme is a cycle, composed of two adiabatic and two isoenergetic reversible trajectories in configuration space. The trajectories are driven by a quasistatic modulation of the external magnetic-field intensity. The second scheme is a variant of the former, where the isoenergetic trajectories are replaced by isothermal ones, along which the system is in contact with macroscopic thermostats. This second scheme constitutes a quantum analog of the classical Carnot cycle.

  11. Quantum random oracle model for quantum digital signature

    Science.gov (United States)

    Shang, Tao; Lei, Qi; Liu, Jianwei

    2016-10-01

    The goal of this work is to provide a general security analysis tool, namely, the quantum random oracle (QRO), for facilitating the security analysis of quantum cryptographic protocols, especially protocols based on quantum one-way function. QRO is used to model quantum one-way function and different queries to QRO are used to model quantum attacks. A typical application of quantum one-way function is the quantum digital signature, whose progress has been hampered by the slow pace of the experimental realization. Alternatively, we use the QRO model to analyze the provable security of a quantum digital signature scheme and elaborate the analysis procedure. The QRO model differs from the prior quantum-accessible random oracle in that it can output quantum states as public keys and give responses to different queries. This tool can be a test bed for the cryptanalysis of more quantum cryptographic protocols based on the quantum one-way function.

  12. Magnetic exchange disorder in low-dimensional quantum magnets

    Energy Technology Data Exchange (ETDEWEB)

    Blackmore, W.J.A. [U. Warwick, Physics; Goddard, P.A. [U. Warwick, Physics; Xiao, F. [U. Bern, Chemistry; Landee, C.P. [Clark University, Chemistry; Turnbull, M. M. [Clark University, Chemistry; Lancaster, T [U. Durham, Physics; Singleton, John [Los Alamos National Laboratory

    2017-02-13

    Low-dimensional quantum magnetism is currently of great interest due to the fact that reduced dimensionality can support strong quantum fluctuations, which may lead to unusual phenomena and quantum-critical behavior. The effect of random exchange strengths in two-dimensional (2D) antiferromagnets is still not fully understood despite much effort. This project aims to rectify this by investigating the high-field properties of the 2D coordination polymer (QuinH)2Cu(ClxBr1-x)4.2H2O. The exchange pathway is through Cu-Halide-Cu bonds, and by randomizing the proportion of chlorine and bromine atoms in the unit cell, disorder can be introduced into the system.

  13. Quantum Theory of Magnetism

    CERN Document Server

    Nolting, Wolfgang

    2009-01-01

    Magnetism is one of the oldest and most fundamental problems of Solid State Physics although not being fully understood up to now. On the other hand it is one of the hottest topic of current research. Practically all branches of modern technological developments are based on ferromagnetism, especially what concerns information technology. The book, written in a tutorial style, starts from the fundamental features of atomic magnetism, discusses the essentially single-particle problems of dia- and paramagnetism, in order to provide the basis for the exclusively interesting collective magnetism (ferro, ferri, antiferro). Several types of exchange interactions, which take care under certain preconditions for a collective ordering of localized or itinerant permanent magnetic moments, are worked out. Under which conditions these exchange interactions are able to provoke a collective moment ordering for finite temperatures is investigated within a series of theoretical models, each of them considered for a very spec...

  14. A Quantum Theory of Magnetism

    Directory of Open Access Journals (Sweden)

    Gift S.

    2009-01-01

    Full Text Available In this paper, a new Quantum Theory of Magnetic Interaction is proposed. This is done under a relaxation of the requirement of covariance for Lorentz Boost Transformations. A modified form of local gauge invariance in which fermion field phase is allowed to vary with each space point but not each time point, leads to the introduction of a new compensatory field different from the electromagnetic field associated with the photon. This new field is coupled to the magnetic flux of the fermions and has quanta called magnatons, which are massless spin 1 particles. The associated equation of motion yields the Poisson equation for magnetostatic potentials. The magnatons mediate the magnetic interaction between magnetic dipoles including magnets and provide plausi- ble explanations for the Pauli exclusion principle, Chemical Reactivity and Chemical Bonds. This new interaction has been confirmed by numerical experiments. It estab- lishes magnetism as a force entirely separate from the electromagnetic interaction and converts all of classical magnetism into a quantum theory.

  15. Random matrix techniques in quantum information theory

    Science.gov (United States)

    Collins, Benoît; Nechita, Ion

    2016-01-01

    The purpose of this review is to present some of the latest developments using random techniques, and in particular, random matrix techniques in quantum information theory. Our review is a blend of a rather exhaustive review and of more detailed examples—coming mainly from research projects in which the authors were involved. We focus on two main topics, random quantum states and random quantum channels. We present results related to entropic quantities, entanglement of typical states, entanglement thresholds, the output set of quantum channels, and violations of the minimum output entropy of random channels.

  16. Random matrix techniques in quantum information theory

    Energy Technology Data Exchange (ETDEWEB)

    Collins, Benoît, E-mail: collins@math.kyoto-u.ac.jp [Department of Mathematics, Kyoto University, Kyoto 606-8502 (Japan); Département de Mathématique et Statistique, Université d’Ottawa, 585 King Edward, Ottawa, Ontario K1N6N5 (Canada); CNRS, Lyon (France); Nechita, Ion, E-mail: nechita@irsamc.ups-tlse.fr [Zentrum Mathematik, M5, Technische Universität München, Boltzmannstrasse 3, 85748 Garching (Germany); Laboratoire de Physique Théorique, CNRS, IRSAMC, Université de Toulouse, UPS, F-31062 Toulouse (France)

    2016-01-15

    The purpose of this review is to present some of the latest developments using random techniques, and in particular, random matrix techniques in quantum information theory. Our review is a blend of a rather exhaustive review and of more detailed examples—coming mainly from research projects in which the authors were involved. We focus on two main topics, random quantum states and random quantum channels. We present results related to entropic quantities, entanglement of typical states, entanglement thresholds, the output set of quantum channels, and violations of the minimum output entropy of random channels.

  17. Quantum Protectorate and Microscopic Models of Magnetism

    OpenAIRE

    Kuzemsky, A. L.

    2002-01-01

    Some physical implications involved in a new concept, termed the "quantum protectorate" (QP), are developed and discussed. This is done by considering the idea of quantum protectorate in the context of quantum theory of magnetism. It is suggested that the difficulties in the formulation of quantum theory of magnetism at the microscopic level, that are related to the choice of relevant models, can be understood better in the light of the QP concept . We argue that the difficulties in the formu...

  18. Quantum random walks with history dependence

    OpenAIRE

    Flitney, Adrian P.; Abbott, Derek; Johnson, Neil F.

    2003-01-01

    We introduce a multi-coin discrete quantum random walk where the amplitude for a coin flip depends upon previous tosses. Although the corresponding classical random walk is unbiased, a bias can be introduced into the quantum walk by varying the history dependence. By mixing the biased random walk with an unbiased one, the direction of the bias can be reversed leading to a new quantum version of Parrondo's paradox.

  19. Open quantum random walk in terms of quantum Bernoulli noise

    Science.gov (United States)

    Wang, Caishi; Wang, Ce; Ren, Suling; Tang, Yuling

    2018-03-01

    In this paper, we introduce an open quantum random walk, which we call the QBN-based open walk, by means of quantum Bernoulli noise, and study its properties from a random walk point of view. We prove that, with the localized ground state as its initial state, the QBN-based open walk has the same limit probability distribution as the classical random walk. We also show that the probability distributions of the QBN-based open walk include those of the unitary quantum walk recently introduced by Wang and Ye (Quantum Inf Process 15:1897-1908, 2016) as a special case.

  20. Quantum oscillations in the chiral magnetic conductivity

    Science.gov (United States)

    Kaushik, Sahal; Kharzeev, Dmitri E.

    2017-06-01

    In strong magnetic field, the longitudinal magnetoconductivity in three-dimensional chiral materials is shown to exhibit a new type of quantum oscillations arising from the chiral magnetic effect (CME). These quantum CME oscillations are predicted to dominate over the Shubnikov-de Haas (SdH) ones in chiral materials with an approximately conserved chirality of quasiparticles at strong magnetic fields. The phase of quantum CME oscillations differs from the phase of the conventional SdH oscillations by π /2 .

  1. The Quantum Theory of Magnetism

    CERN Document Server

    Majlis, Norberto

    2000-01-01

    This book is intended as a basic text for a two-term graduate course for physicists, engineers and chemists with a background in quantum and statistical mechanics. What sets it apart from other publications on the subject is its extensive use of Green’s function techniques and its detailed discussion of the application of the mean-field approximation and dipoleâ€"dipole interactions in one, two and three dimensions. A chapter each has been devoted to low-dimensional systems, surface magnetism and layered systems. A total of 60 exercises have also been included.

  2. Astronomical random numbers for quantum foundations experiments

    OpenAIRE

    Leung, Calvin; Brown, Amy; Nguyen, Hien; Friedman, Andrew S.; Kaiser, David I.; Gallicchio, Jason

    2017-01-01

    Photons from distant astronomical sources can be used as a classical source of randomness to improve fundamental tests of quantum nonlocality, wave-particle duality, and local realism through Bell's inequality and delayed-choice quantum eraser tests inspired by Wheeler's cosmic-scale Mach-Zehnder interferometer gedankenexperiment. Such sources of random numbers may also be useful for information-theoretic applications such as key distribution for quantum cryptography. Building on the design o...

  3. Quantum Statistical Testing of a Quantum Random Number Generator

    Energy Technology Data Exchange (ETDEWEB)

    Humble, Travis S [ORNL

    2014-01-01

    The unobservable elements in a quantum technology, e.g., the quantum state, complicate system verification against promised behavior. Using model-based system engineering, we present methods for verifying the opera- tion of a prototypical quantum random number generator. We begin with the algorithmic design of the QRNG followed by the synthesis of its physical design requirements. We next discuss how quantum statistical testing can be used to verify device behavior as well as detect device bias. We conclude by highlighting how system design and verification methods must influence effort to certify future quantum technologies.

  4. Geometric magnetism in open quantum systems

    OpenAIRE

    Campisi, Michele; Denisov, Sergey; Hänggi, Peter

    2012-01-01

    An isolated classical chaotic system, when driven by the slow change of several parameters, responds with two reaction forces: geometric friction and geometric magnetism. By using the theory of quantum fluctuation relations we show that this holds true also for open quantum systems, and provide explicit expressions for those forces in this case. This extends the concept of Berry curvature to the realm of open quantum systems. We illustrate our findings by calculating the geometric magnetism o...

  5. Quantum optics in multiple scattering random media

    DEFF Research Database (Denmark)

    Lodahl, Peter

    Quantum Optics in Multiple Scattering Random Media Peter Lodahl Research Center COM, Technical University of Denmark, Dk-2800 Lyngby, Denmark. Coherent transport of light in a disordered random medium has attracted enormous attention both from a fundamental and application point of view. Coherent...... quantum optics in multiple scattering media and novel fundamental phenomena have been predicted when examining quantum fluctuations instead of merely the intensity of the light [1]. Here I will present the first experimental study of the propagation of quantum noise through an elastic, multiple scattering...

  6. Quantum nature of edge magnetism in graphene.

    Science.gov (United States)

    Golor, Michael; Wessel, Stefan; Schmidt, Manuel J

    2014-01-31

    It is argued that the subtle crossover from decoherence-dominated classical magnetism to fluctuation-dominated quantum magnetism is experimentally accessible in graphene nanoribbons. We show that the width of a nanoribbon determines whether the edge magnetism is on the classical side, on the quantum side, or in between. In the classical regime, decoherence is dominant and leads to static spin polarizations at the ribbon edges, which are well described by mean-field theories. The quantum Zeno effect is identified as the basic mechanism which is responsible for the spin polarization and thereby enables the application of graphene in spintronics. On the quantum side, however, the spin polarization is destroyed by dynamical processes. The great tunability of graphene magnetism thus offers a viable route for the study of the quantum-classical crossover.

  7. Provable quantum advantage in randomness processing.

    Science.gov (United States)

    Dale, Howard; Jennings, David; Rudolph, Terry

    2015-09-18

    Quantum advantage is notoriously hard to find and even harder to prove. For example the class of functions computable with classical physics exactly coincides with the class computable quantum mechanically. It is strongly believed, but not proven, that quantum computing provides exponential speed-up for a range of problems, such as factoring. Here we address a computational scenario of randomness processing in which quantum theory provably yields, not only resource reduction over classical stochastic physics, but a strictly larger class of problems which can be solved. Beyond new foundational insights into the nature and malleability of randomness, and the distinction between quantum and classical information, these results also offer the potential of developing classically intractable simulations with currently accessible quantum technologies.

  8. Source-Independent Quantum Random Number Generation

    Science.gov (United States)

    Cao, Zhu; Zhou, Hongyi; Yuan, Xiao; Ma, Xiongfeng

    2016-01-01

    Quantum random number generators can provide genuine randomness by appealing to the fundamental principles of quantum mechanics. In general, a physical generator contains two parts—a randomness source and its readout. The source is essential to the quality of the resulting random numbers; hence, it needs to be carefully calibrated and modeled to achieve information-theoretical provable randomness. However, in practice, the source is a complicated physical system, such as a light source or an atomic ensemble, and any deviations in the real-life implementation from the theoretical model may affect the randomness of the output. To close this gap, we propose a source-independent scheme for quantum random number generation in which output randomness can be certified, even when the source is uncharacterized and untrusted. In our randomness analysis, we make no assumptions about the dimension of the source. For instance, multiphoton emissions are allowed in optical implementations. Our analysis takes into account the finite-key effect with the composable security definition. In the limit of large data size, the length of the input random seed is exponentially small compared to that of the output random bit. In addition, by modifying a quantum key distribution system, we experimentally demonstrate our scheme and achieve a randomness generation rate of over 5 ×103 bit /s .

  9. Random Oracles in a Quantum World

    NARCIS (Netherlands)

    D. Boneh; O. Dagdelen; M. Fischlin; D. Lehmann; C. Schaffner (Christian); M. Zhandry

    2012-01-01

    htmlabstractThe interest in post-quantum cryptography - classical systems that remain secure in the presence of a quantum adversary - has generated elegant proposals for new cryptosystems. Some of these systems are set in the random oracle model and are proven secure relative to adversaries that

  10. Quantum random walks circuits with photonic waveguides

    NARCIS (Netherlands)

    Peruzzo, Alberto; Matthews, Jonathan; Politi, Alberto; Lobino, Mirko; Zhou, Xiao-Qi; Thompson, Mark G.; O'Brien, Jeremy; Matsuda, Nobuyuki; Ismail, N.; Worhoff, Kerstin; Bromberg, Yaron; Lahini, Yoav; Silberberg, Yaron

    2010-01-01

    Arrays of 21 evanescently coupled waveguides are fabricated to implement quantum random walks and a generalised form of two-photon non-classical interference, which observed via two photon correlation.

  11. NATO Advanced Study Institute on Quantum Magnetism

    CERN Document Server

    Barbara, Bernard; Sawatzky, G; Stamp, P. C. E

    2008-01-01

    This book is based on some of the lectures during the Pacific Institute of Theoretical Physics (PITP) summer school on "Quantum Magnetism", held during June 2006 in Les Houches, in the French Alps. The school was funded jointly by NATO, the CNRS, and PITP, and entirely organized by PITP. Magnetism is a somewhat peculiar research field. It clearly has a quantum-mechanical basis – the microsopic exchange interactions arise entirely from the exclusion principle, in conjunction with respulsive interactions between electrons. And yet until recently the vast majority of magnetism researchers and users of magnetic phenomena around the world paid no attention to these quantum-mechanical roots. Thus, eg., the huge ($400 billion per annum) industry which manufactures hard discs, and other components in the information technology sector, depends entirely on room-temperature properties of magnets - yet at the macroscopic or mesoscopic scales of interest to this industry, room-temperature magnets behave entirely classic...

  12. Quantum physics: Interactions propel a magnetic dance

    Science.gov (United States)

    Leblanc, Lindsay J.

    2017-06-01

    A combination of leading-edge techniques has enabled interaction-induced magnetic motion to be observed for pairs of ultracold atoms -- a breakthrough in the development of models of complex quantum behaviour. See Letter p.519

  13. Quantum Coherence and Random Fields at Mesoscopic Scales

    Energy Technology Data Exchange (ETDEWEB)

    Rosenbaum, Thomas F. [Univ. of Chicago, IL (United States)

    2016-03-01

    We seek to explore and exploit model, disordered and geometrically frustrated magnets where coherent spin clusters stably detach themselves from their surroundings, leading to extreme sensitivity to finite frequency excitations and the ability to encode information. Global changes in either the spin concentration or the quantum tunneling probability via the application of an external magnetic field can tune the relative weights of quantum entanglement and random field effects on the mesoscopic scale. These same parameters can be harnessed to manipulate domain wall dynamics in the ferromagnetic state, with technological possibilities for magnetic information storage. Finally, extensions from quantum ferromagnets to antiferromagnets promise new insights into the physics of quantum fluctuations and effective dimensional reduction. A combination of ac susceptometry, dc magnetometry, noise measurements, hole burning, non-linear Fano experiments, and neutron diffraction as functions of temperature, magnetic field, frequency, excitation amplitude, dipole concentration, and disorder address issues of stability, overlap, coherence, and control. We have been especially interested in probing the evolution of the local order in the progression from spin liquid to spin glass to long-range-ordered magnet.

  14. Competing magnetic interactions in quantum thin films

    Energy Technology Data Exchange (ETDEWEB)

    Bueno, M.J. [Departamento de Física, CCEN, Universidade Federal da Paraíba, Cidade Universitária, 58051-970 João Pessoa, PB (Brazil); Faria, Jorge L.B. [Instituto de Física, Universidade Federal de Mato Grosso, 78060-900 Cuiabá, MT (Brazil); Arruda, Alberto S. de, E-mail: aarruda@fisica.ufmt.br [Instituto de Física, Universidade Federal de Mato Grosso, 78060-900 Cuiabá, MT (Brazil); Craco, L. [Instituto de Física, Universidade Federal de Mato Grosso, 78060-900 Cuiabá, MT (Brazil); Sousa, J. Ricardo de, E-mail: jsousa@ufam.edu.br [Departamento de Física, Universidade Federal do Amazonas, 69077-000 Manaus, AM (Brazil)

    2013-07-15

    In this work we study the quantum spin-1/2 Heisenberg model in two dimensions, with a nearest-neighbor short-range antiferromagnetic exchange (J) and a long-range ferromagnetic dipole–dipole (E{sub d}) coupling. Using the double-time Green's function method within the random phase approximation (RPA) we obtain the magnon dispersion relation as function of frustration parameter δ (δ being the ratio between exchange and dipolar interactions δ=J/E{sub d}). We study the competition between long-range ferromagnetic dipole–dipole interaction and short-range antiferromagnetic exchange in stabilizing the magnetic long-range order in a two-dimensional system. We find that the ferromagnetic order is stable at small k up to critical value of frustration δ{sub c}=0.04375. For frustration higher than the critical value (δ>δ{sub c}) our magnetic system is disordered. - Highlights: ► Competition between interactions short-range (exchange J) and long-range dipole–dipole (E{sub d}) is studied. ► The quantum spin-1/2 Heisenberg model in two dimensions is used as example. ► The interactions are exchange (antiferromagnetic) and ferromagnetic dipole–dipole. ► The double-time Green's function method and RPA is used to obtain the dispersion relations of the acoustic branch. ► The system has ferromagnetic order stable for values less than critical of frustration (J/E{sub d})

  15. Anyons in Integer Quantum Hall Magnets

    Directory of Open Access Journals (Sweden)

    Armin Rahmani

    2013-08-01

    Full Text Available Strongly correlated fractional quantum Hall liquids support fractional excitations, which can be understood in terms of adiabatic flux insertion arguments. A second route to fractionalization is through the coupling of weakly interacting electrons to topologically nontrivial backgrounds such as in polyacetylene. Here, we demonstrate that electronic fractionalization combining features of both these mechanisms occurs in noncoplanar itinerant magnetic systems, where integer quantum Hall physics arises from the coupling of electrons to the magnetic background. The topologically stable magnetic vortices in such systems carry fractional (in general, irrational electronic quantum numbers and exhibit Abelian anyonic statistics. We analyze the properties of these topological defects by mapping the distortions of the magnetic texture onto effective non-Abelian vector potentials. We support our analytical results with extensive numerical calculations.

  16. Random access quantum information processors using multimode circuit quantum electrodynamics.

    Science.gov (United States)

    Naik, R K; Leung, N; Chakram, S; Groszkowski, Peter; Lu, Y; Earnest, N; McKay, D C; Koch, Jens; Schuster, D I

    2017-12-04

    Qubit connectivity is an important property of a quantum processor, with an ideal processor having random access-the ability of arbitrary qubit pairs to interact directly. This a challenge with superconducting circuits, as state-of-the-art architectures rely on only nearest-neighbor coupling. Here, we implement a random access superconducting quantum information processor, demonstrating universal operations on a nine-qubit memory, with a Josephson junction transmon circuit serving as the central processor. The quantum memory uses the eigenmodes of a linear array of coupled superconducting resonators. We selectively stimulate vacuum Rabi oscillations between the transmon and individual eigenmodes through parametric flux modulation of the transmon frequency. Utilizing these oscillations, we perform a universal set of quantum gates on 38 arbitrary pairs of modes and prepare multimode entangled states, all using only two control lines. We thus achieve hardware-efficient random access multi-qubit control in an architecture compatible with long-lived microwave cavity-based quantum memories.

  17. Random Numbers and Quantum Computers

    Science.gov (United States)

    McCartney, Mark; Glass, David

    2002-01-01

    The topic of random numbers is investigated in such a way as to illustrate links between mathematics, physics and computer science. First, the generation of random numbers by a classical computer using the linear congruential generator and logistic map is considered. It is noted that these procedures yield only pseudo-random numbers since…

  18. Probability Distributions for Random Quantum Operations

    Science.gov (United States)

    Schultz, Kevin

    Motivated by uncertainty quantification and inference of quantum information systems, in this work we draw connections between the notions of random quantum states and operations in quantum information with probability distributions commonly encountered in the field of orientation statistics. This approach identifies natural sample spaces and probability distributions upon these spaces that can be used in the analysis, simulation, and inference of quantum information systems. The theory of exponential families on Stiefel manifolds provides the appropriate generalization to the classical case. Furthermore, this viewpoint motivates a number of additional questions into the convex geometry of quantum operations relative to both the differential geometry of Stiefel manifolds as well as the information geometry of exponential families defined upon them. In particular, we draw on results from convex geometry to characterize which quantum operations can be represented as the average of a random quantum operation. This project was supported by the Intelligence Advanced Research Projects Activity via Department of Interior National Business Center Contract Number 2012-12050800010.

  19. Quantum entanglement and coherence in molecular magnets

    Science.gov (United States)

    Shiddiq, Muhandis

    Quantum computers are predicted to outperform classical computers in certain tasks, such as factoring large numbers and searching databases. The construction of a computer whose operation is based on the principles of quantum mechanics appears extremely challenging. Solid state approaches offer the potential to answer this challenge by tailor-making novel nanomaterials for quantum information processing (QIP). Molecular magnets, which are materials whose energy levels and magnetic quantum states are well defined at the molecular level, have been identified as a class of material with properties that make them attractive for quantum computing purpose. In this dissertation, I explore the possibilities and challenges for molecular magnets to be used in quantum computing architecture. The properties of molecular magnets that are critical for applications in quantum computing, i.e., quantum entanglement and coherence, are comprehensively investigated to probe the feasibility of molecular magnets to be used as quantum bits (qubits). Interactions of qubits with photons are at the core of QIP. Photons can be used to detect and manipulate qubits, after which information can then be transferred over long distances. As a potential candidate for qubits, the interactions between Fe8 single-molecule magnets (SMMs) and cavity photons were studied. An earlier report described that a cavity mode splitting was observed in a spectrum of a cavity filled with a single-crystal of Fe8 SMMs. This splitting was interpreted as a vacuum Rabi splitting (VRS), which is a signature of an entanglement between a large number of SMMs and a cavity photon. However, find that large absorption and dispersion of the magnetic susceptibility are the reasons for this splitting. This finding highlights the fact that an observation of a peak splitting in a cavity transmission spectrum neither represents an unambiguous indication of quantum coherence in a large number of spins, nor a signature of

  20. Quantum information processing and nuclear magnetic resonance

    CERN Document Server

    Cummins, H K

    2001-01-01

    as spectrometer pulse sequence programs. Quantum computers are information processing devices which operate by and exploit the laws of quantum mechanics, potentially allowing them to solve problems which are intractable using classical computers. This dissertation considers the practical issues involved in one of the more successful implementations to date, nuclear magnetic resonance (NMR). Techniques for dealing with systematic errors are presented, and a quantum protocol is implemented. Chapter 1 is a brief introduction to quantum computation. The physical basis of its efficiency and issues involved in its implementation are discussed. NMR quantum information processing is reviewed in more detail in Chapter 2. Chapter 3 considers some of the errors that may be introduced in the process of implementing an algorithm, and high-level ways of reducing the impact of these errors by using composite rotations. Novel general expressions for stabilising composite rotations are presented in Chapter 4 and a new class o...

  1. Quantum Criticality of Hot Random Spin Chains

    Science.gov (United States)

    Vasseur, R.; Potter, A. C.; Parameswaran, S. A.

    2015-05-01

    We study the infinite-temperature properties of an infinite sequence of random quantum spin chains using a real-space renormalization group approach, and demonstrate that they exhibit nonergodic behavior at strong disorder. The analysis is conveniently implemented in terms of SU (2 )k anyon chains that include the Ising and Potts chains as notable examples. Highly excited eigenstates of these systems exhibit properties usually associated with quantum critical ground states, leading us to dub them "quantum critical glasses." We argue that random-bond Heisenberg chains self-thermalize and that the excited-state entanglement crosses over from volume-law to logarithmic scaling at a length scale that diverges in the Heisenberg limit k →∞. The excited state fixed points are generically distinct from their ground state counterparts, and represent novel nonequilibrium critical phases of matter.

  2. History dependent quantum random walks as quantum lattice gas automata

    Energy Technology Data Exchange (ETDEWEB)

    Shakeel, Asif, E-mail: asif.shakeel@gmail.com, E-mail: dmeyer@math.ucsd.edu, E-mail: plove@haverford.edu; Love, Peter J., E-mail: asif.shakeel@gmail.com, E-mail: dmeyer@math.ucsd.edu, E-mail: plove@haverford.edu [Department of Physics, Haverford College, Haverford, Pennsylvania 19041 (United States); Meyer, David A., E-mail: asif.shakeel@gmail.com, E-mail: dmeyer@math.ucsd.edu, E-mail: plove@haverford.edu [Department of Mathematics, University of California/San Diego, La Jolla, California 92093-0112 (United States)

    2014-12-15

    Quantum Random Walks (QRW) were first defined as one-particle sectors of Quantum Lattice Gas Automata (QLGA). Recently, they have been generalized to include history dependence, either on previous coin (internal, i.e., spin or velocity) states or on previous position states. These models have the goal of studying the transition to classicality, or more generally, changes in the performance of quantum walks in algorithmic applications. We show that several history dependent QRW can be identified as one-particle sectors of QLGA. This provides a unifying conceptual framework for these models in which the extra degrees of freedom required to store the history information arise naturally as geometrical degrees of freedom on the lattice.

  3. Embedded random matrix ensembles in quantum physics

    CERN Document Server

    Kota, V K B

    2014-01-01

    Although used with increasing frequency in many branches of physics, random matrix ensembles are not always sufficiently specific to account for important features of the physical system at hand. One refinement which retains the basic stochastic approach but allows for such features consists in the use of embedded ensembles.  The present text is an exhaustive introduction to and survey of this important field. Starting with an easy-to-read introduction to general random matrix theory, the text then develops the necessary concepts from the beginning, accompanying the reader to the frontiers of present-day research. With some notable exceptions, to date these ensembles have primarily been applied in nuclear spectroscopy. A characteristic example is the use of a random two-body interaction in the framework of the nuclear shell model. Yet, topics in atomic physics, mesoscopic physics, quantum information science and statistical mechanics of isolated finite quantum systems can also be addressed using these ensemb...

  4. Quantum phenomena in magnetic nano clusters

    Indian Academy of Sciences (India)

    Unknown

    Quantum phenomena in magnetic nano clusters. 461. Figure 3. Schematic exchange interactions in a V15 cluster. There is no direct exchange interaction amongst the triangle spins. Interactions not shown explicitly can be generated from the C3 symmetry of the system. simplify the calculations, the strongly coupled ...

  5. Quantum information processing and nuclear magnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Cummins, H.K

    2001-07-01

    Quantum computers are information processing devices which operate by and exploit the laws of quantum mechanics, potentially allowing them to solve problems which are intractable using classical computers. This dissertation considers the practical issues involved in one of the more successful implementations to date, nuclear magnetic resonance (NMR). Techniques for dealing with systematic errors are presented, and a quantum protocol is implemented. Chapter 1 is a brief introduction to quantum computation. The physical basis of its efficiency and issues involved in its implementation are discussed. NMR quantum information processing is reviewed in more detail in Chapter 2. Chapter 3 considers some of the errors that may be introduced in the process of implementing an algorithm, and high-level ways of reducing the impact of these errors by using composite rotations. Novel general expressions for stabilising composite rotations are presented in Chapter 4 and a new class of composite rotations, tailored composite rotations, presented in Chapter 5. Chapter 6 describes some of the advantages and pitfalls of combining composite rotations. Experimental evaluations of the composite rotations are given in each case. An actual implementation of a quantum information protocol, approximate quantum cloning, is presented in Chapter 7. The dissertation ends with appendices which contain expansions of some equations and detailed calculations of certain composite rotation results, as well as spectrometer pulse sequence programs. (author)

  6. Realistic finite temperature simulations of magnetic systems using quantum statistics

    Science.gov (United States)

    Bergqvist, Lars; Bergman, Anders

    2018-01-01

    We have performed realistic atomistic simulations at finite temperatures using Monte Carlo and atomistic spin dynamics simulations incorporating quantum (Bose-Einstein) statistics. The description is much improved at low temperatures compared to classical (Boltzmann) statistics normally used in these kind of simulations, while at higher temperatures the classical statistics are recovered. This corrected low-temperature description is reflected in both magnetization and the magnetic specific heat, the latter allowing for improved modeling of the magnetic contribution to free energies. A central property in the method is the magnon density of states at finite temperatures, and we have compared several different implementations for obtaining it. The method has no restrictions regarding chemical and magnetic order of the considered materials. This is demonstrated by applying the method to elemental ferromagnetic systems, including Fe and Ni, as well as Fe-Co random alloys and the ferrimagnetic system GdFe3.

  7. Bipartite quantum states and random complex networks

    Science.gov (United States)

    Garnerone, Silvano; Giorda, Paolo; Zanardi, Paolo

    2012-01-01

    We introduce a mapping between graphs and pure quantum bipartite states and show that the associated entanglement entropy conveys non-trivial information about the structure of the graph. Our primary goal is to investigate the family of random graphs known as complex networks. In the case of classical random graphs, we derive an analytic expression for the averaged entanglement entropy \\bar S while for general complex networks we rely on numerics. For a large number of nodes n we find a scaling \\bar {S} \\sim c log n +g_{ {e}} where both the prefactor c and the sub-leading O(1) term ge are characteristic of the different classes of complex networks. In particular, ge encodes topological features of the graphs and is named network topological entropy. Our results suggest that quantum entanglement may provide a powerful tool for the analysis of large complex networks with non-trivial topological properties.

  8. Grounding the randomness of quantum measurement.

    Science.gov (United States)

    Jaeger, Gregg

    2016-05-28

    Julian Schwinger provided to physics a mathematical reconstruction of quantum mechanics on the basis of the characteristics of sequences of measurements occurring at the atomic level of physical structure. The central component of this reconstruction is an algebra of symbols corresponding to quantum measurements, conceived of as discrete processes, which serve to relate experience to theory; collections of outcomes of identically circumscribed such measurements are attributed expectation values, which constitute the predictive content of the theory. The outcomes correspond to certain phase parameters appearing in the corresponding symbols, which are complex numbers, the algebra of which he finds by a process he refers to as 'induction'. Schwinger assumed these (individually unpredictable) phase parameters to take random, uniformly distributed definite values within a natural range. I have previously suggested that the 'principle of plenitude' may serve as a basis in principle for the occurrence of the definite measured values that are those members of the collections of measurement outcomes from which the corresponding observed statistics derive (Jaeger 2015Found. Phys.45, 806-819. (doi:10.1007/s10701-015-9893-6)). Here, I evaluate Schwinger's assumption in the context of recent critiques of the notion of randomness and explicitly relate the randomness of these phases with the principle of plenitude and, in this way, provide a fundamental grounding for the objective, physically irreducible probabilities, conceived of as graded possibilities, that are attributed to measurement outcomes by quantum mechanics. © 2016 The Author(s).

  9. Random matrix theory of a chaotic Andreev quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Altland, A.; Zirnbauer, M.R. [Institut fuer Theoretische Physik, Universitaet zu Koeln, Zuelpicher Str.77, 50937 Koeln (Germany)

    1996-04-01

    A new universality class distinct from the standard Wigner-Dyson class is identified. This class is realized by putting a metallic quantum dot in contact with a superconductor, while applying a magnetic field so as to make the pairing field effectively vanish on average. A random-matrix description of the spectral and transport properties of such a quantum dot is proposed. The weak-localization correction to the tunnel conductance is nonzero and results from the depletion of the density of states due to the coupling with the superconductor. Semiclassically, the depletion is caused by a singular mode of phase-coherent long-range propagation of particles and holes. {copyright} {ital 1996 The American Physical Society.}

  10. Randomness in Classical Mechanics and Quantum Mechanics

    Science.gov (United States)

    Volovich, Igor V.

    2011-03-01

    The Copenhagen interpretation of quantum mechanics assumes the existence of the classical deterministic Newtonian world. We argue that in fact the Newton determinism in classical world does not hold and in the classical mechanics there is fundamental and irreducible randomness. The classical Newtonian trajectory does not have a direct physical meaning since arbitrary real numbers are not observable. There are classical uncertainty relations: Δ q>0 and Δ p>0, i.e. the uncertainty (errors of observation) in the determination of coordinate and momentum is always positive (non zero). A "functional" formulation of classical mechanics was suggested. The fundamental equation of the microscopic dynamics in the functional approach is not the Newton equation but the Liouville equation for the distribution function of the single particle. Solutions of the Liouville equation have the property of delocalization which accounts for irreversibility. The Newton equation in this approach appears as an approximate equation describing the dynamics of the average values of the position and momenta for not too long time intervals. Corrections to the Newton trajectories are computed. An interpretation of quantum mechanics is attempted in which both classical and quantum mechanics contain fundamental randomness. Instead of an ensemble of events one introduces an ensemble of observers.

  11. Quantum Entanglement Growth under Random Unitary Dynamics

    Directory of Open Access Journals (Sweden)

    Adam Nahum

    2017-07-01

    Full Text Available Characterizing how entanglement grows with time in a many-body system, for example, after a quantum quench, is a key problem in nonequilibrium quantum physics. We study this problem for the case of random unitary dynamics, representing either Hamiltonian evolution with time-dependent noise or evolution by a random quantum circuit. Our results reveal a universal structure behind noisy entanglement growth, and also provide simple new heuristics for the “entanglement tsunami” in Hamiltonian systems without noise. In 1D, we show that noise causes the entanglement entropy across a cut to grow according to the celebrated Kardar-Parisi-Zhang (KPZ equation. The mean entanglement grows linearly in time, while fluctuations grow like (time^{1/3} and are spatially correlated over a distance ∝(time^{2/3}. We derive KPZ universal behavior in three complementary ways, by mapping random entanglement growth to (i a stochastic model of a growing surface, (ii a “minimal cut” picture, reminiscent of the Ryu-Takayanagi formula in holography, and (iii a hydrodynamic problem involving the dynamical spreading of operators. We demonstrate KPZ universality in 1D numerically using simulations of random unitary circuits. Importantly, the leading-order time dependence of the entropy is deterministic even in the presence of noise, allowing us to propose a simple coarse grained minimal cut picture for the entanglement growth of generic Hamiltonians, even without noise, in arbitrary dimensionality. We clarify the meaning of the “velocity” of entanglement growth in the 1D entanglement tsunami. We show that in higher dimensions, noisy entanglement evolution maps to the well-studied problem of pinning of a membrane or domain wall by disorder.

  12. Quantum corrections crossover and ferromagnetism in magnetic topological insulators

    National Research Council Canada - National Science Library

    Bao, Lihong; Wang, Weiyi; Meyer, Nicholas; Liu, Yanwen; Zhang, Cheng; Wang, Kai; Ai, Ping; Xiu, Faxian

    2013-01-01

    ...) accompanied by an increasing carrier density. Our results demonstrate a possibility of manipulating bulk ferromagnetism and quantum transport in magnetic TI, thus providing an alternative way for experimentally realizing exotic quantum states required by spintronic applications.

  13. Quantum random walks and their convergence to Evans–Hudson ...

    Indian Academy of Sciences (India)

    Quantum dynamical semigroup; Evans–Hudson flow; quantum random walk. 1. Introduction. The aim of this article is to investigate convergence of random walks on von Neumann algebra to Evans–Hudson flows. Here the random walks and Evans–Hudson flows are gene- ralizations of classical Markov chains and Markov ...

  14. Spin jam induced by quantum fluctuations in a frustrated magnet.

    Science.gov (United States)

    Yang, Junjie; Samarakoon, Anjana; Dissanayake, Sachith; Ueda, Hiroaki; Klich, Israel; Iida, Kazuki; Pajerowski, Daniel; Butch, Nicholas P; Huang, Q; Copley, John R D; Lee, Seung-Hun

    2015-09-15

    Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr(3+) (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga(3+) impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p > 0.8) and a cluster spin glass for lower magnetic concentration (p < 0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood.

  15. Open quantum systems and random matrix theory

    Science.gov (United States)

    Mulhall, Declan

    2015-01-01

    A simple model for open quantum systems is analyzed with random matrix theory. The system is coupled to the continuum in a minimal way. In this paper the effect on the level statistics of opening the system is seen. In particular the Δ3(L ) statistic, the width distribution and the level spacing are examined as a function of the strength of this coupling. The emergence of a super-radiant transition is observed. The level spacing and Δ3(L ) statistics exhibit the signatures of missed levels or intruder levels as the super-radiant state is formed.

  16. Specific heat in diluted magnetic semiconductor quantum ring

    Science.gov (United States)

    Babanlı, A. M.; Ibragimov, B. G.

    2017-11-01

    In the present paper, we have calculated the specific heat and magnetization of a quantum ring of a diluted magnetic semiconductor (DMS) material in the presence of magnetic field. We take into account the effect of Rashba spin-orbital interaction, the exchange interaction and the Zeeman term on the specific heat. We have calculated the energy spectrum of the electrons in diluted magnetic semiconductor quantum ring. Moreover we have calculated the specific heat dependency on the magnetic field and Mn concentration at finite temperature of a diluted magnetic semiconductor quantum ring.

  17. Random Bosonic States for Robust Quantum Metrology

    Directory of Open Access Journals (Sweden)

    M. Oszmaniec

    2016-12-01

    Full Text Available We study how useful random states are for quantum metrology, i.e., whether they surpass the classical limits imposed on precision in the canonical phase sensing scenario. First, we prove that random pure states drawn from the Hilbert space of distinguishable particles typically do not lead to superclassical scaling of precision even when allowing for local unitary optimization. Conversely, we show that random pure states from the symmetric subspace typically achieve the optimal Heisenberg scaling without the need for local unitary optimization. Surprisingly, the Heisenberg scaling is observed for random isospectral states of arbitrarily low purity and preserved under loss of a fixed number of particles. Moreover, we prove that for pure states, a standard photon-counting interferometric measurement suffices to typically achieve resolution following the Heisenberg scaling for all values of the phase at the same time. Finally, we demonstrate that metrologically useful states can be prepared with short random optical circuits generated from three types of beam splitters and a single nonlinear (Kerr-like transformation.

  18. Selectivity in multiple quantum nuclear magnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Warren, Warren Sloan [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Sciences Division

    1980-11-01

    The observation of multiple-quantum nuclear magnetic resonance transitions in isotropic or anisotropic liquids is shown to give readily interpretable information on molecular configurations, rates of motional processes, and intramolecular interactions. However, the observed intensity of high multiple-quantum transitions falls off dramatically as the number of coupled spins increases. The theory of multiple-quantum NMR is developed through the density matrix formalism, and exact intensities are derived for several cases (isotropic first-order systems and anisotropic systems with high symmetry) to shown that this intensity decrease is expected if standard multiple-quantum pulse sequences are used. New pulse sequences are developed which excite coherences and produce population inversions only between selected states, even though other transitions are simultaneously resonant. One type of selective excitation presented only allows molecules to absorb and emit photons in groups of n. Coherent averaging theory is extended to describe these selective sequences, and to design sequences which are selective to arbitrarily high order in the Magnus expansion. This theory and computer calculations both show that extremely good selectivity and large signal enhancements are possible.

  19. Quantum Dynamics of Skyrmions in Chiral Magnets

    Directory of Open Access Journals (Sweden)

    Christina Psaroudaki

    2017-11-01

    Full Text Available We study the quantum propagation of a Skyrmion in chiral magnetic insulators by generalizing the micromagnetic equations of motion to a finite-temperature path integral formalism, using field theoretic tools. Promoting the center of the Skyrmion to a dynamic quantity, the fluctuations around the Skyrmionic configuration give rise to a time-dependent damping of the Skyrmion motion. From the frequency dependence of the damping kernel, we are able to identify the Skyrmion mass, thus providing a microscopic description of the kinematic properties of Skyrmions. When defects are present or a magnetic trap is applied, the Skyrmion mass acquires a finite value proportional to the effective spin, even at vanishingly small temperature. We demonstrate that a Skyrmion in a confined geometry provided by a magnetic trap behaves as a massive particle owing to its quasi-one-dimensional confinement. An additional quantum mass term is predicted, independent of the effective spin, with an explicit temperature dependence which remains finite even at zero temperature.

  20. Chiral liquid phase of simple quantum magnets

    Science.gov (United States)

    Wang, Zhentao; Feiguin, Adrian E.; Zhu, Wei; Starykh, Oleg A.; Chubukov, Andrey V.; Batista, Cristian D.

    2017-11-01

    We study a T =0 quantum phase transition between a quantum paramagnetic state and a magnetically ordered state for a spin S =1 XXZ Heisenberg antiferromagnet on a two-dimensional triangular lattice. The transition is induced by an easy-plane single-ion anisotropy D . At the mean-field level, the system undergoes a direct transition at a critical D =Dc between a paramagnetic state at D >Dc and an ordered state with broken U(1 ) symmetry at D field the phase diagram is very different and includes an intermediate, partially ordered chiral liquid phase. Specifically, we find that inside the paramagnetic phase the Ising (Jz) component of the Heisenberg exchange binds magnons into a two-particle bound state with zero total momentum and spin. This bound state condenses at D >Dc , before single-particle excitations become unstable, and gives rise to a chiral liquid phase, which spontaneously breaks spatial inversion symmetry, but leaves the spin-rotational U(1 ) and time-reversal symmetries intact. This chiral liquid phase is characterized by a finite vector chirality without long-range dipolar magnetic order. In our analytical treatment, the chiral phase appears for arbitrarily small Jz because the magnon-magnon attraction becomes singular near the single-magnon condensation transition. This phase exists in a finite range of D and transforms into the magnetically ordered state at some D calculations.

  1. Employing online quantum random number generators for generating truly random quantum states in Mathematica

    Science.gov (United States)

    Miszczak, Jarosław Adam

    2013-01-01

    The presented package for the Mathematica computing system allows the harnessing of quantum random number generators (QRNG) for investigating the statistical properties of quantum states. The described package implements a number of functions for generating random states. The new version of the package adds the ability to use the on-line quantum random number generator service and implements new functions for retrieving lists of random numbers. Thanks to the introduced improvements, the new version provides faster access to high-quality sources of random numbers and can be used in simulations requiring large amount of random data. New version program summaryProgram title: TRQS Catalogue identifier: AEKA_v2_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKA_v2_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 18 134 No. of bytes in distributed program, including test data, etc.: 2 520 49 Distribution format: tar.gz Programming language: Mathematica, C. Computer: Any supporting Mathematica in version 7 or higher. Operating system: Any platform supporting Mathematica; tested with GNU/Linux (32 and 64 bit). RAM: Case-dependent Supplementary material: Fig. 1 mentioned below can be downloaded. Classification: 4.15. External routines: Quantis software library (http://www.idquantique.com/support/quantis-trng.html) Catalogue identifier of previous version: AEKA_v1_0 Journal reference of previous version: Comput. Phys. Comm. 183(2012)118 Does the new version supersede the previous version?: Yes Nature of problem: Generation of random density matrices and utilization of high-quality random numbers for the purpose of computer simulation. Solution method: Use of a physical quantum random number generator and an on-line service providing access to the source of true random

  2. Quantum random walks and their convergence to Evans–Hudson ...

    Indian Academy of Sciences (India)

    Using coordinate-free basic operators on toy Fock spaces, quantum random walks are defined following the ideas of Attal and Pautrat. Extending the result for one dimensional noise, strong convergence of quantum random walks associated with bounded structure maps to Evans–Hudson flow is proved under suitable ...

  3. Quantum phase transition of a magnet in a spin bath

    DEFF Research Database (Denmark)

    Rønnow, H.M.; Parthasarathy, R.; Jensen, J.

    2005-01-01

    The excitation spectrum of a model magnetic system, LiHoF(4), was studied with the use of neutron spectroscopy as the system was tuned to its quantum critical point by an applied magnetic field. The electronic mode softening expected for a quantum phase transition was forestalled by hyperfine...

  4. Quantum graphs and random-matrix theory

    Science.gov (United States)

    Pluhař, Z.; Weidenmüller, H. A.

    2015-07-01

    For simple connected graphs with incommensurate bond lengths and with unitary symmetry we prove the Bohigas-Giannoni-Schmit (BGS) conjecture in its most general form. Using supersymmetry and taking the limit of infinite graph size, we show that the generating function for every (P,Q) correlation function for both closed and open graphs coincides with the corresponding expression of random-matrix theory. We show that the classical Perron-Frobenius operator is bistochastic and possesses a single eigenvalue +1. In the quantum case that implies the existence of a zero (or massless) mode of the effective action. That mode causes universal fluctuation properties. Avoiding the saddle-point approximation we show that for graphs that are classically mixing (i.e. for which the spectrum of the classical Perron-Frobenius operator possesses a finite gap) and that do not carry a special class of bound states, the zero mode dominates in the limit of infinite graph size.

  5. Griffiths singularities in the random quantum Ising antiferromagnet: A tree tensor network renormalization group study

    Science.gov (United States)

    Lin, Yu-Ping; Kao, Ying-Jer; Chen, Pochung; Lin, Yu-Cheng

    2017-08-01

    The antiferromagnetic Ising chain in both transverse and longitudinal magnetic fields is one of the paradigmatic models of a quantum phase transition. The antiferromagnetic system exhibits a zero-temperature critical line separating an antiferromagnetic phase and a paramagnetic phase; the critical line connects an integrable quantum critical point at zero longitudinal field and a classical first-order transition point at zero transverse field. Using a strong-disorder renormalization group method formulated as a tree tensor network, we study the zero-temperature phase of the quantum Ising chain with bond randomness. We introduce a new matrix product operator representation of high-order moments, which provides an efficient and accurate tool for determining quantum phase transitions via the Binder cumulant of the order parameter. Our results demonstrate an infinite-randomness quantum critical point in zero longitudinal field accompanied by pronounced quantum Griffiths singularities, arising from rare ordered regions with anomalously slow fluctuations inside the paramagnetic phase. The strong Griffiths effects are signaled by a large dynamical exponent z >1 , which characterizes a power-law density of low-energy states of the localized rare regions and becomes infinite at the quantum critical point. Upon application of a longitudinal field, the quantum phase transition between the paramagnetic phase and the antiferromagnetic phase is completely destroyed. Furthermore, quantum Griffiths effects are suppressed, showing z <1 , when the dynamics of the rare regions is hampered by the longitudinal field.

  6. Quantum Entanglement in Random Physical States

    Science.gov (United States)

    Hamma, Alioscia; Santra, Siddhartha; Zanardi, Paolo

    2012-07-01

    Most states in the Hilbert space are maximally entangled. This fact has proven useful to investigate—among other things—the foundations of statistical mechanics. Unfortunately, most states in the Hilbert space of a quantum many-body system are not physically accessible. We define physical ensembles of states acting on random factorized states by a circuit of length k of random and independent unitaries with local support. We study the typicality of entanglement by means of the purity of the reduced state. We find that for a time k=O(1), the typical purity obeys the area law. Thus, the upper bounds for area law are actually saturated, on average, with a variance that goes to zero for large systems. Similarly, we prove that by means of local evolution a subsystem of linear dimensions L is typically entangled with a volume law when the time scales with the size of the subsystem. Moreover, we show that for large values of k the reduced state becomes very close to the completely mixed state.

  7. Improved classical and quantum random access codes

    Science.gov (United States)

    Liabøtrø, O.

    2017-05-01

    A (quantum) random access code ((Q)RAC) is a scheme that encodes n bits into m (qu)bits such that any of the n bits can be recovered with a worst case probability p >1/2 . We generalize (Q)RACs to a scheme encoding n d -levels into m (quantum) d -levels such that any d -level can be recovered with the probability for every wrong outcome value being less than 1/d . We construct explicit solutions for all n ≤d/2m-1 d -1 . For d =2 , the constructions coincide with those previously known. We show that the (Q)RACs are d -parity oblivious, generalizing ordinary parity obliviousness. We further investigate optimization of the success probabilities. For d =2 , we use the measure operators of the previously best-known solutions, but improve the encoding states to give a higher success probability. We conjecture that for maximal (n =4m-1 ,m ,p ) QRACs, p =1/2 {1 +[(√{3}+1)m-1 ] -1} is possible, and show that it is an upper bound for the measure operators that we use. We then compare (n ,m ,pq) QRACs with classical (n ,2 m ,pc) RACs. We can always find pq≥pc , but the classical code gives information about every input bit simultaneously, while the QRAC only gives information about a subset. For several different (n ,2 ,p ) QRACs, we see the same trade-off, as the best p values are obtained when the number of bits that can be obtained simultaneously is as small as possible. The trade-off is connected to parity obliviousness, since high certainty information about several bits can be used to calculate probabilities for parities of subsets.

  8. Quantum optics in multiple scattering random media

    NARCIS (Netherlands)

    Lodahl, P.; Lagendijk, Aart

    2005-01-01

    The paper presents the first experimental study of the propagation of quantum noise through an elastic, multiple scattering medium. Two different types of quantum noise measurements have been carried out: total transmission and short-range frequency correlations. When comparing shot noise (quantum)

  9. Magnetic susceptibility and Landau diamagnetism of quantum collisional plasma

    Science.gov (United States)

    Latyshev, A. V.; Yushkanov, A. A.

    2017-04-01

    Quantum collisional plasma with an arbitrary degree of degeneracy of the electron gas is considered. Using the exact expression for the transverse electric conductivity of quantum collisional plasma, the magnetic susceptibility is described using the kinetic approach and a formula for calculating Landau diamagnetism is derived. Quantum Maxwellian plasma is considered as a special case. To this end, in the formulas derived, the limit is taken for the chemical potential tending to minus infinity. The properties of the magnetic susceptibility of quantum plasma are compared to those of degenerate and Maxwellian plasmas.

  10. Quantum Random Number Generation on a Mobile Phone

    Directory of Open Access Journals (Sweden)

    Bruno Sanguinetti

    2014-09-01

    Full Text Available Quantum random number generators (QRNGs can significantly improve the security of cryptographic protocols by ensuring that generated keys cannot be predicted. However, the cost, size, and power requirements of current Quantum random number generators have prevented them from becoming widespread. In the meantime, the quality of the cameras integrated in mobile telephones has improved significantly so that now they are sensitive to light at the few-photon level. We demonstrate how these can be used to generate random numbers of a quantum origin.

  11. Quantum Darwinism, Decoherence, and the Randomness of Quantum Jumps

    Energy Technology Data Exchange (ETDEWEB)

    Zurek, Wojciech H. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2014-06-05

    Tracing flows of information in our quantum Universe explains why we see the world as classical. Quantum principle of superposition decrees every combination of quantum states a legal quantum state. This is at odds with our experience. Decoherence selects preferred pointer states that survive interaction with the environment. They are localized and effectively classical. They persist while their superpositions decohere. Here we consider emergence of `the classical' starting at a more fundamental pre-decoherence level, tracing the origin of preferred pointer states and deducing their probabilities from the core quantum postulates. We also explore role of the environment as medium through which observers acquire information. This mode of information transfer leads to perception of objective classical reality.

  12. Electron-Phonon coupling in magnetized semiconductor quantum plasmas

    Science.gov (United States)

    Ghosh, S.; Muley, Apurva

    2017-05-01

    Present paper deals with electron-phonon coupling in piezoelectric n-type magnetized semiconductor plasma under quantum regime. A quantum modified dispersion relation is derived for the evolution of desired electron-phonon coupling in semiconductor plasma using quantum hydrodynamic (QHD) model. The main ingredients of this study are the role of non-dimensional quantum parameter-H and externally applied magneto-static field. The presence of quantum parameter-H includes the contributions of Fermi degenerate pressure and quantum diffraction. It represents the ratio of plasmon energy to Fermi energy of the system, hence is a function of doping concentration n0. An expression for gain coefficient of acoustic wave is obtained in terms of quantum parameter-H and magnetic field under the collision dominated limit. We present the effects of doping in medium and orientation of magnetic field on gain profile of acoustic wave. The results show that the presence of magnetic field and quantum effects through quantum parameter-H effectively modifies the gain per unit length of acoustic wave.

  13. Random magnetic field and quasiparticle transport in the mixed state of high- Tc cuprates.

    Science.gov (United States)

    Ye, J

    2001-01-08

    By a singular gauge transformation, the quasiparticle transport in the mixed state of high- Tc cuprates is mapped into a charge-neutral Dirac moving in short-range correlated random scalar and long-range correlated vector potential. A fully quantum mechanical approach to longitudinal and transverse thermal conductivities is presented. The semiclassical Volovik effect is presented in a quantum mechanical way. The quasiparticle scattering from the random magnetic field which was completely missed in all the previous semiclassical approaches is the dominant scattering mechanism at sufficient high magnetic field. The implications for experiments are discussed.

  14. Using Psychokinesis to Explore the Nature of Quantum Randomness

    Science.gov (United States)

    Burns, Jean E.

    2011-11-01

    In retrocausation different causal events can produce different successor events, yet a successor event reflecting a particular cause occurs before the causal event does. It is sometimes proposed that the successor event is determined by propagation of the causal effect backwards in time via the dynamical equations governing the events. However, because dynamical equations are time reversible, the evolution of the system is not subject to change. Therefore, the backward propagation hypothesis implies that what may have seemed to be an arbitrary selection of a causal factor was in reality predetermined. Yet quantum randomness can be used to determine the causal factor, and a quantum random event is ordinarily thought of as being arbitrarily generated. So we must ask, when quantum random events occur, are they arbitrary (subject to their probabilistic constraints) or are they predetermined? Because psychokinesis (PK) can act on quantum random events, it can be used as a probe to explore questions such as the above. It is found that if quantum random events are predetermined (aside from the action of PK), certain types of experimental design can show enhanced PK through the use of precognition. Actual experiments are examined and compared, and most of those for which the design is especially suitable for showing this effect had unusually low p values for the number of trials. It is concluded that either the experimenter produced a remarkably strong experimenter effect or quantum random events are predetermined, thereby enabling enhanced PK in suitable experimental designs.

  15. Operating Quantum States in Single Magnetic Molecules: Implementation of Grover's Quantum Algorithm.

    Science.gov (United States)

    Godfrin, C; Ferhat, A; Ballou, R; Klyatskaya, S; Ruben, M; Wernsdorfer, W; Balestro, F

    2017-11-03

    Quantum algorithms use the principles of quantum mechanics, such as, for example, quantum superposition, in order to solve particular problems outperforming standard computation. They are developed for cryptography, searching, optimization, simulation, and solving large systems of linear equations. Here, we implement Grover's quantum algorithm, proposed to find an element in an unsorted list, using a single nuclear 3/2 spin carried by a Tb ion sitting in a single molecular magnet transistor. The coherent manipulation of this multilevel quantum system (qudit) is achieved by means of electric fields only. Grover's search algorithm is implemented by constructing a quantum database via a multilevel Hadamard gate. The Grover sequence then allows us to select each state. The presented method is of universal character and can be implemented in any multilevel quantum system with nonequal spaced energy levels, opening the way to novel quantum search algorithms.

  16. Operating Quantum States in Single Magnetic Molecules: Implementation of Grover's Quantum Algorithm

    Science.gov (United States)

    Godfrin, C.; Ferhat, A.; Ballou, R.; Klyatskaya, S.; Ruben, M.; Wernsdorfer, W.; Balestro, F.

    2017-11-01

    Quantum algorithms use the principles of quantum mechanics, such as, for example, quantum superposition, in order to solve particular problems outperforming standard computation. They are developed for cryptography, searching, optimization, simulation, and solving large systems of linear equations. Here, we implement Grover's quantum algorithm, proposed to find an element in an unsorted list, using a single nuclear 3 /2 spin carried by a Tb ion sitting in a single molecular magnet transistor. The coherent manipulation of this multilevel quantum system (qudit) is achieved by means of electric fields only. Grover's search algorithm is implemented by constructing a quantum database via a multilevel Hadamard gate. The Grover sequence then allows us to select each state. The presented method is of universal character and can be implemented in any multilevel quantum system with nonequal spaced energy levels, opening the way to novel quantum search algorithms.

  17. Quantum random number generator based on quantum nature of vacuum fluctuations

    Science.gov (United States)

    Ivanova, A. E.; Chivilikhin, S. A.; Gleim, A. V.

    2017-11-01

    Quantum random number generator (QRNG) allows obtaining true random bit sequences. In QRNG based on quantum nature of vacuum, optical beam splitter with two inputs and two outputs is normally used. We compare mathematical descriptions of spatial beam splitter and fiber Y-splitter in the quantum model for QRNG, based on homodyne detection. These descriptions were identical, that allows to use fiber Y-splitters in practical QRNG schemes, simplifying the setup. Also we receive relations between the input radiation and the resulting differential current in homodyne detector. We experimentally demonstrate possibility of true random bits generation by using QRNG based on homodyne detection with Y-splitter.

  18. Chemically fabricated magnetic quantum dots of InP:Mn.

    Science.gov (United States)

    Sahoo, Y; Poddar, P; Srikanth, H; Lucey, D W; Prasad, P N

    2005-08-18

    Quantum dots of InP:Mn are chemically prepared by following hot colloidal nanochemistry with starting precursors that obviate the need for external surfactant. These quantum dots are uniform spheres with 3-nm diameters; they are crystalline, photoluminescent, and magnetic. The crystallographic and optical properties are similar to those of undoped InP nanocrystallites, while the magnetism is consistent with the ferromagnetic response observed in a class of diluted magnetic semiconductors. Because of the ultrafine sizes, the sample shows superparamagnetic behavior, whereas ferromagnetic hysteresis loops are clearly seen below the blocking temperature. Structural characterization and analysis confirm that the magnetism in these quantum dots is not due to segregated binary MnP or MnO phases and that they truly represent a homogeneous dilute magnetic semiconductor.

  19. Experimental measurement-device-independent quantum random-number generation

    Science.gov (United States)

    Nie, You-Qi; Guan, Jian-Yu; Zhou, Hongyi; Zhang, Qiang; Ma, Xiongfeng; Zhang, Jun; Pan, Jian-Wei

    2016-12-01

    The randomness from a quantum random-number generator (QRNG) relies on the accurate characterization of its devices. However, device imperfections and inaccurate characterizations can result in wrong entropy estimation and bias in practice, which highly affects the genuine randomness generation and may even induce the disappearance of quantum randomness in an extreme case. Here we experimentally demonstrate a measurement-device-independent (MDI) QRNG based on time-bin encoding to achieve certified quantum randomness even when the measurement devices are uncharacterized and untrusted. The MDI-QRNG is randomly switched between the regular randomness generation mode and a test mode, in which four quantum states are randomly prepared to perform measurement tomography in real time. With a clock rate of 25 MHz, the MDI-QRNG generates a final random bit rate of 5.7 kbps. Such implementation with an all-fiber setup provides an approach to construct a fully integrated MDI-QRNG with trusted but error-prone devices in practice.

  20. Quantum Magnetism with Ultracold Fermions in an Optical Lattice

    Science.gov (United States)

    Greif, Daniel

    2014-05-01

    In my thesis, I present the observation of quantum magnetism in an ultracold fermionic quantum gas confined to a 3D optical lattice. Ultracold fermionic atoms in optical lattices have long been proposed as a general platform for studying various model systems in condensed matter physics, ranging from geometries that give rise to Dirac points, to magnetically ordered phases. Of particular interest are models for quantum magnetism, which originates from the exchange coupling between quantum-mechanical spins. Yet, reaching the low temperatures required for entering the quantum magnetism regime has proven to be challenging, and has hindered progress for systems based on ultracold fermions in optical lattices. We have addressed and overcome this challenge. We designed an original scheme that enabled us to locally redistribute entropy, such that a subset of lattice bonds reaches temperatures below the exchange energy. The key to this scheme has been a novel type of optical lattice with tunable geometry. Using this lattice, we successfully observed quantum magnetism emerging in the many-body state of a thermalized Fermi gas. Beyond that, the same lattice was the enabling tool for the realization of a tunable artificial graphene system, highlighting the versatility of our approach. This work was performed at ETH Zurich under the supervision of Prof. Tilman Esslinger.

  1. Field-induced magnetic order in quantum spin liquids.

    Science.gov (United States)

    Wessel, S; Olshanii, M; Haas, S

    2001-11-12

    We study magnetic-field-induced three-dimensional ordering transitions in low-dimensional quantum spin liquids, such as weakly coupled, antiferromagnetic spin- 1/2 Heisenberg dimers and ladders. Using stochastic series expansion quantum Monte Carlo simulations, we obtain the critical scaling exponents which dictate the power-law dependence of the transition temperature on the magnetic field. These are compared with recent experiments on candidate materials and with predictions for the Bose-Einstein condensation of magnons. The critical exponents deviate from isotropic mean-field theory and exhibit different scaling behavior at the lower and upper critical magnetic fields.

  2. Electric and Magnetic Interaction between Quantum Dots and Light

    DEFF Research Database (Denmark)

    Tighineanu, Petru

    a future challenge for the droplet-epitaxy technique. A multipolar theory of spontaneous emission from quantum dots is developed to explain the recent observation that In(Ga)As quantum dots break the dipole theory. The analysis yields a large mesoscopic moment, which contains magnetic-dipole and electric......The present thesis reports research on the optical properties of quantum dots by developing new theories and conducting optical measurements. We demonstrate experimentally singlephoton superradiance in interface-uctuation quantum dots by recording the temporal decay dynamics in conjunction...... with second-order correlation measurements and a theoretical model. We measure an oscillator strength of up to 960:8 and an average quantum eciency of (94:83:0)%. This enhanced light-matter coupling is known as the giant oscillator strength of quantum dots, which is shown to be equivalent to superradiance. We...

  3. Introduction to magnetic random-access memory

    CERN Document Server

    Dieny, Bernard; Lee, Kyung-Jin

    2017-01-01

    Magnetic random-access memory (MRAM) is poised to replace traditional computer memory based on complementary metal-oxide semiconductors (CMOS). MRAM will surpass all other types of memory devices in terms of nonvolatility, low energy dissipation, fast switching speed, radiation hardness, and durability. Although toggle-MRAM is currently a commercial product, it is clear that future developments in MRAM will be based on spin-transfer torque, which makes use of electrons’ spin angular momentum instead of their charge. MRAM will require an amalgamation of magnetics and microelectronics technologies. However, researchers and developers in magnetics and in microelectronics attend different technical conferences, publish in different journals, use different tools, and have different backgrounds in condensed-matter physics, electrical engineering, and materials science. This book is an introduction to MRAM for microelectronics engineers written by specialists in magnetic mat rials and devices. It presents the bas...

  4. Quantum well electronic states in a tilted magnetic field

    Science.gov (United States)

    Trallero-Giner, C.; Padilha, J. X.; Lopez-Richard, V.; Marques, G. E.; Castelano, L. K.

    2017-08-01

    We report the energy spectrum and the eigenstates of conduction and uncoupled valence bands of a quantum well under the influence of a tilted magnetic field. In the framework of the envelope approximation, we implement two analytical approaches to obtain the nontrivial solutions of the tilted magnetic field: (a) the Bubnov-Galerkin spectral method and b) the perturbation theory. We discuss the validity of each method for a broad range of magnetic field intensity and orientation as well as quantum well thickness. By estimating the accuracy of the perturbation method, we provide explicit analytical solutions for quantum wells in a tilted magnetic field configuration that can be employed to study several quantitative phenomena.

  5. Probing electric and magnetic vacuum fluctuations with quantum dots

    OpenAIRE

    Tighineanu, Petru; Andersen, Mads Lykke; Sørensen, Anders Søndberg; Stobbe, Søren; Lodahl, Peter

    2014-01-01

    The electromagnetic-vacuum-field fluctuations are intimately linked to the process of spontaneous emission of light. Atomic emitters cannot probe electric- and magnetic-field fluctuations simultaneously because electric and magnetic transitions correspond to different selection rules. In this paper we show that semiconductor quantum dots are fundamentally different and are capable of mediating electric-dipole, magnetic-dipole, and electric-quadrupole transitions on a single electronic resonan...

  6. Random unitary evolution model of quantum Darwinism with pure decoherence

    Science.gov (United States)

    Balanesković, Nenad

    2015-10-01

    We study the behavior of Quantum Darwinism [W.H. Zurek, Nat. Phys. 5, 181 (2009)] within the iterative, random unitary operations qubit-model of pure decoherence [J. Novotný, G. Alber, I. Jex, New J. Phys. 13, 053052 (2011)]. We conclude that Quantum Darwinism, which describes the quantum mechanical evolution of an open system S from the point of view of its environment E, is not a generic phenomenon, but depends on the specific form of input states and on the type of S-E-interactions. Furthermore, we show that within the random unitary model the concept of Quantum Darwinism enables one to explicitly construct and specify artificial input states of environment E that allow to store information about an open system S of interest with maximal efficiency.

  7. Average subentropy, coherence and entanglement of random mixed quantum states

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Lin, E-mail: godyalin@163.com [Institute of Mathematics, Hangzhou Dianzi University, Hangzhou 310018 (China); Singh, Uttam, E-mail: uttamsingh@hri.res.in [Harish-Chandra Research Institute, Allahabad, 211019 (India); Pati, Arun K., E-mail: akpati@hri.res.in [Harish-Chandra Research Institute, Allahabad, 211019 (India)

    2017-02-15

    Compact expressions for the average subentropy and coherence are obtained for random mixed states that are generated via various probability measures. Surprisingly, our results show that the average subentropy of random mixed states approaches the maximum value of the subentropy which is attained for the maximally mixed state as we increase the dimension. In the special case of the random mixed states sampled from the induced measure via partial tracing of random bipartite pure states, we establish the typicality of the relative entropy of coherence for random mixed states invoking the concentration of measure phenomenon. Our results also indicate that mixed quantum states are less useful compared to pure quantum states in higher dimension when we extract quantum coherence as a resource. This is because of the fact that average coherence of random mixed states is bounded uniformly, however, the average coherence of random pure states increases with the increasing dimension. As an important application, we establish the typicality of relative entropy of entanglement and distillable entanglement for a specific class of random bipartite mixed states. In particular, most of the random states in this specific class have relative entropy of entanglement and distillable entanglement equal to some fixed number (to within an arbitrary small error), thereby hugely reducing the complexity of computation of these entanglement measures for this specific class of mixed states.

  8. Many-body localization in the quantum random energy model

    Science.gov (United States)

    Laumann, Chris; Pal, Arijeet

    2014-03-01

    The quantum random energy model is a canonical toy model for a quantum spin glass with a well known phase diagram. We show that the model exhibits a many-body localization-delocalization transition at finite energy density which significantly alters the interpretation of the statistical ``frozen'' phase at lower temperature in isolated quantum systems. The transition manifests in many-body level statistics as well as the long time dynamics of on-site observables. CRL thanks the Perimeter Institute for hospitality and support.

  9. Hyperdiffusion of quantum waves in random photonic lattices

    Science.gov (United States)

    Iomin, Alexander

    2015-08-01

    A quantum-mechanical analysis of hyperfast (faster than ballistic) diffusion of a quantum wave packet in random optical lattices is presented. The main motivation of the presented analysis is experimental demonstrations of hyperdiffusive spreading of a wave packet in random photonic lattices [L. Levi et al., Nature Phys. 8, 912 (2012), 10.1038/nphys2463]. A rigorous quantum-mechanical calculation of the mean probability amplitude is suggested, and it is shown that the power-law spreading of the mean-squared displacement (MSD) is ˜tα , where 2 <α ≤3 . The values of the transport exponent α depend on the correlation properties of the random potential V (x ,t ) , which describes random inhomogeneities of the medium. In particular, when the random potential is δ correlated in time, the quantum wave packet spreads according Richardson turbulent diffusion with the MSD ˜t3 . Hyperdiffusion with α =12 /5 is also obtained for arbitrary correlation properties of the random potential.

  10. Quantum Hall effect in epitaxial graphene with permanent magnets.

    Science.gov (United States)

    Parmentier, F D; Cazimajou, T; Sekine, Y; Hibino, H; Irie, H; Glattli, D C; Kumada, N; Roulleau, P

    2016-12-06

    We have observed the well-kown quantum Hall effect (QHE) in epitaxial graphene grown on silicon carbide (SiC) by using, for the first time, only commercial NdFeB permanent magnets at low temperature. The relatively large and homogeneous magnetic field generated by the magnets, together with the high quality of the epitaxial graphene films, enables the formation of well-developed quantum Hall states at Landau level filling factors v = ±2, commonly observed with superconducting electro-magnets. Furthermore, the chirality of the QHE edge channels can be changed by a top gate. These results demonstrate that basic QHE physics are experimentally accessible in graphene for a fraction of the price of conventional setups using superconducting magnets, which greatly increases the potential of the QHE in graphene for research and applications.

  11. Randomness in quantum mechanics: philosophy, physics and technology.

    Science.gov (United States)

    Bera, Manabendra Nath; Acín, Antonio; Kuś, Marek; Mitchell, Morgan W; Lewenstein, Maciej

    2017-12-01

    This progress report covers recent developments in the area of quantum randomness, which is an extraordinarily interdisciplinary area that belongs not only to physics, but also to philosophy, mathematics, computer science, and technology. For this reason the article contains three parts that will be essentially devoted to different aspects of quantum randomness, and even directed, although not restricted, to various audiences: a philosophical part, a physical part, and a technological part. For these reasons the article is written on an elementary level, combining simple and non-technical descriptions with a concise review of more advanced results. In this way readers of various provenances will be able to gain while reading the article.

  12. On the reduction criterion for random quantum states

    Energy Technology Data Exchange (ETDEWEB)

    Jivulescu, Maria Anastasia, E-mail: maria.jivulescu@upt.ro; Lupa, Nicolae, E-mail: nicolae.lupa@upt.ro [Department of Mathematics, Politehnica University of Timişoara, Victoriei Square 2, 300006 Timişoara (Romania); Nechita, Ion, E-mail: nechita@irsamc.ups-tlse.fr [CNRS, Laboratoire de Physique Théorique, IRSAMC, Université de Toulouse, UPS, F-31062 Toulouse (France)

    2014-11-15

    In this paper, we study the reduction criterion for detecting entanglement of large dimensional bipartite quantum systems. We first obtain an explicit formula for the moments of a random quantum state to which the reduction criterion has been applied. We show that the empirical eigenvalue distribution of this random matrix converges strongly to a limit that we compute, in three different asymptotic regimes. We then employ tools from free probability theory to study the asymptotic positivity of the reduction operators. Finally, we compare the reduction criterion with other entanglement criteria, via thresholds.

  13. Entanglement dynamics in critical random quantum Ising chain with perturbations

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Yichen, E-mail: ychuang@caltech.edu

    2017-05-15

    We simulate the entanglement dynamics in a critical random quantum Ising chain with generic perturbations using the time-evolving block decimation algorithm. Starting from a product state, we observe super-logarithmic growth of entanglement entropy with time. The numerical result is consistent with the analytical prediction of Vosk and Altman using a real-space renormalization group technique. - Highlights: • We study the dynamical quantum phase transition between many-body localized phases. • We simulate the dynamics of a very long random spin chain with matrix product states. • We observe numerically super-logarithmic growth of entanglement entropy with time.

  14. Randomness in quantum mechanics: philosophy, physics and technology

    Science.gov (United States)

    Nath Bera, Manabendra; Acín, Antonio; Kuś, Marek; Mitchell, Morgan W.; Lewenstein, Maciej

    2017-12-01

    This progress report covers recent developments in the area of quantum randomness, which is an extraordinarily interdisciplinary area that belongs not only to physics, but also to philosophy, mathematics, computer science, and technology. For this reason the article contains three parts that will be essentially devoted to different aspects of quantum randomness, and even directed, although not restricted, to various audiences: a philosophical part, a physical part, and a technological part. For these reasons the article is written on an elementary level, combining simple and non-technical descriptions with a concise review of more advanced results. In this way readers of various provenances will be able to gain while reading the article.

  15. Universal quantum control in zero-field nuclear magnetic resonance

    Science.gov (United States)

    Bian, Ji; Jiang, Min; Cui, Jiangyu; Liu, Xiaomei; Chen, Botao; Ji, Yunlan; Zhang, Bo; Blanchard, John; Peng, Xinhua; Du, Jiangfeng

    2017-05-01

    This paper describes a general method for the manipulation of nuclear spins in zero magnetic field. In the absence of magnetic fields, the spins lose the individual information on chemical shifts and inequivalent spins can only be distinguished by nuclear gyromagnetic ratios and spin-spin couplings. For spin-1/2 nuclei with different gyromagnetic ratios (i.e., different species) in zero magnetic field, we describe the scheme to realize a set of universal quantum logic gates, e.g., arbitrary single-qubit gates and a two-qubit controlled-not gate. This method allows for universal quantum control in systems which might provide promising applications in materials science, chemistry, biology, quantum information processing, and fundamental physics.

  16. Random-matrix theory of quantum transport

    Energy Technology Data Exchange (ETDEWEB)

    Beenakker, C.W. [Instituut-Lorentz, University of Leiden, 2300 RA Leiden, (The Netherlands)

    1997-07-01

    This is a review of the statistical properties of the scattering matrix of a mesoscopic system. Two geometries are contrasted: A quantum dot and a disordered wire. The quantum dot is a confined region with a chaotic classical dynamics, which is coupled to two electron reservoirs via point contacts. The disordered wire also connects two reservoirs, either directly or via a point contact or tunnel barrier. One of the two reservoirs may be in the superconducting state, in which case conduction involves Andreev reflection at the interface with the superconductor. In the case of the quantum dot, the distribution of the scattering matrix is given by either Dyson{close_quote}s circular ensemble for ballistic point contacts or the Poisson kernel for point contacts containing a tunnel barrier. In the case of the disordered wire, the distribution of the scattering matrix is obtained from the Dorokhov-Mello-Pereyra-Kumar equation, which is a one-dimensional scaling equation. The equivalence is discussed with the nonlinear {sigma} model, which is a supersymmetric field theory of localization. The distribution of scattering matrices is applied to a variety of physical phenomena, including universal conductance fluctuations, weak localization, Coulomb blockade, sub-Poissonian shot noise, reflectionless tunneling into a superconductor, and giant conductance oscillations in a Josephson junction. {copyright} {ital 1997} {ital The American Physical Society}

  17. Magnetic polyoxometalates: from molecular magnetism to molecular spintronics and quantum computing.

    Science.gov (United States)

    Clemente-Juan, Juan M; Coronado, Eugenio; Gaita-Ariño, Alejandro

    2012-11-21

    In this review we discuss the relevance of polyoxometalate (POM) chemistry to provide model objects in molecular magnetism. We present several potential applications in nanomagnetism, in particular, in molecular spintronics and quantum computing.

  18. Spontaneous magnetization of quantum XY spin model in joint presence of quenched and annealed disorder

    Science.gov (United States)

    Bera, Anindita; Rakshit, Debraj; SenDe, Aditi; Sen, Ujjwal

    2017-06-01

    We investigate equilibrium statistical properties of the isotropic quantum XY spin-1/2 model in an external magnetic field when the interaction and field parts are subjected to quenched or annealed disorder or both. The randomness present in the system are termed annealed or quenched depending on the relation between two different time scales—the time scale associated with the equilibration of the randomness and the time of observation. Within a mean-field framework, we study the effects of disorders on spontaneous magnetization, both by perturbative and numerical techniques. Our primary interest is to understand the differences between quenched and annealed cases, and also to investigate the interplay when both of them are present in a system. We find that the magnetization survives in the presence of a unidirectional random field, irrespective of its nature, i.e., whether it is quenched or annealed. However, the field breaks the circular symmetry of the magnetization, and the system magnetizes in specific directions, parallel or transverse to the applied magnetic field. Interestingly, while the transverse magnetization is affected by the annealed disordered field, the parallel one remains unfazed by the same. Moreover, the annealed disorder present in the interaction term does not affect the system's spontaneous magnetization and the corresponding critical temperature, irrespective of the presence or absence of quenched or annealed disorder in the field term. We carry out a comparative study of these and all other different combinations of the disorders in the interaction and field terms, and point out their generic features.

  19. Spin-Orbit Coupling, Antilocalization, and Parallel Magnetic Fields in Quantum Dots

    DEFF Research Database (Denmark)

    Zumbuhl, D.; Miller, Jessica; M. Marcus, C.

    2002-01-01

    We investigate antilocalization due to spin-orbit coupling in ballistic GaAs quantum dots. Antilocalization that is prominent in large dots is suppressed in small dots, as anticipated theoretically. Parallel magnetic fields suppress both antilocalization and also, at larger fields, weak...... localization, consistent with random matrix theory results once orbital coupling of the parallel field is included. In situ control of spin-orbit coupling in dots is demonstrated as a gate-controlled crossover from weak localization to antilocalization....

  20. Multiferroic Magnetic Spirals Induced by Random Magnetic Exchanges

    Science.gov (United States)

    Scaramucci, Andrea; Shinaoka, Hiroshi; Mostovoy, Maxim V.; Müller, Markus; Mudry, Christopher; Troyer, Matthias; Spaldin, Nicola A.

    2018-01-01

    Multiferroism can originate from the breaking of inversion symmetry caused by magnetic-spiral order. The usual mechanism for stabilizing a magnetic spiral is competition between magnetic exchange interactions differing by their range and sign, such as nearest-neighbor and next-nearest-neighbor interactions. In insulating compounds, it is unusual for these interactions to be both comparable in magnitude and of a strength that can induce magnetic ordering at room temperature. Therefore, the onset temperatures for multiferroism through this mechanism are typically low. By considering a realistic model for multiferroic YBaCuFeO5 , we propose an alternative mechanism for magnetic-spiral order, and hence for multiferroism, that occurs at much higher temperatures. We show, using Monte Carlo simulations and electronic structure calculations based on density functional theory, that the Heisenberg model on a geometrically nonfrustrated lattice with only nearest-neighbor interactions can have a spiral phase up to high temperature when frustrating bonds are introduced randomly along a single crystallographic direction as caused, e.g., by a particular type of chemical disorder. This long-range correlated pattern of frustration avoids ferroelectrically inactive spin-glass order. Finally, we provide an intuitive explanation for this mechanism and discuss its generalization to other materials.

  1. Quantum Chaos and Random Matrix Theory Some New Results

    CERN Document Server

    Smilansky, U

    1996-01-01

    New insight into the correspondence between Quantum Chaos and Random Matrix Theory is gained by developing a semiclassical theory for the autocorrelation function of spectral determinants. We study in particular the unitary operators which are the quantum versions of area preserving maps. The relevant Random Matrix ensembles are the Circular ensembles. The resulting semiclassical expressions depend on the symmetry of the system with respect to time reversal, and on a classical parameter $\\mu = tr U -1$ where U is the classical 1-step evolution operator. For system without time reversal symmetry, we are able to reproduce the exact Random Matrix predictions in the limit $\\mu \\to 0$. For systems with time reversal symmetry we can reproduce only some of the features of Random Matrix Theory. For both classes we obtain the leading corrections in $\\mu$. The semiclassical theory for integrable systems is also developed, resulting in expressions which reproduce the theory for the Poissonian ensemble to leading order i...

  2. Open quantum systems and random matrix theory

    Energy Technology Data Exchange (ETDEWEB)

    Mulhall, Declan [Department of Physics/Engineering, University of Scranton, Scranton, Pennsylvania 18510-4642 (United States)

    2014-10-15

    A simple model for open quantum systems is analyzed with RMT. The system is coupled to the continuum in a minimal way. In this paper we see the effect of opening the system on the level statistics, in particular the level spacing, width distribution and Δ{sub 3}(L) statistic are examined as a function of the strength of this coupling. The usual super-radiant state is observed, and it is seen that as it is formed, the level spacing and Δ{sub 3}(L) statistic exhibit the signatures of missed levels.

  3. An effective Hamiltonian approach to quantum random walk

    Indian Academy of Sciences (India)

    In this article we present an effective Hamiltonian approach for discrete time quantum random walk. A form of the Hamiltonian ... TARUN KANTI GHOSH2. Inter-University Centre for Astronomy and Astrophysics, Ganeshkhind, Pune 411 007, India; Department of Physics, Indian Institute of Technology, Kanpur 208 016, India ...

  4. Entanglement dynamics in critical random quantum Ising chain with perturbations

    Science.gov (United States)

    Huang, Yichen

    2017-05-01

    We simulate the entanglement dynamics in a critical random quantum Ising chain with generic perturbations using the time-evolving block decimation algorithm. Starting from a product state, we observe super-logarithmic growth of entanglement entropy with time. The numerical result is consistent with the analytical prediction of Vosk and Altman using a real-space renormalization group technique.

  5. Ionization equilibrium of a magnetized quantum plasma

    Energy Technology Data Exchange (ETDEWEB)

    Steinberg, M.; Ortner, J.; Ebeling, W. [Humboldt-Universitaet, Berlin (Germany). Inst. fuer Physik

    2001-07-01

    The influence of a constant uniform magnetic field on the ionization equilibrium and the thermodynamic properties of a nondegenerate partially ionized hydrogen plasma is studied for weak and strong magnetic fields. A simple interpolation formula for an effective partition function is proposed, connecting the the low- and high-field results. Furthermore, a closed analytical approximation for the thermodynamic functions in the chemical picture and a Saha equation for weakly and strongly magnetized plasmas are presented. (orig.)

  6. Embedded Memory Hierarchy Exploration Based on Magnetic Random Access Memory

    Directory of Open Access Journals (Sweden)

    Luís Vitório Cargnini

    2014-08-01

    Full Text Available Static random access memory (SRAM is the most commonly employed semiconductor in the design of on-chip processor memory. However, it is unlikely that the SRAM technology will have a cell size that will continue to scale below 45 nm, due to the leakage current that is caused by the quantum tunneling effect. Magnetic random access memory (MRAM is a candidate technology to replace SRAM, assuming appropriate dimensioning given an operating threshold voltage. The write current of spin transfer torque (STT-MRAM is a known limitation; however, this has been recently mitigated by leveraging perpendicular magnetic tunneling junctions. In this article, we present a comprehensive comparison of spin transfer torque-MRAM (STT-MRAM and SRAM cache set banks. The non-volatility of STT-MRAM allows the definition of new instant on/off policies and leakage current optimizations. Through our experiments, we demonstrate that STT-MRAM is a candidate for the memory hierarchy of embedded systems, due to the higher densities and reduced leakage of MRAM.We demonstrate that adopting STT-MRAM in L1 and L2 caches mitigates the impact of higher write latencies and increased current draw due to the use of MRAM. With the correct system-on-chip (SoC design, we believe that STT-MRAM is a viable alternative to SRAM, which minimizes leakage current and the total power consumed by the SoC.

  7. Theory of Random Anisotropic Magnetic Alloys

    DEFF Research Database (Denmark)

    Lindgård, Per-Anker

    1976-01-01

    A mean-field-crystal-field theory is developed for random, multicomponent, anisotropic magnetic alloys. It is specially applicable to rare-earth alloys. A discussion is given of multicritical points and phase transitions between various states characterized by order parameters with different...... spatial directions or different ordering wave vectors. Theoretical predictions based on known parameters for the phase diagrams and magnetic moments for the binary rare-earth alloys of Tb, Dy, Ho, and Er, Tb-Tm, Nd-Pr, and pure double-hcp Nd agree qualitatively with the experimental observations....... Quantitative agreement can be obtained by increasing the interaction between different alloy elements, in particular for alloys with very different axial anisotropy, e.g., Tb-Tm. A model system consisting of a singlet-singlet and singlet-doublet alloy is discussed in detail. A simple procedure to include...

  8. Curie and Neel Temperatures of Quantum Magnets

    OpenAIRE

    Oitmaa, J.; Zheng, Weihong

    2004-01-01

    We estimate, using high-temperature series expansions, the transition temperatures of the spin 1/2, 1 and 3/2 Heisenberg ferromagnet and antiferromagnet in 3-dimensions. The manner in which the difference between Curie and Neel temperatures vanishes with increasing spin quantum number is investigated.

  9. Magnetic response in ideal quantum gases: the thermodynamic limit

    DEFF Research Database (Denmark)

    Cornean, Horia Decebal

    2003-01-01

    We investigate the thermodynamic behavior of a confined ideal quantum gas when subjected to an external magnetic filed $\\omega$. Roughly speaking, we claim that the derivatives of any order with respect to $\\omega$ of the grand-canonical (canonical) potential admit a certain type of thermodynamic...

  10. Source-Device-Independent Ultrafast Quantum Random Number Generation

    Science.gov (United States)

    Marangon, Davide G.; Vallone, Giuseppe; Villoresi, Paolo

    2017-02-01

    Secure random numbers are a fundamental element of many applications in science, statistics, cryptography and more in general in security protocols. We present a method that enables the generation of high-speed unpredictable random numbers from the quadratures of an electromagnetic field without any assumption on the input state. The method allows us to eliminate the numbers that can be predicted due to the presence of classical and quantum side information. In particular, we introduce a procedure to estimate a bound on the conditional min-entropy based on the entropic uncertainty principle for position and momentum observables of infinite dimensional quantum systems. By the above method, we experimentally demonstrated the generation of secure true random bits at a rate greater than 1.7 Gbit /s .

  11. Convergence rates for arbitrary statistical moments of random quantum circuits.

    Science.gov (United States)

    Brown, Winton G; Viola, Lorenza

    2010-06-25

    We consider a class of random quantum circuits where at each step a gate from a universal set is applied to a random pair of qubits, and determine how quickly averages of arbitrary finite-degree polynomials in the matrix elements of the resulting unitary converge to Haar measure averages. This is accomplished by mapping the superoperator that describes t order moments on n qubits to a multilevel SU(4^{t}) Lipkin-Meshkov-Glick Hamiltonian. We show that, for arbitrary fixed t, the ground-state manifold is exactly spanned by factorized eigenstates and, under the assumption that a mean-field ansatz accurately describes the low-lying excitations, the spectral gap scales as 1/n in the thermodynamic limit. Our results imply that random quantum circuits yield an efficient implementation of ϵ approximate unitary t designs.

  12. Vertically coupled double quantum rings at zero magnetic field

    Science.gov (United States)

    Malet, F.; Barranco, M.; Lipparini, E.; Mayol, R.; Pi, M.; Climente, J. I.; Planelles, J.

    2006-06-01

    Within local-spin-density functional theory, we have investigated the “dissociation” of few-electron circular vertical semiconductor double quantum ring artificial molecules at zero magnetic field as a function of inter-ring distance. In a first step, the molecules are constituted by two identical quantum rings. When the rings are quantum mechanically strongly coupled, the electronic states are substantially delocalized, and the addition energy spectra of the artificial molecule resemble those of a single quantum ring in the few-electron limit. When the rings are quantum mechanically weakly coupled, the electronic states in the molecule are substantially localized in one ring or the other, although the rings can be electrostatically coupled. The effect of a slight mismatch introduced in the molecules from nominally identical quantum wells, or from changes in the inner radius of the constituent rings, induces localization by offsetting the energy levels in the quantum rings. This plays a crucial role in the appearance of the addition spectra as a function of coupling strength particularly in the weak coupling limit.

  13. Quantum-well-driven magnetism in thin films

    DEFF Research Database (Denmark)

    Mirbt, S.; Johansson, B.; Skriver, Hans Lomholt

    1996-01-01

    We have performed local spin-density calculations for an fee (100) Ag substrate covered by 1 to 16 monolayers (ML) of Pd. We find that thin films of Pd are magnetic with a moment of the order of 0.3 mu(B) except for films of 1-2 ML and 5-7 ML where magnetism is completely suppressed. We present...... a physically transparent explanation of this behavior in terms of the Stoner picture and magnetic quantum-well states....

  14. FIT-MART: Quantum Magnetism with a Gentle Learning Curve

    Science.gov (United States)

    Engelhardt, Larry; Garland, Scott C.; Rainey, Cameron; Freeman, Ray A.

    We present a new open-source software package, FIT-MART, that allows non-experts to quickly get started sim- ulating quantum magnetism. FIT-MART can be downloaded as a platform-idependent executable Java (JAR) file. It allows the user to define (Heisenberg) Hamiltonians by electronically drawing pictures that represent quantum spins and operators. Sliders are automatically generated to control the values of the parameters in the model, and when the values change, several plots are updated in real time to display both the resulting energy spectra and the equilibruim magnetic properties. Several experimental data sets for real magnetic molecules are included in FIT-MART to allow easy comparison between simulated and experimental data, and FIT-MART users can also import their own data for analysis and compare the goodness of fit for different models.

  15. Ferroelectricity by Bose-Einstein condensation in a quantum magnet.

    Science.gov (United States)

    Kimura, S; Kakihata, K; Sawada, Y; Watanabe, K; Matsumoto, M; Hagiwara, M; Tanaka, H

    2016-09-26

    The Bose-Einstein condensation is a fascinating phenomenon, which results from quantum statistics for identical particles with an integer spin. Surprising properties, such as superfluidity, vortex quantization or Josephson effect, appear owing to the macroscopic quantum coherence, which spontaneously develops in Bose-Einstein condensates. Realization of Bose-Einstein condensation is not restricted in fluids like liquid helium, a superconducting phase of paired electrons in a metal and laser-cooled dilute alkali atoms. Bosonic quasi-particles like exciton-polariton and magnon in solids-state systems can also undergo Bose-Einstein condensation in certain conditions. Here, we report that the quantum coherence in Bose-Einstein condensate of the magnon quasi particles yields spontaneous electric polarization in the quantum magnet TlCuCl 3 , leading to remarkable magnetoelectric effect. Very soft ferroelectricity is realized as a consequence of the O(2) symmetry breaking by magnon Bose-Einstein condensation. The finding of this ferroelectricity will open a new window to explore multi-functionality of quantum magnets.

  16. Single-atom gating and magnetic interactions in quantum corrals

    Energy Technology Data Exchange (ETDEWEB)

    Ngo, Anh T.; Kim, Eugene H.; Ulloa, Sergio E.

    2017-04-01

    Single-atom gating, achieved by manipulation of adatoms on a surface, has been shown in experiments to allow precise control over superposition of electronic states in quantum corrals. Using a Green's function approach, we demonstrate theoretically that such atom gating can also be used to control the coupling between magnetic degrees of freedom in these systems. Atomic gating enables control not only on the direct interaction between magnetic adatoms, but also over superpositions of many-body states which can then control long distance interactions. We illustrate this effect by considering the competition between direct exchange between magnetic impurities and the Kondo screening mediated by the host electrons, and how this is affected by gating. These results suggest that both magnetic and nonmagnetic single-atom gating may be used to investigate magnetic impurity systems with tailored interactions, and may allow the control of entanglement of different spin states.

  17. Magnetic quantum dots in biotechnology--synthesis and applications.

    Science.gov (United States)

    Mahajan, Kalpesh D; Fan, Qirui; Dorcéna, Jenny; Ruan, Gang; Winter, Jessica O

    2013-12-01

    Quantum dots (QDs) have great promise in biological imaging, and as this promise is realized, there has been increasing interest in combining the benefits of QDs with those of other materials to yield composites with multifunctional properties. One of the most common materials combined with QDs is magnetic materials, either as ions (e.g. gadolinium) or as nanoparticles (e.g. superparamagnetic iron oxide nanoparticles, SPIONs). The fluorescent property of the QDs permits visualization, whereas the magnetic property of the composite enables imaging, magnetic separation, and may even have therapeutic benefit. In this review, the synthesis of fluorescent-magnetic nanoparticles, including magnetic QDs is explored; and the applications of these materials in imaging, separations, and theranostics are discussed. As the properties of these materials continue to improve, QDs have the potential to greatly impact biological imaging, diagnostics, and treatment. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Dynamics in quantum Ising chain driven by inhomogeneous transverse magnetization

    Science.gov (United States)

    Bhattacharyya, Sirshendu; Dasgupta, Subinay

    2017-07-01

    We study the dynamics caused by transport of transverse magnetization in one dimensional transverse Ising chain at zero temperature. We observe that a class of initial states having product structure in fermionic momentum-space and satisfying certain criteria, produce spatial variation in transverse magnetization. Starting from such a state, we obtain the transverse magnetization analytically and then observe its dynamics in presence of a homogeneous constant field Γ. In contradiction with general expectation, whatever be the strength of the field, the magnetization of the system does not become homogeneous even after infinite time. At each site, the dynamics is associated with oscillations having two different timescales. The envelope of the larger timescale oscillation decays algebraically with an exponent which is invariant for all such special initial states. The frequency of this oscillation varies differently with external field in ordered and disordered phases. The local magnetization after infinite time also characterizes the quantum phase transition.

  19. Some comments on quantum magnetic monopoles

    Energy Technology Data Exchange (ETDEWEB)

    Botelho, Luiz C.L. [Universidade Federal Fluminense (UFF), Niteroi, RJ (Brazil). Inst. de Matematica. Dept. de Matematica Aplicada]. E-mail: botelho.luiz@ig.com.br

    2008-07-01

    In this paper we intend to present some path-integral studies in the problem of confinement in the presence of fermionic and scalar magnetic monopole fields through: a Wilson loop path-integral evaluation associated to an effective second-quantized electromagnetic field generated by chiral abelian point-like monopole magnetic field current at its large mass London asymptotic limit; a path-integral bosonization analysis of quarks fields interacting with Kalb-Ramond fields considered as an effective disorder field theory of a Q.C.D. vacuum of heavier monopoles; improvements on the Wilson loops evaluations in the well-known ADHM Antonov-Ebert model for Cooper pairs of point-like fermionic magnetic monopoles. (author)

  20. Quantum statistical mechanics of electron gas in magnetic field

    Directory of Open Access Journals (Sweden)

    I.M.Dubrovskii

    2006-01-01

    Full Text Available Electron eigenstates in a magnetic field are considered. Density of the probability current and an averaged magnetic moment are obtained. Density of states is investigated for two-dimensional electron in a circle that is bound by the infinite potential barrier. The present study shows that the common quantum statistical mechanics of electron gas in a magnetic field leads to incorrect results. The magnetic moment of electron gas can be computed as the sum of averaged moments of the occupied states. The computations lead to the results that differ from the ones obtained as the derivative of the thermodynamical potential with respect to the magnetic field. Other contradictions in common statistical thermodynamics of electron gas in a magnetic field are pointed out. The conclusion is done that these contradictions arise from using the incorrect statistical operator. A new quantum function of distribution is derived from the basic principles, taking into account the law of conservation of an angular momentum. These results are in accord with the theory that has been obtained within the framework of classical statistical thermodynamics in the previous work.

  1. Quantum phenomena in magnetic nano clusters

    Indian Academy of Sciences (India)

    While semiconductor structures have provided paradigms of nanosystems from the stand point of electronic phenomena, the synthesis of high nuclearity transition metal complexes have provided examples of nano magnets. The range and diversity of the properties exhibited by these systems rivals its electronic counterparts ...

  2. A Novel Algorithm of Quantum Random Walk in Server Traffic Control and Task Scheduling

    Directory of Open Access Journals (Sweden)

    Dong Yumin

    2014-01-01

    Full Text Available A quantum random walk optimization model and algorithm in network cluster server traffic control and task scheduling is proposed. In order to solve the problem of server load balancing, we research and discuss the distribution theory of energy field in quantum mechanics and apply it to data clustering. We introduce the method of random walk and illuminate what the quantum random walk is. Here, we mainly research the standard model of one-dimensional quantum random walk. For the data clustering problem of high dimensional space, we can decompose one m-dimensional quantum random walk into m one-dimensional quantum random walk. In the end of the paper, we compare the quantum random walk optimization method with GA (genetic algorithm, ACO (ant colony optimization, and SAA (simulated annealing algorithm. In the same time, we prove its validity and rationality by the experiment of analog and simulation.

  3. Randomness in quantum mechanics - nature's ultimate cryptogram

    Energy Technology Data Exchange (ETDEWEB)

    Erber, T.; Putterman, S.

    1985-11-07

    Will a single atom irradiated by coherent light be equivalent to an infinite computer as regards its ability to generate random numbers. As described in the paper, a search for unexpected patterns of order by cryptanalysis of the telegraph signal generated by the on/off time of the atom's fluorescence will provide new experimental tests of the fundamental principles of the quantum theory. (author).

  4. Random matrices as models for the statistics of quantum mechanics

    Science.gov (United States)

    Casati, Giulio; Guarneri, Italo; Mantica, Giorgio

    1986-05-01

    Random matrices from the Gaussian unitary ensemble generate in a natural way unitary groups of evolution in finite-dimensional spaces. The statistical properties of this time evolution can be investigated by studying the time autocorrelation functions of dynamical variables. We prove general results on the decay properties of such autocorrelation functions in the limit of infinite-dimensional matrices. We discuss the relevance of random matrices as models for the dynamics of quantum systems that are chaotic in the classical limit. Permanent address: Dipartimento di Fisica, Via Celoria 16, 20133 Milano, Italy.

  5. Far-from-equilibrium quantum magnetism with ultracold polar molecules.

    Science.gov (United States)

    Hazzard, Kaden R A; Manmana, Salvatore R; Foss-Feig, Michael; Rey, Ana Maria

    2013-02-15

    Recent theory has indicated how to emulate tunable models of quantum magnetism with ultracold polar molecules. Here we show that present molecule optical lattice experiments can accomplish three crucial goals for quantum emulation, despite currently being well below unit filling and not quantum degenerate. The first is to verify and benchmark the models proposed to describe these systems. The second is to prepare correlated and possibly useful states in well-understood regimes. The third is to explore many-body physics inaccessible to existing theoretical techniques. Our proposal relies on a nonequilibrium protocol that can be viewed either as Ramsey spectroscopy or an interaction quench. The proposal uses only routine experimental tools available in any ultracold molecule experiment. To obtain a global understanding of the behavior, we treat short times pertubatively, develop analytic techniques to treat the Ising interaction limit, and apply a time-dependent density matrix renormalization group to disordered systems with long range interactions.

  6. Quantum Corrections Crossover and Ferromagnetism in Magnetic Topological Insulators

    Science.gov (United States)

    Bao, Lihong; Wang, Weiyi; Meyer, Nicholas; Liu, Yanwen; Zhang, Cheng; Wang, Kai; Ai, Ping; Xiu, Faxian

    2013-01-01

    Revelation of emerging exotic states of topological insulators (TIs) for future quantum computing applications relies on breaking time-reversal symmetry and opening a surface energy gap. Here, we report on the transport response of Bi2Te3 TI thin films in the presence of varying Cr dopants. By tracking the magnetoconductance (MC) in a low doping regime we observed a progressive crossover from weak antilocalization (WAL) to weak localization (WL) as the Cr concentration increases. In a high doping regime, however, increasing Cr concentration yields a monotonically enhanced anomalous Hall effect (AHE) accompanied by an increasing carrier density. Our results demonstrate a possibility of manipulating bulk ferromagnetism and quantum transport in magnetic TI, thus providing an alternative way for experimentally realizing exotic quantum states required by spintronic applications. PMID:23928713

  7. Design of magnetic coordination complexes for quantum computing.

    Science.gov (United States)

    Aromí, Guillem; Aguilà, David; Gamez, Patrick; Luis, Fernando; Roubeau, Olivier

    2012-01-21

    A very exciting prospect in coordination chemistry is to manipulate spins within magnetic complexes for the realization of quantum logic operations. An introduction to the requirements for a paramagnetic molecule to act as a 2-qubit quantum gate is provided in this tutorial review. We propose synthetic methods aimed at accessing such type of functional molecules, based on ligand design and inorganic synthesis. Two strategies are presented: (i) the first consists in targeting molecules containing a pair of well-defined and weakly coupled paramagnetic metal aggregates, each acting as a carrier of one potential qubit, (ii) the second is the design of dinuclear complexes of anisotropic metal ions, exhibiting dissimilar environments and feeble magnetic coupling. The first systems obtained from this synthetic program are presented here and their properties are discussed.

  8. Biosensing utilizing magnetic markers and superconducting quantum interference devices

    Science.gov (United States)

    Enpuku, Keiji; Tsujita, Yuya; Nakamura, Kota; Sasayama, Teruyoshi; Yoshida, Takashi

    2017-05-01

    Magnetic biosensing techniques that are based on the use of bio-functionalized magnetic nanoparticles (magnetic markers) and superconducting quantum interference devices (SQUIDs) are expected to have various advantages when compared with conventional biosensing methods. In this paper, we review the recent progress made in magnetic biosensing techniques. First, we describe the most important parameters of magnetic markers that are intended for use in biosensing, i.e., the magnetic signal and the relaxation time that are determined by the Brownian and/or Néel relaxation mechanisms. We note that these parameters are significantly dependent on the marker size, and as a result, commercial markers exhibit a wide variety of values for these key parameters. Next, we describe three measurement methods that have been developed based on the magnetic properties of these markers, i.e., AC susceptibility, relaxation and remanence-based measurement methods. The weak (picotesla-range) signals emitted by the markers can be measured precisely with a SQUID system using these methods. Finally, we give examples of biosensing for in vitro and in vivo medical diagnosis applications. For in vitro diagnosis, high-sensitivity detection of various biological targets has been demonstrated without use of any washing process to separate the bound and free markers. For in vivo applications, detection of the quantities and the three-dimensional positions of the markers that have been injected into the test subject are demonstrated. These results confirm the effectiveness of magnetic biosensing techniques.

  9. Hidden Magnetic Frustration by Quantum Relaxation in Anisotropic Nd Langasite

    Science.gov (United States)

    Simonet, V.; Ballou, R.; Robert, J.; Canals, B.; Hippert, F.; Bordet, P.; Lejay, P.; Fouquet, P.; Ollivier, J.; Braithwaite, D.

    2008-06-01

    The static and dynamic magnetic properties of the Nd3Ga5SiO14 compound, which appears as the first materialization of a rare-earth kagome-type lattice, were reexamined, owing to contradictory results in the previous studies. Neutron scattering, magnetization, and specific heat measurements were performed and analyzed, in particular, by fully taking account of the crystal electric field effects on the Nd3+ ions. One of the novel findings is that the peculiar temperature independent spin dynamics observed below 10 K expresses single-ion quantum processes. This would short-circuit the frustration induced cooperative dynamics, which would emerge only at very low temperature.

  10. Quantum mechanics with a momentum-space artificial magnetic field.

    Science.gov (United States)

    Price, Hannah M; Ozawa, Tomoki; Carusotto, Iacopo

    2014-11-07

    The Berry curvature is a geometrical property of an energy band which acts as a momentum space magnetic field in the effective Hamiltonian describing single-particle quantum dynamics. We show how this perspective may be exploited to study systems directly relevant to ultracold gases and photonics. Given the exchanged roles of momentum and position, we demonstrate that the global topology of momentum space is crucially important. We propose an experiment to study the Harper-Hofstadter Hamiltonian with a harmonic trap that will illustrate the advantages of this approach and that will also constitute the first realization of magnetism on a torus.

  11. Longitudinal modes of quantum dots in magnetic fields

    Science.gov (United States)

    Serra, Ll.; Pi, M.; Emperador, A.; Barranco, M.; Lipparini, E.

    The far infrared longitudinal spin and density responses of two-dimensional quantum dots are discussed within local spin-density functional theory. The influence of a partial spin polarization, induced by a perpendicular static magnetic field, is taken into account in the coupling of spin and density channels. As an illustrative application, the case of a dot made of 5 electrons in parabolic confinement is discussed.

  12. Single-Particle Quantum Dynamics in a Magnetic Lattice

    Energy Technology Data Exchange (ETDEWEB)

    Venturini, Marco

    2001-02-01

    We study the quantum dynamics of a spinless charged-particle propagating through a magnetic lattice in a transport line or storage ring. Starting from the Klein-Gordon equation and by applying the paraxial approximation, we derive a Schroedinger-like equation for the betatron motion. A suitable unitary transformation reduces the problem to that of a simple harmonic oscillator. As a result we are able to find an explicit expression for the particle wavefunction.

  13. Single cell magnetic imaging using a quantum diamond microscope

    Science.gov (United States)

    Park, H.; Weissleder, R.; Yacoby, A.; Lukin, M. D.; Lee, H.; Walsworth, R. L.; Connolly, C. B.

    2015-01-01

    We apply a quantum diamond microscope to detection and imaging of immunomagnetically labeled cells. This instrument uses nitrogen-vacancy (NV) centers in diamond for correlated magnetic and fluorescence imaging. Our device provides single-cell resolution and two orders of magnitude larger field of view (~1 mm2) than previous NV imaging technologies, enabling practical applications. To illustrate, we quantify cancer biomarkers expressed by rare tumor cells in a large population of healthy cells. PMID:26098019

  14. Quantum speed limit time in a magnetic resonance

    Science.gov (United States)

    Ivanchenko, E. A.

    2017-12-01

    A visualization for dynamics of a qudit spin vector in a time-dependent magnetic field is realized by means of mapping a solution for a spin vector on the three-dimensional spherical curve (vector hodograph). The obtained results obviously display the quantum interference of precessional and nutational effects on the spin vector in the magnetic resonance. For any spin the bottom bounds of the quantum speed limit time (QSL) are found. It is shown that the bottom bound goes down when using multilevel spin systems. Under certain conditions the non-nil minimal time, which is necessary to achieve the orthogonal state from the initial one, is attained at spin S = 2. An estimation of the product of two and three standard deviations of the spin components are presented. We discuss the dynamics of the mutual uncertainty, conditional uncertainty and conditional variance in terms of spin standard deviations. The study can find practical applications in the magnetic resonance, 3D visualization of computational data and in designing of optimized information processing devices for quantum computation and communication.

  15. Lattice Homotopy Constraints on Phases of Quantum Magnets

    Science.gov (United States)

    Po, Hoi Chun; Watanabe, Haruki; Jian, Chao-Ming; Zaletel, Michael P.

    2017-09-01

    The Lieb-Schultz-Mattis (LSM) theorem and its extensions forbid trivial phases from arising in certain quantum magnets. Constraining infrared behavior with the ultraviolet data encoded in the microscopic lattice of spins, these theorems tie the absence of spontaneous symmetry breaking to the emergence of exotic phases like quantum spin liquids. In this work, we take a new topological perspective on these theorems, by arguing they originate from an obstruction to "trivializing" the lattice under smooth, symmetric deformations, which we call the "lattice homotopy problem." We conjecture that all LSM-like theorems for quantum magnets (many previously unknown) can be understood from lattice homotopy, which automatically incorporates the full spatial symmetry group of the lattice, including all its point-group symmetries. One consequence is that any spin-symmetric magnet with a half-integer moment on a site with even-order rotational symmetry must be a spin liquid. To substantiate the claim, we prove the conjecture in two dimensions for some physically relevant settings.

  16. Quantum transport in topological semimetals under magnetic fields

    Science.gov (United States)

    Lu, Hai-Zhou; Shen, Shun-Qing

    2017-06-01

    Topological semimetals are three-dimensional topological states of matter, in which the conduction and valence bands touch at a finite number of points, i.e., the Weyl nodes. Topological semimetals host paired monopoles and antimonopoles of Berry curvature at the Weyl nodes and topologically protected Fermi arcs at certain surfaces. We review our recent works on quantum transport in topological semimetals, according to the strength of the magnetic field. At weak magnetic fields, there are competitions between the positive magnetoresistivity induced by the weak anti-localization effect and negative magnetoresistivity related to the nontrivial Berry curvature. We propose a fitting formula for the magnetoconductivity of the weak anti-localization. We expect that the weak localization may be induced by inter-valley effects and interaction effect, and occur in double-Weyl semimetals. For the negative magnetoresistance induced by the nontrivial Berry curvature in topological semimetals, we show the dependence of the negative magnetoresistance on the carrier density. At strong magnetic fields, specifically, in the quantum limit, the magnetoconductivity depends on the type and range of the scattering potential of disorder. The high-field positive magnetoconductivity may not be a compelling signature of the chiral anomaly. For long-range Gaussian scattering potential and half filling, the magnetoconductivity can be linear in the quantum limit. A minimal conductivity is found at the Weyl nodes although the density of states vanishes there.

  17. Quantum information processing by nuclear magnetic resonance on quadrupolar nuclei.

    Science.gov (United States)

    Teles, João; DeAzevedo, Eduardo R; Freitas, Jair C C; Sarthour, Roberto S; Oliveira, Ivan S; Bonagamba, Tito J

    2012-10-13

    Nuclear magnetic resonance is viewed as an important technique for the implementation of many quantum information algorithms and protocols. Although the most straightforward approach is to use the two-level system composed of spin 1/2 nuclei as qubits, quadrupolar nuclei, which possess a spin greater than 1/2, are being used as an alternative. In this study, we show some unique features of quadrupolar systems for quantum information processing, with an emphasis on the ability to execute efficient quantum state tomography (QST) using only global rotations of the spin system, whose performance is shown in detail. By preparing suitable states and implementing logical operations by numerically optimized pulses together with the QST method, we follow the stepwise execution of Grover's algorithm. We also review some work in the literature concerning the relaxation of pseudo-pure states in spin 3/2 systems as well as its modelling in both the Redfield and Kraus formalisms. These data are used to discuss differences in the behaviour of the quantum correlations observed for two-qubit systems implemented by spin 1/2 and quadrupolar spin 3/2 systems, also presented in the literature. The possibilities and advantages of using nuclear quadrupole resonance experiments for quantum information processing are also discussed.

  18. Transport properties of a two-dimensional electron gas due to a spatially random magnetic field

    Science.gov (United States)

    Rushforth, A. W.; Gallagher, B. L.; Main, P. C.; Neumann, A. C.; Marrows, C. H.; Zoller, I.; Howson, M. A.; Hickey, B. J.; Henini, M.

    2000-02-01

    We have studied the magnetoresistance of a near-surface two-dimensional electron gas (2DEG) in the presence of a random magnetic field produced by CoPd multilayers deposited onto the surface of the heterostructure. This novel method allows us to switch the random field on and off by applying an external magnetic field and also to control the amplitude and correlation length of the random field by varying the growth parameters of the multilayers. The presence of the random field is confirmed by quenching of the Shubnikov-de Haas oscillations and we see an enhanced magnetoresistance which can be interpreted semi-classically. We also observe other unusual features which may be quantum in origin.

  19. Metallic magnets without inversion symmetry and antiferromagnetic quantum critical points

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, I.A.

    2006-07-01

    This thesis focusses on two classes of systems that exhibit non-Fermi liquid behaviour in experiments: we investigated aspects of chiral ferromagnets and of antiferromagnetic metals close to a quantum critical point. In chiral ferromagnets, the absence of inversion symmetry makes spin-orbit coupling possible, which leads to a helical modulation of the ferromagnetically ordered state. We studied the motion of electrons in the magnetically ordered state of a metal without inversion symmetry by calculating their generic band-structure. We found that spin-orbit coupling, although weak, has a profound effect on the shape of the Fermi surface: On a large portion of the Fermi surface the electron motion parallel to the helix practically stops. Signatures of this effect can be expected to show up in measurements of the anomalous Hall effect. Recent neutron scattering experiments uncovered the existence of a peculiar kind of partial order in a region of the phase diagram adjacent to the ordered state of the chiral ferromagnet MnSi. Starting from the premise that this partially ordered state is a thermodynamically distinct phase, we investigated an extended Ginzburg-Landau theory for chiral ferromagnets. In a certain parameter regime of the Ginzburg-Landau theory we identified crystalline phases that are reminiscent of the so-called blue phases in liquid crystals. Many antiferromagnetic heavy-fermion systems can be tuned into a regime where they exhibit non-Fermi liquid exponents in the temperature dependence of thermodynamic quantities such as the specific heat capacity; this behaviour could be due to a quantum critical point. If the quantum critical behaviour is field-induced, the external field does not only suppress antiferromagnetism but also induces spin precession and thereby influences the dynamics of the order parameter. We investigated the quantum critical behavior of clean antiferromagnetic metals subject to a static, spatially uniform external magnetic field. We

  20. Coevolution of quantum and classical strategies on evolving random networks.

    Directory of Open Access Journals (Sweden)

    Qiang Li

    Full Text Available We study the coevolution of quantum and classical strategies on weighted and directed random networks in the realm of the prisoner's dilemma game. During the evolution, agents can break and rewire their links with the aim of maximizing payoffs, and they can also adjust the weights to indicate preferences, either positive or negative, towards their neighbors. The network structure itself is thus also subject to evolution. Importantly, the directionality of links does not affect the accumulation of payoffs nor the strategy transfers, but serves only to designate the owner of each particular link and with it the right to adjust the link as needed. We show that quantum strategies outperform classical strategies, and that the critical temptation to defect at which cooperative behavior can be maintained rises, if the network structure is updated frequently. Punishing neighbors by reducing the weights of their links also plays an important role in maintaining cooperation under adverse conditions. We find that the self-organization of the initially random network structure, driven by the evolutionary competition between quantum and classical strategies, leads to the spontaneous emergence of small average path length and a large clustering coefficient.

  1. A Magnetic Resonance Force Microscopy Quantum Computer with Tellurium Donors in Silicon

    OpenAIRE

    Berman, G. P.; Doolen, G. D.; Tsifrinovich, V. I.

    2000-01-01

    We propose a magnetic resonance force microscopy (MRFM)-based nuclear spin quantum computer using tellurium impurities in silicon. This approach to quantum computing combines the well-developed silicon technology with expected advances in MRFM.

  2. Secure identity-based encryption in the quantum random oracle model

    Science.gov (United States)

    Zhandry, Mark

    2015-04-01

    We give the first proof of security for an identity-based encryption (IBE) scheme in the quantum random oracle model. This is the first proof of security for any scheme in this model that does not rely on the assumed existence of so-called quantum-secure pseudorandom functions (PRFs). Our techniques are quite general and we use them to obtain security proofs for two random oracle hierarchical IBE schemes and a random oracle signature scheme, all of which have previously resisted quantum security proofs, even assuming quantum-secure PRFs. We also explain how to remove quantum-secure PRFs from prior quantum random oracle model proofs. We accomplish these results by developing new tools for arguing that quantum algorithms cannot distinguish between two oracle distributions. Using a particular class of oracle distributions that we call semi-constant distributions, we argue that the aforementioned cryptosystems are secure against quantum adversaries.

  3. Hardware-efficient variational quantum eigensolver for small molecules and quantum magnets

    Science.gov (United States)

    Kandala, Abhinav; Mezzacapo, Antonio; Temme, Kristan; Takita, Maika; Brink, Markus; Chow, Jerry M.; Gambetta, Jay M.

    2017-09-01

    Quantum computers can be used to address electronic-structure problems and problems in materials science and condensed matter physics that can be formulated as interacting fermionic problems, problems which stretch the limits of existing high-performance computers. Finding exact solutions to such problems numerically has a computational cost that scales exponentially with the size of the system, and Monte Carlo methods are unsuitable owing to the fermionic sign problem. These limitations of classical computational methods have made solving even few-atom electronic-structure problems interesting for implementation using medium-sized quantum computers. Yet experimental implementations have so far been restricted to molecules involving only hydrogen and helium. Here we demonstrate the experimental optimization of Hamiltonian problems with up to six qubits and more than one hundred Pauli terms, determining the ground-state energy for molecules of increasing size, up to BeH2. We achieve this result by using a variational quantum eigenvalue solver (eigensolver) with efficiently prepared trial states that are tailored specifically to the interactions that are available in our quantum processor, combined with a compact encoding of fermionic Hamiltonians and a robust stochastic optimization routine. We demonstrate the flexibility of our approach by applying it to a problem of quantum magnetism, an antiferromagnetic Heisenberg model in an external magnetic field. In all cases, we find agreement between our experiments and numerical simulations using a model of the device with noise. Our results help to elucidate the requirements for scaling the method to larger systems and for bridging the gap between key problems in high-performance computing and their implementation on quantum hardware.

  4. Quantum spin ice: a search for gapless quantum spin liquids in pyrochlore magnets.

    Science.gov (United States)

    Gingras, M J P; McClarty, P A

    2014-05-01

    The spin ice materials, including Ho2Ti2O7 and Dy2Ti2O7, are rare-earth pyrochlore magnets which, at low temperatures, enter a constrained paramagnetic state with an emergent gauge freedom. Spin ices provide one of very few experimentally realized examples of fractionalization because their elementary excitations can be regarded as magnetic monopoles and, over some temperature range, spin ice materials are best described as liquids of these emergent charges. In the presence of quantum fluctuations, one can obtain, in principle, a quantum spin liquid descended from the classical spin ice state characterized by emergent photon-like excitations. Whereas in classical spin ices the excitations are akin to electrostatic charges with a mutual Coulomb interaction, in the quantum spin liquid these charges interact through a dynamic and emergent electromagnetic field. In this review, we describe the latest developments in the study of such a quantum spin ice, focusing on the spin liquid phenomenology and the kinds of materials where such a phase might be found.

  5. N-state random switching based on quantum tunnelling

    Science.gov (United States)

    Bernardo Gavito, Ramón; Jiménez Urbanos, Fernando; Roberts, Jonathan; Sexton, James; Astbury, Benjamin; Shokeir, Hamzah; McGrath, Thomas; Noori, Yasir J.; Woodhead, Christopher S.; Missous, Mohamed; Roedig, Utz; Young, Robert J.

    2017-08-01

    In this work, we show how the hysteretic behaviour of resonant tunnelling diodes (RTDs) can be exploited for new functionalities. In particular, the RTDs exhibit a stochastic 2-state switching mechanism that could be useful for random number generation and cryptographic applications. This behaviour can be scaled to N-bit switching, by connecting various RTDs in series. The InGaAs/AlAs RTDs used in our experiments display very sharp negative differential resistance (NDR) peaks at room temperature which show hysteresis cycles that, rather than having a fixed switching threshold, show a probability distribution about a central value. We propose to use this intrinsic uncertainty emerging from the quantum nature of the RTDs as a source of randomness. We show that a combination of two RTDs in series results in devices with three-state outputs and discuss the possibility of scaling to N-state devices by subsequent series connections of RTDs, which we demonstrate for the up to the 4-state case. In this work, we suggest using that the intrinsic uncertainty in the conduction paths of resonant tunnelling diodes can behave as a source of randomness that can be integrated into current electronics to produce on-chip true random number generators. The N-shaped I-V characteristic of RTDs results in a two-level random voltage output when driven with current pulse trains. Electrical characterisation and randomness testing of the devices was conducted in order to determine the validity of the true randomness assumption. Based on the results obtained for the single RTD case, we suggest the possibility of using multi-well devices to generate N-state random switching devices for their use in random number generation or multi-valued logic devices.

  6. Thermal and electrical transport across a magnetic quantum critical point.

    Science.gov (United States)

    Pfau, Heike; Hartmann, Stefanie; Stockert, Ulrike; Sun, Peijie; Lausberg, Stefan; Brando, Manuel; Friedemann, Sven; Krellner, Cornelius; Geibel, Christoph; Wirth, Steffen; Kirchner, Stefan; Abrahams, Elihu; Si, Qimiao; Steglich, Frank

    2012-04-25

    A quantum critical point (QCP) arises when a continuous transition between competing phases occurs at zero temperature. Collective excitations at magnetic QCPs give rise to metallic properties that strongly deviate from the expectations of Landau's Fermi-liquid description, which is the standard theory of electron correlations in metals. Central to this theory is the notion of quasiparticles, electronic excitations that possess the quantum numbers of the non-interacting electrons. Here we report measurements of thermal and electrical transport across the field-induced magnetic QCP in the heavy-fermion compound YbRh(2)Si(2) (refs 2, 3). We show that the ratio of the thermal to electrical conductivities at the zero-temperature limit obeys the Wiedemann-Franz law for magnetic fields above the critical field at which the QCP is attained. This is also expected for magnetic fields below the critical field, where weak antiferromagnetic order and a Fermi-liquid phase form below 0.07 K (at zero field). At the critical field, however, the low-temperature electrical conductivity exceeds the thermal conductivity by about 10 per cent, suggestive of a non-Fermi-liquid ground state. This apparent violation of the Wiedemann-Franz law provides evidence for an unconventional type of QCP at which the fundamental concept of Landau quasiparticles no longer holds. These results imply that Landau quasiparticles break up, and that the origin of this disintegration is inelastic scattering associated with electronic quantum critical fluctuations--these insights could be relevant to understanding other deviations from Fermi-liquid behaviour frequently observed in various classes of correlated materials.

  7. Transport Studies of Quantum Magnetism: Physics and Methods

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Minhyea [Univ. of Colorado, Boulder, CO (United States)

    2017-03-30

    The main goal of this project was to understand novel ground states of spin systems probed by thermal and electrical transport measurements. They are well-suited to characterize the nature of low-energy excitations as unique property of the ground state. More specifically, it was aimed to study the transverse electrical conductivity in the presence of non-collinear and non-coplanar spin ordering and the effects of gauge field as well as novel spin excitations as a coherent heat transport channel in insulating quantum magnets. Most of works done during the grant period focused on these topics. As a natural extension of the project's initial goals, the scope was broadened to include transport studies on the spin systems with strong spin-orbit coupling. One particular focus was an exploration of systems with strong magnetic anisotropy combined with non-trivial spin configuration. Magnetic anisotropy is directly related to implement the non-collinear spin ordering to the existing common geometry of planar devices and thus poses a significant potential. Work in this direction includes the comparison of the topological Hall signal under hydrostatic pressure and chemical doping, as well as the angular dependence dependence of the non-collinear spin ordered phase and their evolution up on temperature and field strength. Another focus was centered around the experimental identification of spin-originated heat carrying excitation in quasi two dimensional honeycomb lattice, where Kitaev type of quantum spin liquid phase is expected to emerge. In fact, when its long range magnetic order is destroyed by the applied field, we discovered anomalously large enhancement of thermal conductivity, for which proximate Kitaev excitations in field-induced spin liquid state are responsible for. This work, combined with further investigations in materials in the similar class may help establish the experimental characterization of new quantum spin liquid and their unique low energy

  8. Electrostatic surface waves on a magnetized quantum plasma half-space

    Energy Technology Data Exchange (ETDEWEB)

    Moradi, Afshin, E-mail: a.moradi@kut.ac.ir [Department of Engineering Physics, Kermanshah University of Technology, Kermanshah, Iran and Department of Nano Sciences, Institute for Studies in Theoretical Physics and Mathematics (IPM), Tehran (Iran, Islamic Republic of)

    2016-03-15

    A theory of electrostatic surface waves on a quantum plasma half-space is developed with the inclusion of external magnetic field effects for the geometry in which the magnetic field is parallel to the surface and the direction of propagation is perpendicular to the magnetic field. A general analytical expression for dispersion relation of surface waves is obtained by solving Poisson and quantum magnetohydrodynamic equations with appropriate quantum boundary conditions.

  9. Few-particle quantum magnetism with ultracold atoms

    Energy Technology Data Exchange (ETDEWEB)

    Murmann, Simon

    2015-11-25

    This thesis reports on the deterministic preparation of magnetically ordered states in systems of few fermionic atoms. We follow the concept of quantum simulation and use {sup 6}Li atoms in two different hyperfine states to mimic the behavior of electrons in a solidstate system. In a first experiment, we simulate the two-site Hubbard model by using two atoms in an isolated double-well potential. We prepare the two-particle ground state of this model with a fidelity exceeding 90%. By introducing strong repulsive interactions, we are able to realize a pure spin model and describe the energy spectrum with a two-site Heisenberg Hamiltonian. In a second experiment, we realize Heisenberg spin chains of up to four atoms in a single strongly-elongated trapping potential. Here, the atoms self-align along the potential axis due to strong repulsive interactions. We introduce two novel measurement techniques to identify the state of the spin chains and thereby confirm that we can deterministically prepare antiferromagnetic ground-state systems. This constitutes the first observation of quantum magnetism with fermionic atoms that exceeds nearest-neighbor correlations. Both the double-well system and the spin chains can be seen as building blocks of larger ground-state spin systems. Their deterministic preparation therefore opens up a new bottom-up approach to the experimental realization of quantum many-body systems with ultracold atoms.

  10. Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Kushwaha, Manvir S. [Department of Physics and Astronomy, Rice University, P.O. Box 1892, Houston, TX 77251 (United States)

    2014-12-15

    Semiconducting quantum dots – more fancifully dubbed artificial atoms – are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement – or the lack of any degree of freedom for the electrons (and/or holes) – in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines’ random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing) the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding) the size of the quantum dots: resulting into a blue (red) shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower) magneto-optical transitions survive even in the extreme instances. However, the intra-Landau level

  11. Magneto-optical absorption in semiconducting spherical quantum dots: Influence of the dot-size, confining potential, and magnetic field

    Directory of Open Access Journals (Sweden)

    Manvir S. Kushwaha

    2014-12-01

    Full Text Available Semiconducting quantum dots – more fancifully dubbed artificial atoms – are quasi-zero dimensional, tiny, man-made systems with charge carriers completely confined in all three dimensions. The scientific quest behind the synthesis of quantum dots is to create and control future electronic and optical nanostructures engineered through tailoring size, shape, and composition. The complete confinement – or the lack of any degree of freedom for the electrons (and/or holes – in quantum dots limits the exploration of spatially localized elementary excitations such as plasmons to direct rather than reciprocal space. Here we embark on a thorough investigation of the magneto-optical absorption in semiconducting spherical quantum dots characterized by a confining harmonic potential and an applied magnetic field in the symmetric gauge. This is done within the framework of Bohm-Pines’ random-phase approximation that enables us to derive and discuss the full Dyson equation that takes proper account of the Coulomb interactions. As an application of our theoretical strategy, we compute various single-particle and many-particle phenomena such as the Fock-Darwin spectrum; Fermi energy; magneto-optical transitions; probability distribution; and the magneto-optical absorption in the quantum dots. It is observed that the role of an applied magnetic field on the absorption spectrum is comparable to that of a confining potential. Increasing (decreasing the strength of the magnetic field or the confining potential is found to be analogous to shrinking (expanding the size of the quantum dots: resulting into a blue (red shift in the absorption spectrum. The Fermi energy diminishes with both increasing magnetic-field and dot-size; and exhibits saw-tooth-like oscillations at large values of field or dot-size. Unlike laterally confined quantum dots, both (upper and lower magneto-optical transitions survive even in the extreme instances. However, the intra

  12. Quantum walks induced by Dirichlet random walks on infinite trees

    Science.gov (United States)

    Higuchi, Yusuke; Segawa, Etsuo

    2018-02-01

    We consider the Grover walk on infinite trees from the viewpoint of spectral analysis. From the previous work, infinite regular trees provide localization. In this paper, we give the complete characterization of the eigenspace of this Grover walk, which involves localization of its behavior and recovers the previous work. Our result suggests that the Grover walk on infinite trees may be regarded as a limit of the quantum walk induced by the isotropic random walk with the Dirichlet boundary condition at the n-th depth rather than one with the Neumann boundary condition.

  13. Far-from-equilibrium spin transport in Heisenberg quantum magnets.

    Science.gov (United States)

    Hild, Sebastian; Fukuhara, Takeshi; Schauß, Peter; Zeiher, Johannes; Knap, Michael; Demler, Eugene; Bloch, Immanuel; Gross, Christian

    2014-10-03

    We study experimentally the far-from-equilibrium dynamics in ferromagnetic Heisenberg quantum magnets realized with ultracold atoms in an optical lattice. After controlled imprinting of a spin spiral pattern with an adjustable wave vector, we measure the decay of the initial spin correlations through single-site resolved detection. On the experimentally accessible time scale of several exchange times, we find a profound dependence of the decay rate on the wave vector. In one-dimensional systems, we observe diffusionlike spin transport with a dimensionless diffusion coefficient of 0.22(1). We show how this behavior emerges from the microscopic properties of the closed quantum system. In contrast to the one-dimensional case, our transport measurements for two-dimensional Heisenberg systems indicate anomalous superdiffusion.

  14. Scaling of magnetic fluctuations near a quantum phase transition

    DEFF Research Database (Denmark)

    Schröder, A.; Aeppli, G.; Bucher, E.

    1998-01-01

    We use inelastic neutron scattering to measure the magnetic fluctuations in a single crystal of the heavy fermion alloy CeCu5.9Au0.1 close to the antiferromagnetic quantum critical point. The energy (E), wave vector (Q), and temperature (T) dependent spectra obey E/T scaling at Q near (1,0,0). Th......We use inelastic neutron scattering to measure the magnetic fluctuations in a single crystal of the heavy fermion alloy CeCu5.9Au0.1 close to the antiferromagnetic quantum critical point. The energy (E), wave vector (Q), and temperature (T) dependent spectra obey E/T scaling at Q near (1......,0,0). The neutron data and earlier bulk susceptibility are consistent with the form chi(-1) similar to f(Q) + (-iE + aT)(alpha), with an anomalous exponent alpha approximate to 0.8 not equal 1. We confirm the earlier observation of quasilow dimensionality and show how both the magnetic fluctuations...

  15. TOPICAL REVIEW: Quantum well states and oscillatory magnetic interlayer coupling

    Science.gov (United States)

    Qiu, Z. Q.; Smith, N. V.

    2002-03-01

    Some interesting magnetic properties of artificially layered metallic materials are strongly connected with the existence of electron standing waves, or quantum well (QW) states. One such property is the oscillation in exchange coupling between two ferromagnetic materials separated by a nonmagnetic spacer layer of varying thicknesses. This article summarizes the findings of an extended investigation of QW states and their relation to oscillatory magnetic interlayer coupling carried out using angle-resolved photoemission with synchrotron radiation and auxiliary techniques such as magnetic x-ray linear dichroism and surface magnetic optical Kerr effect. A key feature of the measurements was the use of wedge-shaped samples, which, in combination with the small spot size of the synchrotron source, permitted investigation of the entire layer thickness range in a single experiment. Single-wedge samples were used as well as double-wedge samples tapered in orthogonal directions. The systematics of QW formation are well understood in terms of the elementary quantum mechanics of a particle in a box. We treat a single well, a double well and a corrugated well. The work on single wells focused on the elucidation of the long and short magnetic oscillatory periods for a Cu spacer layer, and their relation to the belly and neck regions of the Cu Fermi surface. The effects of interfacial roughness and interfacial mixing were investigated. The studies on double wells focused on the controllable degree of tunnelling between the wells and the avoided crossings that occur when the QW energies in one well are swept through those of the other. Finally, we consider the QW wavefunctions and their envelope modulation. The latter can be understood in terms of Bragg diffraction within a corrugated well. With use of a double-wedge-shaped sample it has proved possible to pass a thin probe across the well and to detect experimentally the envelope modulation.

  16. Spin selection rules on the quantum tunneling of magnetization in Mn3 molecule magnets with intermolecular exchange couplings

    Science.gov (United States)

    An, LuLu; Li, YanRong; Mi, ZhenYu; Song, XiaoHui; Wang, YunPing

    2017-09-01

    By means of low-temperature magnetic measurements, it is seen that, quantum spin selection rules also apply to the Mn3 molecule magnets which have intermolecular exchange couplings. The absence of two splitting steps of the tunneling from |6〉 to |‑5〉 indicates that the transitions are confined to the C 3 molecular symmetry. This is the first manifestation of quantum phase interference in the molecule magnets with intermolecular exchange couplings.

  17. Ensembles of physical states and random quantum circuits on graphs

    Science.gov (United States)

    Hamma, Alioscia; Santra, Siddhartha; Zanardi, Paolo

    2012-11-01

    In this paper we continue and extend the investigations of the ensembles of random physical states introduced in Hamma [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.109.040502 109, 040502 (2012)]. These ensembles are constructed by finite-length random quantum circuits (RQC) acting on the (hyper)edges of an underlying (hyper)graph structure. The latter encodes for the locality structure associated with finite-time quantum evolutions generated by physical, i.e., local, Hamiltonians. Our goal is to analyze physical properties of typical states in these ensembles; in particular here we focus on proxies of quantum entanglement as purity and α-Renyi entropies. The problem is formulated in terms of matrix elements of superoperators which depend on the graph structure, choice of probability measure over the local unitaries, and circuit length. In the α=2 case these superoperators act on a restricted multiqubit space generated by permutation operators associated to the subsets of vertices of the graph. For permutationally invariant interactions the dynamics can be further restricted to an exponentially smaller subspace. We consider different families of RQCs and study their typical entanglement properties for finite time as well as their asymptotic behavior. We find that area law holds in average and that the volume law is a typical property (that is, it holds in average and the fluctuations around the average are vanishing for the large system) of physical states. The area law arises when the evolution time is O(1) with respect to the size L of the system, while the volume law arises as is typical when the evolution time scales like O(L).

  18. Linear stability analysis of a levitated nanomagnet in a static magnetic field: Quantum spin stabilized magnetic levitation

    Science.gov (United States)

    Rusconi, C. C.; Pöchhacker, V.; Cirac, J. I.; Romero-Isart, O.

    2017-10-01

    We theoretically study the levitation of a single magnetic domain nanosphere in an external static magnetic field. We show that, apart from the stability provided by the mechanical rotation of the nanomagnet (as in the classical Levitron), the quantum spin origin of its magnetization provides two additional mechanisms to stably levitate the system. Despite the Earnshaw theorem, such stable phases are present even in the absence of mechanical rotation. For large magnetic fields, the Larmor precession of the quantum magnetic moment stabilizes the system in full analogy with magnetic trapping of a neutral atom. For low magnetic fields, the magnetic anisotropy stabilizes the system via the Einstein-de Haas effect. These results are obtained with a linear stability analysis of a single magnetic domain rigid nanosphere with uniaxial anisotropy in a Ioffe-Pritchard magnetic field.

  19. Spin Injection in Thermally Assisted Magnetic Random Access Memory

    National Research Council Canada - National Science Library

    Deak, James G

    2005-01-01

    An integrated thermal, micromagnetic, spin-momentum-transfer (SMT) model was developed to study the effect of SMT on the programming current required for thermally assisted magnetic random access memory (MRAM...

  20. Dirac Magnon Nodal Loops in Quasi-2D Quantum Magnets.

    Science.gov (United States)

    Owerre, S A

    2017-07-31

    In this report, we propose a new concept of one-dimensional (1D) closed lines of Dirac magnon nodes in two-dimensional (2D) momentum space of quasi-2D quantum magnetic systems. They are termed "2D Dirac magnon nodal-line loops". We utilize the bilayer honeycomb ferromagnets with intralayer coupling J and interlayer coupling J L , which is realizable in the honeycomb chromium compounds CrX3 (X ≡ Br, Cl, and I). However, our results can also exist in other layered quasi-2D quantum magnetic systems. Here, we show that the magnon bands of the bilayer honeycomb ferromagnets overlap for J L  ≠ 0 and form 1D closed lines of Dirac magnon nodes in 2D momentum space. The 2D Dirac magnon nodal-line loops are topologically protected by inversion and time-reversal symmetry. Furthermore, we show that they are robust against weak Dzyaloshinskii-Moriya interaction Δ DM  < J L and possess chiral magnon edge modes.

  1. Quantum ring states in magnetic field and delayed half-cycle pulses

    Indian Academy of Sciences (India)

    The present work is dedicated to the time evolution of excitation of a quantum ring in external electric and magnetic fields. Such a ring of mesoscopic dimensions in an external magnetic field is known to exhibit a wide variety of interesting physical phenomena. We have studied the dynamics of the single electron quantum ...

  2. Pressure and compressibility of a quantum plasma in a magnetic field

    NARCIS (Netherlands)

    Suttorp, L.G.

    1993-01-01

    The equilibrium pressure tensor that occurs in the momentum balance equation for a quantum plasma in a magnetic field is shown to be anisotropic. Its relation to the pressure that follows from thermodynamics is elucidated. A general proof of the compressibility rule for a magnetized quantum plasma

  3. Magnetic dipole and electric quadrupole responses of elliptic quantum dots in magnetic fields

    Science.gov (United States)

    Lipparini, E.; Serra, Ll.; Puente, A.

    2002-06-01

    The magnetic dipole (M1) and electric quadupole (E2) responses of two-dimensional quantum dots with an elliptic shape are theoretically investigated as a function of the dot deformation and applied static magnetic field. Neglecting the electron-electron interaction we obtain analytical results which indicate the existence of four characteristic modes, with different B-dispersion of their energies and associated strengths. Interaction effects are numerically studied within the time-dependent local-spin-density and Hartree approximations, assessing the validity of the non-interacting picture.

  4. Microtesla magnetic resonance imaging with a superconducting quantum interference device

    Energy Technology Data Exchange (ETDEWEB)

    McDermott, Robert; Lee, SeungKyun; ten Haken, Bennie; Trabesinger, Andreas H.; Pines, Alexander; Clarke, John

    2004-03-15

    We have constructed a magnetic resonance imaging (MRI) scanner based on a dc Superconducting QUantum Interference Device (SQUID) configured as a second-derivative gradiometer. The magnetic field sensitivity of the detector is independent of frequency; it is therefore possible to obtain high-resolution images by prepolarizing the nuclear spins in a field of 300 mT and detecting the signal at 132 fYT, corresponding to a proton Larmor frequency of 5.6 kHz. The reduction in the measurement field by a factor of 10,000 compared with conventional scanners eliminates inhomogeneous broadening of the nuclear magnetic resonance lines, even in fields with relatively poor homogeneity. The narrow linewidths result in enhanced signal-to-noise ratio and spatial resolution for a fixed strength of the magnetic field gradients used to encode the image. We present two-dimensional images of phantoms and pepper slices, obtained in typical magnetic field gradients of 100 fYT/m, with a spatial resolution of about 1mm. We further demonstrate a slice-selected image of an intact pepper. By varying the time delay between removal of the polarizing field and initiation of the spin echo sequence we acquire T1-weighted contrast images of water phantoms, some of which are doped with a paramagnetic salt; here, T1 is the nuclear spin-lattice relaxation time. The techniques presented here could readily be adapted to existing multichannel SQUID systems used for magnetic source imaging of brain signals. Further potential applications include low-cost systems for tumor screening and imaging peripheral regions of the body.

  5. A delayed random choice quantum mechanics experiment using light quanta

    Science.gov (United States)

    Jakubowicz, O. G.

    1984-01-01

    Wheeler has often articulated during the past seven years several delayed choice Gendanken experiments which are intended to focus attention on the meaning of the elementary quantum phenomenon. Attempts to realize a delayed choice Gendanken xperiment in the spirit John Wheeler's thinking were undertaken. Short laser pulses attenuated to the single photon detection level are introduced into a Mach-Zehnder interferometer one at a time. There is a very fast completely random choice (yes/no) optical switch in one of the arms. Any photons in that arm would be reflected out and into a photomultiplier (PMT) if the optical switch decided to be closed. And any photon in the other arm would have equal probability of going into either of the PMTs that normally monitor interference. If the optical switch chooses to leave the pathway in its arm clear (open) then the photon must split at the beamsplitter and no photons will be detected in the PMT waiting for reflections out of that arm. Additionally, the phase of the interferometer may be set beforehand so that one PMT monitoring interference will register the photon and the other PMT monitoring interference will have zero probability of photon registration. The results are consistent with conventional quantum mechanics even if the decision to block or unblock one arm of the interferometer occurs after the single photon light pulse has passed the entrance beamsplitter of the interferometer.

  6. Formation of current filaments and magnetic field generation in a quantum current-carrying plasma

    Science.gov (United States)

    Niknam, A. R.; Taghadosi, M. R.; Majedi, S.; Khorashadizadeh, S. M.

    2013-09-01

    The nonlinear dynamics of filamentation instability and magnetic field in a current-carrying plasma is investigated in the presence of quantum effects using the quantum hydrodynamic model. A new nonlinear partial differential equation is obtained for the spatiotemporal evolution of the magnetic field in the diffusion regime. This equation is solved by applying the Adomian decomposition method, and then the profiles of magnetic field and electron density are plotted. It is shown that the saturation time of filamentation instability increases and, consequently, the instability growth rate and the magnetic field amplitude decrease in the presence of quantum effects.

  7. Quantum Monte Carlo Calculations Applied to Magnetic Molecules

    Energy Technology Data Exchange (ETDEWEB)

    Engelhardt, Larry [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    We have calculated the equilibrium thermodynamic properties of Heisenberg spin systems using a quantum Monte Carlo (QMC) method. We have used some of these systems as models to describe recently synthesized magnetic molecules, and-upon comparing the results of these calculations with experimental data-have obtained accurate estimates for the basic parameters of these models. We have also performed calculations for other systems that are of more general interest, being relevant both for existing experimental data and for future experiments. Utilizing the concept of importance sampling, these calculations can be carried out in an arbitrarily large quantum Hilbert space, while still avoiding any approximations that would introduce systematic errors. The only errors are statistical in nature, and as such, their magnitudes are accurately estimated during the course of a simulation. Frustrated spin systems present a major challenge to the QMC method, nevertheless, in many instances progress can be made. In this chapter, the field of magnetic molecules is introduced, paying particular attention to the characteristics that distinguish magnetic molecules from other systems that are studied in condensed matter physics. We briefly outline the typical path by which we learn about magnetic molecules, which requires a close relationship between experiments and theoretical calculations. The typical experiments are introduced here, while the theoretical methods are discussed in the next chapter. Each of these theoretical methods has a considerable limitation, also described in Chapter 2, which together serve to motivate the present work. As is shown throughout the later chapters, the present QMC method is often able to provide useful information where other methods fail. In Chapter 3, the use of Monte Carlo methods in statistical physics is reviewed, building up the fundamental ideas that are necessary in order to understand the method that has been used in this work. With these

  8. Efficient Raman generation in a waveguide: A route to ultrafast quantum random number generation

    Energy Technology Data Exchange (ETDEWEB)

    England, D. G.; Bustard, P. J.; Moffatt, D. J.; Nunn, J.; Lausten, R.; Sussman, B. J., E-mail: ben.sussman@nrc.ca [National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6 (Canada)

    2014-02-03

    The inherent uncertainty in quantum mechanics offers a source of true randomness which can be used to produce unbreakable cryptographic keys. We discuss the development of a high-speed random number generator based on the quantum phase fluctuations in spontaneously initiated stimulated Raman scattering (SISRS). We utilize the tight confinement and long interaction length available in a Potassium Titanyl Phosphate waveguide to generate highly efficient SISRS using nanojoule pulse energies, reducing the high pump power requirements of the previous approaches. We measure the random phase of the Stokes output using a simple interferometric setup to yield quantum random numbers at 145 Mbps.

  9. Quantum oscillations of the magnetic moment of graphene and graphite

    Science.gov (United States)

    Petkovic, Ivana; Lollo, Anthony; Wang, Ke; Kim, Philip; Harris, Jack

    Quantum oscillations of the magnetic moment, so called de Haas - van Alphen (dHvA) oscillations, are a powerful tool for the investigation of the Fermi surface. In graphene with a fixed carrier density, the magnetic moment is predicted to oscillate as function of increasing perpendicular field B every time the uppermost Landau level empties out, yielding the characteristic 1/B dependence. To date, it has been challenging to measure the equilibrium magnetic moment of isolated samples of graphene. In graphite a more complex oscillation sequence is observed, due to its complicated Fermi surface with both electron and hole carriers. Historically graphite was one of the first materials in which dHvA oscillations were studied, but recently interest was revived due to an observation of carriers with relativistic dynamics. We have used cantilever torque magnetometry to study diamagnetism and dHvA oscillations of isolated samples of graphene and graphite between 400 mK and 20 K. For graphite, we observe dHvA oscillations which are used to study the composition and nature of carriers. For graphene, we discuss the results in relation to relativistic dispersion and disorder.

  10. Quantum-disordered state of magnetic and electric dipoles in an organic Mott system.

    Science.gov (United States)

    Shimozawa, M; Hashimoto, K; Ueda, A; Suzuki, Y; Sugii, K; Yamada, S; Imai, Y; Kobayashi, R; Itoh, K; Iguchi, S; Naka, M; Ishihara, S; Mori, H; Sasaki, T; Yamashita, M

    2017-11-28

    Strongly enhanced quantum fluctuations often lead to a rich variety of quantum-disordered states. Developing approaches to enhance quantum fluctuations may open paths to realize even more fascinating quantum states. Here, we demonstrate that a coupling of localized spins with the zero-point motion of hydrogen atoms, that is, proton fluctuations in a hydrogen-bonded organic Mott insulator provides a different class of quantum spin liquids (QSLs). We find that divergent dielectric behavior associated with the approach to hydrogen-bond order is suppressed by the quantum proton fluctuations, resulting in a quantum paraelectric (QPE) state. Furthermore, our thermal-transport measurements reveal that a QSL state with gapless spin excitations rapidly emerges upon entering the QPE state. These findings indicate that the quantum proton fluctuations give rise to a QSL-a quantum-disordered state of magnetic and electric dipoles-through the coupling between the electron and proton degrees of freedom.

  11. Quantum wells under an in-plane magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez-Cabrera, A. [Dpto. Fisica Basica, Universidad de La Laguna, La Laguna, 38206 Tenerife (Spain)], E-mail: ajhernan@ull.es; Aceituno, P. [Dpto. Fisica Basica, Universidad de La Laguna, La Laguna, 38206 Tenerife (Spain); Vasko, F.T. [Institute of Semiconductor Physics, NAS Ukraine, Pr. Nauki 41, Kiev 03028 (Ukraine)

    2008-05-15

    The dependence of the electronic spin-splitting energy on the composition parameters (x,y) in In{sub x}Ga{sub 1-x}As-In{sub y}Al{sub 1-y}As-based quantum wells, has been calculated. InGaAs narrow gap structures, subjected to in-plane magnetic fields, have been selected because these structures have a big Lande factor. The dependence of the Lande factor both on the applied fields and composition parameters has been included for fixed well width and external electric field. Contributions from the interfaces and strain, which also depend on the composition, are included. Spin-splitting energy and density of states show a strong dependence on the above parameters.

  12. Magnetism at the Interface of Magnetic Oxide and Nonmagnetic Semiconductor Quantum Dots.

    Science.gov (United States)

    Saha, Avijit; Viswanatha, Ranjani

    2017-03-28

    Engineering interfaces specifically in quantum dot (QD) heterostructures provide several prospects for developing multifunctional building block materials. Precise control over internal structure by chemical synthesis offers a combination of different properties in QDs and allows us to study their fundamental properties, depending on their structure. Herein, we studied the interface of magnetic/nonmagnetic Fe3O4/CdS QD heterostructures. In this work, we demonstrate the decrease in the size of the magnetic core due to annealing at high temperature by the decrease in saturation magnetization and blocking temperature. Furthermore, surprisingly, in a prominently optically active and magnetically inactive material such as CdS, we observe the presence of substantial exchange bias in spite of the nonmagnetic nature of CdS QDs. The presence of exchange bias was proven by the increase in magnetic anisotropy as well as the presence of exchange bias field (HE) during the field-cooled magnetic measurements. This exchange coupling was eventually traced to the in situ formation of a thin antiferromagnetic FeS layer at the interface. This is verified by the study of Fe local structure using X-ray absorption fine structure spectroscopy, demonstrating the importance of interface engineering in QDs.

  13. Magnetic Random Access Memory for Embedded Computing

    Science.gov (United States)

    2007-10-29

    is pointed in the direction of current flow then the resulting magnetic field is oriented like the fingers curled toward the palm . As suggested in the...and Johann Heyen Hinken. Dielectric properties of single crystals of Al2O3, LaAlO3, NdGaO3, SrTiO3 and MgO at cryogenic temperatures. IEEE

  14. Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet.

    Science.gov (United States)

    Banerjee, A; Bridges, C A; Yan, J-Q; Aczel, A A; Li, L; Stone, M B; Granroth, G E; Lumsden, M D; Yiu, Y; Knolle, J; Bhattacharjee, S; Kovrizhin, D L; Moessner, R; Tennant, D A; Mandrus, D G; Nagler, S E

    2016-07-01

    Quantum spin liquids (QSLs) are topological states of matter exhibiting remarkable properties such as the capacity to protect quantum information from decoherence. Whereas their featureless ground states have precluded their straightforward experimental identification, excited states are more revealing and particularly interesting owing to the emergence of fundamentally new excitations such as Majorana fermions. Ideal probes of these excitations are inelastic neutron scattering experiments. These we report here for a ruthenium-based material, α-RuCl3, continuing a major search (so far concentrated on iridium materials) for realizations of the celebrated Kitaev honeycomb topological QSL. Our measurements confirm the requisite strong spin-orbit coupling and low-temperature magnetic order matching predictions proximate to the QSL. We find stacking faults, inherent to the highly two-dimensional nature of the material, resolve an outstanding puzzle. Crucially, dynamical response measurements above interlayer energy scales are naturally accounted for in terms of deconfinement physics expected for QSLs. Comparing these with recent dynamical calculations involving gauge flux excitations and Majorana fermions of the pure Kitaev model, we propose the excitation spectrum of α-RuCl3 as a prime candidate for fractionalized Kitaev physics.

  15. Model C critical dynamics of random anisotropy magnets

    Energy Technology Data Exchange (ETDEWEB)

    Dudka, M [Institute for Condensed Matter Physics, National Acad. Sci. of Ukraine, UA-79011 Lviv (Ukraine); Folk, R [Institut fuer Theoretische Physik, Johannes Kepler Universitaet Linz, A-4040 Linz (Austria); Holovatch, Yu [Institute for Condensed Matter Physics, National Acad. Sci. of Ukraine, UA-79011 Lviv (Ukraine); Moser, G [Institut fuer Physik und Biophysik, Universitaet Salzburg, A-5020 Salzburg (Austria)

    2007-07-20

    We study the relaxational critical dynamics of the three-dimensional random anisotropy magnets with the non-conserved n-component order parameter coupled to a conserved scalar density. In the random anisotropy magnets, the structural disorder is present in the form of local quenched anisotropy axes of random orientation. When the anisotropy axes are randomly distributed along the edges of the n-dimensional hypercube, asymptotical dynamical critical properties coincide with those of the random-site Ising model. However the structural disorder gives rise to considerable effects for non-asymptotic critical dynamics. We investigate this phenomenon by a field-theoretical renormalization group analysis in the two-loop order. We study critical slowing down and obtain quantitative estimates for the effective and asymptotic critical exponents of the order parameter and scalar density. The results predict complex scenarios for the effective critical exponent approaching the asymptotic regime.

  16. Proposed Robust Entanglement-Based Magnetic Field Sensor Beyond the Standard Quantum Limit.

    Science.gov (United States)

    Tanaka, Tohru; Knott, Paul; Matsuzaki, Yuichiro; Dooley, Shane; Yamaguchi, Hiroshi; Munro, William J; Saito, Shiro

    2015-10-23

    Recently, there have been significant developments in entanglement-based quantum metrology. However, entanglement is fragile against experimental imperfections, and quantum sensing to beat the standard quantum limit in scaling has not yet been achieved in realistic systems. Here, we show that it is possible to overcome such restrictions so that one can sense a magnetic field with an accuracy beyond the standard quantum limit even under the effect of decoherence, by using a realistic entangled state that can be easily created even with current technology. Our scheme could pave the way for the realizations of practical entanglement-based magnetic field sensors.

  17. Beating of magnetic oscillations in a graphene device probed by quantum capacitance

    KAUST Repository

    Tahir, M.

    2012-07-05

    We report the quantum capacitance of a monolayergraphene device in an external perpendicular magnetic field including the effects of Rashba spin-orbit interaction(SOI). The SOI mixes the spin up and spin down states of neighbouring Landau levels into two (unequally spaced) energy branches. In order to investigate the role of the SOI for the electronic transport, we study the density of states to probe the quantum capacitance of monolayergraphene.SOIeffects on the quantum magnetic oscillations (Shubnikov de Haas and de Hass-van Alphen) are deduced from the quantum capacitance.

  18. Theoretical/Computational Studies of High-Temperature Superconductivity from Quantum Magnetism

    Science.gov (United States)

    2016-06-09

    AFRL-AFOSR-VA-TR-2016-0204 Theoretical/Computational Studies of High-Temperature Superconductivity from Quantum Magnetism Jose Rodriguez CALIFORNIA...TITLE AND SUBTITLE Theoretical/Computational Studies of High-Temperature Superconductivity from Quantum Magnetism 5a.  CONTRACT NUMBER 5b.  GRANT...SUBJECT TERMS quantum magnetism , HTS, superconductivity 16.  SECURITY CLASSIFICATION OF: 17.  LIMITATION OF       ABSTRACT UU 18.  NUMBER        OF

  19. Illustrating the quantum approach with an Earth magnetic field MRI

    Science.gov (United States)

    Pars Benli, Kami; Dillmann, Baudouin; Louelh, Ryma; Poirier-Quinot, Marie; Darrasse, Luc

    2015-05-01

    Teaching imaging of magnetic resonance (MR) today is still as challenging as it has always been, because it requires admitting that we cannot express fundamental questions of quantum mechanics with straightforward language or without using extensive theory. Here we allow students to face a real MR setup based on the Earth's magnetic field. We address the applied side of teaching MR using a device that is affordable and that proves to be sufficiently robust, at universities in Orsay, France, and San Sebastian, Spain, in experimental practicals at undergraduate and graduate levels. We specifically present some of the advantages of low field for measuring R2 relaxation rates, reaching a power of separation of 1.5 μmol on Mn(II) ions between two water bottles each of half a liter. Finally we propose key approaches for the lecturers to adopt when they are asked to pass from theoretical knowledge to teachable knowhow. The outcomes are fast calibration and the MR acquisition protocols, demonstrating the reproducibility of energy transfer during the saturation pulses, and the quantitative nature of MR, with water protons and a helium-3 sample.

  20. Realization of a Quantum Random Generator Certified with the Kochen-Specker Theorem.

    Science.gov (United States)

    Kulikov, Anatoly; Jerger, Markus; Potočnik, Anton; Wallraff, Andreas; Fedorov, Arkady

    2017-12-15

    Random numbers are required for a variety of applications from secure communications to Monte Carlo simulation. Yet randomness is an asymptotic property, and no output string generated by a physical device can be strictly proven to be random. We report an experimental realization of a quantum random number generator (QRNG) with randomness certified by quantum contextuality and the Kochen-Specker theorem. The certification is not performed in a device-independent way but through a rigorous theoretical proof of each outcome being value indefinite even in the presence of experimental imperfections. The analysis of the generated data confirms the incomputable nature of our QRNG.

  1. Realization of a Quantum Random Generator Certified with the Kochen-Specker Theorem

    Science.gov (United States)

    Kulikov, Anatoly; Jerger, Markus; Potočnik, Anton; Wallraff, Andreas; Fedorov, Arkady

    2017-12-01

    Random numbers are required for a variety of applications from secure communications to Monte Carlo simulation. Yet randomness is an asymptotic property, and no output string generated by a physical device can be strictly proven to be random. We report an experimental realization of a quantum random number generator (QRNG) with randomness certified by quantum contextuality and the Kochen-Specker theorem. The certification is not performed in a device-independent way but through a rigorous theoretical proof of each outcome being value indefinite even in the presence of experimental imperfections. The analysis of the generated data confirms the incomputable nature of our QRNG.

  2. Quantum radiation produced by a uniformly accelerating charged particle in thermal random motion

    Science.gov (United States)

    Oshita, Naritaka; Yamamoto, Kazuhiro; Zhang, Sen

    2016-04-01

    We investigate the properties of quantum radiation produced by a uniformly accelerating charged particle undergoing thermal random motion, which originates from the coupling to the vacuum fluctuations of the electromagnetic field. Because the thermal random motion is regarded to result from the Unruh effect, the quantum radiation might give us hints of the Unruh effect. The energy flux of the quantum radiation is negative and smaller than that of Larmor radiation by one order in a /m , where a is the constant acceleration and m is the mass of the particle. Thus, the quantum radiation appears to be a suppression of the classical Larmor radiation. The quantum interference effect plays an important role in this unique signature. The results are consistent with the predictions of a model consisting of a particle coupled to a massless scalar field as well as those of the previous studies on the quantum effect on the Larmor radiation.

  3. Observation of the Quantum-Anomalous-Hall Insulator to Anderson Insulator Quantum Phase Transition in Magnetic Topological Insulators

    Science.gov (United States)

    Chang, Cui-Zu; Zhao, Wei-Wei; Li, Jian; Jain, J. K.; Liu, Chaoxing; Moodera, Jagadeesh S.; Chan, Moses H. W.

    The quantum anomalous Hall (QAH) effect can be considered as the quantum Hall (QH) effect without external magnetic field, which can be realized by time reversal symmetry breaking in a topologically non-trivial system, and in thin films of magnetically-doped TI. A QAH system carries spin-polarized dissipationless chiral edge transport channels without the need for external energy input, hence may have huge impact on future electronic and spintronic device applications for ultralow-power consumption. The observation of QAH effect has opened up exciting new physics and thus understanding the physical nature of this novel topological quantum state, can lead to a rapid development of this field. In this talk, we will report our recent progress about the experimental observation of a quantum phase transition from a quantum-anomalous-Hall (QAH) insulator to an Anderson insulator by tuning the chemical potential, and finally discuss the existence of scaling behavior for this quantum phase transition. Work Supported by funding from NSF (DMR-1207469), NSF (DMR-0819762) (MIT MRSEC), ONR (N00014-13-1-0301), and the STC Center for Integrated Quantum Materials under NSF Grant DMR-1231319.

  4. Loss of long-range magnetic order in a nanoparticle assembly due to random anisotropy

    Science.gov (United States)

    Binns, C.; Howes, P. B.; Baker, S. H.; Marchetto, H.; Potenza, A.; Steadman, P.; Dhesi, S. S.; Roy, M.; Everard, M. J.; Rushforth, A.

    2008-02-01

    We have used soft x-ray photoemission electron microscopy (XPEEM) combined with x-ray magnetic circular dichroism (XMCD) and DC SQUID (superconducting quantum interference device) magnetometry to probe the magnetic ground state in Fe thin films produced by depositing size-selected gas-phase Fe nanoparticles with a diameter of 1.7 nm (~200 atoms) onto Si substrates. The depositions were carried out in ultrahigh vacuum conditions and thicknesses of the deposited film in the range 5-50 nm were studied. The magnetometry data are consistent with the film forming a correlated super-spin glass with a magnetic correlation length ~5 nm. The XPEEM magnetic maps from the cluster-assembled films were compared to those for a conventional thin Fe film with a thickness of 20 nm produced by a molecular beam epitaxy (MBE) source. Whereas a normal magnetic domain structure is observed in the conventional MBE thin film, no domain structure could be observed in any of the nanoparticle films down to the resolution limit of the XMCD based XPEEM (100 nm) confirming the ground state indicated by the magnetometry measurements. This observation is consistent with the theoretical prediction that an arbitrarily weak random anisotropy field will destroy long-range magnetic order.

  5. Loss of long-range magnetic order in a nanoparticle assembly due to random anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Binns, C [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Howes, P B [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Baker, S H [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Marchetto, H [Diamond Light Source Ltd, Harwell Science and Innovation Campus, Diamond House, Chilton, Didcot, Oxfordshire OX11 0DE (United Kingdom); Potenza, A [Diamond Light Source Ltd, Harwell Science and Innovation Campus, Diamond House, Chilton, Didcot, Oxfordshire OX11 0DE (United Kingdom); Steadman, P [Diamond Light Source Ltd, Harwell Science and Innovation Campus, Diamond House, Chilton, Didcot, Oxfordshire OX11 0DE (United Kingdom); Dhesi, S S [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Roy, M [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Everard, M J [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Rushforth, A [School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)

    2008-02-06

    We have used soft x-ray photoemission electron microscopy (XPEEM) combined with x-ray magnetic circular dichroism (XMCD) and DC SQUID (superconducting quantum interference device) magnetometry to probe the magnetic ground state in Fe thin films produced by depositing size-selected gas-phase Fe nanoparticles with a diameter of 1.7 nm ({approx}200 atoms) onto Si substrates. The depositions were carried out in ultrahigh vacuum conditions and thicknesses of the deposited film in the range 5-50 nm were studied. The magnetometry data are consistent with the film forming a correlated super-spin glass with a magnetic correlation length {approx}5 nm. The XPEEM magnetic maps from the cluster-assembled films were compared to those for a conventional thin Fe film with a thickness of 20 nm produced by a molecular beam epitaxy (MBE) source. Whereas a normal magnetic domain structure is observed in the conventional MBE thin film, no domain structure could be observed in any of the nanoparticle films down to the resolution limit of the XMCD based XPEEM (100 nm) confirming the ground state indicated by the magnetometry measurements. This observation is consistent with the theoretical prediction that an arbitrarily weak random anisotropy field will destroy long-range magnetic order.

  6. Digital quantum simulation of the statistical mechanics of a frustrated magnet.

    Science.gov (United States)

    Zhang, Jingfu; Yung, Man-Hong; Laflamme, Raymond; Aspuru-Guzik, Alán; Baugh, Jonathan

    2012-06-06

    Many problems of interest in physics, chemistry and computer science are equivalent to problems defined on systems of interacting spins. However, most such problems require computational resources that are out of reach with classical computers. A promising solution to overcome this challenge is quantum simulation. Several 'analogue' quantum simulations of interacting spin systems have been realized experimentally, where ground states were prepared using adiabatic techniques. Here we report a 'digital' quantum simulation of thermal states; a three-spin frustrated magnet was simulated using a nuclear magnetic resonance quantum information processor, and we were able to explore the phase diagram of the system at any simulated temperature and external field. These results help to identify the challenges for performing quantum simulations of physical systems at finite temperatures, and suggest methods that may be useful in simulating thermal open quantum systems.

  7. Quantum epistemology from subquantum ontology: Quantum mechanics from theory of classical random fields

    Science.gov (United States)

    Khrennikov, Andrei

    2017-02-01

    The scientific methodology based on two descriptive levels, ontic (reality as it is) and epistemic (observational), is briefly presented. Following Schrödinger, we point to the possible gap between these two descriptions. Our main aim is to show that, although ontic entities may be unaccessible for observations, they can be useful for clarification of the physical nature of operational epistemic entities. We illustrate this thesis by the concrete example: starting with the concrete ontic model preceding quantum mechanics (the latter is treated as an epistemic model), namely, prequantum classical statistical field theory (PCSFT), we propose the natural physical interpretation for the basic quantum mechanical entity-the quantum state ("wave function"). The correspondence PCSFT ↦ QM is not straightforward, it couples the covariance operators of classical (prequantum) random fields with the quantum density operators. We use this correspondence to clarify the physical meaning of the pure quantum state and the superposition principle-by using the formalism of classical field correlations. In classical mechanics the phase space description can be considered as the ontic description, here states are given by points λ =(x , p) of phase space. The dynamics of the ontic state is given by the system of Hamiltonian equations.We can also consider probability distributions on the phase space (or equivalently random variables valued in it). We call them probabilistic ontic states. Dynamics of probabilistic ontic states is given by the Liouville equation.In classical physics we can (at least in principle) measure both the coordinate and momentum and hence ontic states can be treated as epistemic states as well (or it is better to say that here epistemic states can be treated as ontic states). Probabilistic ontic states represent probabilities for outcomes of joint measurement of position and momentum.However, this was a very special, although very important, example of

  8. Photodissociation in quantum chaotic systems: Random-matrix theory of cross-section fluctuations

    Energy Technology Data Exchange (ETDEWEB)

    Fyodorov, Y.V. [Fachbereich Physik, Universitaet-GH Essen, D-45117 Essen (Germany); Alhassid, Y. [Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, Connecticut 06520 (United States)

    1998-11-01

    Using the random matrix description of open quantum chaotic systems we calculate in closed form the universal autocorrelation function and the probability distribution of the total photodissociation cross section in the regime of quantum chaos. {copyright} {ital 1998} {ital The American Physical Society}

  9. Multi-bit quantum random number generation by measuring positions of arrival photons.

    Science.gov (United States)

    Yan, Qiurong; Zhao, Baosheng; Liao, Qinghong; Zhou, Nanrun

    2014-10-01

    We report upon the realization of a novel multi-bit optical quantum random number generator by continuously measuring the arrival positions of photon emitted from a LED using MCP-based WSA photon counting imaging detector. A spatial encoding method is proposed to extract multi-bits random number from the position coordinates of each detected photon. The randomness of bits sequence relies on the intrinsic randomness of the quantum physical processes of photonic emission and subsequent photoelectric conversion. A prototype has been built and the random bit generation rate could reach 8 Mbit/s, with random bit generation efficiency of 16 bits per detected photon. FPGA implementation of Huffman coding is proposed to reduce the bias of raw extracted random bits. The random numbers passed all tests for physical random number generator.

  10. Spatial quantum correlations induced by random multiple scattering of quadrature squeezed light

    DEFF Research Database (Denmark)

    Lodahl, Peter

    2007-01-01

    The authors demonstrates that spatial quantum correlations are induced by multiple scattering of quadrature squeezed light through a random medium. As a consequence, light scattered along two different directions by the random medium will not be independent, but be correlated to an extent that ca...... only be described by a quantum mechanical theory for multiple scattering. The spatial quantum correlation is revealed in the fluctuations of the total intensity transmission or reflection through the multiple scattering medium.......The authors demonstrates that spatial quantum correlations are induced by multiple scattering of quadrature squeezed light through a random medium. As a consequence, light scattered along two different directions by the random medium will not be independent, but be correlated to an extent that can...

  11. Deep Learning the Quantum Phase Transitions in Random Two-Dimensional Electron Systems

    Science.gov (United States)

    Ohtsuki, Tomoki; Ohtsuki, Tomi

    2016-12-01

    Random electron systems show rich phases such as Anderson insulator, diffusive metal, quantum Hall and quantum anomalous Hall insulators, Weyl semimetal, as well as strong/weak topological insulators. Eigenfunctions of each matter phase have specific features, but owing to the random nature of systems, determining the matter phase from eigenfunctions is difficult. Here, we propose the deep learning algorithm to capture the features of eigenfunctions. Localization-delocalization transition, as well as disordered Chern insulator-Anderson insulator transition, is discussed.

  12. First principles modeling of magnetic random access memory devices (invited)

    Energy Technology Data Exchange (ETDEWEB)

    Butler, W.H.; Zhang, X.; Schulthess, T.C.; Nicholson, D.M.; Oparin, A.B. [Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); MacLaren, J.M. [Department of Physics, Tulane University, New Orleans, Louisiana 70018 (United States)

    1999-04-01

    Giant magnetoresistance (GMR) and spin-dependent tunneling may be used to make magnetic random access memory devices. We have applied first-principles based electronic structure techniques to understand these effects and in the case of GMR to model the transport properties of the devices. {copyright} {ital 1999 American Institute of Physics.}

  13. George E. Valley, Jr. Prize Talk: Quantum Frustrated Magnetism and its Expression in the Ground State Selection of Pyrochlore Magnets

    Science.gov (United States)

    Ross, Kate

    In the search for novel quantum states of matter, such as highly entangled Quantum Spin Liquids, ``geometrically frustrated'' magnetic lattices are essential for suppressing conventional magnetic order. In three dimensions, the pyrochlore lattice is the canonical frustrated geometry. Magnetic materials with pyrochlore structures have the potential to realize unusual phases such as ``quantum spin ice'', which is predicted to host emergent magnetic monopoles, electrons, and photons as its fundamental excitations. Even in pyrochlores that form long range ordered phases, this often occurs through unusual routes such as ``order by disorder'', in which the fluctuation spectrum dictates the preferred ordered state. The rare earth-based pyrochlore series R2Ti2O7 provides a fascinating variety of magnetic ground states. I will introduce the general anisotropic interaction Hamiltonian that has been successfully used to describe several materials in this series. Using inelastic neutron scattering, the relevant anisotropic interaction strengths can be extracted quantitatively. I will discuss this approach, and its application to two rare earth pyrochlore materials, Er2Ti2O7 and Yb2Ti<2O7, whose ground state properties have long been enigmatic. From these studies, ErTi2O7 and Yb2Ti2O7 have been suggested to be realizations of "quantum order by disorder" and "quantum spin ice", respectively. This research was supported by NSERC of Canada and the National Science Foundation.

  14. Parisi symmetry of the many-body quantum theory of randomly interacting fermionic systems

    Science.gov (United States)

    Oppermann, R.; Rosenow, B.

    1999-10-01

    We show that fermion systems with random and frustrated interactions display a strong coupling between glassy order and fermionic correlations, which culminates in the implementation of Parisi replica permutation symmetry breaking (RPSB) in their zero-temperature quantum field theories. RPSB effects, setting in below fermionic de Almeida-Thouless (dAT) lines, become stronger as the temperature T decreases and play a crucial role for many physical properties within the entire low-T regime. The Parisi ultrametric structure is shown to determine the dynamic behavior of fermionic correlations (Green's functions) for large times and for the corresponding low-energy excitation spectra, which is predicted to affect transport properties in metallic (and superconducting) spin glasses. Thus we reveal the existence and the detailed form of a number of quantum-dynamical fingerprints of the Parisi scheme. These effects, being strongest as T-->0, are contrasted with the replica-symmetric nature of the critical field theory of quantum spin glass transitions at T=0, which display only small corrections at low T from RPSB. RPSB effects moreover appear to influence the loci of the ground state transitions at O(T0) and hence the phase diagrams. From explicit solutions for arbitrary T we find a representation of the Green's function in the T=0 limit. This leads to a map of the fermionic (insulating) spin glass solution to the local limit of a Hubbard model with random repulsive interaction. This map holds for any number of replica-symmetry-breaking steps K. We obtain the distribution of the Hubbard interaction U and its dependence on the order of RPSB. A generalized mapping between metallic spin glass and random U Hubbard model is conjectured. We also suggest that the new representation of the Green's function at T=0 can be used for generalizations to superconductors with spin glass phases. Further generalizations due to Coulomb effects including a crossover from four-state per site

  15. Effect of chiral selective tunneling on quantum transport in magnetic topological-insulator thin films

    Science.gov (United States)

    Sabze, Tahere; Cheraghchi, Hosein

    2017-10-01

    The electronic transport properties in magnetically doped ultrathin films of topological insulators are investigated by using Landauer-Buttiker formalism. The chiral selective tunneling is addressed in such systems which leads to transport gap and as a consequence current blocking. This quantum blocking of transport occurs when the magnetic states with opposite chirality are aligned energetically. This can be observed when an electron tunnels through a barrier or well of magnetic potential induced by the exchange field. It is proved and demonstrated that this chiral transition rule fails when structural inversion asymmetric potential or an in-plane magnetization is turning on. This finding is useful to interpret quantum transport through topological-insulator thin films especially to shed light on longitudinal conductance behavior of quantum anomalous Hall effect. Besides, one can design electronic devices by means of magnetic topological-insulator thin films based on the chiral selective tunneling leading to negative differential resistance.

  16. Dilute magnetic droplets of a bosonic erbium quantum fluid

    Science.gov (United States)

    Chomaz, Lauriane; Baier, Simon; Petter, Daniel; Faraoni, Giulia; Becher, Jan-Hendrik; van Bijnen, Rick; Mark, Manfred J.; Ferlaino, Francesca

    2017-04-01

    Due to their large magnetic moment and exotic electronic configuration, atoms of the lanthanide family, such as dysprosium (Dy) and erbium (Er), are an ideal platform for exploring the competition between inter-particle interactions of different origins and behaviors. Recently, a novel phase of dilute droplet has been observed in an ultracold gas of bosonic Dy when changing the ratio of the contact and dipole-dipole interactions and setting the mean-field interactions to slightly attractive. This has been attributed to the distinct, non-vanishing, beyond-mean-field effects in dipolar gases when the mean interaction cancels. Here we report on the investigation of droplet physics in fluids of bosonic Er. By precise control of the scattering length a, we quantitatively probe the Bose-Einstein condensate (BEC)-to-droplet phase diagram and the rich underlying dynamics. In a prolate geometry, we observe a crossover from a BEC to a single macro-droplet, prove the stabilizing role of quantum fluctuations and characterize the special dynamical properties of the droplet. In an oblate geometry, we observe the formation of assemblies of tinier droplets arranged in a chain and explore the special state dynamics following a quench of a, marked by successive merging and reformation events. L.C. is supported within the Marie Curie Individual Fellowship DIPPHASE No. 706809 of the European Commission.

  17. Control and manipulation of quantum spin switching and spin correlations in [Tb2] molecular magnet under a pulse magnetic field

    Science.gov (United States)

    Farberovich, Oleg V.; Bazhanov, Dmitry I.

    2017-10-01

    A general study of [Tb2] molecular magnet is presented using the general spin Hamiltonian formalism. A spin-spin correlators determined for a spin wave functions in [Tb2] are analyzed numerically and compared in details with the results obtained by means of conventional quantum mechanics. It is shown that the various expectation values of the spin operators and a study of their corresponding probability distributions allow to have a novel understanding in spin dynamics of entangled qubits in quantum [Tb2] system. The obtained results reveal that the properties of spin-spin correlators are responsible for the entanglement of the spin qubit under a pulse magnetic field. It allows us to present some quantum circuits determined for quantum computing within SSNQ based on [Tb2] molecule, including the CNOT and SWAP gates.

  18. Online evolution reconstruction from a single measurement record with random time intervals for quantum communication

    Science.gov (United States)

    Zhou, Hua; Su, Yang; Wang, Rong; Zhu, Yong; Shen, Huiping; Pu, Tao; Wu, Chuanxin; Zhao, Jiyong; Zhang, Baofu; Xu, Zhiyong

    2017-10-01

    Online reconstruction of a time-variant quantum state from the encoding/decoding results of quantum communication is addressed by developing a method of evolution reconstruction from a single measurement record with random time intervals. A time-variant two-dimensional state is reconstructed on the basis of recovering its expectation value functions of three nonorthogonal projectors from a random single measurement record, which is composed from the discarded qubits of the six-state protocol. The simulated results prove that our method is robust to typical metro quantum channels. Our work extends the Fourier-based method of evolution reconstruction from the version for a regular single measurement record with equal time intervals to a unified one, which can be applied to arbitrary single measurement records. The proposed protocol of evolution reconstruction runs concurrently with the one of quantum communication, which can facilitate the online quantum tomography.

  19. Ground state selection under pressure in the quantum pyrochlore magnet Yb2Ti2O7.

    Science.gov (United States)

    Kermarrec, E; Gaudet, J; Fritsch, K; Khasanov, R; Guguchia, Z; Ritter, C; Ross, K A; Dabkowska, H A; Gaulin, B D

    2017-03-15

    A quantum spin liquid is a state of matter characterized by quantum entanglement and the absence of any broken symmetry. In condensed matter, the frustrated rare-earth pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7, so-called spin ices, exhibit a classical spin liquid state with fractionalized thermal excitations (magnetic monopoles). Evidence for a quantum spin ice, in which the magnetic monopoles become long range entangled and an emergent quantum electrodynamics arises, seems within reach. The magnetic properties of the quantum spin ice candidate Yb2Ti2O7 have eluded a global understanding and even the presence or absence of static magnetic order at low temperatures is controversial. Here we show that sensitivity to pressure is the missing key to the low temperature behaviour of Yb2Ti2O7. By combining neutron diffraction and muon spin relaxation on a stoichiometric sample under pressure, we evidence a magnetic transition from a disordered, non-magnetic, ground state to a splayed ferromagnetic ground state.

  20. Ground state selection under pressure in the quantum pyrochlore magnet Yb2Ti2O7

    Science.gov (United States)

    Kermarrec, E.; Gaudet, J.; Fritsch, K.; Khasanov, R.; Guguchia, Z.; Ritter, C.; Ross, K. A.; Dabkowska, H. A.; Gaulin, B. D.

    2017-01-01

    A quantum spin liquid is a state of matter characterized by quantum entanglement and the absence of any broken symmetry. In condensed matter, the frustrated rare-earth pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7, so-called spin ices, exhibit a classical spin liquid state with fractionalized thermal excitations (magnetic monopoles). Evidence for a quantum spin ice, in which the magnetic monopoles become long range entangled and an emergent quantum electrodynamics arises, seems within reach. The magnetic properties of the quantum spin ice candidate Yb2Ti2O7 have eluded a global understanding and even the presence or absence of static magnetic order at low temperatures is controversial. Here we show that sensitivity to pressure is the missing key to the low temperature behaviour of Yb2Ti2O7. By combining neutron diffraction and muon spin relaxation on a stoichiometric sample under pressure, we evidence a magnetic transition from a disordered, non-magnetic, ground state to a splayed ferromagnetic ground state. PMID:28294118

  1. Microtrap arrays on magnetic film atom chips for quantum information science.

    NARCIS (Netherlands)

    Leung, Y.F.V.; Tauschinsky, A.; van Druten, N.J.; Spreeuw, R.J.C.

    2011-01-01

    We present two different strategies for developing a quantum information science platform, based on our experimental results with magnetic microtrap arrays on a magnetic-film atom chip. The first strategy aims for mesoscopic ensemble qubits in a lattice of ~5 μm period, so that qubits can be

  2. Finite-momentum condensate of magnetic excitons in a bilayer quantum Hall system

    NARCIS (Netherlands)

    Doretto, R.L.; de Morais Smith, C.; Caldeira, A.O.

    2012-01-01

    We study the bilayer quantum Hall system at total filling factor νT=1 within a bosonization formalism which allows us to approximately treat the magnetic exciton as a boson. We show that in the region where the distance between the two layers is comparable to the magnetic length, the ground state of

  3. Randomized dynamical decoupling strategies and improved one-way key rates for quantum cryptography

    Energy Technology Data Exchange (ETDEWEB)

    Kern, Oliver

    2009-05-25

    The present thesis deals with various methods of quantum error correction. It is divided into two parts. In the first part, dynamical decoupling methods are considered which have the task of suppressing the influence of residual imperfections in a quantum memory. Such imperfections might be given by couplings between the finite dimensional quantum systems (qudits) constituting the quantum memory, for instance. The suppression is achieved by altering the dynamics of an imperfect quantum memory with the help of a sequence of local unitary operations applied to the qudits. Whereas up to now the operations of such decoupling sequences have been constructed in a deterministic fashion, strategies are developed in this thesis which construct the operations by random selection from a suitable set. Formulas are derived which estimate the average performance of such strategies. As it turns out, randomized decoupling strategies offer advantages and disadvantages over deterministic ones. It is possible to benefit from the advantages of both kind of strategies by designing combined strategies. Furthermore, it is investigated if and how the discussed decoupling strategies can be employed to protect a quantum computation running on the quantum memory. It is shown that a purely randomized decoupling strategy may be used by applying the decoupling operations and adjusted gates of the quantum algorithm in an alternating fashion. Again this method can be enhanced by the means of deterministic methods in order to obtain a combined decoupling method for quantum computations analogously to the combining strategies for quantum memories. The second part of the thesis deals with quantum error-correcting codes and protocols for quantum key distribution. The focus is on the BB84 and the 6-state protocol making use of only one-way communication during the error correction and privacy amplification steps. It is shown that by adding additional errors to the preliminary key (a process called

  4. Emergence of chiral spin liquids via quantum melting of noncoplanar magnetic orders

    Science.gov (United States)

    Hickey, Ciarán; Cincio, Lukasz; Papić, Zlatko; Paramekanti, Arun

    2017-09-01

    Quantum spin liquids (QSLs) are highly entangled states of quantum magnets which lie beyond the Landau paradigm of classifying phases of matter via broken symmetries. A physical route to arriving at QSLs is via frustration-induced quantum melting of ordered states such as valence bond crystals or magnetic orders. Here we show, using extensive exact diagonalization (ED) and density-matrix renormalization group (DMRG) studies of concrete S U (2 ) invariant spin models on honeycomb, triangular, and square lattices, that chiral spin liquids (CSLs) emerge as descendants of triple-Q spin crystals with tetrahedral magnetic order and a large scalar spin chirality. Such ordered-to-CSL melting transitions may yield lattice realizations of effective Chern-Simons-Higgs field theories. Our work provides a distinct unifying perspective on the emergence of CSLs and suggests that materials with certain noncoplanar magnetic orders might provide a good starting point to search for CSLs.

  5. Lead-position dependent regular oscillations and random fluctuations of conductance in graphene quantum dots.

    Science.gov (United States)

    Huang, Liang; Yang, Rui; Lai, Ying-Cheng; Ferry, David K

    2013-02-27

    Quantum interference causes a wavefunction to have sensitive spatial dependence, and this has a significant effect on quantum transport. For example, in a quantum-dot system, the conductance can depend on the lead positions. We investigate, for graphene quantum dots, the conductance variations with the lead positions. Since for graphene the types of boundaries, e.g., zigzag and armchair, can fundamentally affect the quantum transport characteristics, we focus on rectangular graphene quantum dots, for which the effects of boundaries can be systematically studied. For both zigzag and armchair horizontal boundaries, we find that changing the positions of the leads can induce significant conductance variations. Depending on the Fermi energy, the variations can be either regular oscillations or random conductance fluctuations. We develop a physical theory to elucidate the origin of the conductance oscillation/fluctuation patterns. In particular, quantum interference leads to standing-wave-like-patterns in the quantum dot which, in the absence of leads, are regulated by the energy-band structure of the corresponding vertical graphene ribbon. The observed 'coexistence' of regular oscillations and random fluctuations in the conductance can be exploited for the development of graphene-based nanodevices.

  6. Random matrix theory in biological nuclear magnetic resonance spectroscopy.

    Science.gov (United States)

    Lacelle, S

    1984-01-01

    The statistical theory of energy levels or random matrix theory is presented in the context of the analysis of chemical shifts of nuclear magnetic resonance (NMR) spectra of large biological systems. Distribution functions for the spacing between nearest-neighbor energy levels are discussed for uncorrelated, correlated, and random superposition of correlated energy levels. Application of this approach to the NMR spectra of a vitamin, an antibiotic, and a protein demonstrates the state of correlation of an ensemble of energy levels that characterizes each system. The detection of coherent and dissipative structures in proteins becomes feasible with this statistical spectroscopic technique. PMID:6478032

  7. Electric-field control of magnetism in graphene quantum dots: Ab initio calculations.

    Science.gov (United States)

    Agapito, Luis A; Kioussis, Nicholas; Kaxiras, Efthimios

    2010-11-23

    Employing ab initio calculations we predict that the magnetic states of hydrogenated diamond-shaped zigzag graphene quantum dots (GQDs), each exhibiting unique electronic structure, can be selectively tuned with gate voltage, through Stark or hybridization electric-field modulation of the spatial distribution and energy of the spin-polarized molecular orbitals, leading to transitions between these states. Electrical read-out of the GQD magnetic state can be accomplished by exploiting the distinctive electrical properties of the various magnetic configurations.

  8. Bound states of Dirac electrons in a graphene-based magnetic quantum dot

    Science.gov (United States)

    Wang, Dali; Jin, Guojun

    2009-10-01

    We investigate the magnetically confined states of the massless Dirac fermions in a graphene quantum dot formed by the inhomogeneous distributions of the magnetic fields inside and outside the dot. The calculated energy spectrum exhibits quite different features with and without the magnetic field inside the dot. It is found that the degeneracy of the relativistic Landau level with negative angular momenta can be lifted, and this degeneracy breaking can be modulated by the magnetic field inside the dot. Moreover, such a system can form the strongly localized states within the dot and along its boundary, especially with the magnetic field inside the dot.

  9. Optical studies of current-induced magnetization switching and photonic quantum states

    Science.gov (United States)

    Lorenz, Virginia

    2017-04-01

    The ever-decreasing size of electronic components is leading to a fundamental change in the way computers operate, as at the few-nanometer scale, resistive heating and quantum mechanics prohibit efficient and stable operation. One of the most promising next-generation computing paradigms is Spintronics, which uses the spin of the electron to manipulate and store information in the form of magnetic thin films. I will present our optical studies of the fundamental mechanisms by which we can efficiently manipulate magnetization using electrical current. Although electron spin is a quantum-mechanical property, Spintronics relies on macroscopic magnetization and thus does not take advantage of quantum mechanics in the algorithms used to encode and transmit information. For the second part of my talk, I will present our work under the umbrella of new computing and communication technologies based on the quantum mechanical properties of photons. Quantum technologies often require the carriers of information, or qubits, to have specific properties. Photonic quantum states are good information carriers because they travel fast and are robust to environmental fluctuations, but characterizing and controlling photonic sources so the photons have just the right properties is still a challenge. I will describe our work towards enabling quantum-physics-based secure long-distance communication using photons.

  10. Quantum transport in randomly diluted quantum percolation clusters in two dimensions

    Science.gov (United States)

    Cuansing, Eduardo; Nakanishi, Hisao

    2008-02-01

    We study the hopping transport of a quantum particle through finite, randomly diluted percolation clusters in two dimensions. We investigate how the transmission coefficient T behaves as a function of the energy E of the particle, the occupation concentration p of the disordered cluster, the size of the underlying lattice, and the type of connection chosen between the cluster and the input and output leads. We investigate both the point-to-point contacts and the busbar type of connection. For highly diluted clusters we find the behavior of the transmission to be independent of the type of connection. As the amount of dilution is decreased we find sharp variations in transmission. These variations are the remnants of the resonances at the ordered, zero-dilution, limit. For particles with energies within 0.25≤E≤1.75 (relative to the hopping integral) and with underlying square lattices of size 20×20, the configurations begin transmitting near pα=0.60 with T against p curves following a common pattern as the amount of dilution is decreased. Near pβ=0.90 this pattern is broken and the transmission begins to vary with the energy. In the asymptotic limit of very large clusters we find the systems to be totally reflecting in almost all cases. A few clear exceptions we find are when the amount of dilution is very low, when the particle has energy close to a resonance value at the ordered limit, and when the particle has energy at the middle of the band. These three cases, however, may not exhaust all possible exceptions.

  11. Estimation of quantum correlations in magnetic materials by neutron scattering data

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Ben-Qiong, E-mail: losenq@caep.cn [Key Laboratory of Neutron Physics, Institute of Nuclear Physics and Chemistry, CAEP, Mianyang 621900 (China); Wu, Lian-Ao, E-mail: lianaowu@gmail.com [Department of Theoretical Physics and History of Science, The Basque Country University (EHU/UPV), PO Box 644, 48080 Bilbao (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain); Zeng, Guo-Mo [College of Physics, Jilin University, Changchun 130012 (China); Song, Jian-Ming; Luo, Wei; Lei, Yang; Sun, Guang-Ai; Chen, Bo; Peng, Shu-Ming [Key Laboratory of Neutron Physics, Institute of Nuclear Physics and Chemistry, CAEP, Mianyang 621900 (China)

    2014-10-24

    We demonstrate that inelastic neutron scattering technique can be used to indirectly detect and measure the macroscopic quantum correlations quantified by both entanglement and discord in a quantum magnetic material, VODPO{sub 4}⋅1/2 D{sub 2}O. The amount of quantum correlations is obtained by analyzing the neutron scattering data of magnetic excitations in isolated V{sup 4+} spin dimers. Our quantitative analysis shows that the critical temperature of this material can reach as high as T{sub c}=82.5 K, where quantum entanglement drops to zero. Significantly, quantum discord can even survive at T{sub c}=300 K and may be used in room temperature quantum devices. Taking into account the spin–orbit (SO) coupling, we also predict theoretically that entanglement can be significantly enhanced and the critical temperature T{sub c} increases with the strength of spin–orbit coupling. - Highlights: • We predict macroscopic quantum correlations in VODPO{sub 4} ⋅ 0.5D{sub 2}O by analyzing neutron scattering experimental data. • The critical temperature of VODPO{sub 4} ⋅ 0.5D{sub 2}O can reach as high as 82.5 K, where entanglement drops to 0. • Quantum discord can even survive at room temperature. • Entanglement can be enhanced and the critical temperature increases with the strength of DM interaction.

  12. Field-induced magnetization jumps and quantum criticality in the 2D J-Q model

    Science.gov (United States)

    Iaizzi, Adam; Sandvik, Anders

    The J-Q model is a `designer hamiltonian' formed by adding a four spin `Q' term to the standard antiferromagnetic S = 1 / 2 Heisenberg model. The Q term drives a quantum phase transition to a valence-bond solid (VBS) state: a non-magnetic state with a pattern of local singlets which breaks lattice symmetries. The elementary excitations of the VBS are triplons, i.e. gapped S=1 quasiparticles. There is considerable interest in the quantum phase transition between the Néel and VBS states as an example of deconfined quantum criticality. Near the phase boundary, triplons deconfine into pairs of bosonic spin-1/2 excitations known as spinons. Using exact diagonalization and the stochastic series expansion quantum monte carlo method, we study the 2D J-Q model in the presence of an external magnetic field. We use the field to force a nonzero density of magnetic excitations at T=0 and look for signatures of Bose-Einstein condensation of spinons. At higher magnetic fields, there is a jump in the induced magnetization caused by the onset of an effective attractive interaction between magnons on a ferromagnetic background. We characterize the first order quantum phase transition and determine the minimum value of the coupling ratio q ≡ Q / J required to produce this jump. Funded by NSF DMR-1410126.

  13. Longitudinal wave function control in single quantum dots with an applied magnetic field

    Science.gov (United States)

    Cao, Shuo; Tang, Jing; Gao, Yunan; Sun, Yue; Qiu, Kangsheng; Zhao, Yanhui; He, Min; Shi, Jin-An; Gu, Lin; Williams, David A.; Sheng, Weidong; Jin, Kuijuan; Xu, Xiulai

    2015-01-01

    Controlling single-particle wave functions in single semiconductor quantum dots is in demand to implement solid-state quantum information processing and spintronics. Normally, particle wave functions can be tuned transversely by an perpendicular magnetic field. We report a longitudinal wave function control in single quantum dots with a magnetic field. For a pure InAs quantum dot with a shape of pyramid or truncated pyramid, the hole wave function always occupies the base because of the less confinement at base, which induces a permanent dipole oriented from base to apex. With applying magnetic field along the base-apex direction, the hole wave function shrinks in the base plane. Because of the linear changing of the confinement for hole wave function from base to apex, the center of effective mass moves up during shrinking process. Due to the uniform confine potential for electrons, the center of effective mass of electrons does not move much, which results in a permanent dipole moment change and an inverted electron-hole alignment along the magnetic field direction. Manipulating the wave function longitudinally not only provides an alternative way to control the charge distribution with magnetic field but also a new method to tune electron-hole interaction in single quantum dots. PMID:25624018

  14. Random operators disorder effects on quantum spectra and dynamics

    CERN Document Server

    Aizenman, Michael

    2015-01-01

    This book provides an introduction to the mathematical theory of disorder effects on quantum spectra and dynamics. Topics covered range from the basic theory of spectra and dynamics of self-adjoint operators through Anderson localization-presented here via the fractional moment method, up to recent results on resonant delocalization. The subject's multifaceted presentation is organized into seventeen chapters, each focused on either a specific mathematical topic or on a demonstration of the theory's relevance to physics, e.g., its implications for the quantum Hall effect. The mathematical chapters include general relations of quantum spectra and dynamics, ergodicity and its implications, methods for establishing spectral and dynamical localization regimes, applications and properties of the Green function, its relation to the eigenfunction correlator, fractional moments of Herglotz-Pick functions, the phase diagram for tree graph operators, resonant delocalization, the spectral statistics conjecture, and rela...

  15. Realistic Many-Body Quantum Systems vs. Full Random Matrices: Static and Dynamical Properties

    Directory of Open Access Journals (Sweden)

    Eduardo Jonathan Torres-Herrera

    2016-10-01

    Full Text Available We study the static and dynamical properties of isolated many-body quantum systems and compare them with the results for full random matrices. In doing so, we link concepts from quantum information theory with those from quantum chaos. In particular, we relate the von Neumann entanglement entropy with the Shannon information entropy and discuss their relevance for the analysis of the degree of complexity of the eigenstates, the behavior of the system at different time scales and the conditions for thermalization. A main advantage of full random matrices is that they enable the derivation of analytical expressions that agree extremely well with the numerics and provide bounds for realistic many-body quantum systems.

  16. Dissipation, dephasing and quantum Darwinism in qubit systems with random unitary interactions

    Science.gov (United States)

    Balaneskovic, Nenad; Mendler, Marc

    2016-09-01

    We investigate the influence of dissipation and decoherence on quantum Darwinism by generalizing Zurek's original qubit model of decoherence and the establishment of pointer states [W.H. Zurek, Nat. Phys. 5, 181 (2009); see also arXiv: quant-ph/0707.2832v1, pp. 14-19.]. Our model allows for repeated multiple qubit-qubit couplings between system and environment which are described by randomly applied two-qubit quantum operations inducing entanglement, dissipation and dephasing. The resulting stationary qubit states of system and environment are investigated. They exhibit the intricate influence of entanglement generation, dissipation and dephasing on this characteristic quantum phenomenon.

  17. Confinement in the Bulk, Deconfinement on the Wall: Infrared Equivalence between Compactified QCD and Quantum Magnets

    Science.gov (United States)

    Sulejmanpasic, Tin; Shao, Hui; Sandvik, Anders W.; Ünsal, Mithat

    2017-09-01

    In a spontaneously dimerized quantum antiferromagnet, spin-1 /2 excitations (spinons) are confined in pairs by strings akin to those confining quarks in non-Abelian gauge theories. The system has multiple degenerate ground states (vacua) and domain walls between regions of different vacua. For two vacua, we demonstrate that spinons on a domain wall are liberated, in a mechanism strikingly similar to domain-wall deconfinement of quarks in variants of quantum chromodynamics. This observation not only establishes a novel phenomenon in quantum magnetism, but also provides a new direct link between particle physics and condensed-matter physics. The analogy opens doors to improving our understanding of particle confinement and deconfinement by computational and experimental studies in quantum magnetism.

  18. Quantum Electrodynamics with Semiconductor Quantum Dots Coupled to Anderson‐localized Random Cavities

    DEFF Research Database (Denmark)

    Sapienza, Luca; Nielsen, Henri Thyrrestrup; Stobbe, Søren

    2011-01-01

    of the spontaneous emission decay rate by up to a factor 15 and an efficiency of channeling single photons into Anderson-localized modes reaching values as high as 94%. These results prove that disordered photonic media provide an efficient platform for quantum electrodynamics, offering a novel route to quantum......We demonstrate that the spontaneous emission decay rate of semiconductor quantum dots can be strongly modified by the coupling to disorder-induced Anderson-localized photonic modes. We experimentally measure, by means of time-resolved photoluminescence spectroscopy, the enhancement...

  19. Random matrix theory and critical phenomena in quantum spin chains

    Science.gov (United States)

    Hutchinson, J.; Keating, J. P.; Mezzadri, F.

    2015-09-01

    We compute critical properties of a general class of quantum spin chains which are quadratic in the Fermi operators and can be solved exactly under certain symmetry constraints related to the classical compact groups $U(N)$, $O(N)$ and $Sp(2N)$. In particular we calculate critical exponents $s$, $\

  20. An effective Hamiltonian approach to quantum random walk

    Indian Academy of Sciences (India)

    2017-02-09

    Feb 9, 2017 ... We showed that in the case of two-step walk, the time evolution operator effectively can have multiplicative form. In the case of a square lattice, quantum walk has been studied computationally for different coins and the results for both the additive and the multiplica- tive approaches have been compared.

  1. Quantum cryptography using coherent states: Randomized encryption and key generation

    Science.gov (United States)

    Corndorf, Eric

    With the advent of the global optical-telecommunications infrastructure, an increasing number of individuals, companies, and agencies communicate information with one another over public networks or physically-insecure private networks. While the majority of the traffic flowing through these networks requires little or no assurance of secrecy, the same cannot be said for certain communications between banks, between government agencies, within the military, and between corporations. In these arenas, the need to specify some level of secrecy in communications is a high priority. While the current approaches to securing sensitive information (namely the public-key-cryptography infrastructure and deterministic private-key ciphers like AES and 3DES) seem to be cryptographically strong based on empirical evidence, there exist no mathematical proofs of secrecy for any widely deployed cryptosystem. As an example, the ubiquitous public-key cryptosystems infer all of their secrecy from the assumption that factoring of the product of two large primes is necessarily time consuming---something which has not, and perhaps cannot, be proven. Since the 1980s, the possibility of using quantum-mechanical features of light as a physical mechanism for satisfying particular cryptographic objectives has been explored. This research has been fueled by the hopes that cryptosystems based on quantum systems may provide provable levels of secrecy which are at least as valid as quantum mechanics itself. Unfortunately, the most widely considered quantum-cryptographic protocols (BB84 and the Ekert protocol) have serious implementation problems. Specifically, they require quantum-mechanical states which are not readily available, and they rely on unproven relations between intrusion-level detection and the information available to an attacker. As a result, the secrecy level provided by these experimental implementations is entirely unspecified. In an effort to provably satisfy the cryptographic

  2. Low-frequency surface waves on semi-bounded magnetized quantum plasma

    Energy Technology Data Exchange (ETDEWEB)

    Moradi, Afshin, E-mail: a.moradi@kut.ac.ir [Department of Engineering Physics, Kermanshah University of Technology, Kermanshah (Iran, Islamic Republic of)

    2016-08-15

    The propagation of low-frequency electrostatic surface waves on the interface between a vacuum and an electron-ion quantum plasma is studied in the direction perpendicular to an external static magnetic field which is parallel to the interface. A new dispersion equation is derived by employing both the quantum magnetohydrodynamic and Poisson equations. It is shown that the dispersion equations for forward and backward-going surface waves are different from each other.

  3. Biocompatibility of hydrophilic silica-coated CdTe quantum dots and magnetic nanoparticles

    Directory of Open Access Journals (Sweden)

    Ruan Jing

    2011-01-01

    Full Text Available Abstract Fluorescent magnetic nanoparticles exhibit great application prospects in biomedical engineering. Herein, we reported the effects of hydrophilic silica-coated CdTe quantum dots and magnetic nanoparticles (FMNPs on human embryonic kidney 293 (HEK293 cells and mice with the aim of investigating their biocompatibility. FMNPs with 150 nm in diameter were prepared, and characterized by high-resolution transmission electron microscopy and photoluminescence (PL spectra and magnetometer. HEK293 cells were cultured with different doses of FMNPs (20, 50, and 100μ g/ml for 1-4 days. Cell viability and adhesion ability were analyzed by CCK8 method and Western blotting. 30 mice were randomly divided into three groups, and were, respectively, injected via tail vein with 20, 60, and 100 μg FMNPs, and then were, respectively, raised for 1, 7, and 30 days, then their lifespan, important organs, and blood biochemical parameters were analyzed. Results show that the prepared water-soluble FMNPs had high fluorescent and magnetic properties, less than 50 μg/ml of FMNPs exhibited good biocompatibility to HEK293 cells, the cell viability, and adhesion ability were similar to the control HEK293 cells. FMNPs primarily accumulated in those organs such as lung, liver, and spleen. Lung exposed to FMNPs displayed a dose-dependent inflammatory response, blood biochemical parameters such as white blood cell count (WBC, alanine aminotransferase (ALT, and aspartate aminotransferase (AST, displayed significant increase when the FMNPs were injected into mice at dose of 100μg. In conclusion, FMNPs exhibit good biocompatibility to cells under the dose of less than 50 μg/ml, and to mice under the dose of less than 2mg/kg body weight. The FMNPs' biocompatibility must be considered when FMNPs are used for in vivo diagnosis and therapy.

  4. Transport through a strongly coupled graphene quantum dot in perpendicular magnetic field

    Directory of Open Access Journals (Sweden)

    Güttinger Johannes

    2011-01-01

    Full Text Available Abstract We present transport measurements on a strongly coupled graphene quantum dot in a perpendicular magnetic field. The device consists of an etched single-layer graphene flake with two narrow constrictions separating a 140 nm diameter island from source and drain graphene contacts. Lateral graphene gates are used to electrostatically tune the device. Measurements of Coulomb resonances, including constriction resonances and Coulomb diamonds prove the functionality of the graphene quantum dot with a charging energy of approximately 4.5 meV. We show the evolution of Coulomb resonances as a function of perpendicular magnetic field, which provides indications of the formation of the graphene specific 0th Landau level. Finally, we demonstrate that the complex pattern superimposing the quantum dot energy spectra is due to the formation of additional localized states with increasing magnetic field.

  5. Magnetically induced transparency of a quantum metamaterial composed of twin flux qubits.

    Science.gov (United States)

    Shulga, K V; Il'ichev, E; Fistul, M V; Besedin, I S; Butz, S; Astafiev, O V; Hübner, U; Ustinov, A V

    2018-01-11

    Quantum theory is expected to govern the electromagnetic properties of a quantum metamaterial, an artificially fabricated medium composed of many quantum objects acting as artificial atoms. Propagation of electromagnetic waves through such a medium is accompanied by excitations of intrinsic quantum transitions within individual meta-atoms and modes corresponding to the interactions between them. Here we demonstrate an experiment in which an array of double-loop type superconducting flux qubits is embedded into a microwave transmission line. We observe that in a broad frequency range the transmission coefficient through the metamaterial periodically depends on externally applied magnetic field. Field-controlled switching of the ground state of the meta-atoms induces a large suppression of the transmission. Moreover, the excitation of meta-atoms in the array leads to a large resonant enhancement of the transmission. We anticipate possible applications of the observed frequency-tunable transparency in superconducting quantum networks.

  6. Magnetic Resonance and Fluctuations in Porous Media and Quantum Spin Chains.

    Science.gov (United States)

    Mitra, Partha Pratim

    The first set of problems studied deal with time domain nuclear magnetic resonance (NMR) experiments on fluids in complex environments. The depolarisation of magnetic moments attached to molecules diffusing in a quenched random magnetic field is studied by means of mappings into statistical mechanical models of self-interacting random walks. At long times, the polarisation in free induction decay or spin echo experiments shows unusual time dependence. The diffusion envelope of fluid molecules confined to the pore space of a porous material is directly probed by pulsed field gradient NMR experiments. In this context, the inverse problem of obtaining geometrical information about the pore space from the measured momentum space propagator is studied. This problem is related to the well known problem of 'Hearing the shape of a drum'. A short time expansion is derived for the time-dependent diffusion coefficient of walkers in a porous medium. At long times, the measured propagator carries information about the connectivity as well as the density-density correlation function of the pore space. NMR diffusion measurements on (i) water confined to the interstices of packed glass spheres, and (ii) a biological porous medium with semipermeable membranes have corroborated the theoretical expectations. The second part of the thesis deals with magnetic fluctuations in the S = 1 quantum antiferromagnetic chain compound NENP. Due to the unusual nature of the ground state of the S = 1 Heisenberg chain, S = 1/2 degrees of freedom are obtained at the ends of a finite chain, and are observable in electron spin resonance measurements. The rapid drop with temperature of the corresponding intensities is shown to be the result of the resonant frequency being shifted out of the observation window by the appearance of even a single excitation on the chain. Far infrared absorption lines obtained at the field shifted gap energies in apparent violation of the momentum selection rule present in

  7. Quantum dynamics of a macroscopic magnet operating as an environment of a mechanical oscillator

    Science.gov (United States)

    Foti, C.; Cuccoli, A.; Verrucchi, P.

    2016-12-01

    We study the dynamics of a bipartite quantum system in a way such that its formal description keeps holding even if one of its parts becomes macroscopic; the problem is related to the analysis of the quantum-to-classical crossover, but our approach implies that the whole system stays genuinely quantum. The aim of the work is to understand (1) if, (2) to what extent, and possibly (3) how the evolution of a macroscopic environment testifies to the coupling with its microscopic quantum companion. To this purpose we consider a magnetic environment made of a large number of spin-1/2 particles, coupled with a quantum mechanical oscillator, possibly in the presence of an external magnetic field. We take the value of the total environmental spin S constant and large, which allows us to consider the environment as one single macroscopic system, and further deal with the hurdles of the spin-algebra via approximations that are valid in the large-S limit. We find an insightful expression for the propagator of the whole system, where we identify an effective "back-action" term, i.e., an operator acting on the magnetic environment only, and yet missing in the absence of the quantum principal system. This operator emerges as a time-dependent magnetic anisotropy whose character, whether uniaxial or planar, also depends on the detuning between the frequency of the oscillator and the level splitting in the spectrum of the free magnetic system, induced by the possible presence of the external field. The time dependence of the anisotropy is analyzed, and its effects on the dynamics of the magnet, as well as its relation to the entangling evolution of the overall system, are discussed.

  8. Temperature and Magnetic Field Effects on the Transport Controlled Charge State of a Single Quantum Dot

    Directory of Open Access Journals (Sweden)

    Moskalenko ES

    2010-01-01

    Full Text Available Abstract Individual InAs/GaAs quantum dots are studied by micro-photoluminescence. By varying the strength of an applied external magnetic field and/or the temperature, it is demonstrated that the charge state of a single quantum dot can be tuned. This tuning effect is shown to be related to the in-plane electron and hole transport, prior to capture into the quantum dot, since the photo-excited carriers are primarily generated in the barrier.

  9. Towards developing a compact model for magnetization switching in straintronics magnetic random access memory devices

    Science.gov (United States)

    Barangi, Mahmood; Erementchouk, Mikhail; Mazumder, Pinaki

    2016-08-01

    Strain-mediated magnetization switching in a magnetic tunneling junction (MTJ) by exploiting a combination of piezoelectricity and magnetostriction has been proposed as an energy efficient alternative to spin transfer torque (STT) and field induced magnetization switching methods in MTJ-based magnetic random access memories (MRAM). Theoretical studies have shown the inherent advantages of strain-assisted switching, and the dynamic response of the magnetization has been modeled using the Landau-Lifshitz-Gilbert (LLG) equation. However, an attempt to use LLG for simulating dynamics of individual elements in large-scale simulations of multi-megabyte straintronics MRAM leads to extremely time-consuming calculations. Hence, a compact analytical solution, predicting the flipping delay of the magnetization vector in the nanomagnet under stress, combined with a liberal approximation of the LLG dynamics in the straintronics MTJ, can lead to a simplified model of the device suited for fast large-scale simulations of multi-megabyte straintronics MRAMs. In this work, a tensor-based approach is developed to study the dynamic behavior of the stressed nanomagnet. First, using the developed method, the effect of stress on the switching behavior of the magnetization is investigated to realize the margins between the underdamped and overdamped regimes. The latter helps the designer realize the oscillatory behavior of the magnetization when settling along the minor axis, and the dependency of oscillations on the stress level and the damping factor. Next, a theoretical model to predict the flipping delay of the magnetization vector is developed and tested against LLG-based numerical simulations to confirm the accuracy of findings. Lastly, the obtained delay is incorporated into the approximate solutions of the LLG dynamics, in order to create a compact model to liberally and quickly simulate the magnetization dynamics of the MTJ under stress. Using the developed delay equation, the

  10. Towards developing a compact model for magnetization switching in straintronics magnetic random access memory devices

    Energy Technology Data Exchange (ETDEWEB)

    Barangi, Mahmood, E-mail: barangi@umich.edu; Erementchouk, Mikhail; Mazumder, Pinaki [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2121 (United States)

    2016-08-21

    Strain-mediated magnetization switching in a magnetic tunneling junction (MTJ) by exploiting a combination of piezoelectricity and magnetostriction has been proposed as an energy efficient alternative to spin transfer torque (STT) and field induced magnetization switching methods in MTJ-based magnetic random access memories (MRAM). Theoretical studies have shown the inherent advantages of strain-assisted switching, and the dynamic response of the magnetization has been modeled using the Landau-Lifshitz-Gilbert (LLG) equation. However, an attempt to use LLG for simulating dynamics of individual elements in large-scale simulations of multi-megabyte straintronics MRAM leads to extremely time-consuming calculations. Hence, a compact analytical solution, predicting the flipping delay of the magnetization vector in the nanomagnet under stress, combined with a liberal approximation of the LLG dynamics in the straintronics MTJ, can lead to a simplified model of the device suited for fast large-scale simulations of multi-megabyte straintronics MRAMs. In this work, a tensor-based approach is developed to study the dynamic behavior of the stressed nanomagnet. First, using the developed method, the effect of stress on the switching behavior of the magnetization is investigated to realize the margins between the underdamped and overdamped regimes. The latter helps the designer realize the oscillatory behavior of the magnetization when settling along the minor axis, and the dependency of oscillations on the stress level and the damping factor. Next, a theoretical model to predict the flipping delay of the magnetization vector is developed and tested against LLG-based numerical simulations to confirm the accuracy of findings. Lastly, the obtained delay is incorporated into the approximate solutions of the LLG dynamics, in order to create a compact model to liberally and quickly simulate the magnetization dynamics of the MTJ under stress. Using the developed delay equation, the

  11. Comparison of nuclear electric resonance and nuclear magnetic resonance in integer and fractional quantum Hall states

    Directory of Open Access Journals (Sweden)

    Toru Tomimatsu

    2015-08-01

    Full Text Available Electric-field-induced nuclear resonance (NER: nuclear electric resonance involving quantum Hall states (QHSs was studied at various filling factors by exploiting changes in nuclear spins polarized at quantum Hall breakdown. Distinct from the magnetic dipole interaction in nuclear magnetic resonance, the interaction of the electric-field gradient with the electric quadrupole moment plays the dominant role in the NER mechanism. The magnitude of the NER signal strongly depends on whether electronic states are localized or extended. This indicates that NER is sensitive to the screening capability of the electric field associated with QHSs.

  12. Four-dimensional quantum oscillator and magnetic monopole with U(1) dynamical group

    Science.gov (United States)

    Bakhshi, Z.; Panahi, H.; Golchehre, S. G.

    2017-09-01

    By using an appropriate transformation, it was shown that the quantum system of four-dimensional (4D) simple harmonic oscillator can describe the motion of a charged particle in the presence of a magnetic monopole field. It was shown that the Dirac magnetic monopole has the hidden algebra of U(1) symmetry and by reducing the dimensions of space, the U(1) × U(1) dynamical group for 4D harmonic oscillator quantum system was obtained. Using the group representation and based on explicit solution of the obtained differential equation, the spectrum of system was calculated.

  13. Quantum diffusion of magnetic fields in a numerical worldline approach

    CERN Document Server

    Gies, Holger; Gies, Holger; Langfeld, Kurt

    2001-01-01

    We propose a numerical technique for calculating effective actions of electromagnetic backgrounds based on the worldline formalism. As a conceptually simple example, we consider scalar electrodynamics in three dimensions to one-loop order. Beyond the constant-magnetic-field case, serving as a benchmark test, we analyze the effective action of a step-function-like magnetic field -- a configuration that is inaccessible to derivative expansions. We observe magnetic-field diffusion, i.e., nonvanishing magnetic action density at space points near the magnetic step where the classical field vanishes.

  14. Micrometer-scale magnetic imaging of geological samples using a quantum diamond microscope

    Science.gov (United States)

    Glenn, D. R.; Fu, R. R.; Kehayias, P.; Le Sage, D.; Lima, E. A.; Weiss, B. P.; Walsworth, R. L.

    2017-08-01

    Remanent magnetization in geological samples may record the past intensity and direction of planetary magnetic fields. Traditionally, this magnetization is analyzed through measurements of the net magnetic moment of bulk millimeter to centimeter sized samples. However, geological samples are often mineralogically and texturally heterogeneous at submillimeter scales, with only a fraction of the ferromagnetic grains carrying the remanent magnetization of interest. Therefore, characterizing this magnetization in such cases requires a technique capable of imaging magnetic fields at fine spatial scales and with high sensitivity. To address this challenge, we developed a new instrument, based on nitrogen-vacancy centers in diamond, which enables direct imaging of magnetic fields due to both remanent and induced magnetization, as well as optical imaging, of room-temperature geological samples with spatial resolution approaching the optical diffraction limit. We describe the operating principles of this device, which we call the quantum diamond microscope (QDM), and report its optimized image-area-normalized magnetic field sensitivity (20 µTṡµm/Hz1/2), spatial resolution (5 µm), and field of view (4 mm), as well as trade-offs between these parameters. We also perform an absolute magnetic field calibration for the device in different modes of operation, including three-axis (vector) and single-axis (projective) magnetic field imaging. Finally, we use the QDM to obtain magnetic images of several terrestrial and meteoritic rock samples, demonstrating its ability to resolve spatially distinct populations of ferromagnetic carriers.

  15. Electric-field control of magnetism in graphene quantum dots: Ab initio calculations

    OpenAIRE

    Agapito, Luis A.; Kioussis, Nicholas; Kaxiras, Efthimios

    2010-01-01

    Employing ab initio calculations we predict that the magnetic states of hydrogenated diamond-shaped zigzag graphene quantum dots (GQDs), each exhibiting unique electronic structure, can be selectively tuned with gate voltage, through Stark or hybridization electric-field modulation of the spatial distribution and energy of the spin-polarized molecular orbitals, leading to transitions between these states. Electrical read-out of the GQD magnetic state can be accomplished by exploiting the dist...

  16. Neutron spin-echo on magnetic single crystals in the quantum limit

    Energy Technology Data Exchange (ETDEWEB)

    Blackburn, E. [Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093 0319 (United States) and Institut Laue-Langevin, Boite Postale 156, F-38042 Grenoble (France) and European Commission, JRC, Institute for Transuranium Elements, Postfach 2340, D-76125 Karlsruhe (Germany)]. E-mail: eblackburn@physics.ucsd.edu; Hiess, A. [Institut Laue-Langevin, Boite Postale 156, F-38042 Grenoble (France); Bernhoeft, N. [Departement de la Recherche Fondamentale sur la Matiere Condensee, CEA-Grenoble, F-38054 Grenoble (France); Rheinstaedter, M.C. [Institut Laue-Langevin, Boite Postale 156, F-38042 Grenoble (France); Fouquet, P. [Institut Laue-Langevin, Boite Postale 156, F-38042 Grenoble (France); Lander, G.H. [European Commission, JRC, Institute for Transuranium Elements, Postfach 2340, D-76125 Karlsruhe (Germany)

    2007-07-15

    As interest in low-temperature physics increases, whether for the study of frustrated magnets or for quantum effects, neutron spin-echo will become increasingly important, because of the high-energy resolution achievable. The behaviour of quasielastic scattering for low temperatures relative to the energy scale of interest is investigated. In addition, we note that momentum-transfer selective magnetic scattering may be susceptible to parasitic echoes in certain experimental configurations.

  17. High-speed quantum-random number generation by continuous measurement of arrival time of photons.

    Science.gov (United States)

    Yan, Qiurong; Zhao, Baosheng; Hua, Zhang; Liao, Qinghong; Yang, Hao

    2015-07-01

    We demonstrate a novel high speed and multi-bit optical quantum random number generator by continuously measuring arrival time of photons with a common starting point. To obtain the unbiased and post-processing free random bits, the measured photon arrival time is converted into the sum of integral multiple of a fixed period and a phase time. Theoretical and experimental results show that the phase time is an independent and uniform random variable. A random bit extraction method by encoding the phase time is proposed. An experimental setup has been built and the unbiased random bit generation rate could reach 128 Mb/s, with random bit generation efficiency of 8 bits per detected photon. The random numbers passed all tests in the statistical test suite.

  18. Random Number Generation for Petascale Quantum Monte Carlo

    Energy Technology Data Exchange (ETDEWEB)

    Ashok Srinivasan

    2010-03-16

    The quality of random number generators can affect the results of Monte Carlo computations, especially when a large number of random numbers are consumed. Furthermore, correlations present between different random number streams in a parallel computation can further affect the results. The SPRNG software, which the author had developed earlier, has pseudo-random number generators (PRNGs) capable of producing large numbers of streams with large periods. However, they had been empirically tested on only thousand streams earlier. In the work summarized here, we tested the SPRNG generators with over a hundred thousand streams, involving over 10^14 random numbers per test, on some tests. We also tested the popular Mersenne Twister. We believe that these are the largest tests of PRNGs, both in terms of the numbers of streams tested and the number of random numbers tested. We observed defects in some of these generators, including the Mersenne Twister, while a few generators appeared to perform well. We also corrected an error in the implementation of one of the SPRNG generators.

  19. Modulation of a compressional electromagnetic wave in a magnetized electron-positron quantum plasma.

    Science.gov (United States)

    Amin, M R

    2015-09-01

    Amplitude modulation of a compressional electromagnetic wave in a strongly magnetized electron-positron pair plasma is considered in the quantum magnetohydrodynamic regime. The important ingredients of this study are the inclusion of the external strong magnetic field, Fermi quantum degeneracy pressure, particle exchange potential, quantum diffraction effects via the Bohm potential, and dissipative effect due to collision of the charged carriers. A modified-nonlinear Schödinger equation is developed for the compressional magnetic field of the electromagnetic wave by employing the standard reductive perturbation technique. The linear and nonlinear dispersions of the electromagnetic wave are discussed in detail. For some parameter ranges, relevant to dense astrophysical objects such as the outer layers of white dwarfs, neutron stars, and magnetars, etc., it is found that the compressional electromagnetic wave is modulationally unstable and propagates as a dissipated electromagnetic wave. It is also found that the quantum effects due to the particle exchange potential and the Bohm potential are negligibly small in comparison to the effects of the Fermi quantum degeneracy pressure. The numerical results on the growth rate of the modulation instability is also presented.

  20. Magnetically-Driven Quantum Heat Engines: The Quasi-Static Limit of Their Efficiency

    Directory of Open Access Journals (Sweden)

    Enrique Muñoz

    2016-05-01

    Full Text Available The concept of a quantum heat engine (QHEN has been discussed in the literature, not only due to its intrinsic scientific interest, but also as an alternative to efficiently recover, on a nanoscale device, thermal energy in the form of useful work. The quantum character of a QHEN relies, for instance, on the fact that any of its intermediate states is determined by a density matrix operator. In particular, this matrix can represent a mixed state. For a classical heat engine, a theoretical upper bound for its efficiency is obtained by analyzing its quasi-static operation along a cycle drawn by a sequence of quasi-equilibrium states. A similar analysis can be carried out for a quantum engine, where quasi-static processes are driven by the evolution of ensemble-averaged observables, via variation of the corresponding operators or of the density matrix itself on a tunable physical parameter. We recently proposed two new conceptual designs for a magnetically-driven quantum engine, where the tunable parameter is the intensity of an external magnetic field. Along this article, we shall present the general quantum thermodynamics formalism developed in order to analyze this type of QHEN, and moreover, we shall apply it to describe the theoretical efficiency of two different practical implementations of this concept: an array of semiconductor quantum dots and an ensemble of graphene flakes submitted to mechanical tension.

  1. Structural analysis of strained quantum dots using nuclear magnetic resonance.

    Science.gov (United States)

    Chekhovich, E A; Kavokin, K V; Puebla, J; Krysa, A B; Hopkinson, M; Andreev, A D; Sanchez, A M; Beanland, R; Skolnick, M S; Tartakovskii, A I

    2012-10-01

    Strained semiconductor nanostructures can be used to make single-photon sources, detectors and photovoltaic devices, and could potentially be used to create quantum logic devices. The development of such applications requires techniques capable of nanoscale structural analysis, but the microscopy methods typically used to analyse these materials are destructive. NMR techniques can provide non-invasive structural analysis, but have been restricted to strain-free semiconductor nanostructures because of the significant strain-induced quadrupole broadening of the NMR spectra. Here, we show that optically detected NMR spectroscopy can be used to analyse individual strained quantum dots. Our approach uses continuous-wave broadband radiofrequency excitation with a specially designed spectral pattern and can probe individual strained nanostructures containing only 1 × 10(5) quadrupole nuclear spins. With this technique, we are able to measure the strain distribution and chemical composition of quantum dots in the volume occupied by the single confined electron. The approach could also be used to address problems in quantum information processing such as the precise control of nuclear spins in the presence of strong quadrupole effects.

  2. Linear and nonlinear absorption coefficients of spherical quantum dot inside external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Çakır, Bekir, E-mail: bcakir@selcuk.edu.tr [Physics Department, Faculty of Science, Selcuk University, Campus, 42075 Konya (Turkey); Yakar, Yusuf, E-mail: yuyakar@yahoo.com [Physics Department, Faculty of Arts and Science, Aksaray University, Campus, 68100 Aksaray (Turkey); Özmen, Ayhan [Physics Department, Faculty of Science, Selcuk University, Campus, 42075 Konya (Turkey)

    2017-04-01

    We have calculated the wavefunctions and energy eigenvalues of spherical quantum dot with infinite potential barrier inside uniform magnetic field. In addition, we have investigated the magnetic field effect on optical transitions between Zeeman energy states. The results are expressed as a function of dot radius, incident photon energy and magnetic field strength. The results present that, in large dot radii, the external magnetic field affects strongly the optical transitions between Zeeman states. In the strong spatial confinement case, energy level is relatively insensitive to the magnetic field, and electron spatial confinement prevails over magnetic confinement. Also, while m varies from −1 to +1, the peak positions of the optical transitions shift toward higher energy (blueshift).

  3. Anisotropic pseudopotential characterization of quantum Hall systems under a tilted magnetic field

    Science.gov (United States)

    Yang, Bo; Lee, Ching Hua; Zhang, Chi; Hu, Zi-Xiang

    2017-11-01

    We analytically derived the effective two-body interaction for a finite thickness quantum Hall system with a harmonic perpendicular confinement and an in-plane magnetic field. The anisotropic effective interaction in the lowest Landau level (LLL) and first Landau level (1LL) are expanded in the basis of the generalized pseudopotentials (PPs), and we analyze how the coefficients of some prominent isotropic and anisotropic PPs depend on the thickness of the sample and the strength of the in-plane magnetic field. We also investigate the stability of the topological quantum Hall states, especially the Laughlin state and its emergent guiding center metric, which we can now compute analytically. An interesting reorientation of the anisotropy direction of the Laughlin state in the 1LL is revealed, and we also discuss various possible experimental ramifications for this quantum Hall system with broken rotational symmetry.

  4. Quantum magnetism in strongly interacting one-dimensional spinor Bose systems

    DEFF Research Database (Denmark)

    Salami Dehkharghani, Amin; Volosniev, A. G.; Lindgren, E. J.

    2015-01-01

    -range inter-species interactions much larger than their intra-species interactions and show that they have novel energetic and magnetic properties. In the strongly interacting regime, these systems have energies that are fractions of the basic harmonic oscillator trap quantum and have spatially separated...

  5. Equilibrium fluctuations formulas for the quantum one-component plasma in a magnetic field

    NARCIS (Netherlands)

    John, P.; Suttorp, L.G.

    1993-01-01

    The authors derive a complete set of equilibrium fluctuation formulae for the charge density, the current density and the energy density of the quantum one-component plasma in a magnetic field. The derivation is based on the use of imaginary-time-dependent Green functions and their Kubo transforms.

  6. Fluctuations properties and collective modes of quantum plasmas in a magnetic field

    NARCIS (Netherlands)

    Suttorp, L.G.; Van Horn, H.M.; Ichimaru, S.

    1993-01-01

    A complete set of equilibrium fluctuation formulas for the charge density, the momentum density and the energy density of a magnetized one-component quantum plasma is presented. The derivation is based on the use of equations of motion for Fourier-transformed imaginary-time Green functions. The

  7. Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain

    DEFF Research Database (Denmark)

    Stone, M.B.; Reich, D.H.; Broholm, C.

    2003-01-01

    Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/Jless than or equal to0.025 for H=0 and H=8.7 T, where...

  8. Reduced graphene oxide-germanium quantum dot nanocomposite: electronic, optical and magnetic properties

    Science.gov (United States)

    Amollo, Tabitha A.; Mola, Genene T.; Nyamori, Vincent O.

    2017-12-01

    Graphene provides numerous possibilities for structural modification and functionalization of its carbon backbone. Localized magnetic moments can, as well, be induced in graphene by the formation of structural defects which include vacancies, edges, and adatoms. In this work, graphene was functionalized using germanium atoms, we report the effect of the Ge ad atoms on the structural, electrical, optical and magnetic properties of graphene. Reduced graphene oxide (rGO)-germanium quantum dot nanocomposites of high crystalline quality were synthesized by the microwave-assisted solvothermal reaction. Highly crystalline spherical shaped germanium quantum dots, of diameter ranging between 1.6–9.0 nm, are anchored on the basal planes of rGO. The nanocomposites exhibit high electrical conductivity with a sheet resistance of up to 16 Ω sq‑1. The electrical conductivity is observed to increase with the increase in Ge content in the nanocomposites. High defect-induced magnetization is attained in the composites via germanium adatoms. The evolution of the magnetic moments in the nanocomposites and the coercivity showed marked dependence on the Ge quantum dots size and concentration. Quantum confinement effects is evidenced in the UV–vis absorbance spectra and photoluminescence emission spectra of the nanocomposites which show marked size-dependence. The composites manifest strong absorption in the UV region, strong luminescence in the near UV region, and a moderate luminescence in the visible region.

  9. Bose-Einstein Condensation and Bose Glasses in an S = 1 Organo-metallic quantum magnet

    Energy Technology Data Exchange (ETDEWEB)

    Zapf, Vivien [Los Alamos National Laboratory

    2012-06-01

    I will speak about Bose-Einstein condensation (BEC) in quantum magnets, in particular the compound NiCl2-4SC(NH2)2. Here a magnetic field-induced quantum phase transition to XY antiferromagnetism can be mapped onto BEC of the spins. The tuning parameter for BEC transition is the magnetic field rather than the temperature. Some interesting phenomena arise, for example the fact that the mass of the bosons that condense can be strongly renormalized by quantum fluctuations. I will discuss the utility of this mapping for both understanding the nature of the quantum magnetism and testing the thermodynamic limit of Bose-Einstein Condensation. Furthermore we can dope the system in a clean and controlled way to create the long sought-after Bose Glass transition, which is the bosonic analogy of Anderson localization. I will present experiments and simulations showing evidence for a new scaling exponent, which finally makes contact between theory and experiments. Thus we take a small step towards the difficult problem of understanding the effect of disorder on bosonic wave functions.

  10. Multiparticle equations for interacting Dirac fermions in magnetically confined graphene quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Egger, Reinhold [Institut fuer Theoretische Physik, Heinrich-Heine-Universitaet, Universitaetsstrasse 1, D-40225 Duesseldorf (Germany); De Martino, Alessandro [Institut fuer Theoretische Physik, Universitaet zu Koeln, Zuelpicher Strasse 77, D-50937 Koeln (Germany); Siedentop, Heinz; Stockmeyer, Edgardo, E-mail: egger@thphy.uni-duesseldorf.d, E-mail: ademarti@thp.uni-koeln.d, E-mail: h.s@lmu.d, E-mail: stock@math.lmu.d [Mathematisches Institut, Ludwigs-Maximilians-Universitaet Muenchen, Theresienstrasse 39, D-80333 Muenchen (Germany)

    2010-05-28

    We study the energy of quasi-particles in graphene within the Hartree-Fock approximation. The quasi-particles are confined via an inhomogeneous magnetic field and interact via the Coulomb potential. We show that the associated functional has a minimizer and determines the stability conditions for the N-particle problem in such a graphene quantum dot.

  11. Electron-electron interactions in graphene field-induced quantum dots in a high magnetic field

    DEFF Research Database (Denmark)

    Orlof, A.; Shylau, Artsem; Zozoulenko, I. V.

    2015-01-01

    We study the effect of electron-electron interaction in graphene quantum dots defined by an external electrostatic potential and a high magnetic field. To account for the electron-electron interaction, we use the Thomas-Fermi approximation and find that electron screening causes the formation...

  12. Simplified Magnetically Shielded Cylinder Using Flexible Magnetic Sheets for High-Tc Superconducting Quantum Interference Device Magnetocardiogram Systems

    Science.gov (United States)

    Suzuki, Daisuke; Yokosawa, Koichi; Miyashita, Tsuyoshi; Kandori, Akihiko; Tsukada, Keiji; Tsukamoto, Akira; Arakawa, Shunsuke

    2001-10-01

    A small and simple magnetic-shielding cylinder using a new high-permeability sheet, developed for magnetic shielding, can reduce the amount of effort expended on taking magnetocardiogram (MCG) measurements. This sheet is made of a nanocrystalline soft-magnetic material (an Fe-Cu-Nb-Si-B alloy) and is flexible and easy to handle. Moreover, magnetostriction of the material is nearly zero, unlike that of the materials used in conventional magnetic shielding. The shielding cylinder is made up of three tubes of various diameters (but having the same length), placed one inside the other. The shielding cylinder is 1.0 m in diameter and 2.0 m long, and it has a shielding factor of about 35 dB at 1 Hz. The shielding cylinder was tested by measuring MCGs using a high-Tc superconducting quantum interference device (SQUID) gradiometer.

  13. The art of science from perspective drawing to quantum randomness

    CERN Document Server

    Angelini, Annarita

    2014-01-01

    Like linear perspective, complex numbers and probability are notable discoveries of the Renaissance. History has been quick to recognize the crucial impact of linear perspective on painting, but reluctant to acknowledge the importance of complex numbers and probability. Both were treated with a great deal of suspicion by the scientific establishment and overlooked for many years. It was only in the twentieth century, when quantum theory defined the notion of "complex probability amplitude", that complex numbers merged with probability and transformed the image of the physical world. From a theoretical point of view, however, the space opened to painting by linear perspective and the space opened to science by complex numbers are equally valuable and share significant characteristics. By exploring that common ground, The Art of Science will lead the reader to complement Leonardo’s vision of painting as a science and to see science as an art. Its aim is to restore a visual dimension to mathematical sciences �...

  14. Dipole in a magnetic field, work, and quantum spin.

    Science.gov (United States)

    Deissler, Robert J

    2008-03-01

    The behavior of an atom in a nonuniform magnetic field is analyzed, as well as the motion of a classical magnetic dipole (a spinning charged ball) and a rotating charged ring. For the atom it is shown that, while the magnetic field does no work on the electron-orbital contribution to the magnetic moment (the source of translational kinetic energy being the internal energy of the atom), whether or not it does work on the electron-spin contribution to the magnetic moment depends on whether the electron has an intrinsic rotational kinetic energy associated with its spin. A rotational kinetic energy for the electron is shown to be consistent with the Dirac equation. If the electron does have a rotational kinetic energy, the acceleration of a silver atom in a Stern-Gerlach experiment or the emission of a photon from an electron spin flip can be explained without requiring the magnetic field to do work. For a constant magnetic field gradient along the z axis, it is found that the classical objects oscillate in simple harmonic motion along the z axis, the total kinetic energy -- translational plus rotational -- being a constant of the motion. For the charged ball, the change in rotational kinetic energy is associated only with a change in the precession frequency, the rotation rate about the figure axis remaining constant.

  15. Magnetic Signatures of Quantum Critical Points of the Ferrimagnetic Mixed Spin-(1/2, S) Heisenberg Chains at Finite Temperatures

    Science.gov (United States)

    Strečka, Jozef; Verkholyak, Taras

    2017-06-01

    Magnetic properties of the ferrimagnetic mixed spin-(1/2, S) Heisenberg chains are examined using quantum Monte Carlo simulations for two different quantum spin numbers S=1 and 3/2. The calculated magnetization curves at finite temperatures are confronted with zero-temperature magnetization data obtained within the density matrix renormalization group method, which imply an existence of two quantum critical points determining a breakdown of the gapped Lieb-Mattis ferrimagnetic phase and Tomonaga-Luttinger spin-liquid phase, respectively. While a square root behavior of the magnetization accompanying each quantum critical point is gradually smoothed upon rising temperature, the susceptibility and isothermal entropy change data at low temperatures provide a stronger evidence of the zero-temperature quantum critical points through marked local maxima and minima, respectively.

  16. Experimental realization of Shor's quantum factoring algorithm using nuclear magnetic resonance.

    Science.gov (United States)

    Vandersypen, L M; Steffen, M; Breyta, G; Yannoni, C S; Sherwood, M H; Chuang, I L

    The number of steps any classical computer requires in order to find the prime factors of an l-digit integer N increases exponentially with l, at least using algorithms known at present. Factoring large integers is therefore conjectured to be intractable classically, an observation underlying the security of widely used cryptographic codes. Quantum computers, however, could factor integers in only polynomial time, using Shor's quantum factoring algorithm. Although important for the study of quantum computers, experimental demonstration of this algorithm has proved elusive. Here we report an implementation of the simplest instance of Shor's algorithm: factorization of N = 15 (whose prime factors are 3 and 5). We use seven spin-1/2 nuclei in a molecule as quantum bits, which can be manipulated with room temperature liquid-state nuclear magnetic resonance techniques. This method of using nuclei to store quantum information is in principle scalable to systems containing many quantum bits, but such scalability is not implied by the present work. The significance of our work lies in the demonstration of experimental and theoretical techniques for precise control and modelling of complex quantum computers. In particular, we present a simple, parameter-free but predictive model of decoherence effects in our system.

  17. Phase transition and random-field induced domain wall response in quantum ferroelectrics SrTi18O3: review and perspective

    Directory of Open Access Journals (Sweden)

    Mitsuru Itoh, Toshirou Yagi, Yoshiaki Uesu, Wolfgang Kleemann and Robert Blinc

    2004-01-01

    Full Text Available The oxygen isotope exchange of 16O by 18O in SrTiO3 causes a drastic change from paraelectric to ferroelectric, due to the suppression of quantum fluctuation. The phase transition and origin of the huge domain wall response were evaluated by dielectric, magnetic (NMR, and optical measurements (SHG, light scattering. The results obtained corroborate (1 smeared ferroelectric transition at Tc due to quenched random field, (2 a quite large dielectric contribution from domain walls, (3 incomplete softening of the transverse optic mode, and (4 a large contribution from the relaxational mode to the phase transition. Quantitative explanations, given to individual results, may give hints to grasp the mechanism for the evolution of ferroelectricity, in which quantum fluctuation and random fields are dominant perturbations. Finally, some of the news studies on the SrTiO3 were also introduced.

  18. Quantum theory of the dielectric constant of a magnetized plasma and astrophysical applications. I.

    Science.gov (United States)

    Canuto, V.; Ventura, J.

    1972-01-01

    A quantum mechanical treatment of an electron plasma in a constant and homogeneous magnetic field is considered, with the aim of (1) defining the range of validity of the magnetoionic theory (2) studying the deviations from this theory, in applications involving high densities, and intense magnetic field. While treating the magnetic field exactly, a perturbation approach in the photon field is used to derive general expressions for the dielectric tensor. Numerical estimates on the range of applicability of the magnetoionic theory are given for the case of the 'one-dimensional' electron gas, where only the lowest Landau level is occupied.

  19. A quantum spin system with random interactions I

    Indian Academy of Sciences (India)

    Е3ЖY Ж-. KMS states f&Е3Жg, the spectrum of the generator of the group of unitaries which implement (Е3Ж in the GNS representation is also almost surely independent of 3. Keywords. Spin; system; quasi-local; random; dynamics; evolution; ...

  20. A quantum spin system with random interactions I

    Indian Academy of Sciences (India)

    Keywords. Spin; system; quasi-local; random; dynamics; evolution; independent; Arveson; KMS. ... The notion of ergodicity of a measure preserving group of automorphisms of the probability space , is used to prove the almost sure independence of the Arveson spectrum S p ( T ( ) ) of T t ( ) . As a consequence, for any ...

  1. Edge states in graphene quantum dots: Fractional quantum Hall effect analogies and differences at zero magnetic field

    Science.gov (United States)

    Romanovsky, Igor; Yannouleas, Constantine; Landman, Uzi

    2009-02-01

    We investigate the way that the degenerate manifold of midgap edge states in quasicircular graphene quantum dots with zigzag boundaries supports, under free-magnetic-field conditions, strongly correlated many-body behavior analogous to the fractional quantum Hall effect (FQHE), familiar from the case of semiconductor heterostructures in high-magnetic fields. Systematic exact-diagonalization (EXD) numerical studies are presented for 5≤N≤8 fully spin-polarized electrons and for total angular momenta in the range of N(N-1)/2≤L≤150 . We present a derivation of a rotating-electron-molecule (REM) type wave function based on the methodology introduced earlier [C. Yannouleas and U. Landman, Phys. Rev. B 66, 115315 (2002)] in the context of the FQHE in two-dimensional semiconductor quantum dots. The EXD wave functions are compared with FQHE trial functions of the Laughlin, compact composite fermion, and the derived REM types. It is found that a variational extension of the REM offers a better description for all fractional fillings compared with that of the Laughlin functions (including total energies and overlaps), a fact that reflects the strong azimuthal localization of the edge electrons. In contrast with the multiring arrangements of electrons in circular semiconductor quantum dots, the graphene REMs exhibit in all instances a single (0,N) polygonal-ring molecular (crystalline) structure, with all the electrons localized on the edge. Disruptions in the zigzag boundary condition along the circular edge act effectively as impurities that pin the electron molecule, yielding single-particle densities with broken rotational symmetry that portray directly the azimuthal localization of the edge electrons.

  2. Tuning the Quantum Efficiency of Random Lasers - Intrinsic Stokes-Shift and Gain

    Science.gov (United States)

    Lubatsch, Andreas; Frank, Regine

    2015-11-01

    We report the theoretical analysis for tuning the quantum efficiency of solid state random lasers. Vollhardt-Wölfle theory of photonic transport in disordered non-conserving and open random media, is coupled to lasing dynamics and solved positionally dependent. The interplay of non-linearity and homogeneous non-radiative frequency conversion by means of a Stokes-shift leads to a reduction of the quantum efficiency of the random laser. At the threshold a strong decrease of the spot-size in the stationary state is found due to the increase of non-radiative losses. The coherently emitted photon number per unit of modal surface is also strongly reduced. This result allows for the conclusion that Stokes-shifts are not sufficient to explain confined and extended mode regimes.

  3. Multiple-quantum nuclear magnetic resonance studies of sodium-23 in model and biological systems

    Energy Technology Data Exchange (ETDEWEB)

    Pekar, J.J.

    1988-01-01

    Time-domain multiple-quantum nuclear magnetic resonance spectroscopy is applied to sodium-23 in gels, liquid crystals, cell suspensions, and intact human limbs. In many biological systems, interactions between the nuclear electric quadrupole moment and fluctuating electric field gradients cause the outer transitions, which contribute 60% of the nuclear magnetic resonance signal from the spin-3/2 nuclei, to relax faster than the central transition, which contributes the remains in 40% of the signal. New multiple-quantum experiments, designed specifically for quadrupolar spin-3/2 nuclei, reveal much information not usually available from conventional nuclear magnetic resonance spectroscopy, because they allow indirect measurement of the rapid relaxation rate of the outer transitions, and may highlight the distribution of sodium ions among microscopic physiological compartments such as intracellular space, the interstitium, and the vasculature. The use of venous occlusion plethysmography to alter this distribution is discussed.

  4. Carrier spin relaxation in diluted magnetic quantum wells: Effect of Mn spin correlations

    Science.gov (United States)

    Krainov, I. V.; Vladimirova, M.; Scalbert, D.; Lähderanta, E.; Dmitriev, A. P.; Averkiev, N. S.

    2017-10-01

    We demonstrate theoretically that the presence of holes, either resident or photocreated, in diluted magnetic quantum wells accelerates the spin relaxation of electrons via a mechanism which has been previously overlooked. This effect is due to the spin correlations, which establish between magnetic ions coupled via hole-mediated Ruderman-Kittel-Kasuya-Yoshida interactions in the paramagnetic phase. As a consequence, the electron spin relaxation becomes temperature and hole density dependent, in contrast to existing theories. Our theory qualitatively reproduces the increase of the electron spin relaxation rate with pump power observed in n -doped CdMnTe magnetic quantum wells [Ben Cheikh et al., Phys. Rev. B 88, 201306 (2013), 10.1103/PhysRevB.88.201306]. It also predicts a decrease of the spin relaxation rate with temperature, as observed, although not in the same temperature range.

  5. Numerical Study of Transport Properties in Topological Insulator Quantum Dots Under Magnetic Field

    Science.gov (United States)

    Zhang, Sheng-Nan; Jiang, Hua; Liu, Haiwen

    2013-06-01

    In this paper, we investigate the transport properties of HgTe/CdTe-based topological insulator quantum dots (TIQDs) under magnetic field. Both disk and square shaped TIQDs are considered and the magneto-conductance are calculated numerically for various magnetic field strength. The magnetic field lifts the spin degeneracy, leading to spin polarized current at given Fermi energy. Meanwhile, the magneto-conductance demonstrates the Aharonov-Bohm (AB) oscillation with a period of one flux quantum φ 0 = (h)/(e). Numerical results for AB oscillation features indicate the mismatch between electron (e) and hole (h) doping conditions, which can be attributed to the e-h asymmetry in the full band Hamiltonian. Further, interference effect emerges around bulk and edge energy degenerate points, subsequently suppressing the magneto-conductance in both shaped systems. All these physical characteristics are qualitatively consistent for disk and square shaped TIQDs due to the topological nature of edge modes.

  6. Quantum Magnetism and Topological Ordering via Rydberg Dressing near Förster Resonances.

    Science.gov (United States)

    van Bijnen, R M W; Pohl, T

    2015-06-19

    We devise a cold-atom approach to realizing a broad range of bilinear quantum magnets. Our scheme is based on off-resonant single-photon excitation of Rydberg P states (Rydberg dressing), whose strong interactions are shown to yield controllable XYZ interactions between effective spins, represented by different atomic ground states. The distinctive features of Förster-resonant Rydberg atom interactions are exploited to enhance the effectiveness of Rydberg dressing and, thereby, yield large spin interactions that greatly exceed the corresponding decoherence rates. We illustrate the concept on a spin-1 chain implemented with cold rubidium atoms, and demonstrate that this permits the dynamical preparation of topological magnetic phases. Generally, the described approach provides a viable route to exploring quantum magnetism with dynamically tunable (an)isotropic interactions as well as variable space and spin dimensions in cold-atom experiments.

  7. Magnetic enhancement of photoluminescence from blue-luminescent graphene quantum dots

    Science.gov (United States)

    Chen, Qi; Shi, Chentian; Zhang, Chunfeng; Pu, Songyang; Wang, Rui; Wu, Xuewei; Wang, Xiaoyong; Xue, Fei; Pan, Dengyu; Xiao, Min

    2016-02-01

    Graphene quantum-dots (GQDs) have been predicted and demonstrated with fascinating optical and magnetic properties. However, the magnetic effect on the optical properties remains experimentally unexplored. Here, we conduct a magneto-photoluminescence study on the blue-luminescence GQDs at cryogenic temperatures with magnetic field up to 10 T. When the magnetic field is applied, a remarkable enhancement of photoluminescence emission has been observed together with an insignificant change in circular polarization. The results have been well explained by the scenario of magnetic-field-controlled singlet-triplet mixing in GQDs owing to the Zeeman splitting of triplet states, which is further verified by temperature-dependent experiments. This work uncovers the pivotal role of intersystem crossing in GQDs, which is instrumental for their potential applications such as light-emitting diodes, photodynamic therapy, and spintronic devices.

  8. Comparison of a quantum random number generator with pseudorandom number generators for their use in molecular Monte Carlo simulations.

    Science.gov (United States)

    Ghersi, Dario; Parakh, Abhishek; Mezei, Mihaly

    2017-12-05

    Four pseudorandom number generators were compared with a physical, quantum-based random number generator using the NIST suite of statistical tests, which only the quantum-based random number generator could successfully pass. We then measured the effect of the five random number generators on various calculated properties in different Markov-chain Monte Carlo simulations. Two types of systems were tested: conformational sampling of a small molecule in aqueous solution and liquid methanol under constant temperature and pressure. The results show that poor quality pseudorandom number generators produce results that deviate significantly from those obtained with the quantum-based random number generator, particularly in the case of the small molecule in aqueous solution setup. In contrast, the widely used Mersenne Twister pseudorandom generator and a 64-bit Linear Congruential Generator with a scrambler produce results that are statistically indistinguishable from those obtained with the quantum-based random number generator. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  9. The DSUBm approximation scheme for the coupled cluster method and applications to quantum magnets

    Directory of Open Access Journals (Sweden)

    R.F. Bishop

    2009-01-01

    Full Text Available A new approximate scheme, DSUBm, is described for the coupled cluster method. We apply it to two well-studied (spin-1/2 Heisenberg antiferromagnet spin-lattice models, namely: the XXZ and the XY models on the square lattice in two dimensions. Results are obtained in each case for the ground-state energy, the sublattice magnetization and the quantum critical point. They are in good agreement with those from such alternative methods as spin-wave theory, series expansions, exact diagonalization techniques, quantum Monte Carlo methods and those from the CCM using the LSUBm scheme.

  10. Quantum capacitance in topological insulators under strain in a tilted magnetic field

    KAUST Repository

    Tahir, M.

    2012-12-06

    Topological insulators exhibit unique properties due to surface states of massless Dirac fermions with conserved time reversal symmetry. We consider the quantum capacitance under strain in an external tilted magnetic field and demonstrate a minimum at the charge neutrality point due to splitting of the zeroth Landau level. We also find beating in the Shubnikov de Haas oscillations due to strain, which originate from the topological helical states. Varying the tilting angle from perpendicular to parallel washes out these oscillations with a strain induced gap at the charge neutrality point. Our results explain recent quantum capacitance and transport experiments.

  11. Spin manipulation and spin-lattice interaction in magnetic colloidal quantum dots

    Science.gov (United States)

    Moro, Fabrizio; Turyanska, Lyudmila; Granwehr, Josef; Patanè, Amalia

    2014-11-01

    We report on the spin-lattice interaction and coherent manipulation of electron spins in Mn-doped colloidal PbS quantum dots (QDs) by electron spin resonance. We show that the phase memory time,TM , is limited by Mn-Mn dipolar interactions, hyperfine interactions of the protons (1H) on the QD capping ligands with Mn ions in their proximity (Rabi oscillations. Our findings suggest routes to the rational design of magnetic colloidal QDs with phase memory times exceeding the current limits of relevance for the implementation of QDs as qubits in quantum information processing.

  12. Non-Abelian spin liquid in a spin-one quantum magnet.

    Science.gov (United States)

    Grover, Tarun; Senthil, T

    2011-08-12

    We study a time-reversal invariant non-Abelian spin-liquid state in an SU(2) symmetric spin S=1 quantum magnet on a triangular lattice. The spin liquid is obtained by quantum disordering a noncollinear nematic state. We show that such a spin liquid cannot be obtained by the standard projective construction for spin liquids. We also study the phase transition between the spin liquid and the noncollinear nematic state and show that it cannot be described within the Landau-Ginzburg-Wilson paradigm.

  13. Evidence for the confinement of magnetic monopoles in quantum spin ice

    Science.gov (United States)

    Sarte, P. M.; Aczel, A. A.; Ehlers, G.; Stock, C.; Gaulin, B. D.; Mauws, C.; Stone, M. B.; Calder, S.; Nagler, S. E.; Hollett, J. W.; Zhou, H. D.; Gardner, J. S.; Attfield, J. P.; Wiebe, C. R.

    2017-11-01

    Magnetic monopoles are hypothesised elementary particles connected by Dirac strings that behave like infinitely thin solenoids (Dirac 1931 Proc. R. Soc. A 133 60). Despite decades of searching, free magnetic monopoles and their Dirac strings have eluded experimental detection, although there is substantial evidence for deconfined magnetic monopole quasiparticles in spin ice materials (Castelnovo et al 2008 Nature 326 411). Here we report the detection of a hierarchy of unequally-spaced magnetic excitations via high resolution inelastic neutron spectroscopic measurements on the quantum spin ice candidate Pr2 Sn2 O7 . These excitations are well-described by a simple model of monopole pairs bound by a linear potential (Coldea et al Science 327 177) with an effective tension of 0.642(8) K \\cdot~\\mathringA-1 at 1.65 K. The success of the linear potential model suggests that these low energy magnetic excitations are direct spectroscopic evidence for the confinement of magnetic monopole quasiparticles in the quantum spin ice candidate Pr2 Sn2 O7 .

  14. Giant suppression of phononic heat transport in a quantum magnet BiCu2PO6

    Science.gov (United States)

    Jeon, Byung-Gu; Koteswararao, B.; Park, C. B.; Shu, G. J.; Riggs, S. C.; Moon, E. G.; Chung, S. B.; Chou, F. C.; Kim, Kee Hoon

    2016-11-01

    Thermal transport of quantum magnets has elucidated the nature of low energy elementary excitations and complex interplay between those excited states via strong scattering of thermal carriers. BiCu2PO6 is a unique frustrated spin-ladder compound exhibiting highly anisotropic spin excitations that contain both itinerant and localized dispersion characters along the b- and a-axes respectively. Here, we investigate thermal conductivity κ of BiCu2PO6 under high magnetic fields (H) of up to 30 tesla. A dip-feature in κ, located at ~15 K at zero-H along all crystallographic directions, moves gradually toward lower temperature (T) with increasing H, thus resulting in giant suppression by a factor of ~30 near the critical magnetic field of Hc ≅ 23.5 tesla. The giant H- and T-dependent suppression of κ can be explained by the combined result of resonant scattering of phononic heat carriers with magnetic energy levels and increased phonon scattering due to enhanced spin fluctuation at Hc, unequivocally revealing the existence of strong spin-phonon coupling. Moreover, we find an experimental indication that the remaining magnetic heat transport along the b-axis becomes almost gapless at the magnetic quantum critical point realized at Hc.

  15. Self-bound droplets of a dilute magnetic quantum liquid

    CERN Document Server

    Schmitt, Matthias; Böttcher, Fabian; Ferrier-Barbut, Igor; Pfau, Tilman

    2016-01-01

    Self-bound many-body systems occur in different scenarios all across the fields of physics. For example in the astrophysical context the stellar classification is based on a detailed balance of attractive self-gravitating forces and repulsive terms e.g. due to Fermi pressure. Also liquid droplets are formed by mutual attractive forces due to covalent or van der Waals attraction and repulsive parts of the inter-particle potential due to the electronic Pauli exclusion principle. Self-bound ensembles of ultracold atoms at densities 100 million times lower than in a helium droplet, the only other quantum liquid known so far, have been suggested. However, they have been elusive up to now as they require more than the usual contact interaction, which is either attractive or repulsive but never both. Based on the recent finding that an unstable bosonic dipolar gas can be stabilized by a repulsive many-body term, which is due to quantum depletion and a corresponding exclusion volume at small distances, it was predict...

  16. The effects of pressure and temperature on the exchange energy of a parabolic quantum dot under a magnetic field

    Directory of Open Access Journals (Sweden)

    Faten Bzour

    2017-11-01

    Full Text Available The combined effects of pressure and temperature on the energy levels of a parabolic GaAs quantum dot under a magnetic field have been studied. The exact diagonalization method was used to solve the two-electron quantum dot Hamiltonian and to obtain the eigenenergies. In addition, we investigated the effects of pressure and temperature on the singlet-triplet exchange energy (J=ET−Es of the quantum dot as a function of a magnetic field. The magnetic field-parabolic confinement (ωc−ω0 phase diagram of the quantum dot was calculated. The comparisons show that our results are in very good agreement with the previously published works. Keywords: Quantum dot, Exact diagonalization method, Pressure, Temperature, Exchange energy

  17. Magnetic Excitations in the Stacked Quantum Magnets NaNiO2 and LiNiO2

    Science.gov (United States)

    Clancy, J. P.; Gaulin, B. D.; Ruff, J. P. C.; Ross, K. A.; van Gastel, G. J.; Abernathy, D. L.; Stone, M. B.

    2009-03-01

    NaNiO2 and LiNiO2 are isostructural stacked triangular lattice quantum magnets, in which magnetism is conventionally thought to arise due to spin 1/2 moments carried by Ni^3+ ions. Surprisingly, while NaNiO2 undergoes a cooperative Jahn-Teller transition at 480K and magnetically orders below TN ˜ 23K, LiNiO2 undergoes a glass transition at Tg ˜ 9K and remains disordered down to the lowest measured temperatures. The absence of long-range magnetic order in LiNiO2 has been attributed to either geometric frustration caused by mixing of the Li and Ni sublattices, or orbital degeneracy due to the absence of a coherent Jahn-Teller distortion. We have performed time of flight neutron scattering measurements on polycrystalline samples of NaNiO2 and LiNiO2 using the wide Angular-Range Chopper Spectrometer (ARCS) at the SNS. Our measurements reveal previously unobserved magnetic excitations at relatively high energy transfers, which we associate with ferromagnetic spin waves mediated by in-plane interactions. We also find evidence of critical scattering in NaNiO2 near the magnetic phase transition at TN. These results will be compared with previous measurements collected using the DCS at NIST.

  18. Hacking on decoy-state quantum key distribution system with partial phase randomization

    Science.gov (United States)

    Sun, Shi-Hai; Jiang, Mu-Sheng; Ma, Xiang-Chun; Li, Chun-Yan; Liang, Lin-Mei

    2014-04-01

    Quantum key distribution (QKD) provides means for unconditional secure key transmission between two distant parties. However, in practical implementations, it suffers from quantum hacking due to device imperfections. Here we propose a hybrid measurement attack, with only linear optics, homodyne detection, and single photon detection, to the widely used vacuum + weak decoy state QKD system when the phase of source is partially randomized. Our analysis shows that, in some parameter regimes, the proposed attack would result in an entanglement breaking channel but still be able to trick the legitimate users to believe they have transmitted secure keys. That is, the eavesdropper is able to steal all the key information without discovered by the users. Thus, our proposal reveals that partial phase randomization is not sufficient to guarantee the security of phase-encoding QKD systems with weak coherent states.

  19. Optimization of metabolite detection by quantum mechanics simulations in magnetic resonance spectroscopy.

    Science.gov (United States)

    Gambarota, Giulio

    2017-07-15

    Magnetic resonance spectroscopy (MRS) is a well established modality for investigating tissue metabolism in vivo. In recent years, many efforts by the scientific community have been directed towards the improvement of metabolite detection and quantitation. Quantum mechanics simulations allow for investigations of the MR signal behaviour of metabolites; thus, they provide an essential tool in the optimization of metabolite detection. In this review, we will examine quantum mechanics simulations based on the density matrix formalism. The density matrix was introduced by von Neumann in 1927 to take into account statistical effects within the theory of quantum mechanics. We will discuss the main steps of the density matrix simulation of an arbitrary spin system and show some examples for the strongly coupled two spin system. Copyright © 2016 Elsevier Inc. All rights reserved.

  20. Magnetic Hamiltonian and phase diagram of the quantum spin liquid Ca10Cr7O28

    Science.gov (United States)

    Balz, Christian; Lake, Bella; Nazmul Islam, A. T. M.; Singh, Yogesh; Rodriguez-Rivera, Jose A.; Guidi, Tatiana; Wheeler, Elisa M.; Simeoni, Giovanna G.; Ryll, Hanjo

    2017-05-01

    A spin liquid is a new state of matter with topological order where the spin moments continue to fluctuate coherently down to the lowest temperatures rather than develop static long-range magnetic order as found in conventional magnets. For spin liquid behavior to arise in a material the magnetic Hamiltonian must be "frustrated", where the combination of lattice geometry, interactions, and anisotropies gives rise to competing spin arrangements in the ground state. Theoretical Hamiltonians which produce spin liquids are spin ice, the Kitaev honeycomb model, and the kagome antiferromagnet. Spin liquid behavior, however, in real materials is rare because they can only approximate these Hamiltonians and often have weak higher-order terms that destroy the spin liquid state. Ca10Cr7O28 is a new quantum spin liquid candidate with magnetic Cr5 + ions that possess quantum spin number S =½ . The spins are entirely dynamic in the ground state and the excitation spectrum is broad and diffuse, as is typical of spinons which are the excitations of a spin liquid. In this paper we determine the Hamiltonian of Ca10Cr7O28 using inelastic neutron scattering under high magnetic field to induce a field-polarized paramagnetic ground state and spin-wave excitations that can be fitted to extract the interactions. We further explore the phase diagram by using inelastic neutron scattering and heat capacity measurements and establish the boundaries of the spin liquid phase as a function of magnetic field and temperature. Our results show that Ca10Cr7O28 consists of distorted kagome bilayers with several isotropic ferromagnetic and antiferromagnetic interactions where, unexpectedly, the ferromagnetic interactions are stronger than the antiferromagnetic ones. This complex Hamiltonian does not correspond to any known spin liquid model and points to new directions in the search for quantum spin liquid behavior.

  1. Fortran code for generating random probability vectors, unitaries, and quantum states

    Directory of Open Access Journals (Sweden)

    Jonas eMaziero

    2016-03-01

    Full Text Available The usefulness of generating random configurations is recognized in many areas of knowledge. Fortran was born for scientific computing and has been one of the main programming languages in this area since then. And several ongoing projects targeting towards its betterment indicate that it will keep this status in the decades to come. In this article, we describe Fortran codes produced, or organized, for the generation of the following random objects: numbers, probability vectors, unitary matrices, and quantum state vectors and density matrices. Some matrix functions are also included and may be of independent interest.

  2. Universality in chaotic quantum transport: The concordance between random-matrix and semiclassical theories

    Science.gov (United States)

    Berkolaiko, Gregory; Kuipers, Jack

    2012-04-01

    Electronic transport through chaotic quantum dots exhibits universal, system-independent properties, consistent with random-matrix theory. The quantum transport can also be rooted, via the semiclassical approximation, in sums over the classical scattering trajectories. Correlations between such trajectories can be organized diagrammatically and have been shown to yield universal answers for some observables. Here, we develop the general combinatorial treatment of the semiclassical diagrams, through a connection to factorizations of permutations. We show agreement between the semiclassical and random matrix approaches to the moments of the transmission eigenvalues. The result is valid for all moments to all orders of the expansion in inverse channel number for all three main symmetry classes (with and without time-reversal symmetry and spin-orbit interaction) and extends to nonlinear statistics. This finally explains the applicability of random-matrix theory to chaotic quantum transport in terms of the underlying dynamics as well as providing semiclassical access to the probability density of the transmission eigenvalues.

  3. Complementarity between entanglement-assisted and quantum distributed random access code

    Science.gov (United States)

    Hameedi, Alley; Saha, Debashis; Mironowicz, Piotr; Pawłowski, Marcin; Bourennane, Mohamed

    2017-05-01

    Collaborative communication tasks such as random access codes (RACs) employing quantum resources have manifested great potential in enhancing information processing capabilities beyond the classical limitations. The two quantum variants of RACs, namely, quantum random access code (QRAC) and the entanglement-assisted random access code (EARAC), have demonstrated equal prowess for a number of tasks. However, there do exist specific cases where one outperforms the other. In this article, we study a family of 3 →1 distributed RACs [J. Bowles, N. Brunner, and M. Pawłowski, Phys. Rev. A 92, 022351 (2015), 10.1103/PhysRevA.92.022351] and present its general construction of both the QRAC and the EARAC. We demonstrate that, depending on the function of inputs that is sought, if QRAC achieves the maximal success probability then EARAC fails to do so and vice versa. Moreover, a tripartite Bell-type inequality associated with the EARAC variants reveals the genuine multipartite nonlocality exhibited by our protocol. We conclude with an experimental realization of the 3 →1 distributed QRAC that achieves higher success probabilities than the maximum possible with EARACs for a number of tasks.

  4. Quantum tunneling recombination in a system of randomly distributed trapped electrons and positive ions.

    Science.gov (United States)

    Pagonis, Vasilis; Kulp, Christopher; Chaney, Charity-Grace; Tachiya, M

    2017-09-13

    During the past 10 years, quantum tunneling has been established as one of the dominant mechanisms for recombination in random distributions of electrons and positive ions, and in many dosimetric materials. Specifically quantum tunneling has been shown to be closely associated with two important effects in luminescence materials, namely long term afterglow luminescence and anomalous fading. Two of the common assumptions of quantum tunneling models based on random distributions of electrons and positive ions are: (a) An electron tunnels from a donor to the nearest acceptor, and (b) the concentration of electrons is much lower than that of positive ions at all times during the tunneling process. This paper presents theoretical studies for arbitrary relative concentrations of electrons and positive ions in the solid. Two new differential equations are derived which describe the loss of charge in the solid by tunneling, and they are solved analytically. The analytical solution compares well with the results of Monte Carlo simulations carried out in a random distribution of electrons and positive ions. Possible experimental implications of the model are discussed for tunneling phenomena in long term afterglow signals, and also for anomalous fading studies in feldspars and apatite samples.

  5. Magnetic properties of bilayer graphene quantum dots in the presence of uniaxial strain

    Science.gov (United States)

    Nascimento, J. S.; da Costa, D. R.; Zarenia, M.; Chaves, Andrey; Pereira, J. M.

    2017-09-01

    Using the tight-binding approach coupled with mean-field Hubbard model, we theoretically study the effect of mechanical deformations on the magnetic properties of bilayer graphene (BLG) quantum dots (QDs). Results are obtained for AA- and AB(Bernal)-stacked BLG QDs, considering different geometries (hexagonal, triangular and square shapes) and edge types (armchair and zigzag edges). In the absence of strain, our results show that (i) the magnetization is affected by taking different dot sizes only for hexagonal BLG QDs with zigzag edges, exhibiting different critical Hubbard interactions, and (ii) the magnetization does not depend on the interlayer hopping energies, except for the geometries with zigzag edges and AA stacking. In the presence of in-plane and uniaxial strain, for all geometries we obtain two different magnetization regimes depending on the applied strain amplitude. The appearance of such different regimes is due to the breaking of layer and sublattice symmetries in BLG QDs.

  6. Confinement of an electron in a non-homogeneous magnetic field: Integrable vs superintegrable quantum systems

    Energy Technology Data Exchange (ETDEWEB)

    Contreras-Astorga, A., E-mail: alonso.contreras.astorga@gmail.com [Department of Mathematics and Actuarial Science, Indiana University Northwest, 3400 Broadway, Gary, IN 46408 (United States); Departamento de Física, Cinvestav, A.P. 14-740, 07000 México D.F. (Mexico); Negro, J., E-mail: jnegro@fta.uva.es [Departamento de Física Teórica, Atómica y Óptica and IMUVA, Universidad de Valladolid, E-47011 Valladolid (Spain); Tristao, S., E-mail: hetsudoyaguiu@gmail.com [Departamento de Física Teórica, Atómica y Óptica and IMUVA, Universidad de Valladolid, E-47011 Valladolid (Spain)

    2016-01-08

    This paper deals with the problem of an electron in a non-homogeneous magnetic field perpendicular to a plane. From the classical point of view this is an integrable, but not superintegrable, solvable system. In the quantum framework of the Dirac equation this integrable system is solvable too; the energy levels and wavefunctions of bound states, for its reduction to the plane, are computed. The effective one-dimensional matrix Hamiltonian is shown to belong to a shape-invariant hierarchy. Through this example we will shed some light on the specific properties of a quantum integrable system with respect to those characteristic of superintegrable systems. - Highlights: • The system: an electron in a non-homogeneous magnetic field. • This is a solvable integrable but not superintegrable system. • Solutions to the discrete Dirac spectrum are found. • The shape-invariance of Dirac matrix Hamiltonians is characterized. • Specific properties of integrable, not superintegrable, systems are analyzed.

  7. Electron LO-phonon interaction in wurtzite GaN quantum wells under a magnetic field

    Science.gov (United States)

    Cao, J. C.; Lü, J. T.; Guo, Qixin

    2008-08-01

    We calculate the electron-LO-phonon relaxation rates in wurtzite GaN quantum wells in the presence of a magnetic field parallel to the growth direction. Using the dielectric continuum model (DCM), we are able to include contributions from both the interface and the quasi-confined phonon modes. The relaxation rate expression takes the phonon dispersion into account, and is applicable to all phonon modes. We find that the relaxation rates show strong oscillations as a function of the applied magnetic field. In relatively wide (8 nm) quantum wells, the inclusion of interface phonon mode decreases this oscillation amplitude. But in thin wells (5 nm), the interface phonon mode is of the same importance as the quasi-confined mode, and it strongly modifies the oscillation behavior.

  8. Compact quantum random number generator based on superluminescent light-emitting diodes

    Science.gov (United States)

    Wei, Shihai; Yang, Jie; Fan, Fan; Huang, Wei; Li, Dashuang; Xu, Bingjie

    2017-12-01

    By measuring the amplified spontaneous emission (ASE) noise of the superluminescent light emitting diodes, we propose and realize a quantum random number generator (QRNG) featured with practicability. In the QRNG, after the detection and amplification of the ASE noise, the data acquisition and randomness extraction which is integrated in a field programmable gate array (FPGA) are both implemented in real-time, and the final random bit sequences are delivered to a host computer with a real-time generation rate of 1.2 Gbps. Further, to achieve compactness, all the components of the QRNG are integrated on three independent printed circuit boards with a compact design, and the QRNG is packed in a small enclosure sized 140 mm × 120 mm × 25 mm. The final random bit sequences can pass all the NIST-STS and DIEHARD tests.

  9. Quantum random number generation enhanced by weak-coherent states interference.

    Science.gov (United States)

    Ferreira da Silva, T; Xavier, G B; Amaral, G C; Temporão, G P; von der Weid, J P

    2016-08-22

    We propose and demonstrate a technique for quantum random number generation based on the random population of the output spatial modes of a beam splitter when both inputs are simultaneously fed with indistinguishable weak coherent states. We simulate and experimentally validate the probability of generation of random bits as a function of the average photon number per input, and compare it to the traditional approach of a single weak coherent state transmitted through a beam-splitter, showing an improvement of up to 32%. The ensuing interference phenomenon reduces the probability of coincident counts between the detectors associated with bits 0 and 1, thus increasing the probability of occurrence of a valid output. A long bit string is assessed by a standard randomness test suite with good confidence. Our proposal can be easily implemented and opens attractive performance gains without a significant trade-off.

  10. Note: Fully integrated 3.2 Gbps quantum random number generator with real-time extraction

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiao-Guang; Nie, You-Qi; Liang, Hao; Zhang, Jun, E-mail: zhangjun@ustc.edu.cn; Pan, Jian-Wei [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); CAS Center for Excellence and Synergetic Innovation Center in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Zhou, Hongyi; Ma, Xiongfeng [Center for Quantum Information, Institute for Interdisciplinary Information Sciences, Tsinghua University, Beijing 100084 (China)

    2016-07-15

    We present a real-time and fully integrated quantum random number generator (QRNG) by measuring laser phase fluctuations. The QRNG scheme based on laser phase fluctuations is featured for its capability of generating ultra-high-speed random numbers. However, the speed bottleneck of a practical QRNG lies on the limited speed of randomness extraction. To close the gap between the fast randomness generation and the slow post-processing, we propose a pipeline extraction algorithm based on Toeplitz matrix hashing and implement it in a high-speed field-programmable gate array. Further, all the QRNG components are integrated into a module, including a compact and actively stabilized interferometer, high-speed data acquisition, and real-time data post-processing and transmission. The final generation rate of the QRNG module with real-time extraction can reach 3.2 Gbps.

  11. Quantum effect enhanced magnetism of C-doped phosphorene nanoribbons: first-principles calculations.

    Science.gov (United States)

    Cai, Xiaolin; Niu, Chunyao; He, Yuan-Yao; Wang, Jianjun; Zhu, Zhili; Zhang, Liwei; Jia, Yu

    2017-10-25

    Manipulating magnetism of low-dimensional materials is of great importance for their practical applications. Here, using first-principles calculations, we report a systematic investigation of the magnetic properties of C-doped H saturated zigzag phosphorene nanoribbons (H-ZPNRs), which are rather different from those of 2D periodic systems due to the quantum size effect. First of all, we observed a greatly enhanced magnetic moment locating mainly on the C atom and also slightly on its surrounding P atoms. Our results also indicated a strong dependence of the magnetic moment of the C atom on its location, which decays from the edge to the center site of the nanoribbons with an odd-even oscillating behavior originating from Friedel oscillation in low-dimensional materials. As for the C atom on a specific location, its magnetic moment decreases gradually with increasing width of H-ZPNRs, degenerating to the 2D case. What is more, we found that both the magnitude and the oscillating behavior of the magnetic moment on the C atom can be tuned by the edge saturation atoms. In addition, the case of two C atoms co-doping H-ZPNRs was also studied, showing non-magnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) states depending on the locations of the two C atoms. Our findings suggest a plausible route for manipulating magnetism of the sp element doped H-ZPNRs, which are expected to have potential applications in spintronics.

  12. Optically detected magnetic resonance in CdMnSe/ZnSe submonolayer quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Tolmachev, D.O.; Babunts, R.A.; Romanov, N.G.; Baranov, P.G.; Namozov, B.R.; Kusrayev, Yu.G. [Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Lee, S. [Department of Physics, Korea University, Seoul (Korea); Dobrowolska, M.; Furdyna, J.K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

    2010-06-15

    Fine structure of isolated Mn{sup 2+} ions in CdMnSe/ZnSe quantum wells (QWs) is revealed by optically detected magnetic resonance (ODMR) recorded by monitoring both exciton emission and intra-Mn luminescence in the presence of simultaneous microwave irradiation. A large decrease of photoluminescence (PL) intensity of excitons and an increase of PL intensity of Mn{sup 2+} ions is observed when an applied magnetic field satisfies the Mn{sup 2+} electron paramagnetic resonance (EPR) condition. This suggests that a spin-dependent energy transfer from excitons to intra-Mn excitations occurs at the EPR condition. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  13. Quantum transitions, magnetization and thermal entanglement of the spin-1 Ising-Heisenberg diamond chain

    Science.gov (United States)

    Abgaryan, V. S.; Ananikian, N. S.; Ananikyan, L. N.; Hovhannisyan, V. V.

    2015-12-01

    We consider the quasi-one dimensional spin-1 Ising-Heisenberg model with single-ion anisotropy on a diamond chain. Due to the exact solution of the model, we constructed the ground state phases which, alongside to others, have shown capability to exhibit most interesting frustrated state. The investigation of the magnetization processes showed enrichment of possibilities to form plateaus at zero, one- and two-thirds of the saturation magnetization. Negativity as a measure of the quantum entanglement is considered at low temperatures.

  14. Ab initio quantum chemical calculation as a tool of evaluating diamagnetic susceptibility of magnetically levitating substances

    Energy Technology Data Exchange (ETDEWEB)

    Fujiwara, Y [Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Tanimoto, Y [Faculty of Pharmacy, Osaka Ohtani University, Nishikiorikita, Tondabayashi 584-8540 (Japan)], E-mail: fuji0710@sci.hiroshima-u.ac.jp

    2009-03-01

    On magnetic force evaluation necessary for magnetically levitated diamagnetic substances, isotropic diamagnetic susceptibility estimation by the ab initio quantum chemical calculation using Gaussian03W was verified for more than 300 molecules in a viewpoint of the accuracy in the absolute value and the calculation level affording good cost performance. From comparison, the method of B3PW91 / 6-311+G(d,p) was found to give the adequate absolute value by the relation of (observed) = (1.03 {+-} 0.005) x (calculated) - (1.22 {+-} 0.60) x 10{sup -6} in a unit of cm{sup 3} mol{sup -1} and good cost performance.

  15. Structure and far-infrared edge modes of quantum antidots at zero magnetic field

    Science.gov (United States)

    Emperador, A.; Pi, M.; Barranco, M.; Lipparini, E.; Serra, Ll.

    1998-09-01

    We have investigated edge modes of different multipolarity sustained by quantum antidots at zero magnetic field. The ground state of the antidot is described within a local-density-functional formalism. Two sum rules, which are exact within this formalism, have been derived and used to evaluate the energy of edge collective modes as a function of the surface density and the size of the antidot.

  16. Quantum mechanical grad-B drift velocity operator in a weakly non-uniform magnetic field

    Science.gov (United States)

    Chan, Poh Kam; Oikawa, Shun-ichi; Kosaka, Wataru

    2016-02-01

    This paper presents the analytical solution for quantum mechanical grad-B drift velocity operator by solving the Heisenberg equation of motion. Using the time dependent operators, it is shown the analytical solution of the position operators in x ̂(t ) and y ̂(t ) of the particle in the presence of a weakly non-uniform magnetic field. It is also shown numerically that the grad-B drift velocity operator agrees with the classical counterpart.

  17. Optimization of metabolite detection by quantum mechanics simulations in magnetic resonance spectroscopy

    OpenAIRE

    Gambarota, Giulio

    2016-01-01

    International audience; Magnetic resonance spectroscopy (MRS) is a well established modality for investigating tissue metabolism in vivo. In recent years, many efforts by the scientific community have been directed towards the improvement of metabolite detection and quantitation.Quantum mechanics simulations allow for investigations of the MR signal behaviour of metabolites; thus, they provide an essential tool in the optimization of metabolite detection.In this review, we will examine quantu...

  18. Quantum random flip-flop and its applications in random frequency synthesis and true random number generation

    Energy Technology Data Exchange (ETDEWEB)

    Stipčević, Mario, E-mail: mario.stipcevic@irb.hr [Photonics and Quantum Optics Research Unit, Center of Excellence for Advanced Materials and Sensing Devices, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb (Croatia)

    2016-03-15

    In this work, a new type of elementary logic circuit, named random flip-flop (RFF), is proposed, experimentally realized, and studied. Unlike conventional Boolean logic circuits whose action is deterministic and highly reproducible, the action of a RFF is intentionally made maximally unpredictable and, in the proposed realization, derived from a fundamentally random process of emission and detection of light quanta. We demonstrate novel applications of RFF in randomness preserving frequency division, random frequency synthesis, and random number generation. Possible usages of these applications in the information and communication technology, cryptographic hardware, and testing equipment are discussed.

  19. Electric-field controlled ferromagnetism in MnGe magnetic quantum dots

    Directory of Open Access Journals (Sweden)

    Faxian Xiu

    2011-03-01

    Full Text Available Electric-field control of ferromagnetism in magnetic semiconductors at room temperature has been actively pursued as one of the important approaches to realize practical spintronics and non-volatile logic devices. While Mn-doped III-V semiconductors were considered as potential candidates for achieving this controllability, the search for an ideal material with high Curie temperature (Tc>300 K and controllable ferromagnetism at room temperature has continued for nearly a decade. Among various dilute magnetic semiconductors (DMSs, materials derived from group IV elements such as Si and Ge are the ideal candidates for such materials due to their excellent compatibility with the conventional complementary metal-oxide-semiconductor (CMOS technology. Here, we review recent reports on the development of high-Curie temperature Mn0.05Ge0.95 quantum dots (QDs and successfully demonstrate electric-field control of ferromagnetism in the Mn0.05Ge0.95 quantum dots up to 300 K. Upon the application of gate-bias to a metal-oxide-semiconductor (MOS capacitor, the ferromagnetism of the channel layer (i.e. the Mn0.05Ge0.95 quantum dots was modulated as a function of the hole concentration. Finally, a theoretical model based upon the formation of magnetic polarons has been proposed to explain the observed field controlled ferromagnetism.

  20. Electric-field controlled ferromagnetism in MnGe magnetic quantum dots.

    Science.gov (United States)

    Xiu, Faxian; Wang, Yong; Zou, Jin; Wang, Kang L

    2011-01-01

    Electric-field control of ferromagnetism in magnetic semiconductors at room temperature has been actively pursued as one of the important approaches to realize practical spintronics and non-volatile logic devices. While Mn-doped III-V semiconductors were considered as potential candidates for achieving this controllability, the search for an ideal material with high Curie temperature (T(c)>300 K) and controllable ferromagnetism at room temperature has continued for nearly a decade. Among various dilute magnetic semiconductors (DMSs), materials derived from group IV elements such as Si and Ge are the ideal candidates for such materials due to their excellent compatibility with the conventional complementary metal-oxide-semiconductor (CMOS) technology. Here, we review recent reports on the development of high-Curie temperature Mn(0.05)Ge(0.95) quantum dots (QDs) and successfully demonstrate electric-field control of ferromagnetism in the Mn(0.05)Ge(0.95) quantum dots up to 300 K. Upon the application of gate-bias to a metal-oxide-semiconductor (MOS) capacitor, the ferromagnetism of the channel layer (i.e. the Mn(0.05)Ge(0.95) quantum dots) was modulated as a function of the hole concentration. Finally, a theoretical model based upon the formation of magnetic polarons has been proposed to explain the observed field controlled ferromagnetism.

  1. Random forest regression for magnetic resonance image synthesis.

    Science.gov (United States)

    Jog, Amod; Carass, Aaron; Roy, Snehashis; Pham, Dzung L; Prince, Jerry L

    2017-01-01

    By choosing different pulse sequences and their parameters, magnetic resonance imaging (MRI) can generate a large variety of tissue contrasts. This very flexibility, however, can yield inconsistencies with MRI acquisitions across datasets or scanning sessions that can in turn cause inconsistent automated image analysis. Although image synthesis of MR images has been shown to be helpful in addressing this problem, an inability to synthesize both T2-weighted brain images that include the skull and FLuid Attenuated Inversion Recovery (FLAIR) images has been reported. The method described herein, called REPLICA, addresses these limitations. REPLICA is a supervised random forest image synthesis approach that learns a nonlinear regression to predict intensities of alternate tissue contrasts given specific input tissue contrasts. Experimental results include direct image comparisons between synthetic and real images, results from image analysis tasks on both synthetic and real images, and comparison against other state-of-the-art image synthesis methods. REPLICA is computationally fast, and is shown to be comparable to other methods on tasks they are able to perform. Additionally REPLICA has the capability to synthesize both T2-weighted images of the full head and FLAIR images, and perform intensity standardization between different imaging datasets. Copyright © 2016 Elsevier B.V. All rights reserved.

  2. High temperature radio-frequency superconducting quantum interference device system for detection of magnetic nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Pretzell, Alf

    2012-07-01

    This doctoral thesis was aimed at establishing a set-up with high-temperature superconductor (HTS) radio-frequency (rf) superconducting quantum interference device (SQUID) technology for the detection of magnetic nanoparticles and in particular for testing applications of magnetic nanoparticle immunoassays. It was part of the EU-project ''Biodiagnostics'' running from 2005 to 2008. The method of magnetic binding assays was developed as an alternative to other methods of concentration determination like enzyme linked immunosorbent assay (ELISA), or fluorescent immunoassay. The ELISA has sensitivities down to analyte-concentrations of pg/ml. Multiple incubation and washing steps have to be performed for these techniques, the analyte has to diffuse to the site of binding. The magnetic assay uses magnetic nanoparticles as markers for the substance to be detected. It is being explored by current research and shows similar sensitivity compared to ELISA but in contrast - does not need any washing and can be read out directly after binding - can be applied in solution with opaque media, e.g. blood or muddy water - additionally allows magnetic separation or concentration - in combination with small magnetoresistive or Hall sensors, allows detection of only a few particles or even single beads. For medical or environmental samples, maybe opaque and containing a multitude of substances, it would be advantageous to devise an instrument, which allows to be read out quickly and with high sensitivity. Due to the mentioned items the magnetic assay might be a possibility here.

  3. Ferromagnetic clusters induced by a nonmagnetic random disorder in diluted magnetic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Bui, Dinh-Hoi [Institute of Research and Development, Duy Tan University, K7/25 Quang Trung, Danang (Viet Nam); Physics Department, Hue University’s College of Education, 34 Le Loi, Hue (Viet Nam); Phan, Van-Nham, E-mail: phanvannham@dtu.edu.vn [Institute of Research and Development, Duy Tan University, K7/25 Quang Trung, Danang (Viet Nam)

    2016-12-15

    In this work, we analyze the nonmagnetic random disorder leading to a formation of ferromagnetic clusters in diluted magnetic semiconductors. The nonmagnetic random disorder arises from randomness in the host lattice. Including the disorder to the Kondo lattice model with random distribution of magnetic dopants, the ferromagnetic–paramagnetic transition in the system is investigated in the framework of dynamical mean-field theory. At a certain low temperature one finds a fraction of ferromagnetic sites transiting to the paramagnetic state. Enlarging the nonmagnetic random disorder strength, the paramagnetic regimes expand resulting in the formation of the ferromagnetic clusters.

  4. Using random boundary conditions to simulate disordered quantum spin models in two-dimensional systems

    Science.gov (United States)

    Yuste, A.; Moreno-Cardoner, M.; Sanpera, A.

    2017-05-01

    Disordered quantum antiferromagnets in two-dimensional compounds have been a focus of interest in the last years due to their exotic properties. However, with very few exceptions, the ground states of the corresponding Hamiltonians are notoriously difficult to simulate making their characterization and detection very elusive, both theoretically and experimentally. Here we propose a method to signal quantum disordered antiferromagnets by doing exact diagonalization in small lattices using random boundary conditions and averaging the observables of interest over the different disorder realizations. We apply our method to study the Heisenberg spin-1/2 model in an anisotropic triangular lattice. In this model, the competition between frustration and quantum fluctuations might lead to some spin-liquid phases as predicted from different methods ranging from spin-wave mean-field theory to 2D-DMRG or PEPS. Our method accurately reproduces the ordered phases expected of the model and signals quantum disordered phases by the presence of a large number of quasidegenerate ground states together with an undefined local order parameter. The method presents a weak dependence on finite-size effects.

  5. Quantum anomalous Hall effect in magnetically modulated topological insulator/normal insulator heterostructures

    Science.gov (United States)

    Men'shov, V. N.; Tugushev, V. V.; Chulkov, E. V.

    2016-10-01

    We theoretically study how magnetic modulation can be used to manipulate the transport properties of heterostructures formed by a thin film of a three-dimensional topological insulator sandwiched between slabs of a normal insulator. Employing the k • p scheme, in the framework of a continual approach, we argue that electron states of the system are spin-polarized when ultrathin magnetic insertions are incorporated into the film. We demonstrate that (i) the spin-polarization magnitude depends strongly on the magnetic insertion position in the film and (ii) there is the optimal insertion position to realize quantum anomalous Hall effect, which is a function of the material parameters, the film thickness and the topological insulator/normal insulator interface potential. For the heterostructure with a pair of symmetrically placed magnetic insertions, we calculate a phase diagram that shows a series of transitions between distinct quantum regimes of transverse conductivity. We provide consistent interpretation of recent experimental findings in the context of our results.

  6. Quantum confinement of Bi2S3 in glass with magnetic behavior

    Directory of Open Access Journals (Sweden)

    Rajendra P. Panmand

    2013-02-01

    Full Text Available The novel Bi2S3 quantum dots (QDs glass nanosystems with unique magnetic properties have been investigated. The monodispersed QDs of size in the range of 3 to 15 nm were grown in the glass matrix. The optical study of these nanosystems clearly demonstrated the size quantization effect resulting in a pronounced band gap variation with QD size. The magnetic properties of the pristine glass and the Bi2S3 QD glass nanosystems were investigated by VSM and SQUID magnetometer. The pristine glass did not show any ferromagnetism while the Bi2S3 glass nanosystems showed significant and reproducible ferromagnetism. We also investigated the effect of the size of Bi2S3 QDs on the magnetic properties. The saturation magnetization for the 15 nm QD glass-nanosystem (124 memu/g was observed to be higher as compared to the 3nm QD glass nanosystem (58.2 memu/g. The SQUID measurement gave the excellent hysteresis up to 300K. Surprisingly, the bulk Bi2S3 powder is diamagnetic in nature but Bi2S3 quantum dots glass nanosystem showed the ferromagnetic behavior for the first time. The investigated novel QD glass-nanosystem may have a potential application in spintronic devices and most importantly, this nanosystem can be fabricated in any usable shape as per the device requirement.

  7. Bose glass and Mott glass of quasiparticles in a doped quantum magnet.

    Science.gov (United States)

    Yu, Rong; Yin, Liang; Sullivan, Neil S; Xia, J S; Huan, Chao; Paduan-Filho, Armando; Oliveira, Nei F; Haas, Stephan; Steppke, Alexander; Miclea, Corneliu F; Weickert, Franziska; Movshovich, Roman; Mun, Eun-Deok; Scott, Brian L; Zapf, Vivien S; Roscilde, Tommaso

    2012-09-20

    The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation and superfluidity, which have been tested experimentally in a variety of different systems. When bosons interact, disorder can destroy condensation, leading to a 'Bose glass'. This phase has been very elusive in experiments owing to the absence of any broken symmetry and to the simultaneous absence of a finite energy gap in the spectrum. Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (bromine-doped dichloro-tetrakis-thiourea-nickel, DTN). The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand canonical ensemble; bromine doping introduces disorder into the hopping and interaction strength of the bosons, leading to their localization into a Bose glass down to zero field, where it becomes an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the Bose-Einstein condensate (corresponding to a magnetically ordered phase) is marked by a universal exponent that governs the scaling of the critical temperature with the applied field, in excellent agreement with theoretical predictions. Our study represents a quantitative experimental account of the universal features of disordered bosons in the grand canonical ensemble.

  8. From positive to negative magnetoresistance behavior at low applied magnetic fields for polyaniline:titania quantum dot nanocomposites

    Science.gov (United States)

    Mombrú, Dominique; Romero, Mariano; Faccio, Ricardo; Mombrú, Alvaro W.

    2017-06-01

    Here, we report the tuning from the positive to negative magnetoresistance response at room temperature and low applied magnetic fields (H ˜ 200 mT) for polyaniline nancomposites prepared via in situ growth of titanium oxide quantum dots. In addition, we showed experimental Raman evidence revealing that the positive magnetoresistance response in these polyaniline nanocomposites is mediated by the bipolaron mechanism. Confocal Raman spectroscopy under applied magnetic field analysis showed the decrease of the polaron population to form bipolarons of polyaniline when exposed to an applied magnetic field for the TiO2 quantum dot diluted regime. Negative magnetoresistance, observed for the TiO2 quantum dot higher concentration regime, was attributed to the suppression of polyaniline polarons probably associated with its partial chemical functionalization at the interface due to the increasing concentration of TiO2 quantum dots.

  9. Diverging conductance at the contact between random and pure quantum XX spin chains

    Science.gov (United States)

    Chatelain, Christophe

    2017-11-01

    A model consisting of two quantum XX spin chains, one homogeneous and the second with random couplings drawn from a binary distribution, is considered. The two chains are coupled to two different non-local thermal baths and their dynamics is governed by a Lindblad equation. In the steady state, a current J is induced between the two chains by coupling them together by their edges and imposing different chemical potentials μ to the two baths. While a regime of linear characteristics J versus Δμ is observed in the absence of randomness, a gap opens as the disorder strength is increased. In the infinite-randomness limit, this behavior is related to the density of states of the localized states contributing to the current. The conductance is shown to diverge in this limit.

  10. Violation of Bell’s inequality in a spin 1/2 quantum magnet

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, Tanmoy, E-mail: tanmoybesus@gmail.com; Singh, Harkirat, E-mail: tanmoybesus@gmail.com; Mitra, Chiranjib, E-mail: tanmoybesus@gmail.com [Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, PO: BCKV Campus Main Office, Mohanpur - 741252, Nadia, West Bengal (India)

    2014-04-24

    Violation of Bell’s inequality test has been established as an efficient tool to determine the presence of entanglement in quantum spin 1/2 magnets. Herein, macroscopic thermodynamic quantities, namely, magnetic susceptibility and specific heat have been employed to perform Bell’s inequality test for [NH{sub 4}CuPO{sub 4}, H{sub 2}O], a spin 1/2 antiferromagnet with nearest neighbor interactions. The mean value of the Bell operator is quantified and plotted as a function of temperature. The threshold temperature is determined above which the Bell’s inequality is not violated and a good consistency is found between the analyses done on magnetic and thermal data.

  11. Quantum capacitance of an ultrathin topological insulator film in a magnetic field

    KAUST Repository

    Tahir, M.

    2013-02-12

    We present a theoretical study of the quantum magnetocapacitance of an ultrathin topological insulator film in an external magnetic field. The study is undertaken to investigate the interplay of the Zeeman interaction with the hybridization between the upper and lower surfaces of the thin film. Determining the density of states, we find that the electron-hole symmetry is broken when the Zeeman and hybridization energies are varied relative to each other. This leads to a change in the character of the magnetocapacitance at the charge neutrality point. We further show that in the presence of both Zeeman interaction and hybridization the magnetocapacitance exhibits beating at low and splitting of the Shubnikov de Haas oscillations at high perpendicular magnetic field. In addition, we address the crossover from perpendicular to parallel magnetic field and find consistency with recent experimental data.

  12. Strain and localization effects in InGaAs(N) quantum wells: Tuning the magnetic response

    Energy Technology Data Exchange (ETDEWEB)

    Lopes-Oliveira, V., E-mail: lopes@df.ufscar.br; Herval, L. K. S.; Orsi Gordo, V.; Cesar, D. F.; Godoy, M. P. F. de; Galvão Gobato, Y. [Departamento de Física, Universidade Federal de São Carlos, 13565-905, São Carlos, São Paulo (Brazil); Henini, M. [School of Physics and Astronomy, Nottingham Nanotechnology and Nanoscience Centre, University of Nottingham, NG7 2RD Nottingham (United Kingdom); Khatab, A. [School of Physics and Astronomy, Nottingham Nanotechnology and Nanoscience Centre, University of Nottingham, NG7 2RD Nottingham (United Kingdom); National Institute of Laser Enhanced Sciences, Cairo University (Egypt); Sadeghi, M.; Wang, S. [Photonics Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Goteborg (Sweden); Schmidbauer, M. [Leibniz-Institute for Crystal Growth, Max-Born-Str. 2, D-12489 Berlin (Germany)

    2014-12-21

    We investigated effects of localization and strain on the optical and magneto-optical properties of diluted nitrogen III–V quantum wells theoretically and experimentally. High-resolution x-ray diffraction, photoluminescence (PL), and magneto-PL measurements under high magnetic fields up to 15 T were performed at low temperatures. Bir-Pikus Hamiltonian formalism was used to study the influence of strain, confinement, and localization effects. The circularly polarized magneto-PL was interpreted considering localization aspects in the valence band ground state. An anomalous behavior of the electron-hole pair magnetic shift was observed at low magnetic fields, ascribed to the increase in the exciton reduced mass due to the negative effective mass of the valence band ground state.

  13. Strain and localization effects in InGaAs(N) quantum wells: Tuning the magnetic response

    Science.gov (United States)

    Lopes-Oliveira, V.; Herval, L. K. S.; Orsi Gordo, V.; Cesar, D. F.; de Godoy, M. P. F.; Galvão Gobato, Y.; Henini, M.; Khatab, A.; Sadeghi, M.; Wang, S.; Schmidbauer, M.

    2014-12-01

    We investigated effects of localization and strain on the optical and magneto-optical properties of diluted nitrogen III-V quantum wells theoretically and experimentally. High-resolution x-ray diffraction, photoluminescence (PL), and magneto-PL measurements under high magnetic fields up to 15 T were performed at low temperatures. Bir-Pikus Hamiltonian formalism was used to study the influence of strain, confinement, and localization effects. The circularly polarized magneto-PL was interpreted considering localization aspects in the valence band ground state. An anomalous behavior of the electron-hole pair magnetic shift was observed at low magnetic fields, ascribed to the increase in the exciton reduced mass due to the negative effective mass of the valence band ground state.

  14. Chiral Disorder and Random Matrix Theory with Magnetism

    OpenAIRE

    Nowak, Maciej A.; Sadzikowski, Mariusz; Zahed, Ismail.

    2013-01-01

    We revisit the concept of chiral disorder in QCD in the presence of a QED magnetic field $|eH|$. Weak magnetism corresponds to $|eH|\\le 1/\\rho^2$ with $\\rho\\approx 1/3$\\,fm the vacuum instanton size, while strong magnetism the reverse. Asymptotics (ultra-strong magnetism) is in the realm of perturbative QCD. We analyze weak magnetism using the concept of the quark return probability in the diffusive regime of chiral disorder. The result is in agreement with expectations from chiral perturbati...

  15. Deep Learning the Quantum Phase Transitions in Random Electron Systems: Applications to Three Dimensions

    Science.gov (United States)

    Ohtsuki, Tomi; Ohtsuki, Tomoki

    2017-04-01

    Three-dimensional random electron systems undergo quantum phase transitions and show rich phase diagrams. Examples of the phases are the band gap insulator, Anderson insulator, strong and weak topological insulators, Weyl semimetal, and diffusive metal. As in the previous paper on two-dimensional quantum phase transitions [J. Phys. Soc. Jpn. 85, 123706 (2016)], we use an image recognition algorithm based on a multilayered convolutional neural network to identify which phase the eigenfunction belongs to. The Anderson model for localization-delocalization transition, the Wilson-Dirac model for topological insulators, and the layered Chern insulator model for Weyl semimetal are studied. The situation where the standard transfer matrix approach is not applicable is also treated by this method.

  16. Quantum tricks with femtosecond light pulses teach magnetic devices to think ultrafast

    Science.gov (United States)

    Perakis, I. E.; Lingos, P. C.; Wang, J.

    2014-03-01

    The technological demand to push the gigahertz switching speed limit of today's magnetic memory/logic devices into the terahertz (1THz=1ps-1) regime underlies the entire field of spin-electronics and integrated multi- functional devices. This challenge is met by all-optical magnetic switching based on coherent spin manipulation By analogy to femto-chemistry and photosynthetic dynamics where photo-products of chemical/biochemical re- actions can be influenced by creating suitable superpositions of molecular states, femtosecond (fs) laser-excited coherence between spin/orbital/charge states can switch magnetic orders, by "suddenly" breaking the delicate balance between competing phases of correlated materials, e.g., the colossal magneto-resistive (CMR) manganites suitable for applications. Here we discuss femtosecond (fs) all-optical switching from antiferro- to ferromagnetic ordering via establishment of a magnetization increase within ˜100 fs, while the laser field still interacts with the system. Such non-equilibrium ferromagnetic correlations arise from quantum spin-flip fluctuations corre- lated with coherent superpositions of electronic states. The development of ferromagnetic correlations during the fs laser pulse reveals an initial quantum coherent regime of magnetism, clearly distinguished from the pi- cosecond lattice-heating regime characterized by phase separation. We summarize a microscopic theory based on density matrix equations of motion for composite fermion Hubbard operators, instead of bare electrons, that take into account the strong spin and charge local correlations. Our work merges two fields, femto-magnetism in metals/band insulators and non-equilibrium phase transitions of strongly correlated electrons, where local interactions exceeding the kinetic energy produce a complex balance of competing orders.

  17. Donor impurity-related nonlinear optical rectification in a two-dimensional quantum ring under magnetic field

    Science.gov (United States)

    Bejan, D.

    2017-10-01

    An investigation of the nonlinear optical rectification of a GaAs two-dimensional disc-shaped quantum ring with an off-center donor impurity under magnetic field has been performed by using a variational method in the effective mass approximation. The two-dimensional quantum ring was described by a pseudo-harmonic potential. The results are presented as functions of the incident photon energy for the different values of the impurity position and the magnetic field. It is found that the nonlinear optical rectification spectra are strongly affected by the position of the off-center impurity and the magnetic field.

  18. Hyaluronic Acid Conjugated Magnetic Prussian Blue@Quantum Dot Nanoparticles for Cancer Theranostics.

    Science.gov (United States)

    Yang, Yongbo; Jing, Lijia; Li, Xiaoda; Lin, Li; Yue, Xiuli; Dai, Zhifei

    2017-01-01

    A multifunctional nanotheranostic agent was developed by conjugating both hyaluronic acid and bovine serum albumin coated CuInS2-ZnS quantum dots onto the surface of magnetic Prussian blue nanoparticles. The obtained nanoagent could serve as an efficient contrast agent to simultaneously enhance near infrared (NIR) fluorescence and magnetic resonance (MR) imaging greatly. The coexistence of magnetic core and CD44 ligand hyaluronic acid was found to largely improve the specific uptake of the nanoagent by CD44 overexpressed HeLa cells upon applying an external magnetic field. Both NIR fluorescence and MR imaging in vivo proved high accumulation of the nanoagent at tumor site due to its excellent CD44 receptor/magnetic dual targeting capability. After intravenous injection of the nanoagent and treatment of external magnetic field, the tumor in nude mice was efficiently ablated upon NIR laser irradiation and the tumor growth inhibition was more than 89.95%. Such nanotheranostic agent is of crucial importance for accurately identifying the size and location of the tumor before therapy, monitoring the photothermal treatment procedure in real-time during therapy, assessing the effectiveness after therapy.

  19. Magnetic Field Tuning and Quantum Interference in a Cooper Pair Splitter.

    Science.gov (United States)

    Fülöp, G; Domínguez, F; d'Hollosy, S; Baumgartner, A; Makk, P; Madsen, M H; Guzenko, V A; Nygård, J; Schönenberger, C; Levy Yeyati, A; Csonka, S

    2015-11-27

    Cooper pair splitting (CPS) is a process in which the electrons of the naturally occurring spin-singlet pairs in a superconductor are spatially separated using two quantum dots. Here, we investigate the evolution of the conductance correlations in an InAs CPS device in the presence of an external magnetic field. In our experiments the gate dependence of the signal that depends on both quantum dots continuously evolves from a slightly asymmetric Lorentzian to a strongly asymmetric Fano-type resonance with increasing field. These experiments can be understood in a simple three-site model, which shows that the nonlocal CPS leads to symmetric line shapes, while the local transport processes can exhibit an asymmetric shape due to quantum interference. These findings demonstrate that the electrons from a Cooper pair splitter can propagate coherently after their emission from the superconductor and how a magnetic field can be used to optimize the performance of a CPS device. In addition, the model calculations suggest that the estimate of the CPS efficiency in the experiments is a lower bound for the actual efficiency.

  20. Topological Invariant and Quantum Spin Models from Magnetic π Fluxes in Correlated Topological Insulators

    Directory of Open Access Journals (Sweden)

    F. F. Assaad

    2013-02-01

    Full Text Available The adiabatic insertion of a π flux into a quantum spin Hall insulator gives rise to localized spin and charge fluxon states. We demonstrate that π fluxes can be used in exact quantum Monte Carlo simulations to identify a correlated Z_{2} topological insulator using the example of the Kane-Mele-Hubbard model. In the presence of repulsive interactions, a π flux gives rise to a Kramers doublet of spin-fluxon states with a Curie-law signature in the magnetic susceptibility. Electronic correlations also provide a bosonic mode of magnetic excitons with tunable energy that act as exchange particles and mediate a dynamical interaction of adjustable range and strength between spin fluxons. π fluxes can therefore be used to build models of interacting spins. This idea is applied to a three-spin ring and to one-dimensional spin chains. Because of the freedom to create almost arbitrary spin lattices, correlated topological insulators with π fluxes represent a novel kind of quantum simulator, potentially useful for numerical simulations and experiments.

  1. Observation of new magnetic ground state in frustrated quantum antiferromagnet spin-liquid system Cs2CuCl4

    Science.gov (United States)

    Kim, Hyeong-Jin; Haines, C. R. S.; Liu, C.; Chun, Sae Hwan; Kim, Kee Hoon; Yi, H. T.; Cheong, Sang-Wook; Saxena, Siddharth S.

    2017-08-01

    Cs2CuCl4 is known to possess a quantum spin-liquid phase with antiferromagnetic interaction below 2.8 K. We report the observation of a new metastable magnetic phase of the triangular frustrated quantum spin system Cs2CuCl4 induced by the application of hydrostatic pressure. We measured the magnetic properties of Cs2CuCl4 following the application and release of pressure after 3 days. We observed a previously unknown ordered magnetic phase with a transition temperature of 9 K. Furthermore, the recovered sample with new magnetic ground state possesses an equivalent crystal structure to the uncompressed one with antiferromagnetic quantum spinliquid phase.

  2. Magnetic quantum correlations in the one-dimensional transverse-field X X Z model

    Science.gov (United States)

    Mahdavifar, Salimeh; Mahdavifar, Saeed; Jafari, R.

    2017-11-01

    One-dimensional spin-1/2 systems are well-known candidates to study the quantum correlations between particles. In condensed matter physics, studies often are restricted to first-neighbor particles. In this work, we consider the one-dimensional X X Z model in a transverse magnetic field (TF) which is not integrable except at specific points. Analytical expressions for quantum correlations (entanglement and quantum discord) between spin pairs at any distance are obtained for both zero and finite temperature by using the analytical approach proposed by Caux et al. [Phys. Rev. B 68, 134431 (2003), 10.1103/PhysRevB.68.134431]. We compare the efficiency of the quantum discord (QD) with respect to the entanglement in the detection of critical points as the neighboring spin pairs go farther than the next-nearest neighbors. In the absence of the TF and at zero temperature, we show that the QD for spin pairs farther than the second neighbors is able to capture the critical points while the pairwise entanglement is absent. In contrast with the pairwise entanglement, two-site QD is effectively long range in the critical regimes where it decays algebraically with the distance between pairs. We also show that the thermal QD between neighbor spins possesses strong distinctive behavior at the critical point that can be seen at finite temperature and, therefore, spotlights the critical point while the entanglement fails in this task.

  3. Stability estimate for the aligned magnetic field in a periodic quantum waveguide from Dirichlet-to-Neumann map

    Energy Technology Data Exchange (ETDEWEB)

    Mejri, Youssef, E-mail: josef-bizert@hotmail.fr [Aix Marseille Universite, Toulon Universite, CNRS, CPT, Marseille (France); Dép. des Mathématiques, Faculté des Sciences de Bizerte, 7021 Jarzouna (Tunisia); Laboratoire de Modélisation Mathématique et Numérique dans les Sciences de l’Ingénieur, ENIT BP 37, Le Belvedere, 1002 Tunis (Tunisia)

    2016-06-15

    In this article, we study the boundary inverse problem of determining the aligned magnetic field appearing in the magnetic Schrödinger equation in a periodic quantum cylindrical waveguide, by knowledge of the Dirichlet-to-Neumann map. We prove a Hölder stability estimate with respect to the Dirichlet-to-Neumann map, by means of the geometrical optics solutions of the magnetic Schrödinger equation.

  4. Random matrix theory and higher genus integrability: the quantum chiral Potts model

    Energy Technology Data Exchange (ETDEWEB)

    Angles d' Auriac, J.Ch. [Centre de Recherches sur les Tres Basses Temperatures, BP 166, Grenoble (France)]. E-mail: dauriac@polycnrs-gre.fr; Maillard, J.M.; Viallet, C.M. [LPTHE, Tour 16, Paris (France)]. E-mails: maillard@lpthe.jussieu.fr; viallet@lpthe.jussieu.fr

    2002-06-14

    We perform a random matrix theory (RMT) analysis of the quantum four-state chiral Potts chain for different sizes of the chain up to size L 8. Our analysis gives clear evidence of a Gaussian orthogonal ensemble (GOE) statistics, suggesting the existence of a generalized time-reversal invariance. Furthermore, a change from the (generic) GOE distribution to a Poisson distribution occurs when the integrability conditions are met. The chiral Potts model is known to correspond to a (star-triangle) integrability associated with curves of genus higher than zero or one. Therefore, the RMT analysis can also be seen as a detector of 'higher genus integrability'. (author)

  5. Local random quantum circuits: Ensemble completely positive maps and swap algebras

    Energy Technology Data Exchange (ETDEWEB)

    Zanardi, Paolo [Department of Physics and Astronomy, and Center for Quantum Information Science and Technology, University of Southern California, Los Angeles, California 90089-0484, USA and Centre for Quantum Technologies, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore)

    2014-08-15

    We define different classes of local random quantum circuits (L-RQC) and show that (a) statistical properties of L-RQC are encoded into an associated family of completely positive maps and (b) average purity dynamics can be described by the action of these maps on operator algebras of permutations (swap algebras). An exactly solvable one-dimensional case is analyzed to illustrate the power of the swap algebra formalism. More in general, we prove short time area-law bounds on average purity for uncorrelated L-RQC and infinite time results for both the uncorrelated and correlated cases.

  6. Local random quantum circuits: Ensemble completely positive maps and swap algebras

    Science.gov (United States)

    Zanardi, Paolo

    2014-08-01

    We define different classes of local random quantum circuits (L-RQC) and show that (a) statistical properties of L-RQC are encoded into an associated family of completely positive maps and (b) average purity dynamics can be described by the action of these maps on operator algebras of permutations (swap algebras). An exactly solvable one-dimensional case is analyzed to illustrate the power of the swap algebra formalism. More in general, we prove short time area-law bounds on average purity for uncorrelated L-RQC and infinite time results for both the uncorrelated and correlated cases.

  7. Periodically driven random quantum spin chains: real-space renormalization for Floquet localized phases

    Science.gov (United States)

    Monthus, Cécile

    2017-07-01

    When random quantum spin chains are submitted to some periodic Floquet driving, the eigenstates of the time-evolution operator over one period can be localized in real space. For the case of periodic quenches between two Hamiltonians (or periodic kicks), where the time-evolution operator over one period reduces to the product of two simple transfer matrices, we propose a block-self-dual renormalization procedure to construct the localized eigenstates of the Floquet dynamics. We also discuss the corresponding strong disorder renormalization procedure, that generalizes the RSRG-X procedure to construct the localized eigenstates of time-independent Hamiltonians.

  8. Experimental multipartite entanglement and randomness certification of the W state in the quantum steering scenario

    Science.gov (United States)

    Máttar, A.; Skrzypczyk, P.; Aguilar, G. H.; Nery, R. V.; Souto Ribeiro, P. H.; Walborn, S. P.; Cavalcanti, D.

    2017-03-01

    Recently, Cavalcanti et al (2015) proposed a method to certify the presence of entanglement in asymmetric networks, where some users do not have control over the measurements they are performing. Such asymmetry naturally emerges in realistic situations, such as in cryptographic protocols over quantum networks. Here we implement such ‘semi-device-independent’ techniques to experimentally witness all types of entanglement on a three-qubit photonic W state. Furthermore, we analyse the amount of genuine randomness that can be certified in this scenario from any bipartition of the three-qubit W state.

  9. Exciton in vertically coupled type II quantum dots in threading magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Mendoza-Cantillo, J., E-mail: jhofry@gmail.com [Group of Investigation in Condensed Matter Theory, Universidad del Magdalena, Carrera 32 No 22-08, Santa Marta (Colombia); Universidad de la Guajira, Riohacha (Colombia); Escorcia-Salas, G. Elizabeth, E-mail: elizabethescorcia@gmail.com [Group of Investigation in Condensed Matter Theory, Universidad del Magdalena, Carrera 32 No 22-08, Santa Marta (Colombia); Mikhailov, I.D., E-mail: mikhail2811@gmail.com [Universidad Industrial de Santander, A. A. 678, Bucaramanga (Colombia); Sierra-Ortega, J., E-mail: jsierraortega@gmail.com [Group of Investigation in Condensed Matter Theory, Universidad del Magdalena, Carrera 32 No 22-08, Santa Marta (Colombia)

    2014-11-15

    We analyze the energy spectrum of a neutral exciton confined in a semiconductor heterostructure formed by two vertically coupled axially symmetrical type II quantum dots located close to each other. The electron in the structure is mainly located inside dots tunneling between them while the hole generally is placed in the exterior region close to the symmetry axis. Solutions of the Schrödinger equation are obtained by a variational separation of variables in the adiabatic limit. Numerical results are presented for the energies of bonding and anti-bonding lowest-lying of the exciton states and for the density of states for different InP/GaInP quantum dots' morphologies and the magnetic field strength values.

  10. A type of novel fluorescent magnetic carbon quantum dots for cells imaging and detection.

    Science.gov (United States)

    Su, Xi; Xu, Yi; Che, Yulan; Liao, Xin; Jiang, Yan

    2015-12-01

    A new type of multifunctional fluorescent magnetic carbon quantum dots SPIO@CQDs(n) ([superparamagnetic iron oxide nanoparticles (SPIO), carbon quantum dots, (CQDs)]) with magnetic and fluorescence properties was designed and prepared through layer-by-layer self-assembly method. The as-synthesized SPIO@CQDs(n) exhibited different emission colors including blue, green, and red when they were excited at different excitation wavelengths, and its fluorescent intensity increased as the increase of CQD layer (n). SPIO@CQDs(n) with quite low toxicity could mark cytoplasm with fluorescence by means of nonimmune markers. The mixture sample of liver cells L02 and hepatoma carcinoma cells HepG2 was taken as an example, and HepG2 cells were successfully separated and detected effectively by SPIO@CQDs(n), with a separation rate of 90.31%. Importantly, the designed and prepared SPIO@CQDs( n ) are certified to be wonderful biological imaging and magnetic separation regents. © 2015 Wiley Periodicals, Inc.

  11. Magnetic stimulation for stress urinary incontinence: study protocol for a randomized controlled trial

    National Research Council Canada - National Science Library

    Lim, Renly; Liong, Men Long; Leong, Wing Seng; Khan, Nurzalina Abdul Karim; Yuen, Kah Hay

    2015-01-01

    There is currently a lack of randomized, sham-controlled trials that are adequately powered, using validated outcomes, to allow for firm recommendations on the use of magnetic stimulation for stress urinary incontinence...

  12. Quantum paraelectricity in copper-titanates: Magnetic-order driven vitrification

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Jitender; Awasthi, A. M., E-mail: amawasthi@csr.res.in [Thermodynamics Laboratory, UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001 (India)

    2015-07-21

    Quantum-paraelectric (QP) family character is emergent from shared low-temperature characteristics of SrCu{sub 3}Ti{sub 4}O{sub 12} (SCTO), CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO), and Ca{sub 0.9}Li{sub 0.1}Cu{sub 3}Ti{sub 4}O{sub 12} (CLCTO) A{sub 1/4}A′{sub 3/4}BO{sub 3} structures featuring antiferro-tilted Ti-O{sub 6} octahedra. Above their magnetic ordering temperatures T{sub N}, permittivity of SCTO and CLCTO follow typical Barrett form, whereas in CCTO, quantum paraelectricity is masked by the huge ε′-step. Hidden QP in CCTO gets revealed by Li-doping at the Ca-site, which considerably up-shifts the temperature scale (from ∼100 K to ∼250 K) of the dielectric step-anomaly in CLCTO. Competing magneto-electricity and quantum fluctuations result in glassy-arrest of the QP degrees of freedom near T{sub N}; manifest as dispersive-deviation of the permittivity (in SCTO and CLCTO) from the low-temperature Barrett saturation. However, quantum criticality (QC) regime being well above T{sub N} registers its presence nevertheless, as the ∼T{sup 2} behaviour of their inverse dielectric susceptibility. Non-compliance to the usual behaviours of dispersive-response vs. bias-field and temperature unambiguously rule out a relaxor origin of the glassy state. We determine a dimensionless thermal window (0.3 ≤ T/T{sub 1} ≤ 0.6) of QC signature, covering typical quantum-paraelectrics.

  13. Current-density-functional approach to large quantum dots in intense magnetic fields

    Science.gov (United States)

    Pi, M.; Barranco, M.; Emperador, A.; Lipparini, E.; Serra, Ll.

    1998-06-01

    Within current-density-functional theory, we have studied a quantum dot made of 210 electrons confined in a disk geometry. The ground state of this large dot exhibits some features as a function of the magnetic field (B) that can be attributed in a clear way to the formation of compressible and incompressible states of the system. The orbital and spin angular momenta, the total energy, ionization and electron chemical potentials of the ground state, as well as the frequencies of far-infrared edge modes are calculated as a function of B, and compared with available experimental and theoretical results.

  14. Singlet triplet transition of a two-electron quantum ring in magnetic and electric fields

    Science.gov (United States)

    Malet, F.; Pi, M.; Serra, Ll.; Lipparini, E.

    2008-03-01

    We present an exact numerical calculation of the spin phase diagram of a two-electron quantum ring as a function of an applied in-plane electric field E and a perpendicular magnetic field B. In general, large E and B favour, respectively, singlet and triplet states. At low fields, however, the spin phase diagram shows singlet-triplet oscillations and the formation of spin islands surrounded by the complementary phase. Calculations of the density dipole excitation spectrum as a function of the electric field are also reported.

  15. Highly polarized light emission by isotropic quantum dots integrated with magnetically aligned segmented nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Uran, Can; Erdem, Talha; Guzelturk, Burak [Department of Electrical and Electronics Engineering, Department of Physics, and UNAM - National Nanotechnology Research Center, Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800 (Turkey); Perkgöz, Nihan Kosku [Department of Electrical and Electronics Engineering, Department of Physics, and UNAM - National Nanotechnology Research Center, Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800 (Turkey); Department of Electrical and Electronics Engineering, Faculty of Engineering, Anadolu University, Eskisehir 26555 (Turkey); Jun, Shinae; Jang, Eunjoo [Inorganic Material Laboratory, Material Research Center, Samsung Advanced Institute of Technology, Samsung Electronics Co., 130 Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 443-803 (Korea, Republic of); Demir, Hilmi Volkan, E-mail: volkan@stanfordalumni.org [Department of Electrical and Electronics Engineering, Department of Physics, and UNAM - National Nanotechnology Research Center, Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800 (Turkey); Luminous Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Physical and Materials Sciences, Nanyang Technological University, Singapore, Singapore 639798 (Singapore)

    2014-10-06

    In this work, we demonstrate a proof-of-concept system for generating highly polarized light from colloidal quantum dots (QDs) coupled with magnetically aligned segmented Au/Ni/Au nanowires (NWs). Optical characterizations reveal that the optimized QD-NW coupled structures emit highly polarized light with an s-to p-polarization (s/p) contrast as high as 15:1 corresponding to a degree of polarization of 0.88. These experimental results are supported by the finite-difference time-domain simulations, which demonstrate the interplay between the inter-NW distance and the degree of polarization.

  16. Many-body localization in the droplet spectrum of the random XXZ quantum spin chain

    OpenAIRE

    Elgart, Alexander; Klein, Abel; Stolz, Günter

    2017-01-01

    We study many-body localization properties of the disordered XXZ spin chain in the Ising phase. Disorder is introduced via a random magnetic field in the $z$-direction. We prove a strong form of dynamical exponential clustering for eigenstates in the droplet spectrum: For any pair of local observables separated by a distance $\\ell$, the sum of the associated correlators over these states decays exponentially in $\\ell$, in expectation. This exponential clustering persists under the time evolut...

  17. On the quantum magnetic oscillations of electrical and thermal conductivities of graphene

    Science.gov (United States)

    Alisultanov, Z. Z.; Reis, M. S.

    2016-05-01

    Oscillating thermodynamic quantities of diamagnetic materials, specially graphene, have been attracting attention of the scientific community due to the possibility to experimentally map the Fermi surface of the material. These have been the case of the de Haas-van Alphen and Shubnikov-de Haas effects, found on the magnetization and electrical conductivity, respectively. In this direction, managing the thermodynamic oscillations is of practical purpose, since from the reconstructed Fermi surface it is possible to access, for instance, the electronic density. The present work theoretically explores the quantum oscillations of electrical and thermal conductivities of a monolayer graphene under a crossed magnetic and electric fields. We found that the longitudinal electric field can increase the amplitude of the oscillations and this result is of practical and broad interest for both, experimental and device physics.

  18. Non-equilibrium differential conductance through a quantum dot in a magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Hewson, A C [Department of Mathematics, Imperial College, London SW7 2AZ (United Kingdom); Bauer, J [Department of Mathematics, Imperial College, London SW7 2AZ (United Kingdom); Oguri, A [Department of Material Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585 (Japan)

    2005-09-07

    We derive an exact expression for the differential conductance for a quantum dot in an arbitrary magnetic field for small bias voltage. The derivation is based on the symmetric Anderson model using renormalized perturbation theory and is valid for all values of the on-site interaction U including the Kondo regime. We calculate the critical magnetic field for the splitting of the Kondo resonance to be seen in the differential conductivity as a function of bias voltage. Our calculations for small field show that the peak positions of the component resonances in the differential conductance are reduced substantially from estimates using the equilibrium Green function. We conclude that it is important to take the voltage dependence of the local retarded Green function into account in interpreting experimental results.

  19. Photoinduced quantum spin and valley Hall effects, and orbital magnetization in monolayer MoS2

    KAUST Repository

    Tahir, M.

    2014-09-22

    We theoretically demonstrate that 100% valley-polarized transport in monolayers of MoS2 and other group-VI dichalcogenides can be obtained using off-resonant circularly polarized light. By tuning the intensity of the off-resonant light the intrinsic band gap in one valley is reduced, while it is enhanced in the other valley, enabling single valley quantum transport. As a consequence, we predict (i) enhancement of the longitudinal electrical conductivity, accompanied by an increase in the spin polarization of the flowing electrons, (ii) enhancement of the intrinsic spin Hall effect, together with a reduction of the intrinsic valley Hall effect, and (iii) enhancement of the orbital magnetic moment and orbital magnetization. These mechanisms provide appealing opportunities to the design of nanoelectronics based on dichalcogenides.

  20. Shot noise of charge current in a quantum dot responded by rotating and oscillating magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Hong-Kang, E-mail: zhaohonk@yahoo.com; Zou, Wei-Ke [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Chen, Qiao [Department of Maths and Physics, Hunan Institute of Engineering, Xiangtan 411104 (China)

    2014-09-07

    We have investigated the shot noise and Fano factor of the dynamic spin-polarized quantum dot under the perturbations of a rotating magnetic field (RMF), and an oscillating magnetic field (OMF) by employing the non-equilibrium Green's function approach. The shot noise is enhanced from sub-Poissonian to super-Poissonian due to the application of RMF and OMF, and it is controlled sensitively by the tilt angle θ of RMF. The magnitude of shot noise increases as the photon energy ℏω of OMF increases, and its valley eventually is reversed to peaks as the photon energy is large enough. Double-peak structure of Fano factor is exhibited as the frequency of OMF increases to cover a large regime. The Zeeman energy μ{sub 0}B{sub 0} acts as an effective gate bias to exhibit resonant behavior, and novel peak emerges associated with the applied OMF.

  1. Electric and magnetic field effects on the optical absorption of elliptical quantum wire

    Science.gov (United States)

    Karimi, M. J.; Hosseini, M.

    2017-11-01

    In this work, the effects of electric and magnetic fields on the linear, the third-order nonlinear and the total optical absorption coefficients of a typical GaAs/AlGaAs elliptical quantum wire are investigated. Energy eigenvalues and wave functions are calculated using the two-dimensional finite difference method and optical properties are obtained using the compact density matrix approach. The influences of the electric and magnetic fields on the probability densities are described. Results show that the resonant peak values of the optical absorption coefficients are non-monotonic functions of the external fields. Results also indicate that by applying external fields, the magnitude of total optical absorption coefficient reaches to values about 1.5 times higher than that case without external fields.

  2. Quantum

    CERN Document Server

    Al-Khalili, Jim

    2003-01-01

    In this lively look at quantum science, a physicist takes you on an entertaining and enlightening journey through the basics of subatomic physics. Along the way, he examines the paradox of quantum mechanics--beautifully mathematical in theory but confoundingly unpredictable in the real world. Marvel at the Dual Slit experiment as a tiny atom passes through two separate openings at the same time. Ponder the peculiar communication of quantum particles, which can remain in touch no matter how far apart. Join the genius jewel thief as he carries out a quantum measurement on a diamond without ever touching the object in question. Baffle yourself with the bizzareness of quantum tunneling, the equivalent of traveling partway up a hill, only to disappear then reappear traveling down the opposite side. With its clean, colorful layout and conversational tone, this text will hook you into the conundrum that is quantum mechanics.

  3. Carrier relaxation in (In,Ga)As quantum dots with magnetic field-induced anharmonic level structure

    Energy Technology Data Exchange (ETDEWEB)

    Kurtze, H.; Bayer, M. [Experimentelle Physik 2, TU Dortmund, D-44221 Dortmund (Germany)

    2016-07-04

    Sophisticated models have been worked out to explain the fast relaxation of carriers into quantum dot ground states after non-resonant excitation, overcoming the originally proposed phonon bottleneck. We apply a magnetic field along the quantum dot heterostructure growth direction to transform the confined level structure, which can be approximated by a Fock–Darwin spectrum, from a nearly equidistant level spacing at zero field to strong anharmonicity in finite fields. This changeover leaves the ground state carrier population rise time unchanged suggesting that fast relaxation is maintained upon considerable changes of the level spacing. This corroborates recent models explaining the relaxation by polaron formation in combination with quantum kinetic effects.

  4. Non-equilibrium quantum transport of spin-polarized electrons and back action on molecular magnet tunnel-junction

    Directory of Open Access Journals (Sweden)

    Chao Zhang

    2016-11-01

    Full Text Available We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.

  5. Non-equilibrium quantum transport of spin-polarized electrons and back action on molecular magnet tunnel-junction

    Science.gov (United States)

    Zhang, Chao; Yao, Hui; Nie, Yi-Hang; Liang, J.-Q.

    2016-11-01

    We investigate the non-equilibrium quantum transport through a single-molecule magnet embedded in a tunnel junction with ferromagnetic electrodes, which generate spin-polarized electrons. The lead magnetization direction is non-collinear with the uniaxial anisotropy easy-axis of molecule-magnet. Based on the Pauli rate-equation approach we demonstrate the magnetization reversion of molecule-magnet induced by the back action of spin-polarized current in the sequential tunnel regime. The asymptotic magnetization of molecular magnet and spin-polarization of transport current are obtained as functions of time by means of time-dependent solution of the rate equation. It is found that the antiparallel configuration of the ferromagnetic electrodes and molecular anisotropy easy-axis is an effective structure to reverse both the magnetization of molecule-magnet and spin-polarization of the transport current. Particularly the non-collinear angle dependence provides useful knowledge for the quantum manipulation of molecule-magnet and spin polarized electron-transport.

  6. A heuristic model of damped quantum rotation effects in nuclear magnetic resonance spectra.

    Science.gov (United States)

    Szymański, S

    2011-01-28

    The damped quantum rotation (DQR) theory describes temperature effects in NMR spectra of hindered molecular rotators composed of identical atoms arranged in regular N-gons. In the standard approach, the relevant coherent dynamics are described quantum mechanically and the stochastic, thermally activated motions classically. The DQR theory is consistent. In place of random jumps over one, two, etc., maxima of the hindering potential, here one has damping processes of certain long-lived coherences between spin-space correlated eigenstates of the rotator. The damping-rate constants outnumber the classical jump-rate constants. The jump picture is recovered when the former cluster appropriately around only as many values as the number of the latter. The DQR theory was confirmed experimentally for hindered methyl groups in solids and even in liquids above 170 K. In this paper it is shown that for three-, four-, and sixfold rotators, the Liouville space equations of NMR line shapes, derived previously with the use of the quantum mechanical reduced density matrix approach, can be be given a heuristic justification. It is based on an equation of motion for the effective spin density matrix, where the relevant spin hamiltonian contains randomly fluctuating terms. The occurrence of the latter can be rationalized in terms of fluctuations of the tunneling splittings between the torsional sublevels of the rotator, including momentary liftings of the Kramers degeneracies. The question whether such degeneracy liftings are physical or virtual is discussed. The random terms in the effective hamiltonian can be Monte Carlo modeled as piecewise constant in time, which affords the stochastic equation of motion to be solved numerically in the Hilbert spin space. For sixfold rotators, this way of calculating the spectra can be useful in the instances where the Liouville space formalism of the original DQR theory is numerically unstable.

  7. Modelling copper-phthalocyanine/cobalt-phthalocyanine chains: towards magnetic quantum metamaterials.

    Science.gov (United States)

    Wu, Wei

    2014-07-23

    The magnetic properties of a theoretically designed molecular chain structure CuCoPc2, in which copper-phthalocyanine (CuPc) and cobalt-phthalocyanine (CoPc) alternate, have been investigated across a range of chain structures. The computed exchange interaction for the α-phase CuCoPc2 is ∼ 5 K (ferromagnetic), in strong contrast to the anti-ferromagnetic interaction recently observed in CuPc and CoPc. The computed exchange interactions are strongly dependent on the stacking angle but weakly on the sliding angle, and peak at 20 K (ferromagnetic). These ferromagnetic interactions are expected to arise from direct exchange with the strong suppression of super-exchange interaction. These first-principles calculations show that π-conjugated molecules, such as phthalocyanine, could be used as building blocks for the design of magnetic materials. This therefore extends the concept of quantum metamaterials further into magnetism. The resulting new magnetic materials could find applications in the studies such as organic spintronics.

  8. Approximate solutions to the quantum problem of two opposite charges in a constant magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Ardenghi, J.S., E-mail: jsardenghi@gmail.com [IFISUR, Departamento de Física (UNS-CONICET), Avenida Alem 1253, Bahía Blanca, Buenos Aires (Argentina); Gadella, M., E-mail: manuelgadella1@gmail.com [Department of Theoretical, Atomic Physics and Optics and IMUVA, University of Valladolid, 47011 Valladolid (Spain); Grinnell College, Department of Physics, Grinnell, 50112 IA (United States); Negro, J., E-mail: jnegro@fta.uva.es [Department of Theoretical, Atomic Physics and Optics and IMUVA, University of Valladolid, 47011 Valladolid (Spain)

    2016-05-06

    We consider two particles of equal mass and opposite charge in a plane subject to a perpendicular constant magnetic field. This system is integrable but not superintegrable. From the quantum point of view, the solution is given by two fourth degree Hill differential equations which involve the energy as well as a second constant of motion. There are two solvable approximations in relation to the value of a parameter. Starting from each of these approximations, a consistent perturbation theory can be applied to get approximate values of the energy levels and of the second constant of motion. - Highlights: • We have studied the quantum model of two charged particles on a plane with opposite charges and a perpendicular constant magnetic field. • This model is integrable, although not superintegrable. • The model under study is described by two fourth degree Hill equations, one trigonometric and the other hyperbolic. • We have considered two distinct approximations that have exact solution. • We have applied a perturbative method to improve the approximation.

  9. Quantifying Magnetic Sensitivity of Radical Pair Based Compass by Quantum Fisher Information.

    Science.gov (United States)

    Guo, Li-Sha; Xu, Bao-Ming; Zou, Jian; Shao, Bin

    2017-07-19

    The radical pair (RP) based compass is considered as one of the principal models of avian magnetoreception. Different from the conventional approach where the sensitivity of RP based compass is described by the singlet yield, we introduce the quantum Fisher information (QFI), which represents the maximum information about the magnetic field's direction extracted from the RP state, to quantify the sensitivity of RP based compass. The consistency between our results and experimental observations suggests that the QFI may serve as a measure to describe the sensitivity of RP based compass. Besides, within the framework of quantum metrology, we give two specific possible measurement schemes and find that the conventional singlet yield is corresponding to the measurement of total angular momentum. Moreover, we show that the measurement of fluctuation of the total magnetic moment is much more accurate than the singlet yield measurement, and is close to the optimal measurement scheme. Finally, the effects of entanglement and decoherence are also discussed in the spirit of our approach.

  10. Size dependent magnetic and optical properties in diamond shaped graphene quantum dots: A DFT study

    Science.gov (United States)

    Das, Ritwika; Dhar, Namrata; Bandyopadhyay, Arka; Jana, Debnarayan

    2016-12-01

    The magnetic and optical properties of diamond shaped graphene quantum dots (DSGQDs) have been investigated by varying their sizes with the help of density functional theory (DFT). The study of density of states (DOS) has revealed that the Fermi energy decreases with increase in sizes (number of carbon atoms). The intermediate structure with 30 carbon atoms shows the highest magnetic moment (8 μB, μB being the Bohr magneton). The shifting of optical transitions to higher energy in smallest DSGQD (16 carbon atoms) bears the signature of stronger quantum confinement. However, for the largest structure (48 carbon atoms) multiple broad peaks appear in case of parallel polarization and in this case electron energy loss spectra (EELS) peak (in the energy range 0-5 eV) is sharp in nature (compared to high energy peak). This may be attributed to π plasmon and the broad peak (in the range 10-16 eV) corresponds to π + σ plasmon. A detail calculation of the Raman spectra has indicated some prominent mode of vibrations which can be used to characterize these structures (with hydrogen terminated dangling bonds). We think that these theoretical observations can be utilized for novel device designs involving DSGQDs.

  11. An On-Demand Optical Quantum Random Number Generator with In-Future Action and Ultra-Fast Response.

    Science.gov (United States)

    Stipčević, Mario; Ursin, Rupert

    2015-06-09

    Random numbers are essential for our modern information based society e.g. in cryptography. Unlike frequently used pseudo-random generators, physical random number generators do not depend on complex algorithms but rather on a physical process to provide true randomness. Quantum random number generators (QRNG) do rely on a process, which can be described by a probabilistic theory only, even in principle. Here we present a conceptually simple implementation, which offers a 100% efficiency of producing a random bit upon a request and simultaneously exhibits an ultra low latency. A careful technical and statistical analysis demonstrates its robustness against imperfections of the actual implemented technology and enables to quickly estimate randomness of very long sequences. Generated random numbers pass standard statistical tests without any post-processing. The setup described, as well as the theory presented here, demonstrate the maturity and overall understanding of the technology.

  12. Quantum Hall effect in a bulk antiferromagnet EuMnBi2 with magnetically confined two-dimensional Dirac fermions.

    Science.gov (United States)

    Masuda, Hidetoshi; Sakai, Hideaki; Tokunaga, Masashi; Yamasaki, Yuichi; Miyake, Atsushi; Shiogai, Junichi; Nakamura, Shintaro; Awaji, Satoshi; Tsukazaki, Atsushi; Nakao, Hironori; Murakami, Youichi; Arima, Taka-hisa; Tokura, Yoshinori; Ishiwata, Shintaro

    2016-01-01

    For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm(2)/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.

  13. The interplay of size- and site-dependence of magnetic properties of diluted magnetic semiconductor quantum dots

    Science.gov (United States)

    Zheng, Weiwei

    This dissertation studies the size- and site-dependent optical and magnetic properties of II-VI quantum dots (QDs). The first chapter provides a theoretical background used to analyze the data and the properties expected for diluted magnetic semiconductor materials at the nanoscale. The second chapter probes the size-dependent magnetic properties for Mn doped CdSe QDs. The Curie-Weiss law plots show significant size-dependent carrier concentration in the QDs. The carriers inside the small QDs can mediate the Mn(II)-Mn(II) ferromagnetic interaction by the RKKY model, which helps explain reasons for the observation of a superparamagnetism (SPM) in small Mn:CdSe QDs. The third chapter involves high frequency EPR analysis of possible dopant (Mn(II) ions) sites in CdSe lattice. Surface doped Mn:CdSe QDs and stochastically doped Mn:CdSe QDs were successfully made by traditional thermal decomposition of cluster and microwave irradiation. Two sets of hyperfine splitting were observed for stochastically doped Mn:CdSe QDs from EPR spectra and the ratio of the signal has liner relationship with the surface to volume ratio of QDs. One set of hyperfine splitting can be removed by surface acid treatment enabled us to identify the Mn(II) sites on the surface or core position of Mn:CdSe QDs. The fourth chapter is a study of chromium incorporation in ZnSe QDs by single cubic source precursor method. The formation of ZnCr2Se4 spinel structure was approved by XANES, and 4A2g → 4T 2g transition of Cr (III) ion in absorption spectra.

  14. Magnetically engineered Cd-free quantum dots as dual-modality probes for fluorescence/magnetic resonance imaging of tumors.

    Science.gov (United States)

    Ding, Ke; Jing, Lihong; Liu, Chunyan; Hou, Yi; Gao, Mingyuan

    2014-02-01

    Magnetically engineered Cd-free CuInS2@ZnS:Mn quantum dots (QDs) were designed, synthesized, and evaluated as potential dual-modality probes for fluorescence and magnetic resonance imaging (MRI) of tumors in vivo. The synthesis of Mn-doped core-shell structured CuInS2@ZnS mainly comprised three steps, i.e., the preparation of fluorescent CuInS2 seeds, the particle surface coating of ZnS, and the Mn-doping of the ZnS shells. Systematic spectroscopy studies were carried out to illustrate the impacts of ZnS coating and the following Mn-doping on the optical properties of the QDs. In combination with conventional fluorescence, fluorescence excitation, and time-resolved fluorescence measurements, the structure of CuInS2@ZnS:Mn QDs prepared under optimized conditions presented a Zn gradient CuInS2 core and a ZnS outer shell, while Mn ions were mainly located in the ZnS shell, which well balanced the optical and magnetic properties of the resultant QDs. For the following in vivo imaging experiments, the hydrophobic CuInS2@ZnS:Mn QDs were transferred into water upon ligand exchange reactions by replacing the 1-dodecanethiol ligand with dihydrolipoic acid-poly(ethylene glycol) (DHLA-PEG) ligand. The MTT assays based on HeLa cells were carried out to evaluate the cytotoxicity of the current Cd-free CuInS2@ZnS:Mn QDs for comparing with that of water soluble CdTe QDs. Further in vivo fluorescence and MR imaging experiments suggested that the PEGylated CuInS2@ZnS:Mn QDs could well target both subcutaneous and intraperitoneal tumors in vivo. Copyright © 2013 Elsevier Ltd. All rights reserved.

  15. Characterization of Magnetic Tunnel Junctions For Spin Transfer Torque Magnetic Random Access Memory

    Science.gov (United States)

    Dill, Joshua Luchay

    This thesis details two experimental methods for quantifying magnetic tunnel junction behavior, namely write error rates and field modulated spin-torque ferromagnetic resonance. The former examines how reliably an applied spin-transfer torque can excite magnetization dynamics that lead to a reversal of magnetization direction while the latter studies steady state dynamics provided by an oscillating spin-transfer torque. These characterization techniques reveal write error rate behavior for a particular composition magnetic tunnel junction that qualitatively deviates from theoretical predictions. Possible origins of this phenomenon are also investigated with the field modulated spin-torque ferromagnetic resonance technique. By understanding the dynamics of magnetic moments predicted by theory, one can experimentally confirm or disprove these theories in order to accurately model and predict tunnel junction behavior. By having a better model for what factors are important in magnetization dynamics, one can optimize these factors in terms of improving magnetic tunnel junctions for their use as computer memory.

  16. Quantum correlation of fiber-based telecom-band photon pairs through standard loss and random media.

    Science.gov (United States)

    Sua, Yong Meng; Malowicki, John; Lee, Kim Fook

    2014-08-15

    We study quantum correlation and interference of fiber-based telecom-band photon pairs with one photon of the pair experiencing multiple scattering in a random medium. We measure joint probability of two-photon detection for signal photon in a normal channel and idler photon in a channel, which is subjected to two independent conditions: standard loss (neutral density filter) and random media. We observe that both conditions degrade the correlation of signal and idler photons, and depolarization of the idler photon in random medium can enhance two-photon interference at certain relative polarization angles. Our theoretical calculation on two-photon polarization correlation and interference as a function of mean free path is in agreement with our experiment data. We conclude that quantum correlation of a polarization-entangled photon pair is better preserved than a polarization-correlated photon pair as one photon of the pair scatters through a random medium.

  17. Quantum-memory-assisted entropic uncertainty relation in a Heisenberg XYZ chain with an inhomogeneous magnetic field

    Science.gov (United States)

    Wang, Dong; Huang, Aijun; Ming, Fei; Sun, Wenyang; Lu, Heping; Liu, Chengcheng; Ye, Liu

    2017-06-01

    The uncertainty principle provides a nontrivial bound to expose the precision for the outcome of the measurement on a pair of incompatible observables in a quantum system. Therefore, it is of essential importance for quantum precision measurement in the area of quantum information processing. Herein, we investigate quantum-memory-assisted entropic uncertainty relation (QMA-EUR) in a two-qubit Heisenberg \\boldsymbol{X}\\boldsymbol{Y}\\boldsymbol{Z} spin chain. Specifically, we observe the dynamics of QMA-EUR in a realistic model there are two correlated sites linked by a thermal entanglement in the spin chain with an inhomogeneous magnetic field. It turns out that the temperature, the external inhomogeneous magnetic field and the field inhomogeneity can lift the uncertainty of the measurement due to the reduction of the thermal entanglement, and explicitly higher temperature, stronger magnetic field or larger inhomogeneity of the field can result in inflation of the uncertainty. Besides, it is found that there exists distinct dynamical behaviors of the uncertainty for ferromagnetism \\boldsymbol{}≤ft(\\boldsymbol{J}\\boldsymbol{0}\\right) chains. Moreover, we also verify that the measuring uncertainty is dramatically anti-correlated with the purity of the bipartite spin system, the greater purity can result in the reduction of the measuring uncertainty, vice versa. Therefore, our observations might provide a better understanding of the dynamics of the entropic uncertainty in the Heisenberg spin chain, and thus shed light on quantum precision measurement in the framework of versatile systems, particularly solid states.

  18. Quantum Mechanical Enhancement of the Random Dopant Induced Threshold Voltage Fluctuations and Lowering in Sub 0.1 Micron MOSFETs

    Science.gov (United States)

    Asenov, Asen; Slavcheva, G.; Brown, A. R.; Davies, J. H.; Saini, Subhash

    1999-01-01

    A detailed study of the influence of quantum effects in the inversion layer on the random dopant induced threshold voltage fluctuations and lowering in sub 0.1 micron MOSFETs has been performed. This has been achieved using a full 3D implementation of the density gradient (DG) formalism incorporated in our previously published 3D 'atomistic' simulation approach. This results in a consistent, fully 3D, quantum mechanical picture which implies not only the vertical inversion layer quantisation but also the lateral confinement effects manifested by current filamentation in the 'valleys' of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical fluctuations, is an increase in both threshold voltage fluctuations and lowering.

  19. Magnetically engineered SnO2 quantum dots as a bimodal agent for optical and magnetic resonance imaging

    Science.gov (United States)

    Dutta, Dipa; Gupta, Jagriti; Thakur, Dinbandhu; Bahadur, Dhirendra

    2017-12-01

    Combining more than one imaging technique into a single system can outweigh the limitations of conventional imaging techniques. Pairing optically active quantum dots (QDs) with superparamagnetic MRI agent is an adorable way to develop probes for bimodal imaging. Tiny SnO2 quantum dot embedded iron oxide (IO) nanocomposite (SQD-IO) is synthesized. This combines the superparamagnetic property of IO nanoparticles (NPs) and special optical properties of SnO2 QDs, and is explored as a bimodal imaging agent. Morphological studies of the nanocomposite reveal that 3 nm tiny SnO2 QDs are embedded in ~30 nm γ-Fe2O3 NPs. The SQD-IO preserves the intrinsic superparamagnetic behaviour of its constituent IO NPs with a magnetization ~21.4 emu g‑1 measured at an applied field of 20k Oe. The emission colour of the nanocomposite is tuned by simply varying the excitation wavelength. The centre of the emission band shifts from 570 to 600 nm as the excitation alters from 488 to 535 nm. The cytotoxicity assessment indicates that the nanocomposite is suitable for its in vitro use. Transverse proton relaxivity (141 mM‑1 s‑1) of the nanocomposite is higher than the widely used negative contrast agent Feridex (R2  =  98.3 mM‑1 s‑1). The confocal laser scanning microscope images give evidence of the cellular uptake behaviour of SQD-IO in HeLa cells and it is seen that QDs retain their optical properties within the intracellular environment. The high R2 value for MRI and the tunable florescence images of HeLa cells essentially establish SQD-IO as a potential probe for bimodal imaging.

  20. Methionine-mediated synthesis of magnetic nanoparticles and functionalization with gold quantum dots for theranostic applications.

    Science.gov (United States)

    Jagminas, Arūnas; Mikalauskaitė, Agnė; Karabanovas, Vitalijus; Vaičiūnienė, Jūrate

    2017-01-01

    Biocompatible superparamagnetic iron oxide nanoparticles (NPs) through smart chemical functionalization of their surface with fluorescent species, therapeutic proteins, antibiotics, and aptamers offer remarkable potential for diagnosis and therapy of disease sites at their initial stage of growth. Such NPs can be obtained by the creation of proper linkers between magnetic NP and fluorescent or drug probes. One of these linkers is gold, because it is chemically stable, nontoxic and capable to link various biomolecules. In this study, we present a way for a simple and reliable decoration the surface of magnetic NPs with gold quantum dots (QDs) containing more than 13.5% of Au+. Emphasis is put on the synthesis of magnetic NPs by co-precipitation using the amino acid methionine as NP growth-stabilizing agent capable to later reduce and attach gold species. The surface of these NPs can be further conjugated with targeting and chemotherapy agents, such as cancer stem cell-related antibodies and the anticancer drug doxorubicin, for early detection and improved treatment. In order to verify our findings, high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), FTIR spectroscopy, inductively coupled plasma mass spectroscopy (ICP-MS), and X-ray photoelectron spectroscopy (XPS) of as-formed CoFe2O4 NPs before and after decoration with gold QDs were applied.

  1. Molecular Quantum Spintronics: Supramolecular Spin Valves Based on Single-Molecule Magnets and Carbon Nanotubes

    Directory of Open Access Journals (Sweden)

    Wolfgang Wernsdorfer

    2011-10-01

    Full Text Available We built new hybrid devices consisting of chemical vapor deposition (CVD grown carbon nanotube (CNT transistors, decorated with TbPc2 (Pc = phthalocyanine rare-earth based single-molecule magnets (SMMs. The drafting was achieved by tailoring supramolecular π-π interactions between CNTs and SMMs. The magnetoresistance hysteresis loop measurements revealed steep steps, which we can relate to the magnetization reversal of individual SMMs. Indeed, we established that the electronic transport properties of these devices depend strongly on the relative magnetization orientations of the grafted SMMs. The SMMs are playing the role of localized spin polarizer and analyzer on the CNT electronic conducting channel. As a result, we measured magneto-resistance ratios up to several hundred percent. We used this spin valve effect to confirm the strong uniaxial anisotropy and the superparamagnetic blocking temperature (TB ~ 1 K of isolated TbPc2 SMMs. For the first time, the strength of exchange interaction between the different SMMs of the molecular spin valve geometry could be determined. Our results introduce a new design for operable molecular spintronic devices using the quantum effects of individual SMMs.

  2. Methionine-mediated synthesis of magnetic nanoparticles and functionalization with gold quantum dots for theranostic applications

    Directory of Open Access Journals (Sweden)

    Arūnas Jagminas

    2017-08-01

    Full Text Available Biocompatible superparamagnetic iron oxide nanoparticles (NPs through smart chemical functionalization of their surface with fluorescent species, therapeutic proteins, antibiotics, and aptamers offer remarkable potential for diagnosis and therapy of disease sites at their initial stage of growth. Such NPs can be obtained by the creation of proper linkers between magnetic NP and fluorescent or drug probes. One of these linkers is gold, because it is chemically stable, nontoxic and capable to link various biomolecules. In this study, we present a way for a simple and reliable decoration the surface of magnetic NPs with gold quantum dots (QDs containing more than 13.5% of Au+. Emphasis is put on the synthesis of magnetic NPs by co-precipitation using the amino acid methionine as NP growth-stabilizing agent capable to later reduce and attach gold species. The surface of these NPs can be further conjugated with targeting and chemotherapy agents, such as cancer stem cell-related antibodies and the anticancer drug doxorubicin, for early detection and improved treatment. In order to verify our findings, high-resolution transmission electron microscopy (HRTEM, atomic force microscopy (AFM, FTIR spectroscopy, inductively coupled plasma mass spectroscopy (ICP-MS, and X-ray photoelectron spectroscopy (XPS of as-formed CoFe2O4 NPs before and after decoration with gold QDs were applied.

  3. Shear elastic modulus of magnetic gels with random distribution of magnetizable particles

    Science.gov (United States)

    Iskakova, L. Yu; Zubarev, A. Yu

    2017-04-01

    Magnetic gels present new type of composite materials with rich set of uniquie physical properties, which find active applications in many industrial and bio-medical technologies. We present results of mathematically strict theoretical study of elastic modulus of these systems with randomly distributed magnetizable particles in an elastic medium. The results show that an external magnetic field can pronouncedly increase the shear modulus of these composites.

  4. Itinerancy-enhanced quantum fluctuation of magnetic moments in iron-based superconductors.

    Science.gov (United States)

    Tam, Yu-Ting; Yao, Dao-Xin; Ku, Wei

    2015-09-11

    We investigate the influence of itinerant carriers on the dynamics and fluctuation of local moments in Fe-based superconductors, via linear spin-wave analysis of a spin-fermion model containing both itinerant and local degrees of freedom. Surprisingly, against the common lore, instead of enhancing the (π,0) order, itinerant carriers with well-nested Fermi surfaces are found to induce a significant amount of spatial and temporal quantum fluctuation that leads to the observed small ordered moment. Interestingly, the underlying mechanism is shown to be an intrapocket nesting-associated long-range coupling rather than the previously believed ferromagnetic double-exchange effect. This challenges the validity of ferromagnetically compensated first-neighbor coupling reported from short-range fitting to the experimental dispersion, which turns out to result instead from the ferro-orbital order that is also found instrumental in stabilizing the magnetic order.

  5. Magnetically tuned, robust and efficient filtering system for spatially multimode quantum memory in warm atomic vapors

    Science.gov (United States)

    Dąbrowski, M.; Chrapkiewicz, R.; Wasilewski, W.

    2016-11-01

    Warm atomic vapor quantum memories are simple and robust, yet suffer from a number of parasitic processes which produce excess noise. For operating in a single-photon regime precise filtering of the output light is essential. Here, we report a combination of magnetically tuned absorption and Faraday filters, both light-direction insensitive, which stop the driving lasers and attenuate spurious fluorescence and four-wave mixing while transmitting narrowband Stokes and anti-Stokes photons generated in write-in and readout processes. We characterize both filters with respect to adjustable working parameters. We demonstrate a significant increase in the signal-to-noise ratio upon applying the filters seen qualitatively in measurements of correlation between the Raman scattered photons.

  6. Quantum magnetism in strongly interacting one-dimensional spinor Bose systems.

    Science.gov (United States)

    Dehkharghani, Amin; Volosniev, Artem; Lindgren, Jonathan; Rotureau, Jimmy; Forssén, Christian; Fedorov, Dmitri; Jensen, Aksel; Zinner, Nikolaj

    2015-06-15

    Strongly interacting one-dimensional quantum systems often behave in a manner that is distinctly different from their higher-dimensional counterparts. When a particle attempts to move in a one-dimensional environment it will unavoidably have to interact and 'push' other particles in order to execute a pattern of motion, irrespective of whether the particles are fermions or bosons. A present frontier in both theory and experiment are mixed systems of different species and/or particles with multiple internal degrees of freedom. Here we consider trapped two-component bosons with short-range inter-species interactions much larger than their intra-species interactions and show that they have novel energetic and magnetic properties. In the strongly interacting regime, these systems have energies that are fractions of the basic harmonic oscillator trap quantum and have spatially separated ground states with manifestly ferromagnetic wave functions. Furthermore, we predict excited states that have perfect antiferromagnetic ordering. This holds for both balanced and imbalanced systems, and we show that it is a generic feature as one crosses from few- to many-body systems.

  7. The effect of magnetic field on RbCl quantum pseudodot qubit

    Science.gov (United States)

    Xiao, Jing-Lin

    2015-07-01

    Under the condition of strong electron-LO-phonon coupling in a RbCl quantum pseudodot (QPD) with an applied magnetic field (MF), the eigenenergies and the eigenfunctions of the ground and the first excited states (GFES) are obtained by using a variational method of the Pekar type (VMPT). A single qubit can be realized in this two-level quantum system. The electron’s probability density oscillates in the RbCl QPD with a certain period of T0 = 7.933 fs when the electron is in the superposition state of the GFES. The results indicate that due to the presence of the asymmetrical structure in the z direction of the RbCl QPD, the electron’s probability density shows double-peak configuration, whereas there is only peak if the confinement is a symmetric structure in the x and y directions of the RbCl QPD. The oscillating period is an increasing function of the cyclotron frequency and the polaron radius, whereas it is a decreasing one of the chemical potential of the two-dimensional electron gas and the zero point of the pseudoharmonic potential (PP).

  8. Optical properties of diluted magnetic semiconductor Cu:ZnS quantum dots

    Science.gov (United States)

    Imam, N. G.; Bakr Mohamed, Mohamed

    2014-09-01

    Herein quantum dots (QDs) of diluted magnetic semiconductor Cu:ZnS have been synthesized via a simple chemical synthesis method. A single phase solid solution is formed up to x = 0.1 which confirmed by using X-ray diffraction. Crystal structure and microstructure analyses were performed by Rietveld refinement. Photoluminescence (PL) emission spectra were recorded for pure and Cu doped ZnS QDs excited at 268 and 228 nm respectively. PL emission and excitation spectra were investigated in different wavelength regions within the range of 200-900 nm. PL results in the range of 220-300 nm emission band reveals that the band gap of pure ZnS QDs is about 4.43 eV which greater than that of bulk ZnS (3.7 eV). The band gap of Cu:ZnS QDs is tunable with Cu content (x) as well as the crystalline size, and it is peaked around 4.47 eV. PL emission in the range of 350-650 nm exhibits a green fluorescence band peaking around 552 nm for pure ZnS QDs, which confirms the characteristic feature of Zn2+ as luminescent centers in the lattice, while blue emission bands peaked around 471 nm for Cu:ZnS QDs that is attributed to the transition of electrons from conduction band of ZnS to the Cu impurity level. The blue shift of the absorption peak directly reflects the effect of quantum confinement. The PL results have been supported by X-ray phase analysis, high-resolution electron microscopy (HRTEM and SEM), compositional evaluation (EDX) and magnetic measurements (VSM).

  9. Random field Ising model swept by propagating magnetic field wave: Athermal nonequilibrium phasediagram

    Science.gov (United States)

    Acharyya, Muktish

    2013-05-01

    The dynamical steady state behaviour of the random field Ising ferromagnet swept by a propagating magnetic field wave is studied at zero temperature by Monte Carlo simulation in two dimensions. The distribution of the random field is bimodal type. For a fixed set of values of the frequency, wavelength and amplitude of propagating magnetic field wave and the strength of the random field, four distinct dynamical steady states or nonequilibrium phases were identified. These four nonequilibrium phases are characterised by different values of structure factors. State or phase of first kind, where all spins are parallel (up). This phase is a frozen or pinned where the propagating field has no effect. The second one is the propagating type, where the sharp strips formed by parallel spins are found to move coherently. The third one is also propagating type, where the boundary of the strips of spins is not very sharp. The fourth kind shows no propagation of strips of magnetic spins, forming a homogeneous distribution of up and down spins. This is disordered phase. The existence of these four dynamical phases or modes depends on the value of the amplitude of propagating magnetic field wave and the strength of random (static) field. A phase diagram has also been drawn, in the plane formed by the amplitude of propagating field and the strength of random field. It is also checked that the existence of these dynamical phases is neither a finite size effect nor a transient phenomenon.

  10. Effects of Temperature and Magnetic Field on the Coherence Time of a RbCl Parabolic Quantum Dot Qubit

    Science.gov (United States)

    Sun, Yong; Ding, Zhao-Hua; Xiao, Jing-Lin

    2017-01-01

    Employing the Pekar variational method, quantum statistics theory and the Fermi golden rule, the temperature and magnetic field effects on the qubit in rubidium chloride (RbCl) parabolic quantum dots (PQDs) are investigated. We then obtain the eigenenergies and corresponding eigenfunctions of ground and first-excited states coupled strongly to an electron to bulk longitudinal optical phonons in a RbCl PQD with applied magnetic field. A two-level system of PQDs may be regarded as a single qubit. The spontaneous emission of phonons causes the qubit decoherence. The numerical results indicate that the coherence time decreases with elevating temperature. The coherence increases the effective confinement length, whereas there is a decrease of the magnetic field's cyclotron frequency.

  11. Macroscopic quantum coherence and tunneling of an antiferromagnetic nanoparticle in a magnetic field at an arbitrarily directed angle

    Science.gov (United States)

    Lü, Rong; Zhu, Jia-Lin; Wang, Xiao-Bing; Chang, Lee

    1999-08-01

    Based on the two-sublattice model, we investigate the quantum tunneling behaviors of the Néel vector in single-domain antiferromagnetic nanoparticles placed in an external magnetic field at an arbitrarily directed angle in the ZX plane. We consider the magnetocrystalline anisotropy with biaxial, tetragonal, and hexagonal crystal symmetry, respectively. By applying the standard instanton technique in the spin-coherent-state path-integral representation, we calculate the tunneling level splittings, the tunneling rates, and the crossover temperatures in the low barrier limit for three angle ranges of the external applied magnetic field (θH=π/2, πcrossover temperatures depend on the orientation of the external applied magnetic field distinctly, which provides a possible experimental test for macroscopic quantum tunneling and coherence of the Néel vector in nanometer-scale single-domain antiferromagnets.

  12. Tensile strain-induced magnetism transition in multilayer graphene with excess electrons: Stability of the edge-quantum well

    Directory of Open Access Journals (Sweden)

    Lei Yang

    2015-12-01

    Full Text Available The stability of edge-quantum well-induced strong magnetism of multilayer armchair graphene nanoribbon (AGNR with excess electrons was investigated under applied tensile strain by density functional theory (DFT calculations. The results indicated that: (1 The strain along the armchair edge direction led to a transition of the multilayer AGNRs from ferromagnetic state to nonmagnetic state when the strain increased to a critical value; (2 The strain induced bond length changes reduced the stability of the edge-quantum well in terms of the reduction of the electrons capturing capacity; and (3 The spin splitting of the energy bands near the Fermi level reduced with the increase of the strain, resulting in the decrease of the spin moment. This finding suggests that the magnetic properties of graphene have strong dependence on its strain states, which is crucial to the design of graphene-based magnetic devices.

  13. The rate of separation of magnetic lines of force in a random magnetic field.

    Science.gov (United States)

    Jokipii, J. R.

    1973-01-01

    The mixing of magnetic lines of force, as represented by their rate of separation, as a function of distance along the magnetic field, is considered with emphasis on neighboring lines of force. This effect is particularly important in understanding the transport of charged particles perpendicular to the average magnetic field. The calculation is carried out in the approximation that the separation changes by an amount small compared with the correlation scale normal to the field, in a distance along the field of a few correlation scales. It is found that the rate of separation is very sensitive to the precise form of the power spectrum. Application to the interplanetary and interstellar magnetic fields is discussed, and it is shown that in some cases field lines, much closer together than the correlation scale, separate at a rate which is effectively as rapid as if they were many correlation lengths apart.

  14. Volume of the space of qubit-qubit channels and state transformations under random quantum channels

    OpenAIRE

    Lovas, Attila; Andai, Attila

    2017-01-01

    The simplest building blocks for quantum computations are the qubit-qubit quantum channels. In this paper, we analyze the structure of these channels via their Choi representation. The restriction of a quantum channel to the space of classical states (i.e. probability distributions) is called the underlying classical channel. The structure of quantum channels over a fixed classical channel is studied, the volume of general and unital qubit channels with respect to the Lebesgue measure is comp...

  15. Quantum features of a charged particle in ionized plasma controlled by a time-dependent magnetic field

    Directory of Open Access Journals (Sweden)

    Jeong Ryeol eChoi

    2014-08-01

    Full Text Available Quantum characteristics of a charged particle traveling under the influence of an external time-dependent magnetic field in ionized plasma are investigated using the invariant operator method. The Hamiltonian that gives the radial part of the classical equation of motion for the charged particle is dependent on time. The corresponding invariant operator that satisfies Liouville-von Neumann equation is constructed using fundamental relations. The exact radial wave functions are derived by taking advantage of the eigenstates of the invariant operator. Quantum properties of the system is studied using these wave functions. Especially, the time behavior of the radial component of the quantized energy is addressed in detail.

  16. Quantum factorization of 143 on a dipolar-coupling nuclear magnetic resonance system.

    Science.gov (United States)

    Xu, Nanyang; Zhu, Jing; Lu, Dawei; Zhou, Xianyi; Peng, Xinhua; Du, Jiangfeng

    2012-03-30

    Quantum algorithms could be much faster than classical ones in solving the factoring problem. Adiabatic quantum computation for this is an alternative approach other than Shor's algorithm. Here we report an improved adiabatic factoring algorithm and its experimental realization to factor the number 143 on a liquid-crystal NMR quantum processor with dipole-dipole couplings. We believe this to be the largest number factored in quantum-computation realizations, which shows the practical importance of adiabatic quantum algorithms.

  17. Magnetoresistance of a two-dimensional electron gas in a random magnetic field

    DEFF Research Database (Denmark)

    Smith, Anders; Taboryski, Rafael Jozef; Hansen, Luise Theil

    1994-01-01

    We report magnetoresistance measurements on a two-dimensional electron gas made from a high-mobility GaAs/AlxGa1-xAs heterostructure, where the externally applied magnetic field was expelled from regions of the semiconductor by means of superconducting lead grains randomly distributed...

  18. Electrically Tunable Magnetism in Magnetic Topological Insulators.

    Science.gov (United States)

    Wang, Jing; Lian, Biao; Zhang, Shou-Cheng

    2015-07-17

    The external controllability of the magnetic properties in topological insulators would be important both for fundamental and practical interests. Here we predict the electric-field control of ferromagnetism in a thin film of insulating magnetic topological insulators. The decrease of band inversion by the application of electric fields results in a reduction of magnetic susceptibility, and hence in the modification of magnetism. Remarkably, the electric field could even induce the magnetic quantum phase transition from ferromagnetism to paramagnetism. We further propose a transistor device in which the dissipationless charge transport of chiral edge states is controlled by an electric field. In particular, the field-controlled ferromagnetism in a magnetic topological insulator can be used for voltage based writing of magnetic random access memories in magnetic tunnel junctions. The simultaneous electrical control of magnetic order and chiral edge transport in such devices may lead to electronic and spintronic applications for topological insulators.

  19. Electrically Tunable Magnetism in Magnetic Topological Insulators

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jing; Lian, Biao; Zhang, Shou-Cheng

    2015-07-14

    The external controllability of the magnetic properties in topological insulators would be important both for fundamental and practical interests. Here we predict the electric-field control of ferromagnetism in a thin film of insulating magnetic topological insulators. The decrease of band inversion by the application of electric fields results in a reduction of magnetic susceptibility, and hence in the modification of magnetism. Remarkably, the electric field could even induce the magnetic quantum phase transition from ferromagnetism to paramagnetism. We further propose a transistor device in which the dissipationless charge transport of chiral edge states is controlled by an electric field. In particular, the field-controlled ferromagnetism in a magnetic topological insulator can be used for voltage based writing of magnetic random access memories in magnetic tunnel junctions. The simultaneous electrical control of magnetic order and chiral edge transport in such devices may lead to electronic and spintronic applications for topological insulators.

  20. Potential Applications of Microtesla Magnetic Resonance ImagingDetected Using a Superconducting Quantum Interference Device

    Energy Technology Data Exchange (ETDEWEB)

    Myers, Whittier Ryan [Univ. of California, Berkeley, CA (United States)

    2006-01-01

    This dissertation describes magnetic resonance imaging (MRI) of protons performed in a precession field of 132 μT. In order to increase the signal-to-noise ratio (SNR), a pulsed 40-300 mT magnetic field prepolarizes the sample spins and an untuned second-order superconducting gradiometer coupled to a low transition temperature superconducting quantum interference device (SQUID) detects the subsequent 5.6-kHz spin precession. Imaging sequences including multiple echoes and partial Fourier reconstruction are developed. Calculating the SNR of prepolarized SQUID-detected MRI shows that three-dimensional Fourier imaging yields higher SNR than slice-selection imaging. An experimentally demonstrated field-cycling pulse sequence and post-processing algorithm mitigate image artifacts caused by concomitant gradients in low-field MRI. The magnetic field noise of SQUID untuned detection is compared to the noise of SQUID tuned detection, conventional Faraday detection, and the Nyquist noise generated by conducting biological samples. A second-generation microtesla MRI system employing a low-noise SQUID is constructed to increase SNR. A 2.4-m cubic, eddy-current shield with 6-mm thick aluminum walls encloses the experiment to attenuate external noise. The measured noise is 0.75 fT Hz-1/2 referred to the bottom gradiometer loop. Solenoids wound from 30-strand braided wire to decrease Nyquist noise and cooled by either liquid nitrogen or water polarize the spins. Copper wire coils wound on wooden supports produce the imaging magnetic fields and field gradients. Water phantom images with 0.8 x 0.8 x 10 mm3 resolution have a SNR of 6. Three-dimensional 1.6 x 1.9 x 14 mm3 images of bell peppers and 3 x 3 x 26 mm3 in vivo images of the human arm are presented. Since contrast based on the transverse spin relaxation rate (T1) is enhanced at low magnetic fields, microtesla MRI could potentially be used for tumor imaging. The

  1. Magnetic field and dielectric environment effects on an exciton trapped by an ionized donor in a spherical quantum dot

    Science.gov (United States)

    Aghoutane, N.; Feddi, E.; El-Yadri, M.; Bosch Bailach, J.; Dujardin, F.; Duque, C. A.

    2017-11-01

    Magnetic field and host dielectric environment effects on the binding energy of an exciton trapped by an ionized donor in spherical quantum dot are investigated. In the framework of the effective mass approximation and by using a variational method, the calculations have been performed by developing a robust ten-terms wave function taking into account the different inter-particles correlations and the distortion of symmetry induced by the orientation of the applied magnetic field. The binding and the localization energies are determined as functions of dot size and magnetic field strength. It appears that the variation of magnetic shift obeys a quadratic law for low magnetic fields regime while, for strong magnetic fields, this shift tends to be linear versus the magnetic field strength. The stability of this complex subjected to a magnetic field is also discussed according to the electron-hole ratio and the dielectric constant of the surrounding medium. A last point to highlight is that the Haynes' rule remains valid even in the presence of an applied magnetic field.

  2. Metal-insulator transition of 2d electron gas in a random magnetic field

    CERN Document Server

    Wang, X R; Liu, D Z

    1999-01-01

    We study the metal-insulator transition of a two-dimensional electron gas in the presence of a random magnetic field from the localization property. The localization length is directly calculated using a transfer matrix technique and finite size scaling analysis. We argue that there is a metal-insulator transition in such a system and show strong numerical evidence that the system undergoes a disorder driven Kosterlitz-Thouless type metal-insulator transition. We will also discuss a mean field theory which maps the random field system into a two-dimensional XY-model. The vortex and antivortex excitations in the XY-model correspond to two different kinds of magnetic domains in the random field system.

  3. Paramagnetic, silicon quantum dots for magnetic resonance and two photon imaging of macrophages

    Science.gov (United States)

    Tu, Chuqiao; Ma, Xuchu; Pantazis, Periklis; Kauzlarich, Susan M.; Louie, Angelique Y.

    2010-01-01

    Quantum dots (QDs) are an attractive platform for building multimodality imaging probes, but the toxicity for typical cadmium QDs limits enthusiasm for their clinical use. Nontoxic, silicon QDs are more promising but tend to require short wavelength excitations which are subject to tissue scattering and autofluorescence artifacts. Herein, we report the synthesis of paramagnetic, manganese-doped, silicon QDs ((SiMn QDs) and demonstrate that they are detectable by both MRI and near infrared excited, two-photon imaging. The SiMn QDs are coated with dextran sulfate to target them to scavenger receptors on macrophages, a biomarker of vulnerable plaques. TEM images show that isolated QDs have an average core diameter of 4.3 ± 1.0 nm and the hydrodynamic diameters of coated nanoparticles range from 8.3 to 43 nm measured by Dynamic Light Scattering (DLS). The SiMn QDs have an r1 relaxivity of 25.50 ± 1.44 mM−1s−1 and an r2 relaxivity of 89.01 ± 3.26 mM−1s−1 (37 °C, 1.4 T). They emit strong fluorescence at 441 nm with a quantum yield of 8.1% in water. Cell studies show that the probes specifically accumulate in macrophages by a receptor-mediated process, are nontoxic to mammalian cells, and produce distinct contrast in both T1-weighted magnetic resonance and single- or two-photon excitation fluorescence images. These QDs have promising diagnostic potential as high macrophage density is associated with atherosclerotic plaques vulnerable to rupture. PMID:20092250

  4. Paramagnetic, silicon quantum dots for magnetic resonance and two-photon imaging of macrophages.

    Science.gov (United States)

    Tu, Chuqiao; Ma, Xuchu; Pantazis, Periklis; Kauzlarich, Susan M; Louie, Angelique Y

    2010-02-17

    Quantum dots (QDs) are an attractive platform for building multimodality imaging probes, but the toxicity for typical cadmium QDs limits enthusiasm for their clinical use. Nontoxic, silicon QDs are more promising but tend to require short-wavelength excitations which are subject to tissue scattering and autofluorescence artifacts. Herein, we report the synthesis of paramagnetic, manganese-doped, silicon QDs (Si(Mn) QDs) and demonstrate that they are detectable by both MRI and near-infrared excited, two-photon imaging. The Si(Mn) QDs are coated with dextran sulfate to target them to scavenger receptors on macrophages, a biomarker of vulnerable plaques. TEM images show that isolated QDs have an average core diameter of 4.3 +/- 1.0 nm and the hydrodynamic diameters of coated nanoparticles range from 8.3 to 43 nm measured by dynamic light scattering (DLS). The Si(Mn) QDs have an r(1) relaxivity of 25.50 +/- 1.44 mM(-1) s(-1) and an r(2) relaxivity of 89.01 +/- 3.26 mM(-1) s(-1) (37 degrees C, 1.4 T). They emit strong fluorescence at 441 nm with a quantum yield of 8.1% in water. Cell studies show that the probes specifically accumulate in macrophages by a receptor-mediated process, are nontoxic to mammalian cells, and produce distinct contrast in both T(1)-weighted magnetic resonance and single- or two-photon excitation fluorescence images. These QDs have promising diagnostic potential as high macrophage density is associated with atherosclerotic plaques vulnerable to rupture.

  5. Physical-layer security analysis of PSK quantum-noise randomized cipher in optically amplified links

    Science.gov (United States)

    Jiao, Haisong; Pu, Tao; Xiang, Peng; Zheng, Jilin; Fang, Tao; Zhu, Huatao

    2017-08-01

    The quantitative security of quantum-noise randomized cipher (QNRC) in optically amplified links is analyzed from the perspective of physical-layer advantage. Establishing the wire-tap channel models for both key and data, we derive the general expressions of secrecy capacities for the key against ciphertext-only attack and known-plaintext attack, and that for the data, which serve as the basic performance metrics. Further, the maximal achievable secrecy rate of the system is proposed, under which secrecy of both the key and data is guaranteed. Based on the same framework, the secrecy capacities of various cases can be assessed and compared. The results indicate perfect secrecy is potentially achievable for data transmission, and an elementary principle of setting proper number of photons and bases is given to ensure the maximal data secrecy capacity. But the key security is asymptotically perfect, which tends to be the main constraint of systemic maximal secrecy rate. Moreover, by adopting cascaded optical amplification, QNRC can realize long-haul transmission with secure rate up to Gb/s, which is orders of magnitude higher than the perfect secrecy rates of other encryption systems.

  6. EMR searching of quantum behavior of magnetic γ-Fe2O3 nanoparticles encapsulated into poly(propylene imine) dendrimer

    National Research Council Canada - National Science Library

    Vorobeva V.E., Domracheva N.E., Gruzdev M.S

    2016-01-01

    ...). It has been shown that the model based on the spin value S = 30, corresponding to the total magnetic moment of the nanoparticle, can be used to interpret the experimental results and the proof of the quantum behavior of γ...

  7. Quantum Anomaly Dissociation of Quasibound States Near the Saddle-Point Ionization Limit of a Rydberg Electron in Crossed Electric and Magnetic Fields

    OpenAIRE

    Zhang, Jian-zu; He, Li-Ming; Zhu, Yun-Xia

    2005-01-01

    In the combination of crossed electric and magnetic fields and the Coulomb field of the atomic nucleus the spectrum of the Rydberg electron in the vicinity of the Stark saddle-point are investigated at a quantum mechanical level. The results expose a quantum anomaly dissociation: quasibound states near and above the saddle-point ionization limit predicted at the semi-classical level disappear at a quantum mechanical level.

  8. QUANTUM HALL-EFFECT IN MULTILAYER P-GE/GE1-XSIX HETEROSTRUCTURES AND ENERGY-SPECTRUM OF THE 2D HOLE GAS IN A MAGNETIC-FIELD

    NARCIS (Netherlands)

    ARAPOV, YG; GORODILOV, NA; NEVEROV, VN; YAKUNIN, MV; GERMANENKO, AV; MINKOV, GM; KUZNETSOV, OA; RUBTSOVA, RA; CHERNOV, AL; ORLOV, LK

    1994-01-01

    The quantum Hall effect and the structure of magnetoresistance oscillations observed in multilayer p-Ge/Ge1-xSix heterostructure systems are analyzed on the basis of a picture of magnetic levels of the Ge valence band calculated from the model of an infinitely deep square quantum well. The odd

  9. Elliptically polarized electromagnetic waves in a magnetized quantum electron-positron plasma with effects of exchange-correlation

    Energy Technology Data Exchange (ETDEWEB)

    Shahmansouri, M., E-mail: mshmansouri@gmail.com [Department of Physics, Faculty of Science, Arak University, Arak 38156-8 8349 (Iran, Islamic Republic of); Misra, A. P., E-mail: apmisra@visva-bharati.ac.in, E-mail: apmisra@gmail.com [Department of Mathematics, Siksha Bhavana, Visva-Bharati University, Santiniketan 731 235, West Bengal (India)

    2016-07-15

    The dispersion properties of elliptically polarized electromagnetic waves in a magnetized electron-positron-pair (EP-pair) plasma are studied with the effects of particle dispersion associated with the Bohm potential, the Fermi degenerate pressure, and the exchange-correlation force. Two possible modes of the extraordinary or X wave, modified by these quantum effects, are identified and their propagation characteristics are investigated numerically. It is shown that the upper-hybrid frequency and the cutoff and resonance frequencies are no longer constants but are dispersive due to these quantum effects. It is found that the particle dispersion and the exchange-correlation force can have different dominating roles on each other depending on whether the X waves are of short or long wavelengths (in comparison with the Fermi Debye length). The present investigation should be useful for understanding the collective behaviors of EP plasma oscillations and the propagation of extraordinary waves in magnetized dense EP-pair plasmas.

  10. Self-consistent mean field theory studies of the thermodynamics and quantum spin dynamics of magnetic Skyrmions.

    Science.gov (United States)

    Wieser, R

    2017-05-04

    A self-consistent mean field theory is introduced and used to investigate the thermodynamics and spin dynamics of an S  =  1 quantum spin system with a magnetic Skyrmion. The temperature dependence of the Skyrmion profile as well as the phase diagram are calculated. In addition, the spin dynamics of a magnetic Skyrmion is described by solving the time dependent Schrödinger equation with additional damping term. The Skyrmion annihilation process driven by an electric field is used to compare the trajectories of the quantum mechanical simulation with a semi-classical description for the spin expectation values using a differential equation similar to the classical Landau-Lifshitz-Gilbert equation.

  11. Elliptically polarized electromagnetic waves in a magnetized quantum electron-positron plasma with effects of exchange-correlation

    CERN Document Server

    Shahmansouri, M

    2016-01-01

    The dispersion properties of elliptically polarized electromagnetic (EM) waves in a magnetized electron-positron-pair (EP-pair) plasma are studied with the effects of particle dispersion associated with the Bohm potential, the Fermi degenerate pressure, and the exchange-correlation force. Two possible modes of the extraordinary or X wave, modified by these quantum effects, are identified and their propagation characteristics are investigated numerically. It is shown that the upper-hybrid frequency, and the cutoff and resonance frequencies are no longer constants but are dispersive due to these quantum effects. It is found that the particle dispersion and the exchange-correlation force can have different dominating roles on each other depending on whether the X waves are of short or long wavelengths (in comparison with the Fermi Debye length). The present investigation should be useful for understanding the collective behaviors of EP plasma oscillations and the propagation of extraordinary waves in magnetized ...

  12. Circuit-quantum electrodynamics with direct magnetic coupling to single-atom spin qubits in isotopically enriched 28Si

    Directory of Open Access Journals (Sweden)

    Guilherme Tosi

    2014-08-01

    Full Text Available Recent advances in silicon nanofabrication have allowed the manipulation of spin qubits that are extremely isolated from noise sources, being therefore the semiconductor equivalent of single atoms in vacuum. We investigate the possibility of directly coupling an electron spin qubit to a superconducting resonator magnetic vacuum field. By using resonators modified to increase the vacuum magnetic field at the qubit location, and isotopically purified 28Si substrates, it is possible to achieve coupling rates faster than the single spin dephasing. This opens up new avenues for circuit-quantum electrodynamics with spins, and provides a pathway for dispersive read-out of spin qubits via superconducting resonators.

  13. Hyperfine-induced hysteretic funnel structure in spin blockaded tunneling current of coupled vertical quantum dots at low magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Leary, A.; Wicha, A.; Harack, B.; Coish, W. A.; Hilke, M. [Department of Physics, McGill University, Ernest Rutherford Building, 3600 rue University, Montreal, Quebec H3A 2T8 (Canada); Yu, G.; Gupta, J. A. [National Research Council of Canada, M50, Montreal Road, Ottawa, Ontario K1A 0R6 (Canada); Payette, C.; Austing, D. G. [Department of Physics, McGill University, Ernest Rutherford Building, 3600 rue University, Montreal, Quebec H3A 2T8, Canada and National Research Council of Canada, M50, Montreal Road, Ottawa, Ontario K1A 0R6 (Canada)

    2013-12-04

    We outline the properties of the hyperfine-induced funnel structure observed in the two-electron spin blockade region of a weakly coupled vertical double quantum dot device. Hysteretic steps in the leakage current occur due to dynamic nuclear polarization when either the bias voltage or the magnetic field is swept up and down. When the bias voltage is swept, an intriguing ∼3 mT wide cusp near 0 T appears in the down-sweep position, and when the magnetic field is swept, the current at 0 T can be switched from 'low' to 'high' as the bias is increased.

  14. Cyclotron resonance in InAs/AlSb quantum wells in magnetic fields up to 45 T

    Energy Technology Data Exchange (ETDEWEB)

    Spirin, K. E., E-mail: spirink@ipmras.ru; Krishtopenko, S. S. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Sadofyev, Yu. G. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Drachenko, O. [Laboratoire National des Champs Magn’etiques Intenses (France); Helm, M. [Forschungszentrum Dresden–Rossendorf, Dresden High-Magnetic-Field Laboratory and Institute of Ion-Beam Physics and Materials Research (Germany); Teppe, F.; Knap, W. [GIS-TERALAB Universite Montpellier II, Laboratoire Charles Coulomb UMR CNRS 5221 (L2C) (France); Gavrilenko, V. I. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2015-12-15

    Electron cyclotron resonance in InAs/AlSb heterostructures with quantum wells of various widths in pulsed magnetic fields up to 45 T are investigated. Our experimental cyclotron energies are in satisfactory agreement with the results of theoretical calculations performed using the eight-band kp Hamiltonian. The shift of the cyclotron resonance (CR) line, which corresponds to the transition from the lowest Landau level to the low magnetic-field region, is found upon varying the electron concentration due to the negative persistent photoconductivity effect. It is shown that the observed shift of the CR lines is associated with the finite width of the density of states at the Landau levels.

  15. Comment on “Surface electromagnetic wave equations in a warm magnetized quantum plasma” [Phys. Plasmas 21, 072114 (2014)

    Energy Technology Data Exchange (ETDEWEB)

    Moradi, Afshin, E-mail: a.moradi@kut.ac.ir [Department of Engineering Physics, Kermanshah University of Technology, Kermanshah (Iran, Islamic Republic of)

    2016-07-15

    In a recent article [C. Li et al., Phys. Plasmas 21, 072114 (2014)], Li et al. studied the propagation of surface waves on a magnetized quantum plasma half-space in the Voigt configuration (in this case, the magnetic field is parallel to the surface but is perpendicular to the direction of propagation). Here, we present a fresh look at the problem and obtain a new form of dispersion relation of surface waves of the system. We find that our new dispersion relation does not agree with the result obtained by Li et al.

  16. Quantum phase transitions and local magnetism in Mott insulators: A local probe investigation using muons, neutrons, and photons

    Science.gov (United States)

    Frandsen, Benjamin A.

    Mott insulators are materials in which strong correlations among the electrons induce an unconventional insulating state. Rich interplay between the structural, magnetic, and electronic degrees of freedom resulting from the electron correlation can lead to unusual complexity of Mott materials on the atomic scale, such as microscopically heterogeneous phases or local structural correlations that deviate significantly from the average structure. Such behavior must be studied by suitable experimental techniques, i.e. "local probes", that are sensitive to this local behavior rather than just the bulk, average properties. In this thesis, I will present results from our studies of multiple families of Mott insulators using two such local probes: muon spin relaxation (muSR), a probe of local magnetism; and pair distribution function (PDF) analysis of x-ray and neutron total scattering, a probe of local atomic structure. In addition, I will present the development of magnetic pair distribution function analysis, a novel method for studying local magnetic correlations that is highly complementary to the muSR and atomic PDF techniques. We used muSR to study the phase transition from Mott insulator to metal in two archetypal Mott insulating systems: RENiO3 (RE = rare earth element) and V2O3. In both of these systems, the Mott insulating state can be suppressed by tuning a nonthermal parameter, resulting in a "quantum" phase transition at zero temperature from the Mott insulating state to a metallic state. In RENiO3, this occurs through variation of the rare-earth element in the chemical composition; in V 2O3, through the application of hydrostatic pressure. Our results show that the metallic and Mott insulating states unexpectedly coexist in phase-separated regions across a large portion of parameter space near the Mott quantum phase transition and that the magnitude of the ordered antiferromagnetic moment remains constant across the phase diagram until it is abruptly

  17. Randomized and quantum algorithms for solving initial-value problems in ordinary differential equations of order k

    Directory of Open Access Journals (Sweden)

    Maciej Goćwin

    2008-01-01

    Full Text Available The complexity of initial-value problems is well studied for systems of equations of first order. In this paper, we study the \\(\\varepsilon\\-complexity for initial-value problems for scalar equations of higher order. We consider two models of computation, the randomized model and the quantum model. We construct almost optimal algorithms adjusted to scalar equations of higher order, without passing to systems of first order equations. The analysis of these algorithms allows us to establish upper complexity bounds. We also show (almost matching lower complexity bounds. The \\(\\varepsilon\\-complexity in the randomized and quantum setting depends on the regularity of the right-hand side function, but is independent of the order of equation. Comparing the obtained bounds with results known in the deterministic case, we see that randomized algorithms give us a speed-up by \\(1/2\\, and quantum algorithms by \\(1\\ in the exponent. Hence, the speed-up does not depend on the order of equation, and is the same as for the systems of equations of first order. We also include results of some numerical experiments which confirm theoretical results.

  18. Phonon Confinement Effect on the Binding Energy of a Hydrogenic Impurity in Quantum Wires in the Electric and Magnetic Fields

    Science.gov (United States)

    Shahbandari, Abbas

    The effect of phonon confinement on ground state binding energy of bound polaron in polar quantum wires with a finite confining potential investigated by Landau-Pekar variation technique. The effect of external electric and magnetic fields is taken into account as well. The obtained results show that the polar optical phonon confinement leads to a considerable enhancement of the polaron effect and these corrections increase with increasing of applied fields.

  19. Magnetic localization and orientation of the capsule endoscope based on a random complex algorithm

    Directory of Open Access Journals (Sweden)

    He XQ

    2015-04-01

    Full Text Available Xiaoqi He,1 Zizhao Zheng,1,2 Chao Hu1 1Ningbo Institute of Technology, Zhejiang University, Ningbo, People's Republic of China; 2Taiyuan University of Science and Technology, Taiyuan, People's Republic of China Abstract: The development of the capsule endoscope has made possible the examination of the whole gastrointestinal tract without much pain. However, there are still some important problems to be solved, among which, one important problem is the localization of the capsule. Currently, magnetic positioning technology is a suitable method for capsule localization, and this depends on a reliable system and algorithm. In this paper, based on the magnetic dipole model as well as magnetic sensor array, we propose nonlinear optimization algorithms using a random complex algorithm, applied to the optimization calculation for the nonlinear function of the dipole, to determine the three-dimensional position parameters and two-dimensional direction parameters. The stability and the antinoise ability of the algorithm is compared with the Levenberg–Marquart algorithm. The simulation and experiment results show that in terms of the error level of the initial guess of magnet location, the random complex algorithm is more accurate, more stable, and has a higher “denoise” capacity, with a larger range for initial guess values. Keywords: wireless capsule endoscope, magnet, optimization 

  20. Enhancement and sign change of magnetic correlations in a driven quantum many-body system.

    Science.gov (United States)

    Görg, Frederik; Messer, Michael; Sandholzer, Kilian; Jotzu, Gregor; Desbuquois, Rémi; Esslinger, Tilman

    2018-01-24

    Periodic driving can be used to control the properties of a many-body state coherently and to realize phases that are not accessible in static systems. For example, exposing materials to intense laser pulses makes it possible to induce metal-insulator transitions, to control magnetic order and to generate transient superconducting behaviour well above the static transition temperature. However, pinning down the mechanisms underlying these phenomena is often difficult because the response of a material to irradiation is governed by complex, many-body dynamics. For static systems, extensive calculations have been performed to explain phenomena such as high-temperature superconductivity. Theoretical analyses of driven many-body Hamiltonians are more challenging, but approaches have now been developed, motivated by recent observations. Here we report an experimental quantum simulation in a periodically modulated hexagonal lattice and show that antiferromagnetic correlations in a fermionic many-body system can be reduced, enhanced or even switched to ferromagnetic correlations (sign reversal). We demonstrate that the description of the many-body system using an effective Floquet-Hamiltonian with a renormalized tunnelling energy remains valid in the high-frequency regime by comparing the results to measurements in an equivalent static lattice. For near-resonant driving, the enhancement and sign reversal of correlations is explained by a microscopic model of the system in which the particle tunnelling and magnetic exchange energies can be controlled independently. In combination with the observed sufficiently long lifetimes of the correlations in this system, periodic driving thus provides an alternative way of investigating unconventional pairing in strongly correlated systems experimentally.

  1. Inelastic electron and Raman scattering from the collective excitations in quantum wires: Zero magnetic field

    Directory of Open Access Journals (Sweden)

    Manvir S. Kushwaha

    2013-04-01

    Full Text Available The nanofabrication technology has taught us that an m-dimensional confining potential imposed upon an n-dimensional electron gas paves the way to a quasi-(n-m-dimensional electron gas, with m ⩽ n and 1 ⩽ n, m ⩽ 3. This is the road to the (semiconducting quasi-n dimensional electron gas systems we have been happily traversing on now for almost two decades. Achieving quasi-one dimensional electron gas (Q-1DEG [or quantum wire(s for more practical purposes] led us to some mixed moments in this journey: while the reduced phase space for the scattering led us believe in the route to the faster electron devices, the proximity to the 1D systems left us in the dilemma of describing it as a Fermi liquid or as a Luttinger liquid. No one had ever suspected the potential of the former, but it took quite a while for some to convince the others on the latter. A realistic Q-1DEG system at the low temperatures is best describable as a Fermi liquid rather than as a Luttinger liquid. In the language of condensed matter physics, a critical scrutiny of Q-1DEG systems has provided us with a host of exotic (electronic, optical, and transport phenomena unseen in their higher- or lower-dimensional counterparts. This has motivated us to undertake a systematic investigation of the inelastic electron scattering (IES and the inelastic light scattering (ILS from the elementary electronic excitations in quantum wires. We begin with the Kubo's correlation functions to derive the generalized dielectric function, the inverse dielectric function, and the Dyson equation for the dynamic screened potential in the framework of Bohm-Pines’ random-phase approximation. These fundamental tools then lead us to develop methodically the theory of IES and ILS for the Q-1DEG systems. As an application of the general formal results, which know no bounds regarding the subband occupancy, we compute the density of states, the Fermi energy, the full excitation spectrum [comprised of

  2. Quantum spin liquid and magnetic order in a two-dimensional nonsymmorphic lattice: Considering the distorted kagome lattice of volborthite

    Science.gov (United States)

    Chern, Li Ern; Hwang, Kyusung; Mizoguchi, Tomonari; Huh, Yejin; Kim, Yong Baek

    2017-07-01

    The Kagome-lattice-based material, volborthite, Cu3V2O7(OH) 2.2 H2O , has been considered as a promising platform for discovery of unusual quantum ground states due to the frustrated nature of spin interaction. We explore possible quantum spin liquid and magnetically ordered phases in a two-dimensional nonsymmorphic lattice, which is described by the plane group p 2 g g , consistent with the spatial anisotropy of the spin model derived from density functional theory (DFT) for volborthite. Using the projective symmetry group (PSG) analysis and Schwinger boson mean field theory, we classify possible spin liquid phases with bosonic spinons and investigate magnetically ordered phases connected to such states. It is shown, in general, that only translationally invariant mean field spin liquid ansatzes are allowed in two-dimensional nonsymmorphic lattices. We study the mean field phase diagram of the DFT-derived spin model and find that possible quantum spin liquid phases are connected to two types of magnetically ordered phases, a coplanar incommensurate (q ,0 ) spiral order as the ground state and a closely competing coplanar commensurate (π ,π ) spin density wave order. In addition, periodicity enhancement of the two-spinon continuum, a consequence of symmetry fractionalization, is found in the spin liquid state connected to the (π ,π ) spin density wave order. We discuss relevance of these results to recent and future experiments on volborthite.

  3. Magnetic phase diagram and quantum phase transitions in a two-species boson model

    Science.gov (United States)

    Belemuk, A. M.; Chtchelkatchev, N. M.; Mikheyenkov, A. V.; Kugel, K. I.

    2017-09-01

    We analyze the possible types of ordering in a boson-fermion model. The Hamiltonian is inherently related to the Bose-Hubbard model for vector two-species bosons in optical lattices. We show that such a model can be reduced to the Kugel-Khomskii type spin-pseudospin model, but in contrast to the usual version of the latter model, we are dealing here with the case of spin S =1 and pseudospin 1 /2 . We show that the interplay of spin and pseudospin degrees of freedom leads to a rather nontrivial magnetic phase diagram including the spin-nematic configurations. Tuning the spin-channel interaction parameter Us gives rise to quantum phase transitions. We find that the ground state of the system always has the pseudospin domain structure. On the other hand, the sign change of Us switches the spin arrangement of the ground state within domains from a ferro- to antiferromagnetic one. Finally, we revisit the spin (pseudospin)-1/2 Kugel-Khomskii model and see the inverse picture of phase transitions.

  4. Plastic-adherent DNA aptamer-magnetic bead and quantum dot sandwich assay for Campylobacter detection.

    Science.gov (United States)

    Bruno, John G; Phillips, Taylor; Carrillo, Maria P; Crowell, Randy

    2009-05-01

    DNA aptamers were developed against MgCl(2)-extracted surface proteins from Campylobacter jejuni. The two highest affinity aptamers were selected for use in a magnetic bead (MB) and red quantum dot (QD)-based sandwich assay scheme. The assay was evaluated using both heat-killed and live C. jejuni and exhibits detection limits as low as an average of 2.5 colony forming unit (cfu) equivalents in buffer and 10-250 cfu in various food matrices. The assay exhibits low cross-reactivity with bacterial species outside the Campylobacter genus, but exhibits substantial cross-reactivity with C. coli and C. lari. The assay was evaluated with a spectrofluorometer and a commercially available handheld fluorometer, which yielded comparable detection limits and ranges. Remarkably, the sandwich assay components adhere to the inside face of polystyrene cuvettes even in food matrices near neutral pH, thereby enabling a rapid homogeneous assay, because fluorescence is concentrated to a small, thin planar area and background fluorescence from the bulk solution is minimized. The plastic cuvette-adherent technology coupled to a sensitive handheld fluorometer may enable rapid (15-20 min), portable detection of foodborne pathogens from "farm-to-fork" by obviating the slow enrichment culture phase used by other food safety tests.

  5. Magnetic monopole plasma phase in (2+1)d compact quantum electrodynamics with fermionic matter

    CERN Document Server

    Armour, Wesley; Kogut, John B; Lucini, Biagio; Strouthos, Costas; Vranas, Pavlos

    2011-01-01

    We present the first evidence from lattice simulations that the magnetic monopoles in three dimensional compact quantum electrodynamics (cQED3) with N_f=2 and N_f= 4 four-component fermion flavors are in a plasma phase. The evidence is based mainly on the divergence of the monopole susceptibility (polarizability) with the lattice size at weak gauge couplings. A weak four-Fermi term added to the cQED3 action enabled simulations with massless fermions. The exact chiral symmetry of the interaction terms forbids symmetry breaking lattice discretization counterterms to appear in the theory's effective action. It is also shown that the scenario of a monopole plasma does not depend on the strength of the four-Fermi coupling. Other observables such as the densities of "isolated" dipoles and monopoles and the so-called specific heat show that a crossover from a dense monopole plasma to a dilute monopole gas occurs at strong couplings. The implications of our results on the stability of U(1) spin liquids in two spatial...

  6. Microstructure and random magnetic anisotropy in Fe-Ni based nanocrystalline thin films

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, Senoy; Anantharaman, M R [Department of Physics, Cochin University of Science and Technology, Cochin, India-682022 (India); Al-Harthi, S H; Al-Omari, I A [Department of Physics, College of Science, Sultan Qaboos University, PO Box 36, Postal Code 123, Muscat, Sultanate of Oman (Oman); Sakthikumar, D; Yoshida, Yasuhiko [Bio-Nano Electronics Research Centre, Department of Applied Chemistry, Toyo University, Kawagoe, Saitama 350-8585 (Japan); Ramanujan, R V [School of Materials Science and Engineering, Nanyang Avenue, Nanyang Technological University, Singapore 639798 (Singapore)], E-mail: senoythomas@yahoo.co.in, E-mail: mra@cusat.ac.in

    2008-08-07

    Nanocrystalline Fe-Ni thin films were prepared by partial crystallization of vapour deposited amorphous precursors. The microstructure was controlled by annealing the films at different temperatures. X-ray diffraction, transmission electron microscopy and energy dispersive x-ray spectroscopy investigations showed that the nanocrystalline phase was that of Fe-Ni. Grain growth was observed with an increase in the annealing temperature. X-ray photoelectron spectroscopy observations showed the presence of a native oxide layer on the surface of the films. Scanning tunnelling microscopy investigations support the biphasic nature of the nanocrystalline microstructure that consists of a crystalline phase along with an amorphous phase. Magnetic studies using a vibrating sample magnetometer show that coercivity has a strong dependence on grain size. This is attributed to the random magnetic anisotropy characteristic of the system. The observed coercivity dependence on the grain size is explained using a modified random anisotropy model.

  7. Critical side channel effects in random bit generation with multiple semiconductor lasers in a polarization-based quantum key distribution system.

    Science.gov (United States)

    Ko, Heasin; Choi, Byung-Seok; Choe, Joong-Seon; Kim, Kap-Joong; Kim, Jong-Hoi; Youn, Chun Ju

    2017-08-21

    Most polarization-based BB84 quantum key distribution (QKD) systems utilize multiple lasers to generate one of four polarization quantum states randomly. However, random bit generation with multiple lasers can potentially open critical side channels that significantly endangers the security of QKD systems. In this paper, we show unnoticed side channels of temporal disparity and intensity fluctuation, which possibly exist in the operation of multiple semiconductor laser diodes. Experimental results show that the side channels can enormously degrade security performance of QKD systems. An important system issue for the improvement of quantum bit error rate (QBER) related with laser driving condition is further addressed with experimental results.

  8. Quantum Cryptography Beyond Quantum Key Distribution

    OpenAIRE

    Broadbent, A.; Schaffner, C

    2015-01-01

    textabstractQuantum cryptography is the art and science of exploiting quantum mechanical effects in order to perform cryptographic tasks. While the most well-known example of this discipline is quantum key distribution (QKD), there exist many other applications such as quantum money, randomness generation, secure two- and multi-party computation and delegated quantum computation. Quantum cryptography also studies the limitations and challenges resulting from quantum adversaries—including the ...

  9. Distortion of the Stoner-Wohlfarth Astroid by Perpendicular Polarizer in Magnetic Random Access Memory

    Science.gov (United States)

    Chang, Jui-Hang; Chang, Ching-Ray

    2012-02-01

    For a spin-transfer-torque (STT) magnetic random access memory (MRAM) with a perpendicular polarizer under an external in-plane magnetic field, a distorted astroid of critical strength of STT and field is derived from an one-dimensional effective free energy. The modified astroid not only separates the multiple stable states from the monostable state, but also delimit the region of dynamical stable state as the STT achieving a critical magnitude. Taking into account of the STT, multiple-step magnetization switching of the STT-MRAM has been investigated. We gave a phase diagram for the single-step, double-step, and triple-step switchings, which are observed at a certain range of the external field angle and of the current density.

  10. Second and third harmonic generation associated to infrared transitions in a Morse quantum well under applied electric and magnetic fields

    Science.gov (United States)

    Restrepo, R. L.; Kasapoglu, E.; Sakiroglu, S.; Ungan, F.; Morales, A. L.; Duque, C. A.

    2017-09-01

    The effects of electric and magnetic fields on the second and third harmonic generation coefficients in a Morse potential quantum well are theoretically studied. The energy levels and corresponding wave functions are obtained by solving the Schrödinger equation for the electron in the parabolic band scheme and effective mass approximations and the envelope function approach. The results show that both the electric and the magnetic fields have significant influence on the magnitudes and resonant peak energy positions of the second and third harmonic generation responses. In general, the Morse potential profile becomes wider and shallower as γ -parameter increases and so the energies of the bound states will be functions of this parameter. Therefore, we can conclude that the effects of the electric and magnetic fields can be used to tune and control the optical properties of interest in the range of the infrared electromagnetic spectrum.

  11. Combined effects of magnetic and electric fields on the interband optical transitions in InAs/InP quantum wire

    Science.gov (United States)

    Saravanan, S.; John Peter, A.; Lee, ChangWoo

    2015-03-01

    Combined effects of magnetic and electric fields on the confined exciton in an InAs1-xPx/InP (x=0.2) quantum well wire are investigated taking into account the geometrical confinement effect. Variational formulism, within the frame work of effective mass approximation, is applied to obtain the exciton binding energy. The second order harmonic generation and the optical gain are carried out using compact density method. The strain effects are included with the confinement potential in the Hamiltonian. The energy difference of the ground and the first excited state is found in the presence of magnetic and electric fields taking into the consideration of spatial confinement effect. The result shows that the optical properties are more influenced taking into account the effects of geometrical confinement, magnetic field and electric field. It is shown that the telecommunication wavelength can be achieved with the suitable doping barrier material with the wire material and the external perturbations.

  12. Hyperfine-interaction-driven suppression of quantum tunneling at zero field in a holmium(III) single-ion magnet

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yan-Cong; Liu, Jun-Liang; Chen, Xiao-Ming; Tong, Ming-Liang [Key Lab. of Bioinorganic and Synthetic Chemistry of Ministry of Education, School of Chemistry, Sun Yat-Sen Univ., Guangzhou (China); Wernsdorfer, Wolfgang [Institut Neel, CNRS and Universite Joseph Fournier, Grenoble (France); Institute of Nanotechnology, Karlsruhe Institute of Technology (Germany); Physikalisches Institut, Karlsruhe Institute of Technology (Germany); Liu, Dan; Chibotaru, Liviu F. [Theory of Nanomaterials Group and INPAC-Institute of Nanoscale Physics and Chemistry, Katholieke Universiteit Leuven (Belgium)

    2017-04-24

    An extremely rare non-Kramers holmium(III) single-ion magnet (SIM) is reported to be stabilized in the pentagonal-bipyramidal geometry by a phosphine oxide with a high energy barrier of 237(4) cm{sup -1}. The suppression of the quantum tunneling of magnetization (QTM) at zero field and the hyperfine structures originating from field-induced QTMs can be observed even from the field-dependent alternating-current magnetic susceptibility in addition to single-crystal hysteresis loops. These dramatic dynamics were attributed to the combination of the favorable crystal-field environment and the hyperfine interactions arising from {sup 165}Ho (I=7/2) with a natural abundance of 100 %. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Open Quantum Random Walks on the Half-Line: The Karlin-McGregor Formula, Path Counting and Foster's Theorem

    Science.gov (United States)

    Jacq, Thomas S.; Lardizabal, Carlos F.

    2017-09-01

    In this work we consider open quantum random walks on the non-negative integers. By considering orthogonal matrix polynomials we are able to describe transition probability expressions for classes of walks via a matrix version of the Karlin-McGregor formula. We focus on absorbing boundary conditions and, for simpler classes of examples, we consider path counting and the corresponding combinatorial tools. A non-commutative version of the gambler's ruin is studied by obtaining the probability of reaching a certain fortune and the mean time to reach a fortune or ruin in terms of generating functions. In the case of the Hadamard coin, a counting technique for boundary restricted paths in a lattice is also presented. We discuss an open quantum version of Foster's Theorem for the expected return time together with applications.

  14. Structure-Related Optical Fingerprints in the Absorption Spectra of Colloidal Quantum Dots: Random Alloy vs. Core/Shell Systems

    CERN Document Server

    Mourad, Daniel

    2016-01-01

    We argue that the experimentally easily accessible optical absorption spectrum can often be used to distinguish between a random alloy phase and a stoichiometrically equivalent core/shell realization of ensembles of monodisperse colloidal semiconductor quantum dots without the need for more advanced structural characterization tools. Our proof-of-concept is performed by conceptually straightforward exact-disorder tight-binding calculations. The underlying stochastical tight-binding scheme only parametrizes bulk band structure properties and does not employ additional free parameters to calculate the optical absorption spectrum, which is an easily accessible experimental property. The method is applied to selected realizations of type-I Cd(Se,S) and type-II (Zn,Cd)(Se,S) alloyed quantum dots with an underlying zincblende crystal structure and the corresponding core/shell counterparts.

  15. Open Quantum Random Walks on the Half-Line: The Karlin-McGregor Formula, Path Counting and Foster's Theorem

    Science.gov (United States)

    Jacq, Thomas S.; Lardizabal, Carlos F.

    2017-11-01

    In this work we consider open quantum random walks on the non-negative integers. By considering orthogonal matrix polynomials we are able to describe transition probability expressions for classes of walks via a matrix version of the Karlin-McGregor formula. We focus on absorbing boundary conditions and, for simpler classes of examples, we consider path counting and the corresponding combinatorial tools. A non-commutative version of the gambler's ruin is studied by obtaining the probability of reaching a certain fortune and the mean time to reach a fortune or ruin in terms of generating functions. In the case of the Hadamard coin, a counting technique for boundary restricted paths in a lattice is also presented. We discuss an open quantum version of Foster's Theorem for the expected return time together with applications.

  16. N-(sulfoethyl) iminodiacetic acid-based lanthanide coordination polymers: Synthesis, magnetism and quantum Monte Carlo studies

    Energy Technology Data Exchange (ETDEWEB)

    Zhuang Guilin, E-mail: glzhuang@zjut.edu.cn [Institute of Industrial Catalysis, College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310032 (China); Chen Wulin [Institute of Industrial Catalysis, College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310032 (China); Zheng Jun [Center of Modern Experimental Technology, Anhui University, Hefei 230039 (China); Yu Huiyou [Institute of Industrial Catalysis, College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310032 (China); Wang Jianguo, E-mail: jgw@zjut.edu.cn [Institute of Industrial Catalysis, College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310032 (China)

    2012-08-15

    A series of lanthanide coordination polymers have been obtained through the hydrothermal reaction of N-(sulfoethyl) iminodiacetic acid (H{sub 3}SIDA) and Ln(NO{sub 3}){sub 3} (Ln=La, 1; Pr, 2; Nd, 3; Gd, 4). Crystal structure analysis exhibits that lanthanide ions affect the coordination number, bond length and dimension of compounds 1-4, which reveal that their structure diversity can be attributed to the effect of lanthanide contraction. Furthermore, the combination of magnetic measure with quantum Monte Carlo(QMC) studies exhibits that the coupling parameters between two adjacent Gd{sup 3+} ions for anti-anti and syn-anti carboxylate bridges are -1.0 Multiplication-Sign 10{sup -3} and -5.0 Multiplication-Sign 10{sup -3} cm{sup -1}, respectively, which reveals weak antiferromagnetic interaction in 4. - Graphical abstract: Four lanthanide coordination polymers with N-(sulfoethyl) iminodiacetic acid were obtained under hydrothermal condition and reveal the weak antiferromagnetic coupling between two Gd{sup 3+} ions by Quantum Monte Carlo studies. Highlights: Black-Right-Pointing-Pointer Four lanthanide coordination polymers of H{sub 3}SIDA ligand were obtained. Black-Right-Pointing-Pointer Lanthanide ions play an important role in their structural diversity. Black-Right-Pointing-Pointer Magnetic measure exhibits that compound 4 features antiferromagnetic property. Black-Right-Pointing-Pointer Quantum Monte Carlo studies reveal the coupling parameters of two Gd{sup 3+} ions.

  17. From Random Telegraph to Gaussian Stochastic Noises: Decoherence and Spectral Diffusion in a Semiconductor Quantum Dot

    Directory of Open Access Journals (Sweden)

    A. Berthelot

    2010-01-01

    We emphasize the generality and the versatility of our model where the inclusion of asymmetric jump processes appears as an essential extension for the understanding of semiconductor quantum dot physics.

  18. Analytic Theory and Numerical Study of the Magnetic Field Line Random Walk in Reduced Magnetohydrodynamic Turbulence

    Science.gov (United States)

    Ruffolo, D. J.; Snodin, A. P.; Oughton, S.; Servidio, S.; Matthaeus, W. H.

    2013-12-01

    The random walk of magnetic field lines is examined analytically and numerically in the context of reduced magnetohydrodynamic (RMHD) turbulence, which provides a useful description of plasmas dominated by a strong mean field, such as in the solar corona. A nonperturbative theory of magnetic field line diffusion [1] is compared with the diffusion coefficients obtained by accurate numerical tracing of magnetic field lines for both synthetic models and direct numerical simulations of RMHD. Statistical analysis of an ensemble of trajectories confirms the applicability of the theory, which very closely matches the numerical field line diffusion coefficient as a function of distance z along the mean magnetic field for a wide range of the Kubo number R. The theory employs Corrsin's independence hypothesis, sometimes thought to be valid only at low R. However, the results demonstrate that it works well up to R=10, both for a synthetic RMHD model and an RMHD simulation. The numerical results from RMHD simulation are compared with and without phase randomization, demonstrating an effect of coherent structures on the field line random walk for low Kubo number. Partially supported by a postdoctoral fellowship from Mahidol University, the Thailand Research Fund, POR Calabria FSE-2007/2013, the US NSF (AGS-1063439 and SHINE AGS-1156094), NASA (Heliophysics Theory NNX08AI47G & NNX11AJ44G), by the Solar Probe Plus Project through the ISIS Theory team, by the MMS Theory and Modeling team, and by EU Marie Curie Project FP7 PIRSES-2010-269297 'Turboplasmas' at Università della Calabria. [1] D. Ruffolo and W. H. Matthaeus, Phys. Plasmas, 20, 012308 (2013).

  19. General classical and quantum-mechanical description of magnetic resonance: an application to electric-dipole-moment experiments

    Science.gov (United States)

    Silenko, Alexander J.

    2017-05-01

    A general theoretical description of a magnetic resonance is presented. This description is necessary for a detailed analysis of spin dynamics in electric-dipole-moment experiments in storage rings. General formulas describing a behavior of all components of the polarization vector at the magnetic resonance are obtained for an arbitrary initial polarization. These formulas are exact on condition that the nonresonance rotating field is neglected. The spin dynamics is also calculated at frequencies far from resonance with allowance for both rotating fields. A general quantum-mechanical analysis of the spin evolution at the magnetic resonance is fulfilled and the full agreement between the classical and quantum-mechanical approaches is shown. Quasimagnetic resonances for particles and nuclei moving in noncontinuous perturbing fields of accelerators and storage rings are considered. Distinguishing features of quasimagnetic resonances in storage ring electric-dipole-moment experiments are investigated in detail. The exact formulas for the effect caused by the electric dipole moment are derived. The difference between the resonance effects conditioned by the rf electric-field flipper and the rf Wien filter is found and is calculated for the first time. The existence of this difference is crucial for the establishment of a consent between analytical derivations and computer simulations and for checking spin tracking programs. The main systematical errors are considered.

  20. Heat capacity peak at the quantum critical point of the transverse Ising magnet CoNb2O6.

    Science.gov (United States)

    Liang, Tian; Koohpayeh, S M; Krizan, J W; McQueen, T M; Cava, R J; Ong, N P

    2015-07-06

    The transverse Ising magnet Hamiltonian describing the Ising chain in a transverse magnetic field is the archetypal example of a system that undergoes a transition at a quantum critical point (QCP). The columbite CoNb2O6 is the closest realization of the transverse Ising magnet found to date. At low temperatures, neutron diffraction has observed a set of discrete collective spin modes near the QCP. Here, we ask if there are low-lying spin excitations distinct from these relatively high-energy modes. Using the heat capacity, we show that a significant band of gapless spin excitations exists. At the QCP, their spin entropy rises to a prominent peak that accounts for 30% of the total spin degrees of freedom. In a narrow field interval below the QCP, the gapless excitations display a fermion-like, temperature-linear heat capacity below 1 K. These novel gapless modes are the main spin excitations participating in, and affected by, the quantum transition.

  1. General classical and quantum-mechanical description of magnetic resonance: an application to electric-dipole-moment experiments

    Energy Technology Data Exchange (ETDEWEB)

    Silenko, Alexander J. [Belarusian State University, Research Institute for Nuclear Problems, Minsk (Belarus); Joint Institute for Nuclear Research, Bogoliubov Laboratory of Theoretical Physics, Dubna (Russian Federation)

    2017-05-15

    A general theoretical description of a magnetic resonance is presented. This description is necessary for a detailed analysis of spin dynamics in electric-dipole-moment experiments in storage rings. General formulas describing a behavior of all components of the polarization vector at the magnetic resonance are obtained for an arbitrary initial polarization. These formulas are exact on condition that the nonresonance rotating field is neglected. The spin dynamics is also calculated at frequencies far from resonance with allowance for both rotating fields. A general quantum-mechanical analysis of the spin evolution at the magnetic resonance is fulfilled and the full agreement between the classical and quantum-mechanical approaches is shown. Quasimagnetic resonances for particles and nuclei moving in noncontinuous perturbing fields of accelerators and storage rings are considered. Distinguishing features of quasimagnetic resonances in storage ring electric-dipole-moment experiments are investigated in detail. The exact formulas for the effect caused by the electric dipole moment are derived. The difference between the resonance effects conditioned by the rf electric-field flipper and the rf Wien filter is found and is calculated for the first time. The existence of this difference is crucial for the establishment of a consent between analytical derivations and computer simulations and for checking spin tracking programs. The main systematical errors are considered. (orig.)

  2. The effects of random field at surface on the magnetic properties in the Ising nanotube and nanowire

    Science.gov (United States)

    Kaneyoshi, T.

    2016-12-01

    The phase diagrams and temperature dependences of total magnetization mT in two nanosystems (nanotube and nanowire) with a random magnetic field at the surface shell are studied by the uses of the effective-field theory with correlations. Some characteristic phenomena (reentrant phenomena and unconventional thermal variation of total magnetization) are found in the two systems. They are rather different between the two systems, which mainly come from the structural differences of the cores

  3. Quantum anomalous Hall effect and a nontrivial spin-texture in ultra-thin films of magnetic topological insulators

    Energy Technology Data Exchange (ETDEWEB)

    Duong, Le Quy; Das, Tanmoy; Feng, Y. P.; Lin, Hsin, E-mail: nilnish@gmail.com [Graphene Research Centre and Department of Physics, National University of Singapore, Singapore 117546 (Singapore)

    2015-05-07

    We study the evolution of quantum anomalous Hall (QAH) effect for a Z{sub 2} topological insulator (TI) thin films in a proximity induced magnetic phase by a realistic layered k·p model with interlayer coupling. We examine three different magnetic configurations in which ferromagnetic (FM) layer(s) is added either from one side (FM-TI), from both sides (FM-TI-FM), or homogeneously distributed (magnetically doped) in a TI slab. We map out the thickness-dependent topological phase diagram under various experimental conditions. The critical magnetic exchange energy for the emergence of QAH effect in the latter two cases decreases monotonically with increasing number of quintuple layers (QLs), while it becomes surprisingly independent of the film thickness in the former case. The gap size of the emergent QAH insulator depends on the non-magnetic “parent” gap of the TI thin film and is tuned by the FM exchange energy, opening a versatile possibility to achieve room-temperature QAH insulator in various topological nanomaterials. Finally, we find that the emergent spin-texture in the QAH effect is very unconventional, non-“hedgehog” type; and it exhibits a chiral out-of-plane spin-flip texture within the same valence band which is reminiscent of dynamical “skyrmion” pattern, except our results are in the momentum space.

  4. Unveiling magnetic interactions of ruthenium trichloride via constraining direction of orbital moments: Potential routes to realize a quantum spin liquid

    Science.gov (United States)

    Hou, Y. S.; Xiang, H. J.; Gong, X. G.

    2017-08-01

    Recent experiments reveal that the honeycomb ruthenium trichloride α -RuC l3 is a prime candidate of the Kitaev quantum spin liquid (QSL). However, there is no theoretical model which can properly describe its experimental dynamical response due to the lack of a full understanding of its magnetic interactions. Here, we propose a general scheme to calculate the magnetic interactions in systems (e.g., α -RuC l3 ) with nonnegligible orbital moments by constraining the directions of orbital moments. With this scheme, we put forward a minimal J1-K1-Γ1-J3-K3 model for α -RuC l3 and find that: (I) The third nearest neighbor (NN) antiferromagnetic Heisenberg interaction J3 stabilizes the zigzag antiferromagnetic order; (II) The NN symmetric off-diagonal exchange Γ1 plays a pivotal role in determining the preferred direction of magnetic moments and generating the spin wave gap. An exact diagonalization study on this model shows that the Kitaev QSL can be realized by suppressing the NN symmetric off-diagonal exchange Γ1 and the third NN Heisenberg interaction J3. Thus, we not only propose a powerful general scheme for investigating the intriguing magnetism of Jeff=1 /2 magnets, but also point out future directions for realizing the Kitaev QSL in the honeycomb ruthenium trichloride α -RuC l3 .

  5. Unconventional superconductivity and an ambient-pressure magnetic quantum critical point in single-crystal LaNiC2

    Science.gov (United States)

    Landaeta, J. F.; Subero, D.; Machado, P.; Honda, F.; Bonalde, I.

    2017-11-01

    Superconductivity in noncentrosymmetric LaNiC2 is expected to be induced by electron-phonon interactions due to its lack of magnetic instabilities. The non-Bardeen-Cooper-Schrieffer (BCS) behaviors found in this material call into question the long-standing idea that relates unconventional superconductivity with magnetic interactions. Here we report magnetic penetration-depth measurements in a high-purity single crystal of LaNiC2 at pressures up to 2.5 GPa and temperatures down to 0.04 K. At ambient pressure and below 0.5 Tc the penetration depth goes as T4 for the in-plane and T2 for the out-of-plane component, firmly implying the existence of point nodes in the energy gap and the unconventional character of this superconductor. The present study also provides evidence of magnetism in LaNiC2 by unraveling a pressure-induced antiferromagnetic phase inside the superconducting state at temperatures below 0.5 K, with a quantum critical point around ambient pressure. The results presented here maintain a solid base for the notion that unconventional superconductivity only arises near magnetic order or fluctuations.

  6. Role of spin-orbit interaction in the chemical potential of quantum dots in a magnetic field

    Science.gov (United States)

    Emperador, Agustí; Lipparini, E.; Pederiva, F.

    2004-09-01

    We have studied the relevance of spin-orbit coupling to the chemical potential of semiconductor dots submitted to a perpendicularly applied magnetic field B . The energy of the ground state of the dot is calculated within Hartree-Fock (HF), local spin-density functional theory (LSDA) and fixed phase quantum Monte Carlo (FP-DMC) and the interplay between spin-orbit and exchange-correlation interactions is carefully investigated. The results are compared with the experimental curves obtained by means of conductance spectroscopy.

  7. Controlled synthesis of Eu2+ and Eu3+ doped ZnS quantum dots and their photovoltaic and magnetic properties

    OpenAIRE

    Sabit Horoz; Baichhabi Yakami; Uma Poudyal; Jon M. Pikal; Wenyong Wang; Jinke Tang

    2016-01-01

    Eu-doped ZnS quantum dots (QDs) have been synthesized by wet-chemical method and found to form in zinc blende (cubic) structure. Both Eu2+ and Eu3+ doped ZnS can be controllably synthesized. The Eu2+ doped ZnS QDs show broad photoluminescence emission peak around 512 nm, which is from the Eu2+ intra-ion transition of 4f6d1 – 4f7, while the Eu3+ doped samples exhibit narrow emission lines characteristic of transitions between the 4f levels. The investigation of the magnetic properties shows th...

  8. Quantum random number generator based on ‘Fermi–Dirac’ statistics of photocounts of faint laser pulses with a 75 Mbit s‑1 rate

    Science.gov (United States)

    Balygin, K. A.; Zaitsev, V. I.; Klimov, A. N.; Kulik, S. P.; Molotkov, S. N.; Popova, E.; Vinogradov, S.

    2017-12-01

    We implemented experimentally a quantum random number generator, based on the registration of quasi-single-photon light by a silicon photo-multiplier, which allows one to reliably achieve the Poisson statistics of photocounts. The use of the optimal grouping of photocounts and a polynomial-length sequence of the method for extracting the random sequence 0 and 1 made it possible to achieve the output rate of a provably random sequence up to 75 Mbit s-1 .

  9. Quantum criticality out of equilibrium: steady state in a magnetic single-electron transistor.

    Science.gov (United States)

    Kirchner, Stefan; Si, Qimiao

    2009-11-13

    Quantum critical systems out of equilibrium are of extensive interest, but are difficult to study theoretically. We consider here the steady-state limit of a single-electron transistor with ferromagnetic leads. In equilibrium (i.e., bias voltage V = 0), this system features a continuous quantum phase transition with a critical destruction of the Kondo effect. We construct an exact quantum Boltzmann treatment in a dynamical large-N limit, and determine the universal scaling functions of both the nonlinear conductance and fluctuation-dissipation ratios. We also elucidate the decoherence properties as encoded in the local spin response.

  10. Random field Ising model in a uniform magnetic field: Ground states, pinned clusters and scaling laws.

    Science.gov (United States)

    Kumar, Manoj; Banerjee, Varsha; Puri, Sanjay

    2017-11-08

    In this paper, we study the random field Ising model (RFIM) in an external magnetic field h . A computationally efficient graph-cut method is used to study ground state (GS) morphologies in this system for three different disorder types: Gaussian, uniform and bimodal. We obtain the critical properties of this system and find that they are independent of the disorder type. We also study GS morphologies via pinned-cluster distributions, which are scale-free at criticality. The spin-spin correlation functions (and structure factors) are characterized by a roughness exponent [Formula: see text]. The corresponding scaling function is universal for all disorder types and independent of h.

  11. A generator for unique quantum random numbers based on vacuum states

    DEFF Research Database (Denmark)

    Gabriel, C.; Wittmann, C.; Sych, D.

    2010-01-01

    Random numbers are a valuable component in diverse applications that range from simulations(1) over gambling to cryptography(2,3). The quest for true randomness in these applications has engendered a large variety of different proposals for producing random numbers based on the foundational unpre...

  12. Out-of-equilibrium Kondo effect in a quantum dot: Interplay of magnetic field and spin accumulation

    Science.gov (United States)

    Sahoo, Shaon; Crépieux, Adeline; Lavagna, Mireille

    2016-12-01

    We present a theoretical study of low-temperature nonequilibrium transport through an interacting quantum dot in the presence of Zeeman magnetic field and current injection into one of its leads. By using a self-consistent renormalized equation of motion approach, we show that the injection of a spin-polarized current leads to a modulation of the Zeeman splitting of the Kondo peak in the differential conductance. We find that an appropriate amount of spin accumulation in the lead can restore the Kondo peak by compensating the splitting due to magnetic field. By contrast when the injected current is spin-unpolarized, we establish that both Zeeman-split Kondo peaks are equally shifted and the splitting remains unchanged. Our results quantitatively explain the experimental findings reported in Kobayashi T. et al., Phys. Rev. Lett., 104 (2010) 036804. These features could be nicely exploited for the control and manipulation of spin in nanoelectronic and spintronic devices.

  13. Tight-binding electrons on triangular and kagome lattices under staggered modulated magnetic fields: quantum Hall effects and Hofstadter butterflies

    Energy Technology Data Exchange (ETDEWEB)

    Li Juan; Wang Yifei; Gong Changde, E-mail: yfwang_nju@hotmail.com [Center for Statistical and Theoretical Condensed Matter Physics, and Department of Physics, Zhejiang Normal University, Jinhua 321004 (China)

    2011-04-20

    We consider the tight-binding models of electrons on a two-dimensional triangular lattice and kagome lattice under staggered modulated magnetic fields. Such fields have two components: a uniform-flux part with strength {phi}, and a staggered-flux part with strength {Delta}{phi}. Various properties of the Hall conductances and Hofstadter butterflies are studied. When {phi} is fixed, variation of {Delta}{phi} leads to the quantum Hall transitions and Chern numbers of Landau subbands being redistributed between neighboring pairs. The energy spectra with nonzero {Delta}{phi}s have similar fractal structures but quite different energy gaps compared with the original Hofstadter butterflies of {Delta}{phi} = 0. Moreover, the fan-like structure of Landau levels in the low magnetic field region is also modified appreciably by {Delta}{phi}.

  14. Parsimonious Continuous Time Random Walk Models and Kurtosis for Diffusion in Magnetic Resonance of Biological Tissue

    Directory of Open Access Journals (Sweden)

    Carson eIngo

    2015-03-01

    Full Text Available In this paper, we provide a context for the modeling approaches that have been developed to describe non-Gaussian diffusion behavior, which is ubiquitous in diffusion weighted magnetic resonance imaging of water in biological tissue. Subsequently, we focus on the formalism of the continuous time random walk theory to extract properties of subdiffusion and superdiffusionthrough novel simplifications of the Mittag-Leffler function. For the case of time-fractional subdiffusion, we compute the kurtosis for the Mittag-Leffler function, which provides both a connection and physical context to the much-used approach of diffusional kurtosis imaging. We provide Monte Carlo simulations to illustrate the concepts of anomalous diffusion as stochastic processes of the random walk. Finally, we demonstrate the clinical utility of the Mittag-Leffler function as a model to describe tissue microstructure through estimations of subdiffusion and kurtosis with diffusion MRI measurements in the brain of a chronic ischemic stroke patient.

  15. Parsimonious continuous time random walk models and kurtosis for diffusion in magnetic resonance of biological tissue.

    Science.gov (United States)

    Ingo, Carson; Sui, Yi; Chen, Yufen; Parrish, Todd B; Webb, Andrew G; Ronen, Itamar

    2015-03-01

    In this paper, we provide a context for the modeling approaches that have been developed to describe non-Gaussian diffusion behavior, which is ubiquitous in diffusion weighted magnetic resonance imaging of water in biological tissue. Subsequently, we focus on the formalism of the continuous time random walk theory to extract properties of subdiffusion and superdiffusion through novel simplifications of the Mittag-Leffler function. For the case of time-fractional subdiffusion, we compute the kurtosis for the Mittag-Leffler function, which provides both a connection and physical context to the much-used approach of diffusional kurtosis imaging. We provide Monte Carlo simulations to illustrate the concepts of anomalous diffusion as stochastic processes of the random walk. Finally, we demonstrate the clinical utility of the Mittag-Leffler function as a model to describe tissue microstructure through estimations of subdiffusion and kurtosis with diffusion MRI measurements in the brain of a chronic ischemic stroke patient.

  16. Parsimonious Continuous Time Random Walk Models and Kurtosis for Diffusion in Magnetic Resonance of Biological Tissue

    Science.gov (United States)

    Ingo, Carson; Sui, Yi; Chen, Yufen; Parrish, Todd; Webb, Andrew; Ronen, Itamar

    2015-03-01

    In this paper, we provide a context for the modeling approaches that have been developed to describe non-Gaussian diffusion behavior, which is ubiquitous in diffusion weighted magnetic resonance imaging of water in biological tissue. Subsequently, we focus on the formalism of the continuous time random walk theory to extract properties of subdiffusion and superdiffusion through novel simplifications of the Mittag-Leffler function. For the case of time-fractional subdiffusion, we compute the kurtosis for the Mittag-Leffler function, which provides both a connection and physical context to the much-used approach of diffusional kurtosis imaging. We provide Monte Carlo simulations to illustrate the concepts of anomalous diffusion as stochastic processes of the random walk. Finally, we demonstrate the clinical utility of the Mittag-Leffler function as a model to describe tissue microstructure through estimations of subdiffusion and kurtosis with diffusion MRI measurements in the brain of a chronic ischemic stroke patient.

  17. Nuclear magnetic resonance with dc SQUID (Super-conducting QUantum Interference Device) preamplifiers

    Science.gov (United States)

    Fan, N. Q.; Heaney, Michael B.; Clark, John; Newitt, D.; Wald, Lawrence L.; Hahn, Erwin L.; Bierlecki, A.; Pines, A.

    1988-08-01

    Sensitive radio-frequency (RF) amplifiers based on dc Superconducting QUantum Interface Devices (SQUIDS) are available for frequencies up to 200 MHz. At 4.2 K, the gain and noise temperature of a typical tuned amplifier are 18.6 + or - 0.5 dB and 1.7 + or - 0.5 K at 93 MHz. These amplifiers are being applied to a series of novel experiments on nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR). The high sensitivity of these amplifiers was demonstrated in the observation of nuclear spin noise, the emission of photons by Cl-35 nuclei in a state of zero polarization. In the more conventional experiments in which one applies a large RF pulse to the spins, a Q-spoiler, consisting of a series array of Josephson junctions, is used to reduce the Q of the input circuit to a very low value during the pulse. The Q-spoiler enables the circuit to recover quickly after the pulse, and has been used in an NQR experiment to achieve a sensitivity of about 2 x 10(16) nuclear Bohr magnetons in a single free precession signal with a bandwidth of 10 kHz. In a third experiment, a sample containing Cl-35 nuclei was placed in a capacitor and the signal detected electrically using a tuned SQUID amplifier and Q-spoiler. In this way, the electrical polarization induced by the precessing Cl nuclear quadrupole moments was detected: this is the inverse of the Stark effect in NQR. Two experiments involving NMR have been carried out. In the first, the 30 MHz resonance in Sn-119 nuclei is detected with a tuned amplifier and Q-spoiler, and a single pulse resolution of 10(18) nuclear Bohr magnetons in a bandwidth of 25 kHz has been achieved. For the second, a low frequency NMR system has been developed that uses an untuned input circuit coupled to the SQUID. The resonance in Pt-195 nuclei has been observed at 55 kHz in a field of 60 gauss.

  18. Increased coincidence detection for quantum versus pseudo-generated random numbers

    NARCIS (Netherlands)

    Boshoff, Lieze; Jolij, Jacob

    2015-01-01

    People often see meaning in stimuli that are typically considered meaningless. According to Von Lucadou’s idea of Generalized Quantum Teory (GQT), such perceived coincidences, or examples of synchronicity, may be the result of entanglement between a conscious observer and the physical world. Here we

  19. Generation of non-equilibrium thermal quantum discord and entanglement in a three-spin XX chain by multi-spin interaction and an external magnetic field

    Science.gov (United States)

    Zhang, Xiu-xing; Li, Fu-li

    2011-11-01

    The generation of non-equilibrium thermal quantum discord and entanglement is investigated in a three-spin chain whose two end spins are respectively coupled to two thermal reservoirs at different temperatures. We show that the spin chain can be decoupled from the thermal reservoirs by homogeneously applying a magnetic field and including a strong three-spin interaction, and then the maximal steady-state quantum discord and entanglement in the two end spins can always be created. In addition, the present investigation may provide a useful approach to control coupling between a quantum system and its environment.

  20. Temperature dependence of X-ray absorption and nuclear magnetic resonance spectra: probing quantum vibrations of light elements in oxides.

    Science.gov (United States)

    Nemausat, Ruidy; Gervais, Christel; Brouder, Christian; Trcera, Nicolas; Bordage, Amélie; Coelho-Diogo, Cristina; Florian, Pierre; Rakhmatullin, Aydar; Errea, Ion; Paulatto, Lorenzo; Lazzeri, Michele; Cabaret, Delphine

    2017-02-22

    A combined experimental-theoretical study on the temperature dependence of the X-ray absorption near-edge structure (XANES) and nuclear magnetic resonance (NMR) spectra of periclase (MgO), spinel (MgAl2O4), corundum (α-Al2O3), berlinite (α-AlPO4), stishovite and α-quartz (SiO2) is reported. Predictive calculations are presented when experimental data are not available. For these light-element oxides, both experimental techniques detect systematic effects related to quantum thermal vibrations which are well reproduced by density-functional theory simulations. In calculations, thermal fluctuations of the nuclei are included by considering nonequilibrium configurations according to finite-temperature quantum statistics at the quasiharmonic level. The influence of nuclear quantum fluctuations on XANES and NMR spectroscopies is particularly sensitive to the coordination number of the probed cation. Furthermore, the relative importance of nuclear dynamics and thermal expansion is quantified over a large range of temperatures.

  1. Spin power and efficiency in an Aharnov-Bohm ring with an embedded magnetic impurity quantum dot

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Xi; Guo, Yong, E-mail: guoy66@tsinghua.edu.cn [Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Zheng, Jun [College of New Energy, Bohai University, Jinzhou 121013 (China); Chi, Feng [School of Physical Science and Technology, Inner Mongolia University, Huhehaote 010023 (China)

    2015-05-11

    Spin thermoelectric effects in an Aharnov-Bohm ring with a magnetic impurity quantum dot (QD) are theoretically investigated by using the nonequilibrium Green's function method. It is found that due to the exchange coupling between the impurity and the electrons in QD, spin output power, and efficiency can be significant and be further modulated by the gate voltage. The spin thermoelectric effect can be modulated effectively by adjusting the Rashba spin-orbit interaction (RSOI) and the magnetic flux. The spin power and efficiency show zigzag oscillations, and thus spin thermoelectric effect can be switched by adjusting the magnetic flux phase factor and RSOI ones. In addition, the spin efficiency can be significantly enhanced by the coexistence of the RSOI and the magnetic flux, and the maximal value of normalized spin efficiency η{sub max}/η{sub C} = 0.35 is obtained. Our results show that such a QD ring device may be used as a manipulative spin thermoelectric generator.

  2. Storage of quantum coherences as phase-labelled local polarization in solid-state nuclear magnetic resonance.

    Science.gov (United States)

    Franzoni, María Belén; Acosta, Rodolfo H; Pastawski, Horacio M; Levstein, Patricia R

    2012-10-13

    Nuclear spins are promising candidates for quantum information processing because their good isolation from the environment precludes the rapid loss of quantum coherence. Many strategies have been developed to further extend their decoherence times. Some of them make use of decoupling techniques based on the Carr-Purcell and Carr-Purcell-Meiboom-Gill pulse sequences. In many cases, when applied to inhomogeneous samples, they yield a magnetization decay much slower than that of the Hahn echo. However, we have proved that these decays cannot be associated with longer decoherence times, as coherences remain frozen. They result from coherences recovered after their storage as local polarization and thus they can be used as memories. We show here how this freezing of the coherent state, which can subsequently be recovered after times longer than the natural decoherence time of the system, can be generated in a controlled way with the use of field gradients. A similar behaviour of homogeneous samples in inhomogeneous fields is demonstrated. It is emphasized that the effects of inhomogeneities in solid-state nuclear magnetic resonance, independently of their origin, should not be disregarded, as they play a crucial role in multipulse sequences.

  3. Fluorescent/magnetic micro/nano-spheres based on quantum dots and/or magnetic nanoparticles: preparation, properties, and their applications in cancer studies

    Science.gov (United States)

    Wen, Cong-Ying; Xie, Hai-Yan; Zhang, Zhi-Ling; Wu, Ling-Ling; Hu, Jiao; Tang, Man; Wu, Min; Pang, Dai-Wen

    2016-06-01

    The study of cancer is of great significance to human survival and development, due to the fact that cancer has become one of the greatest threats to human health. In recent years, the rapid progress of nanoscience and nanotechnology has brought new and bright opportunities to this field. In particular, the applications of quantum dots (QDs) and magnetic nanoparticles (MNPs) have greatly promoted early diagnosis and effective therapy of cancer. In this review, we focus on fluorescent/magnetic micro/nano-spheres based on QDs and/or MNPs (we may call them ``nanoparticle-sphere (NP-sphere) composites'') from their preparation to their bio-application in cancer research. Firstly, we outline and compare the main four kinds of methods for fabricating NP-sphere composites, including their design principles, operation processes, and characteristics (merits and limitations). The NP-sphere composites successfully inherit the unique fluorescence or magnetic properties of QDs or MNPs. Moreover, compared with the nanoparticles (NPs) alone, the NP-sphere composites show superior properties, which are also discussed in this review. Then, we summarize their recent applications in cancer research from three aspects, that is: separation and enrichment of target tumor cells or biomarkers; cancer diagnosis mainly through medical imaging or tumor biomarker detection; and cancer therapy via targeted drug delivery systems. Finally, we provide some perspectives on the future challenges and development trends of the NP-sphere composites.

  4. Quantum cryptography beyond quantum key distribution

    NARCIS (Netherlands)

    Broadbent, A.; Schaffner, C.

    2016-01-01

    Quantum cryptography is the art and science of exploiting quantum mechanical effects in order to perform cryptographic tasks. While the most well-known example of this discipline is quantum key distribution (QKD), there exist many other applications such as quantum money, randomness generation,

  5. Quantum cryptography beyond quantum key distribution

    NARCIS (Netherlands)

    A. Broadbent (Anne); C. Schaffner (Christian)

    2016-01-01

    textabstractQuantum cryptography is the art and science of exploiting quantum mechanical effects in order to perform cryptographic tasks. While the most well-known example of this discipline is quantum key distribution (QKD), there exist many other applications such as quantum money, randomness

  6. Analysis of self-heating of thermally assisted spin-transfer torque magnetic random access memory

    Directory of Open Access Journals (Sweden)

    Austin Deschenes

    2016-11-01

    Full Text Available Thermal assistance has been shown to significantly reduce the required operation power for spin torque transfer magnetic random access memory (STT-MRAM. Proposed heating methods include modified material stack compositions that result in increased self-heating or external heat sources. In this work we analyze the self-heating process of a standard perpendicular magnetic anisotropy STT-MRAM device through numerical simulations in order to understand the relative contributions of Joule, thermoelectric Peltier and Thomson, and tunneling junction heating. A 2D rotationally symmetric numerical model is used to solve the coupled electro-thermal equations including thermoelectric effects and heat absorbed or released at the tunneling junction. We compare self-heating for different common passivation materials, positive and negative electrical current polarity, and different device thermal anchoring and boundaries resistance configurations. The variations considered are found to result in significant differences in maximum temperatures reached. Average increases of 3 K, 10 K, and 100 K for different passivation materials, positive and negative polarity, and different thermal anchoring configurations, respectively, are observed. The highest temperatures, up to 424 K, are obtained for silicon dioxide as the passivation material, positive polarity, and low thermal anchoring with thermal boundary resistance configurations. Interestingly it is also found that due to the tunneling heat, Peltier effect, device geometry, and numerous interfacial layers around the magnetic tunnel junction (MTJ, most of the heat is dissipated on the lower potential side of the magnetic junction. This asymmetry in heating, which has also been observed experimentally, is important as thermally assisted switching requires heating of the free layer specifically and this will be significantly different for the two polarity operations, set and reset.

  7. Preoperative Magnetic Resonance Imaging in Patients With Stage I Invasive Ductal Breast Cancer: A Prospective Randomized Study.

    Science.gov (United States)

    Brück, N; Koskivuo, I; Boström, P; Saunavaara, J; Aaltonen, R; Parkkola, R

    2018-03-01

    Preoperative magnetic resonance imaging has become an important complementary imaging technique in patients with breast cancer, providing additional information for preoperative local staging. Magnetic resonance imaging is recommended selectively in lobular breast cancer and in patients with dense breast tissue in the case when mammography and ultrasound fail to fully evaluate the lesion, but the routine use of magnetic resonance imaging in all patients with invasive ductal carcinoma is controversial. The purpose of this randomized study was to investigate the diagnostic value of preoperative magnetic resonance imaging and its impact on short-term surgical outcome in newly diagnosed unifocal stage I invasive ductal carcinoma. A total of 100 patients were randomized to either receive preoperative breast magnetic resonance imaging or to be scheduled directly to operation without magnetic resonance imaging on a 1:1 basis. There were 50 patients in both study arms. In 14 patients (28%), breast magnetic resonance imaging detected an additional finding and seven of them were found to be malignant. Six additional cancer foci were found in the ipsilateral breast and one in the contralateral breast. Magnetic resonance imaging findings caused a change in planned surgical management in 10 patients (20%). Mastectomy was performed in six patients (12%) in the magnetic resonance imaging group and in two patients (4%) in the control group ( p = 0.140). The breast reoperation rate was 14% in the magnetic resonance imaging group and 24% in the control group ( p = 0.202). The mean interval between referral and first surgical procedure was 34 days in the magnetic resonance imaging group and 21 days in the control group ( p magnetic resonance imaging may be beneficial for some patients with early-stage invasive ductal carcinoma, but its routine use is not recommended without specific indications.

  8. Comparison of quantum discord and local quantum uncertainty in a vertical quantum dot

    OpenAIRE

    Faizi, E.; Eftekhari, H.

    2014-01-01

    In this paper, we consider quantum correlations (quantum discord and local quantum uncertainty) in a vertical quantum dot. Their dependencies on magnetic field and temperature are presented in detail. It is noticeable that, quantum discord and local quantum uncertainty behavior is similar to a large extent. In addition, the time evolution of quantum discord and local quantum uncertainty under dephasing and amplitude damping channels is investigated. It has been found that, for some Belldiagon...

  9. Jeans instability of magnetized quantum plasma: Effect of viscosity, rotation and finite Larmor radius corrections

    Energy Technology Data Exchange (ETDEWEB)

    Jain, Shweta, E-mail: jshweta09@gmail.com; Sharma, Prerana [Department of Physics, Ujjain Engineering College, Ujjain, M.P.456010 (India); Chhajlani, R. K. [School of Studies in Physics, Vikram University Ujjain, M. P. - 456010 (India)

    2015-07-31

    The Jeans instability of self-gravitating quantum plasma is examined considering the effects of viscosity, finite Larmor radius (FLR) corrections and rotation. The analysis is done by normal mode analysis theory with the help of relevant linearized perturbation equations of the problem. The general dispersion relation is obtained using the quantum magneto hydrodynamic model. The modified condition of Jeans instability is obtained and the numerical calculations have been performed to show the effects of various parameters on the growth rate of Jeans instability.

  10. A novel multiplexer-based structure for random access memory cell in quantum-dot cellular automata

    Science.gov (United States)

    Naji Asfestani, Mazaher; Rasouli Heikalabad, Saeed

    2017-09-01

    Quantum-dot cellular automata (QCA) is a new technology in scale of nano and perfect replacement for CMOS circuits in the future. Memory is one of the basic components in any digital system, so designing the random access memory (RAM) with high speed and optimal in QCA is important. In this paper, by employing the structure of multiplexer, a novel RAM cell architecture is proposed. The proposed architecture is implemented without the coplanar crossover approach. The proposed architecture is simulated using the QCADesigner version 2.0.3 and QCAPro. The simulation results demonstrate that the proposed QCA RAM architecture has the best performance in terms of delay, circuit complexity, area, cell count and energy consumption in comparison with other QCA RAM architectures.

  11. Photocurrent, Rectification, and Magnetic Field Symmetry of Induced Current Through Quantum Dots

    DEFF Research Database (Denmark)

    DiCarlo, L.; M. Marcus, C.; Harris jr, J.

    2003-01-01

    We report mesoscopic dc current generation in an open chaotic quantum dot with ac excitation applied to one of the shape-defining gates. For excitation frequencies large compared to the inverse dwell time of electrons in the dot (i.e., GHz), we find mesoscopic fluctuations of induced current...

  12. Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum Dots

    DEFF Research Database (Denmark)

    Grove-Rasmussen, Kasper; Grap, S.; Paaske, Jens

    2012-01-01

    By means of sequential and cotunneling spectroscopy, we study the tunnel couplings between metallic leads and individual levels in a carbon nanotube quantum dot. The levels are ordered in shells consisting of two doublets with strong- and weak-tunnel couplings, leading to gate-dependent level...

  13. Quantum-well states and induced magnetism in Fe/CuN/Fe bcc (001) trilayers

    DEFF Research Database (Denmark)

    Niklasson, A.M.N.; Mirbt, S.; Skriver, Hans Lomholt

    1996-01-01

    profiles of two single Fe/Cu interfaces. The small deviations from this simple superposition are shown to be a consequence of quantum-well states confined within the paramagnetic spacer. This connection is confirmed by direct calculation of the state density. The results are of conceptual interest...

  14. Thermoelectric power in carbon nanotubes and quantum wires of nonlinear optical, optoelectronic, and related materials under strong magnetic field : Simplified theory and relative comparison

    NARCIS (Netherlands)

    Ghatak, K.P.; Bhattacharya, S.; Bhowmik, S.; Benedictus, R.; Choudhury, S.

    2008-01-01

    We study thermoelectric power under strong magnetic field (TPM) in carbon nanotubes (CNTs) and quantum wires (QWs) of nonlinear optical, optoelectronic, and related materials. The corresponding results for QWs of III-V, ternary, and quaternary compounds form a special case of our generalized

  15. Large Quantum Probability Backflow and the Azimuthal Angle-Angular Momentum Uncertainty Relation for an Electron in a Constant Magnetic Field

    Science.gov (United States)

    Strange, P.

    2012-01-01

    In this paper we demonstrate a surprising aspect of quantum mechanics that is accessible to an undergraduate student. We discuss probability backflow for an electron in a constant magnetic field. It is shown that even for a wavepacket composed entirely of states with negative angular momentum the effective angular momentum can take on positive…

  16. Measuring broadband magnetic fields on the nanoscale using a hybrid quantum register

    Science.gov (United States)

    Jakobi, Ingmar; Neumann, Philipp; Wang, Ya; Dasari, Durga Bhaktavatsala Rao; El Hallak, Fadi; Bashir, Muhammad Asif; Markham, Matthew; Edmonds, Andrew; Twitchen, Daniel; Wrachtrup, Jörg

    2017-01-01

    The generation and control of fast switchable magnetic fields with large gradients on the nanoscale is of fundamental interest in material science and for a wide range of applications. However, it has not yet been possible to characterize those fields at high bandwidth with arbitrary orientations. Here, we measure the magnetic field generated by a hard-disk-drive write head with high spatial resolution and large bandwidth by coherent control of single electron and nuclear spins. We are able to derive field profiles from coherent spin Rabi oscillations close to the gigahertz range, measure magnetic field gradients on the order of 1 mT nm-1 and quantify axial and radial components of a static and dynamic magnetic field independent of its orientation. Our method paves the way for precision measurement of the magnetic fields of nanoscale write heads, which is important for future miniaturization of these devices.

  17. Generation of non-equilibrium thermal quantum discord and entanglement in a three-spin XX chain by multi-spin interaction and an external magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xiu-xing [MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, and Department of Applied Physics, Xi' an Jiaotong University, Xi' an 710049 (China); Li, Fu-li, E-mail: flli@mail.xjtu.edu.cn [MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, and Department of Applied Physics, Xi' an Jiaotong University, Xi' an 710049 (China)

    2011-11-07

    The generation of non-equilibrium thermal quantum discord and entanglement is investigated in a three-spin chain whose two end spins are respectively coupled to two thermal reservoirs at different temperatures. We show that the spin chain can be decoupled from the thermal reservoirs by homogeneously applying a magnetic field and including a strong three-spin interaction, and then the maximal steady-state quantum discord and entanglement in the two end spins can always be created. In addition, the present investigation may provide a useful approach to control coupling between a quantum system and its environment. -- Highlights: → Spin chain decoupled from thermal reservoirs. → Thermal excitation depressed. → Maximal quantum correlations created.

  18. Magnetic resonance therapy for knee osteoarthritis: a randomized, double blind placebo controlled trial.

    Science.gov (United States)

    Gökşen, Nurgül; Çaliş, Mustafa; Doğan, Serap; Çaliş, Havva T; Özgöçmen, Salih

    2016-08-01

    Therapeutic nuclear magnetic resonance therapy (MRT) works based on the electromagnetic fields. To investigate efficacy of MRT in knee osteoarthritis (OA). Prospective, randomized, double-blind, placebo controlled trial. Outpatient clinic, university hospital. Patients who had mild to moderate knee OA at a single knee joint and between 30-75-years-old were randomized by blinded chip cards (1:1). The treatment group received ten sessions of one hour daily MRT, controls received placebo MRT. All patients underwent clinical examination at baseline, after 2 weeks, and 12 weeks. Imaging included blindly assessed ultrasonography and magnetic resonance (MR) of the knee. Ninety-seven patients completed the study. Both groups improved significantly but the average change from baseline in outcome parameters was similar in MRT group (on VAS-pain,-2.6; WOMAC-pain, -2.09; WOMAC-stiffness, -1.81; WOMAC-physical, -1.96) compared to placebo after two weeks (VAS-pain,-1.6; WOMAC-pain, -1.91; WOMAC-stiffness, -1.27; WOMAC-physical, -1.54). Also changes were quite similar at the 12th week after the treatment. SF-36 components at 12th week improved but changes were not significant. Imaging arm also failed to show significant differences between groups in terms of cartilage thickness on US and MR scores. No adverse events were recorded. MRT is safe, but not superior to placebo in terms of improvement in clinical or imaging parameters after a 10-day course of treatment in mild to moderate knee OA. The present study does not promote use of a 10-day course of MRT in mild to moderate knee OA.

  19. Organic analogues of diluted magnetic semiconductors: bridging quantum chemistry to condensed matter physics

    Science.gov (United States)

    Furis, Madalina; Rawat, Naveen; Cherian, Judy G.; Wetherby, Anthony; Waterman, Rory; McGill, Stephen

    2015-09-01

    The selective coupling between polarized photons and electronic states in materials enables polarization-resolved spectroscopy studies of exchange interactions, spin dynamics, and collective magnetic behavior of conduction electrons in semiconductors. Here we report on Magnetic Circular Dichroism (MCD) studies of magnetic properties of electrons in crystalline thin films of small molecule organic semiconductors. Specifically, the focus was on the magnetic exchange interaction properties of d-shell ions (Cu2+, Co2+ and Mn2+) metal phthalocyanine (Pc) thin films that one may think of as organic analogues of diluted magnetic semiconductors (DMS). These films were deposited in-house using a recently developed pen-writing method that results in crystalline films with macroscopic long range ordering and improved electronic properties, ideally suited for spectroscopy techniques. Our experiments reveal that, in analogy to DMS, the extended π-orbitals of the Pc molecule mediate the spin exchange between highly localized d-like unpaired spins. We established that exchange mechanisms involve different electronic states in each species and/or hybridization between d-like orbitals and certain delocalized π-orbitals. Unprecedented 25T MCD and PL conducted in the unique 25T Split Florida HELIX magnet at the National High Magnetic Field Laboratory (NHMFL) will prove useful in probing these exchange interactions.

  20. N-(sulfoethyl) iminodiacetic acid-based lanthanide coordination polymers: Synthesis, magnetism and quantum Monte Carlo studies

    Science.gov (United States)

    Zhuang, Gui-lin; Chen, Wu-lin; Zheng, Jun; Yu, Hui-you; Wang, Jian-guo

    2012-08-01

    A series of lanthanide coordination polymers have been obtained through the hydrothermal reaction of N-(sulfoethyl) iminodiacetic acid (H3SIDA) and Ln(NO3)3 (Ln=La, 1; Pr, 2; Nd, 3; Gd, 4). Crystal structure analysis exhibits that lanthanide ions affect the coordination number, bond length and dimension of compounds 1-4, which reveal that their structure diversity can be attributed to the effect of lanthanide contraction. Furthermore, the combination of magnetic measure with quantum Monte Carlo(QMC) studies exhibits that the coupling parameters between two adjacent Gd3+ ions for anti-anti and syn-anti carboxylate bridges are -1.0×10-3 and -5.0×10-3 cm-1, respectively, which reveals weak antiferromagnetic interaction in 4.

  1. Electric and magnetic field modulated energy dispersion, conductivity and optical response in double quantum wire with spin-orbit interactions

    Science.gov (United States)

    Karaaslan, Y.; Gisi, B.; Sakiroglu, S.; Kasapoglu, E.; Sari, H.; Sokmen, I.

    2018-02-01

    We study the influence of electric field on the electronic energy band structure, zero-temperature ballistic conductivity and optical properties of double quantum wire. System described by double-well anharmonic confinement potential is exposed to a perpendicular magnetic field and Rashba and Dresselhaus spin-orbit interactions. Numerical results show up that the combined effects of internal and external agents cause the formation of crossing, anticrossing, camel-back/anomaly structures and the lateral, downward/upward shifts in the energy dispersion. The anomalies in the energy subbands give rise to the oscillation patterns in the ballistic conductance, and the energy shifts bring about the shift in the peak positions of optical absorption coefficients and refractive index changes.

  2. k centre dot p Hamiltonians for quantum dots in a magnetic field

    CERN Document Server

    Planelles, J

    2003-01-01

    The problem of multiband k centre dot p Hamiltonians describing the hole energy structure of semiconductor nanosystems in a magnetic field is addressed. The approximate formulation given previously by Luttinger is revisited. We show that interaction with a magnetic field enters into the multiband equations for the envelope function components through the usual quadratic term and two linear Zeeman terms. The first linear term corresponds to the envelope angular momentum, while the other corresponds to the Bloch band-edge angular momentum. Several approximate ways of including the magnetic field in a four-band valence Hamiltonian are discussed and numerically compared. (letter to the editor)

  3. A Rapid Detection Method of Brucella with Quantum Dots and Magnetic Beads Conjugated with Different Polyclonal Antibodies

    Science.gov (United States)

    Song, Dandan; Qu, Xiaofeng; Liu, Yushen; Li, Li; Yin, Dehui; Li, Juan; Xu, Kun; Xie, Renguo; Zhai, Yue; Zhang, Huiwen; Bao, Hao; Zhao, Chao; Wang, Juan; Song, Xiuling; Song, Wenzhi

    2017-03-01

    Brucella spp. are facultative intracellular bacteria that cause zoonotic disease of brucellosis worldwide. Traditional methods for detection of Brucella spp. take 48-72 h that does not meet the need of rapid detection. Herein, a new rapid detection method of Brucella was developed based on polyclonal antibody-conjugating quantum dots and antibody-modified magnetic beads. First, polyclonal antibodies IgG and IgY were prepared and then the antibody conjugated with quantum dots (QDs) and immunomagnetic beads (IMB), respectively, which were activated by N-(3-dimethylaminopropyl)- N'-ethylcar-bodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) to form probes. We used the IMB probe to separate the Brucella and labeled by the QD probe, and then detected the fluorescence intensity with a fluorescence spectrometer. The detection method takes 105 min with a limit of detection of 103 CFU/mL and ranges from 10 to 105 CFU/mL ( R 2 = 0.9983), and it can be well used in real samples.

  4. Alternating current magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a micro superconducting quantum interference device

    Energy Technology Data Exchange (ETDEWEB)

    Martínez-Pérez, M. J.; Luis, F., E-mail: fluis@unizar.es [Instituto de Ciencia de Materiales de Aragón (ICMA), CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza (Spain); Dpto. de Física de la Materia Condensada, Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza (Spain); Bellido, E.; Ruiz-Molina, D., E-mail: druiz@cin2.es [Centro de Investigación en Nanociencia y Nanotecnología (CIN2, CSIC-ICN) Edificio CM7, Esfera UAB, Campus UAB, E-08193 Cerdanyola del Vallés (Spain); Miguel, R. de [Laboratorio de Microscopías Avanzadas (LMA)—Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza (Spain); Sesé, J. [Laboratorio de Microscopías Avanzadas (LMA)—Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza (Spain); Dpto. de Física de la Materia Condensada, Universidad de Zaragoza, Pedro Cerbuna 12, E-50009 Zaragoza (Spain); Lostao, A. [Laboratorio de Microscopías Avanzadas (LMA)—Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza (Spain); Fundación ARAID, E-50004, Aragón (Spain); and others

    2011-07-18

    We report the controlled integration, via dip pen nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 μ{sub B}) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 10{sup 2}, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.

  5. Quantum-like Viewpoint on the Complexity and Randomness of the Financial Market

    Science.gov (United States)

    Choustova, Olga

    In economics and financial theory, analysts use random walk and more general martingale techniques to model behavior of asset prices, in particular share prices on stock markets, currency exchange rates and commodity prices. This practice has its basis in the presumption that investors act rationally and without bias, and that at any moment they estimate the value of an asset based on future expectations. Under these conditions, all existing information affects the price, which changes only when new information comes out. By definition, new information appears randomly and influences the asset price randomly. Corresponding continuous time models are based on stochastic processes (this approach was initiated in the thesis of [4]), see, e.g., the books of [33] and [37] for historical and mathematical details.

  6. Design of high-throughput and low-power true random number generator utilizing perpendicularly magnetized voltage-controlled magnetic tunnel junction

    Directory of Open Access Journals (Sweden)

    Hochul Lee

    2017-05-01

    Full Text Available A true random number generator based on perpendicularly magnetized voltage-controlled magnetic tunnel junction devices (MRNG is presented. Unlike MTJs used in memory applications where a stable bit is needed to store information, in this work, the MTJ is intentionally designed with small perpendicular magnetic anisotropy (PMA. This allows one to take advantage of the thermally activated fluctuations of its free layer as a stochastic noise source. Furthermore, we take advantage of the voltage dependence of anisotropy to temporarily change the MTJ state into an unstable state when a voltage is applied. Since the MTJ has two energetically stable states, the final state is randomly chosen by thermal fluctuation. The voltage controlled magnetic anisotropy (VCMA effect is used to generate the metastable state of the MTJ by lowering its energy barrier. The proposed MRNG achieves a high throughput (32 Gbps by implementing a 64×64 MTJ array into CMOS circuits and executing operations in a parallel manner. Furthermore, the circuit consumes very low energy to generate a random bit (31.5 fJ/bit due to the high energy efficiency of the voltage-controlled MTJ switching.

  7. Design of high-throughput and low-power true random number generator utilizing perpendicularly magnetized voltage-controlled magnetic tunnel junction

    Science.gov (United States)

    Lee, Hochul; Ebrahimi, Farbod; Amiri, Pedram Khalili; Wang, Kang L.

    2017-05-01

    A true random number generator based on perpendicularly magnetized voltage-controlled magnetic tunnel junction devices (MRNG) is presented. Unlike MTJs used in memory applications where a stable bit is needed to store information, in this work, the MTJ is intentionally designed with small perpendicular magnetic anisotropy (PMA). This allows one to take advantage of the thermally activated fluctuations of its free layer as a stochastic noise source. Furthermore, we take advantage of the voltage dependence of anisotropy to temporarily change the MTJ state into an unstable state when a voltage is applied. Since the MTJ has two energetically stable states, the final state is randomly chosen by thermal fluctuation. The voltage controlled magnetic anisotropy (VCMA) effect is used to generate the metastable state of the MTJ by lowering its energy barrier. The proposed MRNG achieves a high throughput (32 Gbps) by implementing a 64 ×64 MTJ array into CMOS circuits and executing operations in a parallel manner. Furthermore, the circuit consumes very low energy to generate a random bit (31.5 fJ/bit) due to the high energy efficiency of the voltage-controlled MTJ switching.

  8. Magnetic cooling close to a quantum phase transition—The case of Er{sub 2}Ti{sub 2}O{sub 7}

    Energy Technology Data Exchange (ETDEWEB)

    Wolf, B.; Tutsch, U.; Dörschug, S.; Krellner, C.; Ritter, F.; Assmus, W.; Lang, M. [Physikalisches Institut, Goethe Universität, SFB-TR49, 60438 Frankfurt (Germany)

    2016-10-14

    Magnetic cooling, first introduced in the late twenties of last century, has regained considerable interest recently as a cost-efficient and easy-to-handle alternative to {sup 3}He-based refrigeration techniques. Especially, adiabatic demagnetization of paramagnets—the standard materials for magnetic refrigeration—has become indispensable for the present space applications. To match the growing demand for increasing the efficiency in these applications, a new concept for magnetic cooling based on many-body effects around a quantum-critical-point has been introduced and successfully tested [B. Wolf et al., Proc. Natl. Acad. Sci. U.S.A. 108, 6862 (2011)]. By extending this concept to three-dimensional magnetic systems, we present here the magnetothermal response of the cubic pyrochlore material Er{sub 2}Ti{sub 2}O{sub 7} in the vicinity of its B-induced quantum-critical point which is located around 1.5 T. We discuss performance characteristics such as the range of operation, the efficiency, and the hold time. These figures are compared with those of state-of-the-art paramagnetic coolants and with other quantum-critical systems which differ by the dimensionality of the magnetic interactions and the degree of frustration.

  9. Transcranial Magnetic Stimulation to Address Mild Cognitive Impairment in the Elderly: A Randomized Controlled Study

    Directory of Open Access Journals (Sweden)

    Hellen Livia Drumond Marra

    2015-01-01

    Full Text Available Transcranial magnetic stimulation (TMS is a noninvasive brain stimulation technique with potential to improve memory. Mild cognitive impairment (MCI, which still lacks a specific therapy, is a clinical syndrome associated with increased risk of dementia. This study aims to assess the effects of high-frequency repetitive TMS (HF rTMS on everyday memory of the elderly with MCI. We conducted a double-blinded randomized sham-controlled trial using rTMS over the left dorsolateral prefrontal cortex (DLPFC. Thirty-four elderly outpatients meeting Petersen’s MCI criteria were randomly assigned to receive 10 sessions of either active TMS or sham, 10 Hz rTMS at 110% of motor threshold, 2,000 pulses per session. Neuropsychological assessment at baseline, after the last session (10th and at one-month follow-up, was applied. ANOVA on the primary efficacy measure, the Rivermead Behavioural Memory Test, revealed a significant group-by-time interaction p=0.05, favoring the active group. The improvement was kept after one month. Other neuropsychological tests were heterogeneous. rTMS at 10 Hz enhanced everyday memory in elderly with MCI after 10 sessions. These findings suggest that rTMS might be effective as a therapy for MCI and probably a tool to delay deterioration.

  10. Gradual stiffness versus magnetic imaging-guided variable stiffness colonoscopes: A randomized noninferiority trial.

    Science.gov (United States)

    Garborg, Kjetil; Wiig, Håvard; Hasund, Audun; Matre, Jon; Holme, Øyvind; Noraberg, Geir; Løberg, Magnus; Kalager, Mette; Adami, Hans-Olov; Bretthauer, Michael

    2017-02-01

    Colonoscopes with gradual stiffness have recently been developed to enhance cecal intubation. We aimed to determine if the performance of gradual stiffness colonoscopes is noninferior to that of magnetic endoscopic imaging (MEI)-guided variable stiffness colonoscopes. Consecutive patients were randomized to screening colonoscopy with Fujifilm gradual stiffness or Olympus MEI-guided variable stiffness colonoscopes. The primary endpoint was cecal intubation rate (noninferiority limit 5%). Secondary endpoints included cecal intubation time. We estimated absolute risk differences with 95% confidence intervals (CIs). We enrolled 475 patients: 222 randomized to the gradual stiffness instrument, and 253 to the MEI-guided variable stiffness instrument. Cecal intubation rate was 91.7% in the gradual stiffness group versus 95.6% in the variable stiffness group. The adjusted absolute risk for cecal intubation failure was 4.3% higher in the gradual stiffness group than in the variable stiffness group (upper CI border 8.1%). Median cecal intubation time was 13 minutes in the gradual stiffness group and 10 minutes in the variable stiffness group (p < 0.001). The study is inconclusive with regard to noninferiority because the 95% CI for the difference in cecal intubation rate between the groups crosses the noninferiority margin. (ClinicalTrials.gov identifier: NCT01895504).

  11. Magnetic anisotropy of graphene quantum dots decorated with a ruthenium adatom

    Directory of Open Access Journals (Sweden)

    Igor Beljakov

    2013-07-01

    Full Text Available The creation of magnetic storage devices by decoration of a graphene sheet by magnetic transition-metal adatoms, utilizing the high in-plane versus out-of-plane magnetic anisotropy energy (MAE, has recently been proposed. This concept is extended in our density-functional-based modeling study by incorporating the influence of the graphene edge on the MAE. We consider triangular graphene flakes with both armchair and zigzag edges in which a single ruthenium adatom is placed at symmetrically inequivalent positions. Depending on the edge-type, the graphene edge was found to influence the MAE in opposite ways: for the armchair flake the MAE increases close to the edge, while the opposite is true for the zigzag edge. Additionally, in-plane pinning of the magnetization direction perpendicular to the edge itself is observed for the first time.

  12. Valence-bond-solid domain walls in a 2D quantum magnet

    Science.gov (United States)

    Shao, Hui; Guo, Wenan; Sandvik, Anders

    sing quantum Monte Carlo simulations, we study properties of domain walls in a square-lattice S=1/2 Heisenberg model with additional interactions which can drive the system from an antiferromagnetic (AFM) ground state to a valence-bond solid (VBS). We study the finite-size scaling of the domain-wall energy at the putative ''deconfined'' critical AFM-VBS point, which gives access to the critical exponent governing the domain-wall width. This length-scale diverges faster than the correlation length and also is related to the scale of spinon deconfinement. Our results show additional evidence of deconfied quantum criticality and are compatible with critical exponents extracted from finite-size scaling of other quantities. NSFC Grant No. 11175018, NSF Grant No. DMR-1410126.

  13. Effects of temperature on the ground state of a strongly-coupling magnetic polaron and mean phonon number in RbCl quantum pseudodot

    Science.gov (United States)

    Sun, Yong; Ding, Zhao-Hua; Xiao, Jing-Lin

    2016-07-01

    On the condition of strong electron-LO phonon coupling in a RbCl quantum pseudodot (QPD), the ground state energy and the mean number of phonons are calculated by using the Pekar variational method and quantum statistical theory. The variations of the ground state energy and the mean number with respect to the temperature and the cyclotron frequency of the magnetic field are studied in detail. We find that the absolute value of the ground state energy increases (decreases) with increasing temperature when the temperature is in the lower (higher) temperature region, and that the mean number increases with increasing temperature. The absolute value of the ground state energy is a decreasing function of the cyclotron frequency of the magnetic field whereas the mean number is an increasing function of it. We find two ways to tune the ground state energy and the mean number: controlling the temperature and controlling the cyclotron frequency of the magnetic field.

  14. Perturbation approach for nuclear magnetic resonance solid-state quantum computation

    Directory of Open Access Journals (Sweden)

    G. P. Berman

    2003-01-01

    Full Text Available A dynamics of a nuclear-spin quantum computer with a large number (L=1000 of qubits is considered using a perturbation approach. Small parameters are introduced and used to compute the error in an implementation of an entanglement between remote qubits, using a sequence of radio-frequency pulses. The error is computed up to the different orders of the perturbation theory and tested using exact numerical solution.

  15. Testing Nonassociative Quantum Mechanics.

    Science.gov (United States)

    Bojowald, Martin; Brahma, Suddhasattwa; Büyükçam, Umut

    2015-11-27

    The familiar concepts of state vectors and operators in quantum mechanics rely on associative products of observables. However, these notions do not apply to some exotic systems such as magnetic monopoles, which have long been known to lead to nonassociative algebras. Their quantum physics has remained obscure. This Letter presents the first derivation of potentially testable physical results in nonassociative quantum mechanics, based on effective potentials. They imply new effects which cannot be mimicked in usual quantum mechanics with standard magnetic fields.

  16. Hydrodynamic and kinetic models for spin-1/2 electron-positron quantum plasmas: Annihilation interaction, helicity conservation, and wave dispersion in magnetized plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Andreev, Pavel A., E-mail: andreevpa@physics.msu.ru [Faculty of Physics, Lomonosov Moscow State University, Moscow (Russian Federation)

    2015-06-15

    We discuss the complete theory of spin-1/2 electron-positron quantum plasmas, when electrons and positrons move with velocities mach smaller than the speed of light. We derive a set of two fluid quantum hydrodynamic equations consisting of the continuity, Euler, spin (magnetic moment) evolution equations for each species. We explicitly include the Coulomb, spin-spin, Darwin and annihilation interactions. The annihilation interaction is the main topic of the paper. We consider the contribution of the annihilation interaction in the quantum hydrodynamic equations and in the spectrum of waves in magnetized electron-positron plasmas. We consider the propagation of waves parallel and perpendicular to an external magnetic field. We also consider the oblique propagation of longitudinal waves. We derive the set of quantum kinetic equations for electron-positron plasmas with the Darwin and annihilation interactions. We apply the kinetic theory to the linear wave behavior in absence of external fields. We calculate the contribution of the Darwin and annihilation interactions in the Landau damping of the Langmuir waves. We should mention that the annihilation interaction does not change number of particles in the system. It does not related to annihilation itself, but it exists as a result of interaction of an electron-positron pair via conversion of the pair into virtual photon. A pair of the non-linear Schrodinger equations for the electron-positron plasmas including the Darwin and annihilation interactions is derived. Existence of the conserving helicity in electron-positron quantum plasmas of spinning particles with the Darwin and annihilation interactions is demonstrated. We show that the annihilation interaction plays an important role in the quantum electron-positron plasmas giving the contribution of the same magnitude as the spin-spin interaction.

  17. Electron in the field of flexural vibrations of a membrane: Quantum time, magnetic oscillations, and coherence breaking

    Energy Technology Data Exchange (ETDEWEB)

    Gornyi, I. V. [Karlsruhe Institute of Technology, Institut für Nanotechnologie (Germany); Dmitriev, A. P., E-mail: apd1812@hotmail.com [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation); Mirlin, A. D.; Protopopov, I. V. [Karlsruhe Institute of Technology, Institut für Nanotechnologie (Germany)

    2016-08-15

    We have studied the motion of an electron in a membrane under the influence of flexural vibrations with a correlator that decreases upon an increase in the distance in accordance with the law r–{sup 2η}. We have conducted a detailed consideration of the case with η < 1/2, in which the perturbation theory is inapplicable, even for an arbitrarily weak interaction. It is shown that, in this case, reciprocal quantum time 1/τ{sub q} is proportional to g{sup 1/(1–η)}T{sup (2–η)/(2–2η)}, where g is the electron–phonon interaction constant and T is the temperature. The method developed here is applied for calculating the electron density of states in a magnetic field perpendicular to the membrane. In particular, it is shown that the Landau levels in the regime with ω{sub c}τ{sub q} » 1 have a Gaussian shape with a width that depends on the magnetic field as B{sup η}. In addition, we calculate the time τ{sub φ} of dephasing of the electron wave function that emerges due to the interaction with flexural phonons for η < 1/2. It has been shown that, in several temperature intervals, quantity 1/τ{sub φ} can be expressed by various power functions of the electron–phonon interaction constant, temperature, and electron energy.

  18. Quantum Physics Without Quantum Philosophy

    CERN Document Server

    Dürr, Detlef; Zanghì, Nino

    2013-01-01

    It has often been claimed that without drastic conceptual innovations a genuine explanation of quantum interference effects and quantum randomness is impossible. This book concerns Bohmian mechanics, a simple particle theory that is a counterexample to such claims. The gentle introduction and other contributions collected here show how the phenomena of non-relativistic quantum mechanics, from Heisenberg's uncertainty principle to non-commuting observables, emerge from the Bohmian motion of particles, the natural particle motion associated with Schrödinger's equation. This book will be of value to all students and researchers in physics with an interest in the meaning of quantum theory as well as to philosophers of science.

  19. One-Dimensional Disordered Quantum Mechanics and Sinai Diffusion with Random Absorbers

    Science.gov (United States)

    Grabsch, Aurélien; Texier, Christophe; Tourigny, Yves

    2014-04-01

    We study the one-dimensional Schrödinger equation with a disordered potential of the form where is a Gaussian white noise with mean and variance , and is a random superposition of delta functions distributed uniformly on the real line with mean density and mean strength . Our study is motivated by the close connection between this problem and classical diffusion in a random environment (the Sinai problem) in the presence of random absorbers: models the force field acting on the diffusing particle and models the absorption properties of the medium in which the diffusion takes place. The focus is on the calculation of the complex Lyapunov exponent , where is the integrated density of states per unit length and the reciprocal of the localisation length. By using the continuous version of the Dyson-Schmidt method, we find an exact formula, in terms of a Hankel function, in the particular case where the strength of the delta functions is exponentially-distributed with mean . Building on this result, we then solve the general case— in the low-energy limit— in terms of an infinite sum of Hankel functions. Our main result, valid without restrictions on the parameters of the model, is that the integrated density of states exhibits the power law behaviour This confirms and extends several results obtained previously by approximate methods.

  20. Numerical study of the effect of disorder and magnetic field on the quantum transport of two-dimensional nanostructures modeled by tight-binding approximation

    Directory of Open Access Journals (Sweden)

    E Taghizdehsiskht

    2013-09-01

    Full Text Available  In recent years, semiconductor nanostructures have become the model systems of choice for investigation of electrical conduction on short length scales. Quantum transport is studied in a two dimensional electron gas because of the combination of a large Fermi wavelength and large mean free path. In the present work, a numerical method is implemented in order to contribute to the understanding of quantum transport in narrow channels in different conditions of disorder and magnetic fields. We have used an approach that has proved to be very useful in describing mesoscopic transport. We have assumed zero temperature and phase coherent transport. By using the trick that a conductor connected to infinite leads can be replaced by a finite conductor with the effect of the leads incorporated through a 'self-energy' function, a convenient method was provided for evaluating the Green's function of the whole device numerically. Then, Fisher-Lee relations was used for calculating the transmission coefficients through coherent mesoscopic conductors. Our calculations were done in a model system with Hard-wall boundary conditions in the transverse direction, and the Anderson model of disorder was used in disordered samples. We have presented the results of quantum transport for different strengths of disorder and introduced magnetic fields. Our results confirmed the Landauer formalism for calculation of electronic transport. We observed that weak localization effect can be removed by application of a weak perpendicular magnetic field. Finally, we numerically showed the transition to the integral quantum Hall effect regime through the suppression of backscattering on a disordered model system by calculating the two­ terminal conductance of a quasi-one-dimensional quantum conductor as a strong magnetic field is applied. Our results showed that this regime is entered when there is a negligible overlap between electron edge states localized at opposite sides of

  1. Cooper pairing of two-dimensional electrons in a quantizing magnetic field and the fractional quantum Hall effect

    Science.gov (United States)

    Pashitskiĭ , E. A.

    1999-08-01

    A brief review of the current state of the theory of fractional quantum Hall effect (FQHE) is given along with the assumption of possible connection between the experimentally observed features of the Hall resistance RH of a two-dimensional (2D) electron system in a strong quantizing magnetic field for a fractional filling factor of the lowest Landau level ν=q/(2n+1) with q⩾2, which cannot be described by the Laughlin wave function antisymmetric relative to pair transpositions, and the Cooper pairing of 2D electrons. It is assumed that the electron-electron attraction essential for Cooper pairing can be due to the interaction of 2D electrons with the surface acoustic waves (2D phonons) and the surface 2D plasmons localized near the crystal interfaces (heterojunctions) in the vicinity of inversion layers in the metal-insulator-semiconductor (MIS) structures and heterostructures. The coexistence of coupled electron pairs and unpaired electrons under the FQHE conditions must lead to peculiarities of RH for values of ν described by the Halperin relation following from the symmetry properties of the "mixed" wave function of pairs (bosons) and electrons (fermions). This relation makes it possible in principle to describe all experimental data on FQHE. The summation of "ladder" diagrams diverging according to a power law for T→0 leads to a Bethe-Salpeter-type equation for the vertex part of the electron-electron interaction for a 2D system in a quantizing magnetic field taking into account electron-electron and electron-hole pairing in the Cooper and zero-sound channels. This equation is used to calculate the critical temperature Tc of the phase transition to the state with coupled Cooper pairs and to prove that the value of Tc in the ultra-quantum limit is independent of the effective mass of electrons, i.e., on the 2D density of states. The phase diagram of the 2D system is constructed for the variable electron concentration and magnetic field. It is shown that

  2. A quantum mechanical approach to establishing the magnetic field orientation from a maser Zeeman profile

    Science.gov (United States)

    Green, J. A.; Gray, M. D.; Robishaw, T.; Caswell, J. L.; McClure-Griffiths, N. M.

    2014-06-01

    Recent comparisons of magnetic field directions derived from maser Zeeman splitting with those derived from continuum source rotation measures have prompted new analysis of the propagation of the Zeeman split components, and the inferred field orientation. In order to do this, we first review differing electric field polarization conventions used in past studies. With these clearly and consistently defined, we then show that for a given Zeeman splitting spectrum, the magnetic field direction is fully determined and predictable on theoretical grounds: when a magnetic field is oriented away from the observer, the left-hand circular polarization is observed at higher frequency and the right-hand polarization at lower frequency. This is consistent with classical Lorentzian derivations. The consequent interpretation of recent measurements then raises the possibility of a reversal between the large-scale field (traced by rotation measures) and the small-scale field (traced by maser Zeeman splitting).

  3. Scale magnetic effect in quantum electrodynamics and the Wigner-Weyl formalism

    Science.gov (United States)

    Chernodub, M. N.; Zubkov, M. A.

    2017-09-01

    The scale magnetic effect (SME) is the generation of electric current due to a conformal anomaly in an external magnetic field in curved spacetime. The effect appears in a vacuum with electrically charged massless particles. Similarly to the Hall effect, the direction of the induced anomalous current is perpendicular to the direction of the external magnetic field B and to the gradient of the conformal factor τ , while the strength of the current is proportional to the beta function of the theory. In massive electrodynamics the SME remains valid, but the value of the induced current differs from the current generated in the system of massless fermions. In the present paper we use the Wigner-Weyl formalism to demonstrate that in accordance with the decoupling property of heavy fermions the corresponding anomalous conductivity vanishes in the large-mass limit with m2≫|e B | and m ≫|∇τ | .

  4. The influence of polar optical phonon confinement on the binding energy of a hydrogenic impurity in quantum wires in the perpendicular electric and magnetic fields

    Science.gov (United States)

    Vartanian, A. L.; Shahbandari, A.; Yeranosyan, M. A.; Kirakosyan, A. A.

    2012-03-01

    The hydrogenic impurity binding energy in cylindrical quantum well wire with a finite confining potential including both barriers of finite height and an applied electric and magnetic fields are studied. The polaron effect on the ground-state binding energy are investigated by means of Landau-Pekar variation technique. The results for the binding energy as well as polaronic correction with taking into account polar optical phonon confinement effect are obtained as a function of the applied fields for different position of the impurity. Our calculations are compared with previous results in quantum wires of comparable dimensions.

  5. Quantum potential theory

    CERN Document Server

    Schürmann, Michael

    2008-01-01

    This volume contains the revised and completed notes of lectures given at the school "Quantum Potential Theory: Structure and Applications to Physics," held at the Alfried-Krupp-Wissenschaftskolleg in Greifswald from February 26 to March 10, 2007. Quantum potential theory studies noncommutative (or quantum) analogs of classical potential theory. These lectures provide an introduction to this theory, concentrating on probabilistic potential theory and it quantum analogs, i.e. quantum Markov processes and semigroups, quantum random walks, Dirichlet forms on C* and von Neumann algebras, and boundary theory. Applications to quantum physics, in particular the filtering problem in quantum optics, are also presented.

  6. Hexagonal plaquette spin-spin interactions and quantum magnetism in a two-dimensional ion crystal

    Science.gov (United States)

    Nath, R.; Dalmonte, M.; Glaetzle, A. W.; Zoller, P.; Schmidt-Kaler, F.; Gerritsma, R.

    2015-06-01

    We propose a trapped ion scheme en route to realize spin Hamiltonians on a Kagome lattice which, at low energies, are described by emergent {{{Z}}}2 gauge fields, and support a topological quantum spin liquid ground state. The enabling element in our scheme is the hexagonal plaquette spin-spin interactions in a two-dimensional ion crystal. For this, the phonon-mode spectrum of the crystal is engineered by standing-wave optical potentials or by using Rydberg excited ions, thus generating localized phonon-modes around a hexagon of ions selected out of the entire two-dimensional crystal. These tailored modes can mediate spin-spin interactions between ion-qubits on a hexagonal plaquette when subject to state-dependent optical dipole forces. We discuss how these interactions can be employed to emulate a generalized Balents-Fisher-Girvin model in minimal instances of one and two plaquettes. This model is an archetypical Hamiltonian in which gauge fields are the emergent degrees of freedom on top of the classical ground state manifold. Under realistic situations, we show the emergence of a discrete Gauss’s law as well as the dynamics of a deconfined charge excitation on a gauge-invariant background using the two-plaquettes trapped ions spin-system. The proposed scheme in principle allows further scaling in a future trapped ion quantum simulator, and we conclude that our work will pave the way towards the simulation of emergent gauge theories and quantum spin liquids in trapped ion systems.

  7. Magnetic-field- and pressure-induced quantum phases in complex materials.

    Science.gov (United States)

    Kim, Minjung; Barath, Harini; Chen, Xiaoqian; Joe, Young-Il; Fradkin, Eduardo; Abbamonte, Peter; Cooper, S Lance

    2010-03-12

    This Progress Report presents temperature-, magnetic-field-, and pressure-dependent Raman measurements of strongly correlated materials such as the charge-ordering manganese perovskites, the multiferroic material TbMnO(3), and the charge-density wave (CDW) materials 1T-TiSe(2) and Cu(x)TiSe(2). These studies illustrate the rich array of phases and properties that can be accessed with field and pressure tuning in these materials, and demonstrate the efficacy of using magnetic-field- and pressure-dependent scattering methods to elucidate the microscopic changes associated with highly tunable behavior in complex materials.

  8. Can repetitive magnetic stimulation improve cognition in schizophrenia? Pilot data from a randomized controlled trial.

    Science.gov (United States)

    Barr, Mera S; Farzan, Faranak; Rajji, Tarek K; Voineskos, Aristotle N; Blumberger, Daniel M; Arenovich, Tamara; Fitzgerald, Paul B; Daskalakis, Zafiris J

    2013-03-15

    Working memory represents a core cognitive domain that is impaired in schizophrenia for which there are currently no satisfactory treatments. Repetitive transcranial magnetic stimulation (rTMS) targeted over the dorsolateral prefrontal cortex has been shown to modulate neurophysiological mechanisms linked to working memory in schizophrenia and improves working memory performance in healthy subjects and might therefore represent a treatment modality for schizophrenia patients. The objectives were to evaluate the effects of rTMS on working memory performance in schizophrenia patients and evaluate whether rTMS normalizes performance to healthy subject levels. In a 4-week randomized double-blind sham-controlled pilot study design, 27 medicated schizophrenia patients were tested at the Centre for Addiction and Mental Health (a university teaching hospital that provides psychiatric care to a large urban catchment area and serves as a tertiary referral center for the province of Ontario). Patients performed the verbal working memory n-back task before and after rTMS magnetic resonance image targeted bilaterally sequentially to left and right dorsolateral prefrontal cortex 750 pulses/side at 20 Hz for 20 treatments. The main outcome measure was mean magnitude of change in the n-back accuracy for target responses with active (n = 13) or sham (n = 12) rTMS treatment course. The rTMS significantly improved 3-back accuracy for targets compared with placebo sham (Cohen's d = .92). The improvement in 3-back accuracy was also found to be at a level comparable to healthy subjects. These pilot data suggest that bilateral rTMS might be a novel, efficacious, and safe treatment for working memory deficits in patients with schizophrenia. Copyright © 2013 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

  9. Magnetic-film atom chip with 10 μm period lattices of microtraps for quantum information science with Rydberg atoms

    Energy Technology Data Exchange (ETDEWEB)

    Leung, V. Y. F. [Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, PO Box 94485, 1090 GL Amsterdam (Netherlands); Complex Photonic Systems (COPS), MESA Institute for Nanotechnology, University of Twente, PO Box 217, 7500 AE Enschede (Netherlands); Pijn, D. R. M.; Schlatter, H.; Torralbo-Campo, L.; La Rooij, A. L.; Mulder, G. B.; Naber, J.; Soudijn, M. L.; Tauschinsky, A.; Spreeuw, R. J. C., E-mail: r.j.c.spreeuw@uva.nl [Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, PO Box 94485, 1090 GL Amsterdam (Netherlands); Abarbanel, C.; Hadad, B.; Golan, E. [Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Be' er Sheva 84105 (Israel); Folman, R. [Department of Physics and Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Be' er Sheva 84105 (Israel)

    2014-05-15

    We describe the fabrication and construction of a setup for creating lattices of magnetic microtraps for ultracold atoms on an atom chip. The lattice is defined by lithographic patterning of a permanent magnetic film. Patterned magnetic-film atom chips enable a large variety of trapping geometries over a wide range of length scales. We demonstrate an atom chip with a lattice constant of 10 μm, suitable for experiments in quantum information science employing the interaction between atoms in highly excited Rydberg energy levels. The active trapping region contains lattice regions with square and hexagonal symmetry, with the two regions joined at an interface. A structure of macroscopic wires, cutout of a silver foil, was mounted under the atom chip in order to load ultracold {sup 87}Rb atoms into the microtraps. We demonstrate loading of atoms into the square and hexagonal lattice sections simultaneously and show resolved imaging of individual lattice sites. Magnetic-film lattices on atom chips provide a versatile platform for experiments with ultracold atoms, in particular for quantum information science and quantum simulation.

  10. Magnetic-film atom chip with 10 μm period lattices of microtraps for quantum information science with Rydberg atoms.

    Science.gov (United States)

    Leung, V Y F; Pijn, D R M; Schlatter, H; Torralbo-Campo, L; La Rooij, A L; Mulder, G B; Naber, J; Soudijn, M L; Tauschinsky, A; Abarbanel, C; Hadad, B; Golan, E; Folman, R; Spreeuw, R J C

    2014-05-01

    We describe the fabrication and construction of a setup for creating lattices of magnetic microtraps for ultracold atoms on an atom chip. The lattice is defined by lithographic patterning of a permanent magnetic film. Patterned magnetic-film atom chips enable a large variety of trapping geometries over a wide range of length scales. We demonstrate an atom chip with a lattice constant of 10 μm, suitable for experiments in quantum information science employing the interaction between atoms in highly excited Rydberg energy levels. The active trapping region contains lattice regions with square and hexagonal symmetry, with the two regions joined at an interface. A structure of macroscopic wires, cutout of a silver foil, was mounted under the atom chip in order to load ultracold (87)Rb atoms into the microtraps. We demonstrate loading of atoms into the square and hexagonal lattice sections simultaneously and show resolved imaging of individual lattice sites. Magnetic-film lattices on atom chips provide a versatile platform for experiments with ultracold atoms, in particular for quantum information science and quantum simulation.

  11. Structure of the incommensurate phase of the quantum magnet TiOCl

    Czech Academy of Sciences Publication Activity Database

    Schönleber, A.; van Smaalen, S.; Palatinus, Lukáš

    2006-01-01

    Roč. 73, č. 21 (2006), 214410/1-214410/4 ISSN 1098-0121 Institutional research plan: CEZ:AV0Z10100521 Keywords : spin-Peierls transition * incommensurate phase Subject RIV: BM - Solid Matter Physics ; Magnet ism Impact factor: 3.107, year: 2006

  12. Optical absorption and magnetic circular dichroism spectra of thiouracils: a quantum mechanical study in solution

    DEFF Research Database (Denmark)

    Martínez-Fernández, L.; Fahleson, Tobias; Norman, Patrick

    2017-01-01

    The excited electronic states of 2-thiouracil, 4-thiouracil and 2,4-dithiouracil, the analogues of uracil where the carbonyl oxygens are substituted by sulphur atoms, have been investigated by computing the magnetic circular dichroism (MCD) and one-photon absorption (OPA) spectra at the time-depe...

  13. Reduction of claustrophobia during magnetic resonance imaging: methods and design of the "CLAUSTRO" randomized controlled trial.

    Science.gov (United States)

    Enders, Judith; Zimmermann, Elke; Rief, Matthias; Martus, Peter; Klingebiel, Randolf; Asbach, Patrick; Klessen, Christian; Diederichs, Gerd; Bengner, Thomas; Teichgräber, Ulf; Hamm, Bernd; Dewey, Marc

    2011-02-10

    Magnetic resonance (MR) imaging has been described as the most important medical innovation in the last 25 years. Over 80 million MR procedures are now performed each year and on average 2.3% (95% confidence interval: 2.0 to 2.5%) of all patients scheduled for MR imaging suffer from claustrophobia. Thus, prevention of MR imaging by claustrophobia is a common problem and approximately 2,000,000 MR procedures worldwide cannot be completed due to this situation. Patients with claustrophobic anxiety are more likely to be frightened and experience a feeling of confinement or being closed in during MR imaging. In these patients, conscious sedation and additional sequences (after sedation) may be necessary to complete the examinations. Further improvements in MR design appear to be essential to alleviate this situation and broaden the applicability of MR imaging. A more open scanner configuration might help reduce claustrophobic reactions while maintaining image quality and diagnostic accuracy. We propose to analyze the rate of claustrophobic reactions, clinical utility, image quality, patient acceptance, and cost-effectiveness of an open MR scanner in a randomized comparison with a recently designed short-bore but closed scanner with 97% noise reduction. The primary aim of this study is thus to determine whether an open MR scanner can reduce claustrophobic reactions, thereby enabling more examinations of claustrophobic patients without incurring the safety issues associated with conscious sedation. In this manuscript we detail the methods and design of the prospective "CLAUSTRO" trial. This randomized controlled trial will be the first direct comparison of open vertical and closed short-bore MR systems in regards to claustrophobia and image quality as well as diagnostic utility. ClinicalTrials.gov: NCT00715806.

  14. Reduction of claustrophobia during magnetic resonance imaging: methods and design of the "CLAUSTRO" randomized controlled trial

    Directory of Open Access Journals (Sweden)

    Teichgräber Ulf

    2011-02-01

    Full Text Available Abstract Background Magnetic resonance (MR imaging has been described as the most important medical innovation in the last 25 years. Over 80 million MR procedures are now performed each year and on average 2.3% (95% confidence interval: 2.0 to 2.5% of all patients scheduled for MR imaging suffer from claustrophobia. Thus, prevention of MR imaging by claustrophobia is a common problem and approximately 2,000,000 MR procedures worldwide cannot be completed due to this situation. Patients with claustrophobic anxiety are more likely to be frightened and experience a feeling of confinement or being closed in during MR imaging. In these patients, conscious sedation and additional sequences (after sedation may be necessary to complete the examinations. Further improvements in MR design appear to be essential to alleviate this situation and broaden the applicability of MR imaging. A more open scanner configuration might help reduce claustrophobic reactions while maintaining image quality and diagnostic accuracy. Methods/Design We propose to analyze the rate of claustrophobic reactions, clinical utility, image quality, patient acceptance, and cost-effectiveness of an open MR scanner in a randomized comparison with a recently designed short-bore but closed scanner with 97% noise reduction. The primary aim of this study is thus to determine whether an open MR scanner can reduce claustrophobic reactions, thereby enabling more examinations of claustrophobic patients without incurring the safety issues associated with conscious sedation. In this manuscript we detail the methods and design of the prospective "CLAUSTRO" trial. Discussion This randomized controlled trial will be the first direct comparison of open vertical and closed short-bore MR systems in regards to claustrophobia and image quality as well as diagnostic utility. Trial Registration ClinicalTrials.gov: NCT00715806

  15. Quantum physics without quantum philosophy

    Energy Technology Data Exchange (ETDEWEB)

    Duerr, Detlef [Muenchen Univ. (Germany). Mathematisches Inst.; Goldstein, Sheldon [Rutgers State Univ., Piscataway, NJ (United States). Dept. of Mathematics; Zanghi, Nino [Genova Univ. (Italy); Istituto Nazionale Fisica Nucleare, Genova (Italy)

    2013-02-01

    Integrates and comments on the authors' seminal papers in the field. Emphasizes the natural way in which quantum phenomena emerge from the Bohmian picture. Helps to answer many of the objections raised to Bohmian quantum mechanics. Useful overview and summary for newcomers and students. It has often been claimed that without drastic conceptual innovations a genuine explanation of quantum interference effects and quantum randomness is impossible. This book concerns Bohmian mechanics, a simple particle theory that is a counterexample to such claims. The gentle introduction and other contributions collected here show how the phenomena of non-relativistic quantum mechanics, from Heisenberg's uncertainty principle to non-commuting observables, emerge from the Bohmian motion of particles, the natural particle motion associated with Schroedinger's equation. This book will be of value to all students and researchers in physics with an interest in the meaning of quantum theory as well as to philosophers of science.

  16. Efficient quantum walk on a quantum processor

    Science.gov (United States)

    Qiang, Xiaogang; Loke, Thomas; Montanaro, Ashley; Aungskunsiri, Kanin; Zhou, Xiaoqi; O'Brien, Jeremy L.; Wang, Jingbo B.; Matthews, Jonathan C. F.

    2016-01-01

    The random walk formalism is used across a wide range of applications, from modelling share prices to predicting population genetics. Likewise, quantum walks have shown much potential as a framework for developing new quantum algorithms. Here we present explicit efficient quantum circuits for implementing continuous-time quantum walks on the circulant class of graphs. These circuits allow us to sample from the output probability distributions of quantum walks on circulant graphs efficiently. We also show that solving the same sampling problem for arbitrary circulant quantum circuits is intractable for a classical computer, assuming conjectures from computational complexity theory. This is a new link between continuous-time quantum walks and computational complexity theory and it indicates a family of tasks that could ultimately demonstrate quantum supremacy over classical computers. As a proof of principle, we experimentally implement the proposed quantum circuit on an example circulant graph using a two-qubit photonics quantum processor. PMID:27146471

  17. Efficient quantum walk on a quantum processor.

    Science.gov (United States)

    Qiang, Xiaogang; Loke, Thomas; Montanaro, Ashley; Aungskunsiri, Kanin; Zhou, Xiaoqi; O'Brien, Jeremy L; Wang, Jingbo B; Matthews, Jonathan C F

    2016-05-05

    The random walk formalism is used across a wide range of applications, from modelling share prices to predicting population genetics. Likewise, quantum walks have shown much potential as a framework for developing new quantum algorithms. Here we present explicit efficient quantum circuits for implementing continuous-time quantum walks on the circulant class of graphs. These circuits allow us to sample from the output probability distributions of quantum walks on circulant graphs efficiently. We also show that solving the same sampling problem for arbitrary circulant quantum circuits is intractable for a classical computer, assuming conjectures from computational complexity theory. This is a new link between continuous-time quantum walks and computational complexity theory and it indicates a family of tasks that could ultimately demonstrate quantum supremacy over classical computers. As a proof of principle, we experimentally implement the proposed quantum circuit on an example circulant graph using a two-qubit photonics quantum processor.

  18. Crystalline structure and magnetic properties of Fe2CrSi Heusler alloy films: New ferromagnetic material for high-performance magnetic random access memory

    Science.gov (United States)

    Yoshimura, S.; Asano, H.; Nakamura, Y.; Yamaji, K.; Takeda, Y.; Matsui, M.; Ishida, S.; Nozaki, Y.; Matsuyama, K.

    2008-04-01

    A new Heusler alloy, Fe2CrSi, which has high spin polarization (P), low saturation magnetization (Ms), and a low Curie temperature (TC), was investigated in order to fabricate high-performance magnetic tunnel junctions (MTJs) with a high tunnel magnetoresistance ratio and with low critical current for the spin-transfer switching method, or a low switching field for the thermally assisted magnetization reversal technique. The main results are as follows: (1) P and the magnetic moment of Fe2CrSi with an L21 structure were 0.98 and 1.98μB/f.u., respectively, according to density of states calculations. (2) Fe2CrSi films show the (100) orientation with a B2 structure on a MgO substrate upon a thermal treatment with optimum temperature and duration. (3) Fe2CrSi films have Ms and TC values of 385emu /cm3 and 630K, respectively. (4) The (100) oriented epitaxial MTJs are produced with Fe2CrSi films fabricated with the optimized thermal treatment condition. It is found that the Fe2CrSi Heusler alloy films are a suitable ferromagnetic material for high-performance magnetic random access memory.

  19. Rapid detection of hendra virus using magnetic particles and quantum dots.

    Science.gov (United States)

    Lisi, Fabio; Falcaro, Paolo; Buso, Dario; Hill, Anita J; Barr, Jennifer A; Crameri, Gary; Nguyen, Tich-Lam; Wang, Lin-Fa; Mulvaney, Paul

    2012-09-01

    A proof-of-concept for the development of a fast and portable Hendra virus biosensor is presented. Hendra virus, a deadly emerging pathogen in Australia, can be co-localized, concentrated and revealed using simultaneously magnetic and luminescent functional particles. This method should be applicable for the early detection of any other virus by targeting the specific virus with the corresponding antibody. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Construction of magnetic-carbon-quantum-dots-probe-labeled apoferritin nanocages for bioimaging and targeted therapy.

    Science.gov (United States)

    Yao, Hanchun; Su, Li; Zeng, Man; Cao, Li; Zhao, Weiwei; Chen, Chengqun; Du, Bin; Zhou, Jie

    Carbon dots (CDs) are one of the most highlighted carbon-based materials for biological applications, such as optical imaging nanoprobes, which are used for labeling cells in cancer treatment mainly due to their biocompatibility and unique optical properties. In this study, gadolinium (Gd)-complex-containing CDs were obtained through a one-step microwave method to develop multimodal nanoprobes integrating the advantages of optical and magnetic imaging. The obtained Gd-CDs exhibited highly fluorescent properties with excellent water solubility and biological compatibility. Natural apoferritin (AFn) nanocages, an excellent drug delivery carrier, are hollow in structure, with their pH-dependent, unfolding-refolding process at pH 2.0 and 7.4. The chemotherapeutic drug doxorubicin (DOX) can be highly effective and encapsulated into AFn cavity. A widely used tumor-targeting molecule, folic acid (FA), functionalized the surface of AFn to obtain an active tumor targeting effect on MCF-7 cells and malignant tumors in mice models. In this study, an AFn nanocarrier encapsulating high concentration of DOX labeled with magnetic and fluorescent Gd-CDs probe was developed. Gd-CDs exhibited a unique green photoluminescence and almost no toxicity compared with free GdCl3. Furthermore, Gd-doped CDs significantly increased the circulation time and decreased the toxicity of Gd(3+) in in vitro and in vivo magnetic resonance imaging, which demonstrated that the AFn nanocages labeled with Gd-CD compounds could serve as an excellent T1 contrast agent for magnetic resonance imaging. The self-assembling multifunctional Gd-CDs/AFn (DOX)/FA nanoparticles have a great potential for cancer theranostic applications.