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Sample records for two-dimensional quantum heisenberg

  1. Evidence for an unconventional universality class from a two-dimensional dimerized quantum heisenberg model.

    Science.gov (United States)

    Wenzel, Sandro; Bogacz, Leszek; Janke, Wolfhard

    2008-09-19

    The two-dimensional J-J' dimerized quantum Heisenberg model is studied on the square lattice by means of (stochastic series expansion) quantum Monte Carlo simulations as a function of the coupling ratio alpha=J'/J. The critical point of the order-disorder quantum phase transition in the J-J' model is determined as alpha_c=2.5196(2) by finite-size scaling for up to approximately 10 000 quantum spins. By comparing six dimerized models we show, contrary to the current belief, that the critical exponents of the J-J' model are not in agreement with the three-dimensional classical Heisenberg universality class. This lends support to the notion of nontrivial critical excitations at the quantum critical point.

  2. Effect of Quantum Fluctuation on Two-Dimensional Spatially Anisotropic Heisenberg Antiferromagnet with Integer Spin

    Institute of Scientific and Technical Information of China (English)

    JI An-Chun; TIAN Guang-Shan

    2006-01-01

    In the present paper, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuation in a two-dimensional spatially anisotropic Heisenberg antiferromagnet with integer spin S. Previously, someauthors computed this quantity by the mean-field theory based on the Schwinger boson representation of spin operators.However, for S = 1, their result is much less than the one derived by numerical calculations. By taking the effect ofquantum spin fluctuation into consideration, we are able to produce a greatly improved result.

  3. Spin dynamics and magnetic correlation length in two-dimensional quantum heisenberg antiferromagnets

    Science.gov (United States)

    Carretta; Ciabattoni; Cuccoli; Mognaschi; Rigamonti; Tognetti; Verrucchi

    2000-01-10

    The correlated spin dynamics and temperature dependence of the correlation length xi(T) in two-dimensional quantum (S = 1/2) Heisenberg antiferromagnets (2DQHAF) on a square lattice are discussed in light of experimental results of proton spin lattice relaxation in copper formiate tetradeuterate. In this compound the exchange constant is much smaller than the one in recently studied 2DQHAF, such as La2CuO4 and Sr2CuO2Cl2. Thus the spin dynamics can be probed in detail over a wider temperature range. The NMR relaxation rates turn out to be in excellent agreement with a theoretical mode-coupling calculation. The deduced temperature behavior of xi(T) is in agreement with high-temperature expansions, quantum Monte Carlo simulations, and the pure quantum self-consistent harmonic approximation. Contrary to the predictions of the theories based on the nonlinear sigma model, no evidence of crossover between different quantum regimes is observed.

  4. Spin transport in the two-dimensional quantum disordered anisotropic Heisenberg model

    Energy Technology Data Exchange (ETDEWEB)

    Lima, L.S. [Departamento de Física e Matemática, Centro Federal de Educação Tecnológica de Minas Gerais, 30510-000 Belo Horizonte, MG (Brazil); Pires, A.S.T.; Costa, B.V. [Departamento de Física ICEx, UFMG, CP 702, 31270-901 Belo Horizonte, MG (Brazil)

    2014-12-15

    We use the self consistent harmonic approximation together with the Linear Response Theory to study the effect of nonmagnetic disorder on spin transport in the quantum diluted two-dimensional anisotropic Heisenberg model with spin S=1 in a square lattice. The model has a BKT transition at zero dilution. We calculate the regular part of the spin conductivity σ{sup reg}(ω) and the Drude weight D{sub S}(T) as a function of the non-magnetic concentration, x. Our calculations show that the spin conductivity drops abruptly to zero at x{sub c}{sup SCHA}≈0.5 indicating that the system changes from an ideal spin conductor state to an insulator. This value is far above the site percolation threshold x{sub c}{sup site}≈0.41. Although the SCHA fails in determining precisely the percolation threshold, both the spin conductivity and the Drude weight show a quite regular behavior inside 0≤x≤x{sub c}{sup SCHA} indicating that the transition stays in the same universality class all along the interval. - Highlights: • The site dilution generates a large influence on regular part of the spin conductivity, σ{sup reg}(ω), and in the Drude weight, D(T). • In a concentration of impurities about x≈0.5, the regular part of the spin conductivity and the Drude weight fall to zero. • In this point we have a change in the state of the system from an ideal spin conductor to a spin insulator.

  5. Quantum Phase Transition in Quasi-two-dimensional Heisenberg Antiferromagnet with Single-Ion Anisotropy

    Institute of Scientific and Technical Information of China (English)

    JI An-Chun; TIAN Guang-Shan

    2007-01-01

    In the present paper, we investigate the quantum phase transition in a spatially anisotropic antiferromagnetic Heisenberg model of S = 1 with single-ion energy anisotropy. By using the Schwinger boson representation, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuations. We find that, for the positive single-ion energy, a nonzero value of Jc⊥ is always needed to stabilize the antiferromagnetic long-range order in this model. It resolves a difference among literature and shows clearly that the effect of quantum fluctuations may qualitatively change a result obtained by the mean-field theories on lower-dimensional systems.

  6. Evidence for deconfined quantum criticality in a two-dimensional Heisenberg model with four-spin interactions.

    Science.gov (United States)

    Sandvik, Anders W

    2007-06-01

    Using ground-state projector quantum Monte Carlo simulations in the valence-bond basis, it is demonstrated that nonfrustrating four-spin interactions can destroy the Néel order of the two-dimensional S=1/2 Heisenberg antiferromagnet and drive it into a valence-bond solid (VBS) phase. Results for spin and dimer correlations are consistent with a single continuous transition, and all data exhibit finite-size scaling with a single set of exponents, z=1, nu=0.78+/-0.03, and eta=0.26+/-0.03. The unusually large eta and an emergent U(1) symmetry, detected using VBS order parameter histograms, provide strong evidence for a deconfined quantum critical point.

  7. Two-Dimensional Toda-Heisenberg Lattice

    Directory of Open Access Journals (Sweden)

    Vadim E. Vekslerchik

    2013-06-01

    Full Text Available We consider a nonlinear model that is a combination of the anisotropic two-dimensional classical Heisenberg and Toda-like lattices. In the framework of the Hirota direct approach, we present the field equations of this model as a bilinear system, which is closely related to the Ablowitz-Ladik hierarchy, and derive its N-soliton solutions.

  8. Quantum Monte Carlo study on the phase transition for a generalized two-dimensional staggered dimerized Heisenberg model

    Institute of Scientific and Technical Information of China (English)

    Zheng Rui; Liu Bang-Gui

    2012-01-01

    In order to gain a deeper understanding of the quantum criticality in the explicitly staggered dimerized Heisenberg models,we study a generalized staggered dimer model named the J0 J1-J2 model,which corresponds to the staggered J J’ model on a square lattice and a honeycomb lattice when J1/J0 equals 1 and 0,respectively.Using the quantum Monte Carlo method,we investigate all the quantum critical points of these models with J1/J0 changing from 0 to 1as a function of coupling ratio α =J2/J0.We extract all the critical values of the coupling ratio αc for these models,and we also obtain the critical exponents v,β/v,and η using different finite-size scaling ans(a)tz,.All these exponents are not consistent with the three-dimensional Heisenberg universality class,indicating some unconventional quantum ciritcial points in these models.

  9. Two-dimensional quantum repeaters

    Science.gov (United States)

    Wallnöfer, J.; Zwerger, M.; Muschik, C.; Sangouard, N.; Dür, W.

    2016-11-01

    The endeavor to develop quantum networks gave rise to a rapidly developing field with far-reaching applications such as secure communication and the realization of distributed computing tasks. This ultimately calls for the creation of flexible multiuser structures that allow for quantum communication between arbitrary pairs of parties in the network and facilitate also multiuser applications. To address this challenge, we propose a two-dimensional quantum repeater architecture to establish long-distance entanglement shared between multiple communication partners in the presence of channel noise and imperfect local control operations. The scheme is based on the creation of self-similar multiqubit entanglement structures at growing scale, where variants of entanglement swapping and multiparty entanglement purification are combined to create high-fidelity entangled states. We show how such networks can be implemented using trapped ions in cavities.

  10. High-energy magnon dispersion and multimagnon continuum in the two-dimensional Heisenberg antiferromagnet.

    Science.gov (United States)

    Sandvik, A W; Singh, R R

    2001-01-15

    We use quantum Monte Carlo simulations and numerical analytic continuation to study high-energy spin excitations in the two-dimensional S = 1/2 Heisenberg antiferromagnet at low temperature. We present results for both the transverse (x) and longitudinal (z) dynamic spin structure factors Sx,z(q,omega) at q = (pi,0) and (pi/2, pi/2). Linear spin-wave theory predicts no dispersion on the line connecting these momenta. Our calculations show that in fact the magnon energy at (pi,0) is 10% lower than at (pi/2, pi/2). We also discuss the transverse and longitudinal multimagnon continua and their relevance to neutron scattering experiments.

  11. Quantum Heisenberg--Weyl Algebras

    OpenAIRE

    Ballesteros, Angel; Herranz, Francisco J.; Parashar, Preeti

    1996-01-01

    All Lie bialgebra structures on the Heisenberg--Weyl algebra $[A_+,A_-]=M$ are classified and explicitly quantized. The complete list of quantum Heisenberg--Weyl algebras so obtained includes new multiparameter deformations, most of them being of the non-coboundary type.

  12. Phase transitions in the two-dimensional Anisotropic Biquadratic Heisenberg Model

    Energy Technology Data Exchange (ETDEWEB)

    Moura, A.R., E-mail: armoura@infis.ufu.br [Universidade Federal de Uberlândia (Brazil); Pires, A.S.T., E-mail: antpires@fisica.ufmg.br [Universidade Federal de Minas Gerais (Brazil); Pereira, A.R., E-mail: apereira@ufv.br [Universidade Federal de Viçosa (Brazil)

    2014-05-01

    In this paper we study the influence of the single-ion anisotropy in the two-dimensional biquadratic Heisenberg model (ABHM) on the square lattice at zero and finite low temperatures. It is common to represent the bilinear and biquadratic terms by J{sub 1}=Jcosθ and J{sub 2}=Jsinθ, respectively, and the many phases present in the model as a function of θ are well documented. However we have adopted a constant value for the bilinear constant (J{sub 1}=1) and small values of the biquadratic term (|J{sub 2}|quantum phase transition due to the single-ion anisotropic constant D. For values below a critical anisotropic constant D{sub c} the energy spectrum is gapless and at low finite temperatures the order parameter correlation has an algebraic decay (quasi-long-range order). Moreover, in DD{sub c}, the excited states are gapped and there is no spin long-range order (LRO) even at zero temperature. Using Schwinger bosonic representation and Self-Consistent Harmonic Approximation (SCHA), we have studied the quantum and thermal phase transitions as a function of the bilinear and biquadratic constants. - Highlights: • We study the anisotropic biquadric bilinear Heisenberg model on a square lattice. • We show the quantum phase transition associated with the anisotropic constant. • We obtain a thermal phase transition similar to the BKT transition.

  13. Neel order in the two-dimensional S=1/2 Heisenberg Model

    OpenAIRE

    Löw, Ute

    2007-01-01

    The existence of Neel order in the S=1/2 Heisenberg model on the square lattice at T=0 is shown using inequalities set up by Kennedy, Lieb and Shastry in combination with high precision Quantum Monte Carlo data.

  14. Properties of the two-dimensional spin-1/2 Heisenberg model on a honeycomb lattice with interlayer coupling

    Directory of Open Access Journals (Sweden)

    U. Löw

    2009-01-01

    Full Text Available The magnetic properties of the two-dimensional S=1/2 (quantum antiferromagnetic Heisenberg model on a honeycomb lattice with and without interlayer coupling are studied by means of a continuous Euclidean time Quantum Monte-Carlo algorithm. The internal energy, the magnetic susceptibility and the staggered magnetization are determined in the full temperature range. For the two-dimensional system the ground-state energy/bond is found to be E0hc=-0.36303(13, and the zero temperature staggered magnetization mst=0.2681(8. For coupled planes of honeycomb systems a phase transition from an ordered phase to a disordered phase is found at T/J=0.695(10.

  15. Spin Dynamics of $La_{2}CuO_{4}$ and the Two-Dimensional Heisenberg Model

    CERN Document Server

    Sandvik, A W; Barbara, U C S; Barbara, UC Santa

    1994-01-01

    The spin-lattice relaxation rate $1/T_1$ and the spin echo decay rate $1/T_{2G}$ for the 2D Heisenberg model are calculated using quantum Monte Carlo and maximum entropy analytic continuation. The results are compared to recent experiments on La$_2$CuO$_4$, as well as predictions based on the non-linear $\\sigma$-model.

  16. Quantum computation with two-dimensional graphene quantum dots

    Institute of Scientific and Technical Information of China (English)

    Li Jie-Sen; Li Zhi-Bing; Yao Dao-Xin

    2012-01-01

    We study an array of graphene nano sheets that form a two-dimensional S =1/2 Kagome spin lattice used for quantum computation.The edge states of the graphene nano sheets axe used to form quantum dots to confine electrons and perform the computation.We propose two schemes of bang-bang control to combat decoherence and realize gate operations on this array of quantum dots.It is shown that both schemes contain a great amount of information for quantum computation.The corresponding gate operations are also proposed.

  17. Bond-Dilution Effects on Two-Dimensional Spin-Gapped Heisenberg Antiferromagnets

    OpenAIRE

    Yasuda, Chitoshi; Todo, Synge; Matsumoto, Munehisa; Takayama, Hajime

    2001-01-01

    Bond-dilution effects on spin-1/2 spin-gapped Heisenberg antiferromagnets of coupled alternating chains on a square lattice are investigated by means of the quantum Monte Carlo method. It is found that, in contrast with the site-diluted system having an infinitesimal critical concentration, the bond-diluted system has a finite critical concentration of diluted bonds, $x_{c}$, above which the system is in an antiferromagnetic (AF) long-range ordered phase. In the disordered phase below $x_{c}$...

  18. A two-dimensional spin liquid in quantum kagome ice.

    Science.gov (United States)

    Carrasquilla, Juan; Hao, Zhihao; Melko, Roger G

    2015-06-22

    Actively sought since the turn of the century, two-dimensional quantum spin liquids (QSLs) are exotic phases of matter where magnetic moments remain disordered even at zero temperature. Despite ongoing searches, QSLs remain elusive, due to a lack of concrete knowledge of the microscopic mechanisms that inhibit magnetic order in materials. Here we study a model for a broad class of frustrated magnetic rare-earth pyrochlore materials called quantum spin ices. When subject to an external magnetic field along the [111] crystallographic direction, the resulting interactions contain a mix of geometric frustration and quantum fluctuations in decoupled two-dimensional kagome planes. Using quantum Monte Carlo simulations, we identify a set of interactions sufficient to promote a groundstate with no magnetic long-range order, and a gap to excitations, consistent with a Z2 spin liquid phase. This suggests an experimental procedure to search for two-dimensional QSLs within a class of pyrochlore quantum spin ice materials.

  19. Quantum entanglement in a two-dimensional ion trap

    Institute of Scientific and Technical Information of China (English)

    王成志; 方卯发

    2003-01-01

    In this paper, we investigate the quantum entanglement in a two-dimensional ion trap system. We discuss the quantum entanglement between the ion and phonons by using reduced entropy, and that between two degrees of freedom of the vibrational motion along x and y directions by using quantum relative entropy. We discuss also the influence of initial state of the system on the quantum entanglement and the relation between two entanglements in the trapped ion system.

  20. 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.

  1. Spin dynamics in a two-dimensional quantum gas

    DEFF Research Database (Denmark)

    Pedersen, Poul Lindholm; Gajdacz, Miroslav; Deuretzbacher, Frank

    2014-01-01

    We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimp......We have investigated spin dynamics in a two-dimensional quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions...

  2. Non perturbative methods in two dimensional quantum field theory

    CERN Document Server

    Abdalla, Elcio; Rothe, Klaus D

    1991-01-01

    This book is a survey of methods used in the study of two-dimensional models in quantum field theory as well as applications of these theories in physics. It covers the subject since the first model, studied in the fifties, up to modern developments in string theories, and includes exact solutions, non-perturbative methods of study, and nonlinear sigma models.

  3. Phase transitions in the two-dimensional single-ion anisotropic Heisenberg model with long-range interactions

    Energy Technology Data Exchange (ETDEWEB)

    Moura, A.R., E-mail: armoura@infis.ufu.br

    2014-11-15

    In the present work, we investigate the effects of long-range interactions on the phase transitions of a two-dimensional Heisenberg model with single-ion anisotropy at zero and finite temperatures. The Hamiltonian is given by H=∑{sub i≠j}J{sub ij}(S{sub i}{sup x}S{sub j}{sup x}+S{sub i}{sup y}S{sub j}{sup y}+λS{sub i}{sup z}S{sub j}{sup z})+D∑{sub i}(S{sub i}{sup z}){sup 2}, where J{sub ij}=−J|r{sub j}−r{sub i}|{sup −p}(p≥3) is a long-range ferromagnetic interaction (J>0), 0≤λ≤1 is an anisotropic constant and D is the single-ion anisotropic constant. It is well-known that the single-ion anisotropy D creates a competition between an ordered state (favored by the exchange interaction) and a disordered state, even at zero temperature. For small values of D, the system has a spontaneous magnetization m{sub z}≠0, while in the large-D phase m{sub z}=0 because a state with 〈S{sup z}〉≠0 is energetically unfavorable. Therefore a phase transition takes a place in some critical value D{sub c} due to quantum fluctuations. For systems with short-range interaction D{sub c}≈6 J (depending of λ constant) but in our model we have found larger values of D due to the higher cost to flip a spin. Since low-dimensional magnetic systems with long range interaction can be ordered at finite temperature, we also have analyzed the thermal phase transitions (similar to the BKT transition). The model has been studied by using a Schwinger boson formalism as well as the self-consistent harmonic approximation (SCHA) and both methods provide according results. - Highlights: • We study the two-dimensional single-ion anisotropic ferromagnetic model with long-range interactions. • We show the quantum phase transition associated with the single-ion anisotropic constant. • We investigate the influence of the power-law exponent in the phase transitions. • We obtain a thermal phase transition similar to the BKT transition.

  4. Quantum skyrmions in two-dimensional chiral magnets

    Science.gov (United States)

    Takashima, Rina; Ishizuka, Hiroaki; Balents, Leon

    2016-10-01

    We study the quantum mechanics of magnetic skyrmions in the vicinity of the skyrmion-crystal to ferromagnet phase boundary in two-dimensional magnets. We show that the skyrmion excitation has an energy dispersion that splits into multiple bands due to the combination of magnus force and the underlying lattice. Condensation of the skyrmions can give rise to an intermediate phase between the skyrmion crystal and ferromagnet: a quantum liquid, in which skyrmions are not spatially localized. We show that the critical behavior depends on the spin size S and the topological number of the skyrmion. Experimental signatures of quantum skyrmions in inelastic neutron-scattering measurements are also discussed.

  5. Classical and quantum anisotropic Heisenberg antiferromagnets

    Directory of Open Access Journals (Sweden)

    W. Selke

    2009-01-01

    Full Text Available We study classical and quantum Heisenberg antiferromagnets with exchange anisotropy of XXZ-type and crystal field single-ion terms of quadratic and quartic form in a field. The magnets display a variety of phases, including the spin-flop (or, in the quantum case, spin-liquid and biconical (corresponding, in the quantum lattice gas description, to supersolid phases. Applying ground-state considerations, Monte Carlo and density matrix renormalization group methods, the impact of quantum effects and lattice dimension is analysed. Interesting critical and multicritical behaviour may occur at quantum and thermal phase transitions.

  6. Multiple Potts Models Coupled to Two-Dimensional Quantum Gravity

    CERN Document Server

    Baillie, C F

    1992-01-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of {\\it multiple} $q=2,3,4$ state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the $c>1$ region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for $c>1$. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for $c>1$.

  7. Multiple Potts models coupled to two-dimensional quantum gravity

    Science.gov (United States)

    Baillie, C. F.; Johnston, D. A.

    1992-07-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of multiple q=2, 3, 4 state Potts models on dynamical phi-cubed graphs of spherical topology in order to investigate the c>1 region of two-dimensional quantum gravity. Contrary to naive expectation we find no obvious signs of pathological behaviour for c>1. We discuss the results in the light of suggestions that have been made for a modified DDK ansatz for c>1.

  8. Topological Quantum Optics in Two-Dimensional Atomic Arrays

    Science.gov (United States)

    Perczel, J.; Borregaard, J.; Chang, D. E.; Pichler, H.; Yelin, S. F.; Zoller, P.; Lukin, M. D.

    2017-07-01

    We demonstrate that two-dimensional atomic emitter arrays with subwavelength spacing constitute topologically protected quantum optical systems where the photon propagation is robust against large imperfections while losses associated with free space emission are strongly suppressed. Breaking time-reversal symmetry with a magnetic field results in gapped photonic bands with nontrivial Chern numbers and topologically protected, long-lived edge states. Due to the inherent nonlinearity of constituent emitters, such systems provide a platform for exploring quantum optical analogs of interacting topological systems.

  9. Quantum Correlations in Heisenberg XY Chain

    Institute of Scientific and Technical Information of China (English)

    ZHU Yin-Yan; ZHANG Yong

    2013-01-01

    Quantum correlations measured by quantum discord (QD),measurement-induced distance (MID),and geometric measure of quantum discord (GMQD) in two-qubit Heisenberg XY spin chain are investigated.The effects of DM interaction and anisotropic on the three correlations are considered.Characteristics of various correlation measures for the two-qubit states are compared.The increasing Dz increases QD,MID and GMQD monotonously while the increasing anisotropy both increases and decreases QD and GMQD.The three quantum correlations are always existent at very high temperature.MID is always larger than QD,but there is no definite ordering between QD and GMQD.

  10. Quantum Entanglement in Heisenberg Antiferromagnets

    CERN Document Server

    Subramanian, V

    2004-01-01

    Entanglement sharing among pairs of spins in Heisenberg antiferromagnets is investigated using the concurrence measure. For a nondegenerate S=0 ground state, a simple formula relates the concurrence to the diagonal correlation function. The concurrence length is seen to be extremely short. A few finite clusters are studied numerically, to see the trend in higher dimensions. It is argued that nearest-neighbour concurrence is zero for triangular and Kagome lattices. The concurrences in the maximal-spin states are explicitly calculated, where the concurrence averaged over all pairs is larger than the S=0 states.

  11. Entropic Barriers for Two-Dimensional Quantum Memories

    Science.gov (United States)

    Brown, Benjamin J.; Al-Shimary, Abbas; Pachos, Jiannis K.

    2014-03-01

    Comprehensive no-go theorems show that information encoded over local two-dimensional topologically ordered systems cannot support macroscopic energy barriers, and hence will not maintain stable quantum information at finite temperatures for macroscopic time scales. However, it is still well motivated to study low-dimensional quantum memories due to their experimental amenability. Here we introduce a grid of defect lines to Kitaev's quantum double model where different anyonic excitations carry different masses. This setting produces a complex energy landscape which entropically suppresses the diffusion of excitations that cause logical errors. We show numerically that entropically suppressed errors give rise to superexponential inverse temperature scaling and polynomial system size scaling for small system sizes over a low-temperature regime. Curiously, these entropic effects are not present below a certain low temperature. We show that we can vary the system to modify this bound and potentially extend the described effects to zero temperature.

  12. Heisenberg scaling in relativistic quantum metrology

    CERN Document Server

    Friis, Nicolai; Fuentes, Ivette; Dür, Wolfgang

    2015-01-01

    We address the issue of precisely estimating small parameters encoded in a general linear transformation of the modes of a bosonic quantum field. Such Bogoliubov transformations frequently appear in the context of quantum optics. We provide a recipe for computing the quantum Fisher information for arbitrary pure initial states. We show that the maximally achievable precision of estimation is inversely proportional to the squared average particle number, and that such Heisenberg scaling requires non-classical, but not necessarily entangled states. Our method further allows to quantify losses in precision arising from being able to monitor only finitely many modes, for which we identify a lower bound.

  13. Heisenberg scaling in Gaussian quantum metrology

    Science.gov (United States)

    Friis, Nicolai; Skotiniotis, Michalis; Fuentes, Ivette; Dür, Wolfgang

    2015-08-01

    We address the issue of precisely estimating small parameters encoded in a general linear transformation of the modes of a bosonic quantum field. Such Bogoliubov transformations frequently appear in the context of quantum optics. We provide a set of instructions for computing the quantum Fisher information for arbitrary pure initial states. We show that the maximally achievable precision of estimation is inversely proportional to the squared average particle number and that such Heisenberg scaling requires nonclassical but not necessarily entangled states. Our method further allows us to quantify losses in precision arising from being able to monitor only finitely many modes, for which we identify a lower bound.

  14. Quantum creep in a highly crystalline two-dimensional superconductor

    Science.gov (United States)

    Saito, Yu; Kasahara, Yuichi; Ye, Jianting; Iwasa, Yoshihiro; Nojima, Tsutomu

    Conventional studies on quantum phase transitions, especially on superconductor-insulator or superconductor-metal-insulator transitions have been performed in deposited metallic thin films such as Bismuth or MoGe. Although the techniques of thin films deposition have been considerably improved, unintentional disorder such as impurities and deficiencies, generating the pinning centers, seems to still exist in such systems. The mechanical exfoliated highly crystalline two-dimensional material can be a good candidate to realize a less-disordered 2D superconductor with extremely weak pinning, combined with transfer method or ionic-liquid gating. We report on the quantum metal, namely, magnetic-field-induced metallic state observed in an ion-gated two-dimensional superconductor based on an ultra-highly crystalline layered band insulator, ZrNCl. We found that the superconducting state is extremely fragile against external magnetic fields; that is, zero resistance state immediately disappears, once an external magnetic field switches on. This is because the present system is relatively clean and the pinning potential is extremely weak, which cause quantum tunneling and flux flow of vortices, resulting in metallic ground state.

  15. The XY model coupled to two-dimensional quantum gravity

    Science.gov (United States)

    Baillie, C. F.; Johnston, D. A.

    1992-09-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of the XY model on both fixed and dynamical phi-cubed graphs (i.e. without and with coupling to two-dimensional quantum gravity). We compare the numerical results with the theoretical expectation that the phase transition remains of KT type when the XY model is coupled to gravity. We also examine whether the universality we discovered in our earlier work on various Potts models with the same value of the central charge, c, carries over to the XY model, which has c=1.

  16. Magnetic quantum dot in two-dimensional topological insulators

    Science.gov (United States)

    Li, Guo; Zhu, Jia-Lin; Yang, Ning

    2017-03-01

    Magnetic quantum dots in two-dimensional band and topological insulators are studied by solving the modified Dirac model under nonuniform magnetic fields. The Landau levels split into discrete states with certain angular momentum. The states splitting from the zero Landau levels lie in the energy gap for topological insulators but are out of the gap for band insulators. It is found that the ground states oscillate between the spin-up and spin-down states when the magnetic field or the dot size changes. The oscillation manifests itself as changes of sign and strength of charge currents near the dot's edge.

  17. The XY Model Coupled to Two-Dimensional Quantum Gravity

    CERN Document Server

    Baillie, C F; 10.1016/0370-2693(92)91037-A

    2009-01-01

    We perform Monte Carlo simulations using the Wolff cluster algorithm of the XY model on both fixed and dynamical phi-cubed graphs (i.e. without and with coupling to two-dimensional quantum gravity). We compare the numerical results with the theoretical expectation that the phase transition remains of KT type when the XY model is coupled to gravity. We also examine whether the universality we discovered in our earlier work on various Potts models with the same value of the central charge, $c$, carries over to the XY model, which has $c=1$.

  18. Bond diluted anisotropic quantum Heisenberg model

    Energy Technology Data Exchange (ETDEWEB)

    Akıncı, Ümit, E-mail: umit.akinci@deu.edu.tr

    2013-10-15

    Effects of the bond dilution on the critical temperatures, phase diagrams and the magnetization behaviors of the isotropic and anisotropic quantum Heisenberg model have been investigated in detail. For the isotropic case, bond percolation threshold values have been determined for several numbers of two (2D) and three (3D) dimensional lattices. In order to investigate the effect of the anisotropy in the exchange interaction on the results obtained for the isotropic model, a detailed investigation has been made on a honeycomb lattice. Some interesting results, such as second order reentrant phenomena in the phase diagrams have been found. - Highlights: • Anisotropic quantum Heisenberg model with bond dilution investigated. • Bond percolation threshold values given for 2D and 3D lattices in isotropic case. • Phase diagrams and ground state magnetizations investigated in detail. • Variation of the bond percolation threshold values with anisotropy determined.

  19. Magnon Breakdown in a Two Dimensional Triangular Lattice Heisenberg Antiferromagnet of Multiferroic LuMnO3

    Science.gov (United States)

    Oh, Joosung; Le, Manh Duc; Jeong, Jaehong; Lee, Jung-hyun; Woo, Hyungje; Song, Wan-Young; Perring, T. G.; Buyers, W. J. L.; Cheong, S.-W.; Park, Je-Geun

    2013-12-01

    The breakdown of magnons, the quasiparticles of magnetic systems, has rarely been seen. By using an inelastic neutron scattering technique, we report the observation of spontaneous magnon decay in multiferroic LuMnO3, a simple two dimensional Heisenberg triangular lattice antiferromagnet, with large spin S=2. The origin of this rare phenomenon lies in the nonvanishing cubic interaction between magnons in the spin Hamiltonian arising from the noncollinear 120° spin structure. We observed all three key features of the nonlinear effects as theoretically predicted: a rotonlike minimum, a flat mode, and a linewidth broadening, in our inelastic neutron scattering measurements of single crystal LuMnO3. Our results show that quasiparticles in a system hitherto thought of as “classical” can indeed break down.

  20. Magnon breakdown in a two dimensional triangular lattice Heisenberg antiferromagnet of multiferroic LuMnO3.

    Science.gov (United States)

    Oh, Joosung; Le, Manh Duc; Jeong, Jaehong; Lee, Jung-hyun; Woo, Hyungje; Song, Wan-Young; Perring, T G; Buyers, W J L; Cheong, S-W; Park, Je-Geun

    2013-12-20

    The breakdown of magnons, the quasiparticles of magnetic systems, has rarely been seen. By using an inelastic neutron scattering technique, we report the observation of spontaneous magnon decay in multiferroic LuMnO3, a simple two dimensional Heisenberg triangular lattice antiferromagnet, with large spin S=2. The origin of this rare phenomenon lies in the nonvanishing cubic interaction between magnons in the spin Hamiltonian arising from the noncollinear 120° spin structure. We observed all three key features of the nonlinear effects as theoretically predicted: a rotonlike minimum, a flat mode, and a linewidth broadening, in our inelastic neutron scattering measurements of single crystal LuMnO3. Our results show that quasiparticles in a system hitherto thought of as "classical" can indeed break down.

  1. Spin from defects in two-dimensional quantum field theory

    CERN Document Server

    Novak, Sebastian

    2015-01-01

    We build two-dimensional quantum field theories on spin surfaces starting from theories on oriented surfaces with networks of topological defect lines and junctions. The construction uses a combinatorial description of the spin structure in terms of a triangulation equipped with extra data. The amplitude for the spin surfaces is defined to be the amplitude for the underlying oriented surface together with a defect network dual to the triangulation. Independence of the triangulation and of the other choices follows if the line defect and junctions are obtained from a Delta-separable Frobenius algebra with involutive Nakayama automorphism in the monoidal category of topological defects. For rational conformal field theory we can give a more explicit description of the defect category, and we work out two examples related to free fermions in detail: the Ising model and the so(n) WZW model at level 1.

  2. Soliton nanoantennas in two-dimensional arrays of quantum dots

    CERN Document Server

    Gligorić, G; Hadžievski, Lj; Slepyan, G Ya; Malomed, B A

    2015-01-01

    We consider two-dimensional (2D) arrays of self-organized semiconductor quantum dots (QDs) strongly interacting with electromagnetic field in the regime of Rabi oscillations. The QD array built of two-level states is modelled by two coupled systems of discrete nonlinear Schr\\"{o}dinger equations. Localized modes in the form of single-peaked fundamental and vortical stationary Rabi solitons and self-trapped breathers have been found. The results for the stability, mobility and radiative properties of the Rabi modes suggest a concept of a self-assembled 2D \\textit{% soliton-based nano-antenna}, which should be stable against imperfections In particular, we discuss the implementation of such a nano-antenna in the form of surface plasmon solitons in graphene, and illustrate possibilities to control their operation by means of optical tools.

  3. Ultrabroadband two-quantum two-dimensional electronic spectroscopy

    Science.gov (United States)

    Gellen, Tobias A.; Bizimana, Laurie A.; Carbery, William P.; Breen, Ilana; Turner, Daniel B.

    2016-08-01

    A recent theoretical study proposed that two-quantum (2Q) two-dimensional (2D) electronic spectroscopy should be a background-free probe of post-Hartree-Fock electronic correlations. Testing this theoretical prediction requires an instrument capable of not only detecting multiple transitions among molecular excited states but also distinguishing molecular 2Q signals from nonresonant response. Herein we describe a 2Q 2D spectrometer with a spectral range of 300 nm that is passively phase stable and uses only beamsplitters and mirrors. We developed and implemented a dual-chopping balanced-detection method to resolve the weak molecular 2Q signals. Experiments performed on cresyl violet perchlorate and rhodamine 6G revealed distinct 2Q signals convolved with nonresonant response. Density functional theory computations helped reveal the molecular origin of these signals. The experimental and computational results demonstrate that 2Q electronic spectra can provide a singular probe of highly excited electronic states.

  4. Crossed Andreev effects in two-dimensional quantum Hall systems

    Science.gov (United States)

    Hou, Zhe; Xing, Yanxia; Guo, Ai-Min; Sun, Qing-Feng

    2016-08-01

    We study the crossed Andreev effects in two-dimensional conductor/superconductor hybrid systems under a perpendicular magnetic field. Both a graphene/superconductor hybrid system and an electron gas/superconductor one are considered. It is shown that an exclusive crossed Andreev reflection, with other Andreev reflections being completely suppressed, is obtained in a high magnetic field because of the chiral edge states in the quantum Hall regime. Importantly, the exclusive crossed Andreev reflection not only holds for a wide range of system parameters, e.g., the size of system, the width of central superconductor, and the quality of coupling between the graphene and the superconductor, but also is very robust against disorder. When the applied bias is within the superconductor gap, a robust Cooper-pair splitting process with high-efficiency can be realized in this system.

  5. Quantum magnetotransport in a modulated two-dimensional electron gas

    Science.gov (United States)

    Park, Tae-ik; Gumbs, Godfrey

    1997-09-01

    Quantum mechanical calculations of the magnetotransport coefficients of a modulated two-dimensional electron gas in a perpendicular magnetic field are presented using the Kubo method. The model modulation potential used is such that the effect of the steepness of the potential and its strength on the band part of the longitudinal resistivity ρxxand the Hall resistivity ρxycould be studied. In the extreme limit of a very steep potential, a two-dimensional square array of antidots is simulated. Impurity scattering is included in the self-consistent t-matrix approximation. The results show that for a strong lateral superlattice potential, ρxyis quenched in the low magnetic field regime and as the magnetic field increases there is a large negative Hall resistivity. The intensity of this negative peak is suppressed as the strength of the modulation potential is decreased. It is also shown that the height of the negative peak depends on the steepness of the potential. The longitudinal resistivity also has some interesting features. There are Aharonov-Bohm oscillations and a double peak structure which depends on both the strength of the modulation potential as well as its slope. The numerical results show that the position and intensity of the lower peak is not very sensitive to a change in the strength of the lattice potential or its steepness. However, the upper peak is greatly reduced when the lattice potential is diminished in strength. The double peak feature in ρxxand the negative peak and quenching of the Hall effect at low magnetic fields have been observed experimentally for antidots in both the quasiclassical and quantum regimes.

  6. Dilution Effects on Two-Dimensional Heisenberg Antiferromagnets with Non-Magnetic Spin-Gapped Ground State

    OpenAIRE

    Yasuda, Chitoshi; Todo, Synge; Matsumoto, Munehisa; Takayama, Hajime

    2002-01-01

    Dilution effects on spin-1/2 quantum Heisenberg antiferromagnets with a non-magnetic spin-gapped ground state are studied by means of the qunatum Monte Carlo simulation. In the site-diluted system, an antiferromagnetic long-range order (AF-LRO) is induced at an infinitesimal concentration of dilution due to an effective coupling $\\tilde{J}_{mn}$ between induced magnetic moments. In the bond-diluted case, on the other hand, the AF-LRO is not induced up to a certain concentration of dilution du...

  7. A model of the two-dimensional quantum harmonic oscillator in an $AdS_3$ background

    CERN Document Server

    Frick, Rudolf

    2016-01-01

    In this paper we study a model of the two-dimensional quantum harmonic oscillator in a 3-dimensional anti-de Sitter background. We use a generalized Schr\\"odinger picture in which the analogs of the Schr\\"odinger operators of the particle are independent of both the time and the space coordinates in different representations. The spacetime independent operators of the particle induce the Lie algebra of Killing vector fields of the $AdS_3$ spacetime. In this picture, we have a metamorphosis of the Heisenberg's uncertainty relations.

  8. A model of the two-dimensional quantum harmonic oscillator in an AdS{sub 3} background

    Energy Technology Data Exchange (ETDEWEB)

    Frick, R. [Universitaet zu Koeln, Institut fuer Theoretische Physik, Cologne (Germany)

    2016-10-15

    In this paper we study a model of the two-dimensional quantum harmonic oscillator in a three-dimensional anti-de Sitter background. We use a generalized Schroedinger picture in which the analogs of the Schroedinger operators of the particle are independent of both the time and the space coordinates in different representations. The spacetime independent operators of the particle induce the Lie algebra of Killing vector fields of the AdS{sub 3} spacetime. In this picture, we have a metamorphosis of the Heisenberg uncertainty relations. (orig.)

  9. Magnon breakdown in a two dimensional triangular Heisenberg antiferromagnet LuMnO3

    Science.gov (United States)

    Oh, Joosung; Le, Manh-Duc; Jeong, Jaehong; Park, Je-Geun; Lee, Jung-Hyun; Song, Wan-Young; Perring, T. G.; Woo, Hyungje; Buyers, W. J. L.; Cheong, S.-W.

    2014-03-01

    Magnons, the quasi-particles of long range ordered magnetic systems, have long been viewed as long lived excitations with spectra that are well described by linear spin wave theory (LSWT). Recent theoretical works, though, suggest that the magnon spectrum of 2D triangular Heisenberg antiferromagnet (THA) is highly renormalized downward with a roton-like minimum at the M point. This, as well as the decay of single magnons into two magnon states, was interpreted as the effects of a cubic interaction between magnons arising from the noncollinear spin structure LuMnO3 is a good 2D THA candidate to test this prediction since it has a noncollinear 120° spin structure with S =2. We have conducted inelastic neutron scattering experiments using a LuMnO3 single crystal. Much of the observed spectrum is well described by LSWT, but, a closer inspection of the M point show deviations: a minimum at the lowest energy mode, a flat dispersion at upper modes and line width broadening at the top of the dispersion due to magnon decay. These features agree qualitatively with the theoretical predictions, revealing the importance of the cubic interaction between magnons in 2D THA

  10. Criticality in Two-Dimensional Quantum Systems: Tensor Network Approach

    CERN Document Server

    Ran, Shi-Ju; Li, Wei; Lewenstein, Maciej; Su, Gang

    2016-01-01

    Determination and characterization of criticality in two-dimensional (2D) quantum many-body systems belong to the most important challenges and problems of quantum physics. In this paper we propose an efficient scheme to solve this problem by utilizing the infinite projected entangled pair state (iPEPS), and tensor network (TN) representations. We show that the criticality of a 2D state is faithfully reproduced by the ground state (dubbed as boundary state) of a one-dimensional effective Hamiltonian constructed from its iPEPS representation. We demonstrate that for a critical state the correlation length and the entanglement spectrum of the boundary state are essentially different from those of a gapped iPEPS. This provides a solid indicator that allows to identify the criticality of the 2D state. Our scheme is verified on the resonating valence bond (RVB) states on kagom\\'e and square lattices, where the boundary state of the honeycomb RVB is found to be described by a $c=1$ conformal field theory. We apply ...

  11. Quantum holographic encoding in a two-dimensional electron gas

    Energy Technology Data Exchange (ETDEWEB)

    Moon, Christopher

    2010-05-26

    The advent of bottom-up atomic manipulation heralded a new horizon for attainable information density, as it allowed a bit of information to be represented by a single atom. The discrete spacing between atoms in condensed matter has thus set a rigid limit on the maximum possible information density. While modern technologies are still far from this scale, all theoretical downscaling of devices terminates at this spatial limit. Here, however, we break this barrier with electronic quantum encoding scaled to subatomic densities. We use atomic manipulation to first construct open nanostructures - 'molecular holograms' - which in turn concentrate information into a medium free of lattice constraints: the quantum states of a two-dimensional degenerate Fermi gas of electrons. The information embedded in the holograms is transcoded at even smaller length scales into an atomically uniform area of a copper surface, where it is densely projected into both two spatial degrees of freedom and a third holographic dimension mapped to energy. In analogy to optical volume holography, this requires precise amplitude and phase engineering of electron wavefunctions to assemble pages of information volumetrically. This data is read out by mapping the energy-resolved electron density of states with a scanning tunnelling microscope. As the projection and readout are both extremely near-field, and because we use native quantum states rather than an external beam, we are not limited by lensing or collimation and can create electronically projected objects with features as small as {approx}0.3 nm. These techniques reach unprecedented densities exceeding 20 bits/nm{sup 2} and place tens of bits into a single fermionic state.

  12. Low-energy dynamics of the two-dimensional S=1/2 Heisenberg antiferromagnet on percolating clusters.

    Science.gov (United States)

    Wang, Ling; Sandvik, Anders W

    2006-09-15

    We investigate the quantum dynamics of site diluted S=1/2 Heisenberg antiferromagnetic clusters at the 2D percolation threshold. We use Lanczos diagonalization to calculate the lowest excitation gap Delta and, to reach larger sizes, use quantum Monte Carlo simulations to study an upper bound for Delta obtained from sum rules involving the staggered structure factor and susceptibility. Scaling the gap distribution with the cluster length L, Delta approximately L(-), we obtain a dynamic exponent z approximately 2D(f), where D(f)=91/48 is the fractal dimensionality of the percolating cluster. This is in contrast with previous expectations of z=D(f). We argue that the low-energy excitations are due to weakly coupled effective moments formed due to local imbalance in sublattice occupation.

  13. Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Cundiff, Steven T. [Univ. of Colorado, Boulder, CO (United States)

    2016-05-03

    This final report describes the activities undertaken under grant "Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots". The goal of this program was to implement optical 2-dimensional Fourier transform spectroscopy and apply it to electronic excitations, including excitons, in semiconductors. Specifically of interest are quantum wells that exhibit disorder due to well width fluctuations and quantum dots. In both cases, 2-D spectroscopy will provide information regarding coupling among excitonic localization sites.

  14. Exotic versus conventional scaling and universality in a disordered bilayer quantum heisenberg antiferromagnet.

    Science.gov (United States)

    Sknepnek, Rastko; Vojta, Thomas; Vojta, Matthias

    2004-08-27

    We present Monte Carlo simulations of a two-dimensional bilayer quantum Heisenberg antiferromagnet with random dimer dilution. In contrast with exotic scaling scenarios found in other random quantum systems, the quantum phase transition in this system is characterized by a finite-disorder fixed point with power-law scaling. After accounting for corrections to scaling, with a leading irrelevant exponent of omega approximately 0.48, we find universal critical exponents z=1.310(6) and nu=1.16(3). We discuss the consequences of these findings and suggest new experiments.

  15. XYZ Quantum Heisenberg Models with p-Orbital Bosons

    DEFF Research Database (Denmark)

    Pinheiro, Fernanda; Bruun, Georg; Martikainen, Jani-Petri

    2013-01-01

    We demonstrate how the spin-1/2 XYZ quantum Heisenberg model can be realized with bosonic atoms loaded in the p band of an optical lattice in the Mott regime. The combination of Bose statistics and the symmetry of the p-orbital wave functions leads to a nonintegrable Heisenberg model...

  16. General optimality of the Heisenberg limit for quantum metrology.

    Science.gov (United States)

    Zwierz, Marcin; Pérez-Delgado, Carlos A; Kok, Pieter

    2010-10-29

    Quantum metrology promises improved sensitivity in parameter estimation over classical procedures. However, there is a debate over the question of how the sensitivity scales with the resources and the number of queries that are used in estimation procedures. Here, we reconcile the physical definition of the relevant resources used in parameter estimation with the information-theoretical scaling in terms of the query complexity of a quantum network. This leads to a completely general optimality proof of the Heisenberg limit for quantum metrology. We give an example of how our proof resolves paradoxes that suggest sensitivities beyond the Heisenberg limit, and we show that the Heisenberg limit is an information-theoretic interpretation of the Margolus-Levitin bound, rather than Heisenberg's uncertainty relation.

  17. Quantum phase transition of the randomly diluted heisenberg antiferromagnet on a square lattice

    Science.gov (United States)

    Kato; Todo; Harada; Kawashima; Miyashita; Takayama

    2000-05-01

    Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on a square lattice are investigated by means of the quantum Monte Carlo method with the continuous-time loop algorithm. It is found that the critical concentration of magnetic sites is independent of the spin size S, and equal to the two-dimensional percolation threshold. However, the existence of quantum fluctuations makes the critical exponents deviate from those of the classical percolation transition. Furthermore, we found that the transition is not universal, i.e., the critical exponents significantly depend on S.

  18. Hidden zero-temperature bicritical point in the two-dimensional anisotropic Heisenberg model: Monte Carlo simulations and proper finite-size scaling

    OpenAIRE

    Zhou, Chenggang; Landau, D. P.; Schulthess, Thomas C.

    2006-01-01

    By considering the appropriate finite-size effect, we explain the connection between Monte Carlo simulations of two-dimensional anisotropic Heisenberg antiferromagnet in a field and the early renormalization group calculation for the bicritical point in $2+\\epsilon$ dimensions. We found that the long length scale physics of the Monte Carlo simulations is indeed captured by the anisotropic nonlinear $\\sigma$ model. Our Monte Carlo data and analysis confirm that the bicritical point in two dime...

  19. Heisenberg picture approach to the stability of quantum Markov systems

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Yu, E-mail: yu.pan@anu.edu.au, E-mail: zibo.miao@anu.edu.au; Miao, Zibo, E-mail: yu.pan@anu.edu.au, E-mail: zibo.miao@anu.edu.au [Research School of Engineering, Australian National University, Canberra, ACT 0200 (Australia); Amini, Hadis, E-mail: nhamini@stanford.edu [Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305 (United States); Gough, John, E-mail: jug@aber.ac.uk [Institute of Mathematics and Physics, Aberystwyth University, SY23 3BZ Wales (United Kingdom); Ugrinovskii, Valery, E-mail: v.ugrinovskii@gmail.com [School of Engineering and Information Technology, University of New South Wales at ADFA, Canberra, ACT 2600 (Australia); James, Matthew R., E-mail: matthew.james@anu.edu.au [ARC Centre for Quantum Computation and Communication Technology, Research School of Engineering, Australian National University, Canberra, ACT 0200 (Australia)

    2014-06-15

    Quantum Markovian systems, modeled as unitary dilations in the quantum stochastic calculus of Hudson and Parthasarathy, have become standard in current quantum technological applications. This paper investigates the stability theory of such systems. Lyapunov-type conditions in the Heisenberg picture are derived in order to stabilize the evolution of system operators as well as the underlying dynamics of the quantum states. In particular, using the quantum Markov semigroup associated with this quantum stochastic differential equation, we derive sufficient conditions for the existence and stability of a unique and faithful invariant quantum state. Furthermore, this paper proves the quantum invariance principle, which extends the LaSalle invariance principle to quantum systems in the Heisenberg picture. These results are formulated in terms of algebraic constraints suitable for engineering quantum systems that are used in coherent feedback networks.

  20. Heisenberg picture approach to the stability of quantum Markov systems

    Science.gov (United States)

    Pan, Yu; Amini, Hadis; Miao, Zibo; Gough, John; Ugrinovskii, Valery; James, Matthew R.

    2014-06-01

    Quantum Markovian systems, modeled as unitary dilations in the quantum stochastic calculus of Hudson and Parthasarathy, have become standard in current quantum technological applications. This paper investigates the stability theory of such systems. Lyapunov-type conditions in the Heisenberg picture are derived in order to stabilize the evolution of system operators as well as the underlying dynamics of the quantum states. In particular, using the quantum Markov semigroup associated with this quantum stochastic differential equation, we derive sufficient conditions for the existence and stability of a unique and faithful invariant quantum state. Furthermore, this paper proves the quantum invariance principle, which extends the LaSalle invariance principle to quantum systems in the Heisenberg picture. These results are formulated in terms of algebraic constraints suitable for engineering quantum systems that are used in coherent feedback networks.

  1. Heisenberg Picture Approach to the Stability of Quantum Markov Systems

    OpenAIRE

    Pan, Yu; Amini, Hadis; Miao, Zibo; Gough, John; Ugrinovskii, Valery; James, Matthew R.

    2014-01-01

    Quantum Markovian systems, modeled as unitary dilations in the quantum stochastic calculus of Hudson and Parthasarathy, have become standard in current quantum technological applications. This paper investigates the stability theory of such systems. Lyapunov-type conditions in the Heisenberg picture are derived in order to stabilize the evolution of system operators as well as the underlying dynamics of the quantum states. In particular, using the quantum Markov semigroup associated with this...

  2. Deformed oscillator algebras for two dimensional quantum superintegrable systems

    CERN Document Server

    Bonatsos, Dennis; Kokkotas, K D; Bonatsos, Dennis

    1994-01-01

    Quantum superintegrable systems in two dimensions are obtained from their classical counterparts, the quantum integrals of motion being obtained from the corresponding classical integrals by a symmetrization procedure. For each quantum superintegrable systema deformed oscillator algebra, characterized by a structure function specific for each system, is constructed, the generators of the algebra being functions of the quantum integrals of motion. The energy eigenvalues corresponding to a state with finite dimensional degeneracy can then be obtained in an economical way from solving a system of two equations satisfied by the structure function, the results being in agreement to the ones obtained from the solution of the relevant Schrodinger equation. The method shows how quantum algebraic techniques can simplify the study of quantum superintegrable systems, especially in two dimensions.

  3. Superconformal Quantum Mechanics via Wigner-Heisenberg Algebra

    CERN Document Server

    Carrion, H L

    2004-01-01

    We show the natural relation between the Wigner Hamiltonian and the conformal Hamiltonian, by presenting a model in (super)conformal quantum mechanics with (super)conformal symmetry in the Wigner-Heisenberg algebra picture $ [x,p_{x}]= i(1+c{\\bf P}).$ We define its energy spectrum and construct the Casimir, creation and annihilation operators using the Wigner-Heisenberg algebra. It is also found a super-Hamiltonian of the Calogero interaction's type for a two-particle model.

  4. Quantum spin liquid ground states of the Heisenberg-Kitaev model on the triangular lattice

    Science.gov (United States)

    Kos, Pavel; Punk, Matthias

    2017-01-01

    We study quantum disordered ground states of the two-dimensional Heisenberg-Kitaev model on the triangular lattice using a Schwinger boson approach. Our aim is to identify and characterize potential gapped quantum spin liquid phases that are stabilized by anisotropic Kitaev interactions. For antiferromagnetic Heisenberg and Kitaev couplings and sufficiently small spin S , we find three different symmetric Z2 spin liquid phases, separated by two continuous quantum phase transitions. Interestingly, the gap of elementary excitations remains finite throughout the transitions. The first spin liquid phase corresponds to the well-known zero-flux state in the Heisenberg limit, which is stable with respect to small Kitaev couplings and develops 120∘ order in the semiclassical limit at large S . In the opposite Kitaev limit, we find a different spin liquid ground state, which is a quantum disordered version of a magnetically ordered state with antiferromagnetic chains, in accordance with results in the classical limit. Finally, at intermediate couplings, we find a spin liquid state with unusual spin correlations. Upon spinon condensation, this state develops Bragg peaks at incommensurate momenta in close analogy to the magnetically ordered Z2 vortex crystal phase, which has been analyzed in recent theoretical works.

  5. Quasi-two-dimensional Dirac fermions and quantum magnetoresistance in LaAgBi$_2$

    OpenAIRE

    Wang, Kefeng; Graf, D.; Petrovic, C.

    2016-01-01

    We report quasi-two-dimensional Dirac fermions and quantum magnetoresistance in LaAgBi$_2$. The band structure shows several narrow bands with nearly linear energy dispersion and Dirac-cone-like points at the Fermi level. The quantum oscillation experiments revealed one quasi-two-dimensional Fermi pocket and another complex pocket with small cyclotron resonant mass. The in-plane transverse magnetoresistance exhibits a crossover at a critical field $B^*$ from semiclassical weak-field $B^2$ dep...

  6. Two-dimensional ion trap lattice on a microchip for quantum simulation

    CERN Document Server

    Sterling, R C; Weidt, S; Lake, K; Srinivasan, P; Webster, S C; Kraft, M; Hensinger, W K

    2013-01-01

    Using a controllable quantum system it is possible to simulate other highly complex quantum systems efficiently overcoming an in-principle limitation of classical computing. Trapped ions constitute such a highly controllable quantum system. So far, no dedicated architectures for the simulation of two-dimensional spin lattices using trapped ions in radio-frequency ion traps have been produced, limiting the possibility of carrying out such quantum simulations on a large scale. We report the operation of a two-dimensional ion trap lattice integrated in a microchip capable of implementing quantum simulations of two-dimensional spin lattices. Our device provides a scalable microfabricated architecture for trapping such ion lattices with coupling strengths between neighbouring ions sufficient to provide a powerful platform for the implementation of quantum simulations. In order to realize this device we developed a specialist fabrication process that allows for the application of very large voltages. We fabricated ...

  7. Quantum search on the two-dimensional lattice using the staggered model with Hamiltonians

    Science.gov (United States)

    Portugal, R.; Fernandes, T. D.

    2017-04-01

    Quantum search on the two-dimensional lattice with one marked vertex and cyclic boundary conditions is an important problem in the context of quantum algorithms with an interesting unfolding. It avails to test the ability of quantum walk models to provide efficient algorithms from the theoretical side and means to implement quantum walks in laboratories from the practical side. In this paper, we rigorously prove that the recent-proposed staggered quantum walk model provides an efficient quantum search on the two-dimensional lattice, if the reflection operators associated with the graph tessellations are used as Hamiltonians, which is an important theoretical result for validating the staggered model with Hamiltonians. Numerical results show that on the two-dimensional lattice staggered models without Hamiltonians are not as efficient as the one described in this paper and are, in fact, as slow as classical random-walk-based algorithms.

  8. Dipolar quantum electrodynamics of the two-dimensional electron gas

    Science.gov (United States)

    Todorov, Yanko

    2015-03-01

    Similarly to a previous work on the homogeneous electron gas [Y. Todorov, Phys. Rev. B 89, 075115 (2014), 10.1103/PhysRevB.89.075115], we apply the Power-Zienau-Wooley (PZW) formulation of the quantum electrodynamics to the case of an electron gas quantum confined by one-dimensional potential. We provide a microscopic description of all collective plasmon modes of the gas, oscillating both along and perpendicular to the direction of quantum confinement. Furthermore, we study the interaction of the collective modes with a photonic structure, planar metallic waveguide, by using the full expansion of the electromagnetic field into normal modes. We show how the boundary conditions for the electromagnetic field influence both the transverse light-matter coupling and the longitudinal particle-particle interactions. The PZW descriptions appear thus as a convenient tool to study semiconductor quantum optics in geometries where quantum-confined particles interact with strongly confined electromagnetic fields in microresonators, such as the ones used to achieve the ultrastrong light-matter coupling regime.

  9. Laser driven impurity states in two-dimensional quantum dots and quantum rings

    Science.gov (United States)

    Laroze, D.; Barseghyan, M.; Radu, A.; Kirakosyan, A. A.

    2016-11-01

    The hydrogenic donor impurity states in two-dimensional GaAs/Ga0.7Al0.3As quantum dot and quantum ring have been investigated under the action of intense laser field. A laser dressed effect on both electron confining and electron-impurity Coulomb interaction potentials has been considered. The single electron energy spectrum and wave functions have been found using the effective mass approximation and exact diagonalization technique. The accidental degeneracy of the impurity states have been observed for different positions of the impurity and versus values of the laser field parameter. The obtained theoretical results indicate a novel opportunity to tune the performance of quantum dots and quantum rings and to control their specific properties by means of laser field.

  10. Two-dimensional lattice gauge theories with superconducting quantum circuits

    Energy Technology Data Exchange (ETDEWEB)

    Marcos, D., E-mail: david.marcos@me.com [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Widmer, P. [Albert Einstein Center, Institute for Theoretical Physics, Bern University, CH-3012, Bern (Switzerland); Rico, E. [IPCMS (UMR 7504) and ISIS (UMR 7006), University of Strasbourg and CNRS, 67000 Strasbourg (France); Hafezi, M. [Joint Quantum Institute, NIST/University of Maryland, College Park 20742 (United States); Department of Electrical Engineering and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742 (United States); Rabl, P. [Institute of Atomic and Subatomic Physics, TU Wien, Stadionallee 2, 1020 Wien (Austria); Wiese, U.-J. [Albert Einstein Center, Institute for Theoretical Physics, Bern University, CH-3012, Bern (Switzerland); Zoller, P. [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria)

    2014-12-15

    A quantum simulator of U(1) lattice gauge theories can be implemented with superconducting circuits. This allows the investigation of confined and deconfined phases in quantum link models, and of valence bond solid and spin liquid phases in quantum dimer models. Fractionalized confining strings and the real-time dynamics of quantum phase transitions are accessible as well. Here we show how state-of-the-art superconducting technology allows us to simulate these phenomena in relatively small circuit lattices. By exploiting the strong non-linear couplings between quantized excitations emerging when superconducting qubits are coupled, we show how to engineer gauge invariant Hamiltonians, including ring-exchange and four-body Ising interactions. We demonstrate that, despite decoherence and disorder effects, minimal circuit instances allow us to investigate properties such as the dynamics of electric flux strings, signaling confinement in gauge invariant field theories. The experimental realization of these models in larger superconducting circuits could address open questions beyond current computational capability.

  11. Quantum vortex dynamics in two-dimensional neutral superfluids

    NARCIS (Netherlands)

    Wang, C. -C J.; Duine, R.A.; MacDonald, A.H.

    2010-01-01

    We derive an effective action for the vortex-position degree of freedom in a superfluid by integrating out condensate phase- and density-fluctuation environmental modes. When the quantum dynamics of environmental fluctuations is neglected, we confirm the occurrence of the vortex Magnus force and

  12. Two-Dimensional Arrays of Neutral Atom Quantum Gates

    Science.gov (United States)

    2012-10-20

    Isenhower, X. Zhang, A. Gill, T. Walker, M. Saffman. Deterministic entanglement of two neutral atoms via Rydberg blockade, Physical Review A, (09 2010...squeezing of atomic ensembles by multicolor quantum nondemolition measurements, Physical Review A, (02 2009): 0. doi: 10.1103/PhysRevA.79.023831 10/19/2012...collective encoding in holmium atoms, Physical Review A, (07 2008): 0. doi: 10.1103/PhysRevA.78.012336 10/19/2012 10.00 M Saffman, X L Zhang, A T

  13. Topological magnon bound-states in quantum Heisenberg chains

    CERN Document Server

    Qin, Xizhou; Ke, Yongguan; Zhang, Li; Lee, Chaohong

    2016-01-01

    It is still an outstanding challenge to characterize and understand the topological features of strongly correlated states such as bound-states in interacting multi-particle quantum systems. Recently, bound states of elementary spin waves (magnons) in quantum magnets have been experimentally observed in quantum Heisenberg chains comprising ultracold Bose atoms in optical lattices. Here, we explore an unprecedented topological state called topological magnon bound-state in the quantum Heisenberg chain under cotranslational symmetry. We find that the cotranslational symmetry allows us to formulate a direct topological invariant for the multi-particle quantum states, which can be used to characterize the topological features of multi-magnon excitations. We calculate energy spectra, density distributions, correlations and topological invariants of the two-magnon bound-states and show the existence of topological magnon bound-states. Our study not only opens a new prospect to pursue topological bound-states, but a...

  14. Non-linear excitation of quantum emitters in two-dimensional hexagonal boron nitride

    CERN Document Server

    Schell, Andreas W; Takashima, Hideaki; Takeuchi, Shigeki; Aharonovich, Igor

    2016-01-01

    Two-photon absorption is an important non-linear process employed for high resolution bio-imaging and non-linear optics. In this work we realize two-photon excitation of a quantum emitter embedded in a two-dimensional material. We examine defects in hexagonal boron nitride and show that the emitters exhibit similar spectral and quantum properties under one-photon and two-photon excitation. Furthermore, our findings are important to deploy two-dimensional hexagonal boron nitride for quantum non-linear photonic applications.

  15. Calculating Two-Dimensional Spectra with the Mixed Quantum-Classical Ehrenfest Method

    NARCIS (Netherlands)

    van der Vegte, C. P.; Dijkstra, A. G.; Knoester, J.; Jansen, T. L. C.

    2013-01-01

    We present a mixed quantum-classical simulation approach to calculate two-dimensional spectra of coupled two-level electronic model systems. We include the change in potential energy of the classical system due to transitions in the quantum system using the Ehrenfest method. We study how this

  16. Let Students Derive, by Themselves, Two-Dimensional Atomic and Molecular Quantum Chemistry from Scratch

    Science.gov (United States)

    Ge, Yingbin

    2016-01-01

    Hands-on exercises are designed for undergraduate physical chemistry students to derive two-dimensional quantum chemistry from scratch for the H atom and H[subscript 2] molecule, both in the ground state and excited states. By reducing the mathematical complexity of the traditional quantum chemistry teaching, these exercises can be completed…

  17. Calculating Two-Dimensional Spectra with the Mixed Quantum-Classical Ehrenfest Method

    NARCIS (Netherlands)

    van der Vegte, C. P.; Dijkstra, A. G.; Knoester, J.; Jansen, T. L. C.

    2013-01-01

    We present a mixed quantum-classical simulation approach to calculate two-dimensional spectra of coupled two-level electronic model systems. We include the change in potential energy of the classical system due to transitions in the quantum system using the Ehrenfest method. We study how this feedba

  18. Exact two-body solutions and quantum defect theory of two-dimensional dipolar quantum gas

    Science.gov (United States)

    Jie, Jianwen; Qi, Ran

    2016-10-01

    In this paper, we provide the two-body exact solutions of the two-dimensional (2D) Schrödinger equation with isotropic +/- 1/{r}3 interactions. An analytic quantum defect theory is constructed based on these solutions and it is applied to investigate the scattering properties as well as two-body bound states of an ultracold polar molecules confined in a quasi-2D geometry. Interestingly, we find that for the attractive case, the scattering resonance happens simultaneously in all partial waves, which has not been observed in other systems. The effect of this feature on the scattering phase shift across such resonances is also illustrated.

  19. Hysteresis behavior of the anisotropic quantum Heisenberg model

    Energy Technology Data Exchange (ETDEWEB)

    Akıncı, Ümit, E-mail: umit.akinci@deu.edu.tr

    2013-10-15

    The effect of the anisotropy in the exchange interaction on the hysteresis loops within the anisotropic quantum Heisenberg model has been investigated with the effective field theory for two spin cluster. Particular attention has been devoted on the behavior of the hysteresis loop area, coercive field and remanent magnetization with the anisotropy in the exchange interaction for both ferromagnetic and paramagnetic phases.

  20. XYZ quantum Heisenberg models with p-orbital bosons.

    Science.gov (United States)

    Pinheiro, Fernanda; Bruun, Georg M; Martikainen, Jani-Petri; Larson, Jonas

    2013-11-15

    We demonstrate how the spin-1/2 XYZ quantum Heisenberg model can be realized with bosonic atoms loaded in the p band of an optical lattice in the Mott regime. The combination of Bose statistics and the symmetry of the p-orbital wave functions leads to a nonintegrable Heisenberg model with antiferromagnetic couplings. Moreover, the sign and relative strength of the couplings characterizing the model are shown to be experimentally tunable. We display the rich phase diagram in the one-dimensional case and discuss finite size effects relevant for trapped systems. Finally, experimental issues related to preparation, manipulation, detection, and imperfections are considered.

  1. Semi-phenomenological analysis of neutron scattering results for quasi-two dimensional quantum anti-ferromagnet

    Science.gov (United States)

    Sarkar, Subhajit; Chaudhury, Ranjan; Paul, Samir K.

    2017-01-01

    The available results from the inelastic neutron scattering experiment performed on the quasi-two dimensional spin 1/2 anti-ferromagnetic material La2CuO4 have been analysed theoretically. The formalism of ours is based on a semi-classical like treatment involving a model of an ideal gas of mobile vortices and anti-vortices built on the background of the Néel state, using the bipartite classical spin configuration corresponding to an XY-anisotropic Heisenberg anti-ferromagnet on a square lattice. The results for the integrated intensities for our spin 1/2 model corresponding to different temperatures, show occurrence of vigorous unphysical oscillations, when convoluted with a realistic spectral window function. These results indicate failure of the conventional semi-classical theoretical model of ideal vortex/anti-vortex gas arising in the Berezinskii-Kosterlitz-Thouless theory for the low spin magnetic systems. A full fledged quantum mechanical formalism and calculations seem crucial for the understanding of topological excitations in such low spin systems. Furthermore, a severe disagreement is found to occur at finite values of energy transfer between the integrated intensities obtained theoretically from the conventional formalism and those obtained experimentally. This further suggests strongly that the full quantum treatment should also incorporate the interaction between the fragile-magnons and the topological excitations. This is quite plausible in view of the recent work establishing such a process in XXZ quantum ferromagnet on 2D lattice. The high spin XXZ quasi-two dimensional antiferromagnet like MnPS3 however follows the conventional theory quite well.

  2. Freely configurable quantum simulator based on a two-dimensional array of individually trapped ions

    CERN Document Server

    Mielenz, Manuel; Wittemer, Matthias; Hakelberg, Frederick; Schmied, Roman; Blain, Matthew; Maunz, Peter; Leibfried, Dietrich; Warring, Ulrich; Schaetz, Tobias

    2015-01-01

    A custom-built and precisely controlled quantum system may offer access to a fundamental understanding of another, less accessible system of interest. A universal quantum computer is currently out of reach, but an analog quantum simulator that makes the relevant observables, interactions, and states of a quantum model accessible could permit experimental insight into complex quantum dynamics that are intractable on conventional computers. Several platforms have been suggested and proof-of-principle experiments have been conducted. Here we characterise two-dimensional arrays of three ions trapped by radio-frequency fields in individually controlled harmonic wells forming equilateral triangles with side lengths 40 and 80 micrometer. In our approach, which is scalable to arbitrary two dimensional lattices, we demonstrate individual control of the electronic and motional degrees of freedom, preparation of a fiducial initial state with ion motion close to the ground state, as well as tuning of crucial couplings be...

  3. Large-N theory of the Sp(N) Heisenberg quantum antiferromagnet on an anisotropic triangular lattice

    Science.gov (United States)

    Chung, Chung-Hou; Marston, Brad

    2000-03-01

    The magnetic properties of the two-dimensional layered organic superconductors κ-(BEDT-TTF)_2X are modeled by a spin-1/2 Heisenberg quantum antiferromagnet on an anisotropic triangular lattice. The phase diagram is ascertained by means of a large-N expansion of the Sp(N) generalization of the physical SU(2) \\cong Sp(1) Heisenberg magnet.(S. Sachdev and N. Reed, Int. J. Mod. Phys. B5), 219 (1991). The phase diagram is presented in the two-dimensional parameter space of J_1/J_2, the ratio of the nearest to next-nearest neighbor Heisenberg exchange, and the ratio nb / N, which sets the strength of the quantum fluctuations. At large nb / N (equivalent to the large-spin limit of the physical SU(2) model) quantum effects are small, the ground states break global Sp(N) spin-rotational symmetry, and exhibit magnetic long-range-order (LRO). At small nb / N, however, quantum fluctuations overwhelm the tendency to order and there is only short-range magnetic order (SRO). The LRO and SRO phases can be further classified into two types depending on the size of the anisotropy: (i) ground states with commensurate, collinear, spin correlations; and (ii) ground states with incommensurate, coplanar, spin correlations. Finite-N corrections due to a Berry's phase term modify the character of the SRO phases, leading in the case of the commensurate state to spin-Peierls order and the confinement of spinons.

  4. Emergent topology and dynamical quantum phase transitions in two-dimensional closed quantum systems

    Science.gov (United States)

    Bhattacharya, Utso; Dutta, Amit

    2017-07-01

    Dynamical quantum phase transitions (DQPTs) manifested in the nonanalyticities in the temporal evolution of a closed quantum system generated by the time-independent final Hamiltonian, following a quench (or ramping) of a parameter of the Hamiltonian, is an emerging frontier of nonequilibrium quantum dynamics. We, here, introduce the notion of a dynamical topological order parameter (DTOP) that characterizes these DQPTs occurring in quenched (or ramped) two-dimensional closed quantum systems; this is quite a nontrivial generalization of the notion of DTOP introduced in Budich and Heyl [Phys. Rev. B 93, 085416 (2016), 10.1103/PhysRevB.93.085416] for one-dimensional situations. This DTOP is obtained from the "gauge-invariant" Pancharatnam phase extracted from the Loschmidt overlap, i.e., the modulus of the overlap between the initially prepared state and its time-evolved counterpart reached following a temporal evolution generated by the time-independent final Hamiltonian. This generic proposal is illustrated considering DQPTs occurring in the subsequent temporal evolution following a sudden quench of the staggered mass of the topological Haldane model on a hexagonal lattice where it stays fixed to zero or unity and makes a discontinuous jump between these two values at critical times at which DQPTs occur. What is remarkable is that while the topology of the equilibrium model is characterized by the Chern number, the emergent topology associated with the DQPTs is characterized by a generalized winding number.

  5. Spin correlations in the two-dimensional quantum s=1/2 XY model

    Science.gov (United States)

    Sznajd, J.

    1995-08-01

    A quantum version of the Niemeijer-van Leeuwen real-space renormalization-group method is used to study the temperature dependence of the two- and four-spin correlations in the quantum XY model on the triangular lattice. The first-order cumulant expansion results suggest, similarly to other methods, a low-temperature phase of an essentially different kind from that predicted for the classical model. The possible explanation of the origin of the spurious 2D Heisenberg-like nontrivial fixed point in some renormalization-group calculations is also proposed.

  6. Origin of the inverse energy cascade in two-dimensional quantum turbulence

    CERN Document Server

    Skaugen, Audun

    2016-01-01

    We unravel the intimate connection between fundamental characteristics of two dimensional turbulence, i.e. the large-scale coherent structures and the inverse energy cascade. We propose a driven, dissipative point vortex model that is able to capture the dynamics of two-dimensional quantum turbulence by the emergent clustering of same-sign vortices, which form a non-equilibrium analogue of Onsager vortex equilibria. The inverse energy cascade developing in a statistically neutral system originates from this clustering of co-rotating and counter-rotating vortices. The Kolmogorov energy spectrum $k^{-5/3}$ is attributed to the scale-free correlations in the vorticity field fluctuations, here measured by the weighted pair correlation function that has a power-law decay as $r^{-4/3}$ on inertial separation lengthscales $r$. This scale-invariant statistics of vorticity, attributed to a conformal symmetry of two-dimensional classical turbulence, draws further analogies between classical and quantum turbulence beyon...

  7. Two-dimensional quantum compass model in a staggered field: some rigorous results

    Institute of Scientific and Technical Information of China (English)

    He Pei-Song; You Wen-Long; Tian Guang-Shan

    2011-01-01

    We study the properties of the two-dimensional quantum compass model in a staggered field. Using the PerronFr(o)enius theorem and the reflection positivity method, we rigorously determine the low energy spectrum of this model and its global ground state Ψ0. Furthermore, we show that Ψ0 has a directional long-range order.

  8. Expectation value of composite field $T{\\bar T}$ in two-dimensional quantum field theory

    OpenAIRE

    Zamolodchikov, Alexander B.

    2004-01-01

    I show that the expectation value of the composite field $T{\\bar T}$, built from the components of the energy-momentum tensor, is expressed exactly through the expectation value of the energy-momentum tensor itself. The relation is derived in two-dimensional quantum field theory under broad assumptions, and does not require integrability.

  9. Quantum computing via defect states in two-dimensional antidot lattices.

    Science.gov (United States)

    Flindt, Christian; Mortensen, Niels Asger; Jauho, Antti-Pekka

    2005-12-01

    We propose a new structure suitable for quantum computing in a solid-state environment: designed defect states in antidot lattices superimposed on a two-dimensional electron gas at a semiconductor heterostructure. State manipulation can be obtained with gate control. Model calculations indicate that it is feasible to fabricate structures whose energy level structure is robust against thermal dephasing.

  10. Scaling dimensions of manifestly generally covariant operators in two-dimensional quantum gravity

    CERN Document Server

    Nishimura, J; Tsuchiya, A; Jun Nishimura; Shinya Tamura; Asato Tsuchiya

    1994-01-01

    Using (2+$\\epsilon$)-dimensional quantum gravity recently formulated by Kawai, Kitazawa and Ninomiya, we calculate the scaling dimensions of manifestly generally covariant operators in two-dimensional quantum gravity coupled to $(p,q)$ minimal conformal matter. In the spectrum appear all the scaling dimensions of the scaling operators in the matrix model except the boundary operators, while there are also many others which have no corresponding scaling dimensions in the matrix model.

  11. Multicritical point in a diluted bilayer Heisenberg quantum antiferromagnet.

    Science.gov (United States)

    Sandvik, Anders W

    2002-10-21

    The S=1/2 Heisenberg bilayer antiferromagnet with randomly removed interlayer dimers is studied using quantum Monte Carlo simulations. A zero-temperature multicritical point (p(*),g(*)) at the classical percolation density p=p(*) and interlayer coupling g(*) approximately equal 0.16 is demonstrated. The quantum critical exponents of the percolating cluster are determined using finite-size scaling. It is argued that the associated finite-temperature quantum critical regime extends to zero interlayer coupling and could be relevant for antiferromagnetic cuprates doped with nonmagnetic impurities.

  12. Effect of quantum phase transition on spin transport in the spatially frustrated Heisenberg model

    Science.gov (United States)

    Lima, L. S.

    2017-03-01

    We have used the Schwinger's boson theory to study the spin transport in the anisotropic two-dimensional spatially frustrated Heisenberg antiferromagnetic model in the square lattice. Our results show a sudden change in the AC spin conductivity σreg (ω) in the quantum phase transition point, where we have the gap of the system going to zero at critical point Dc=0. We have found a sudden change for a superconductor state in the DC limit ω → 0 independent of the value of the Drude's weight found in the quantum phase transition point. Away from it, we have obtained that the behavior of the spin conductivity changes for single peak at ω =ωp and in this case, σreg (ω) goes to zero in small ω and large ω limits.

  13. Ba8CoNb6O24 : A spin-1/2 triangular-lattice Heisenberg antiferromagnet in the two-dimensional limit

    Science.gov (United States)

    Rawl, R.; Ge, L.; Agrawal, H.; Kamiya, Y.; Dela Cruz, C. R.; Butch, N. P.; Sun, X. F.; Lee, M.; Choi, E. S.; Oitmaa, J.; Batista, C. D.; Mourigal, M.; Zhou, H. D.; Ma, J.

    2017-02-01

    The perovskite Ba8CoNb6O24 comprises equilateral effective spin-1/2 Co2 + triangular layers separated by six nonmagnetic layers. Susceptibility, specific heat, and neutron scattering measurements combined with high-temperature series expansions and spin-wave calculations confirm that Ba8CoNb6O24 is basically a two-dimensional magnet with no detectable spin anisotropy and no long-range magnetic ordering down to 0.06 K. In other words, Ba8CoNb6O24 is very close to be a realization of the paradigmatic spin-1/2 triangular Heisenberg model, which is not expected to exhibit symmetry breaking at finite temperatures according to the Mermin and Wagner theorem.

  14. Synthesis and characterization of the new two-dimensional Heisenberg antiferromagnet double perovskite BaLaCuSbO6.

    Science.gov (United States)

    Blanco, M Cecilia; Paz, Sergio Alexis; Nassif, Vivian M; Guimpel, Julio J; Carbonio, Raúl E

    2015-06-21

    The BaLaCuSbO(6) double perovskite has been successfully synthesized by solid state reaction under an air atmosphere. Its structure was refined using powder neutron diffraction in the monoclinic space group I2/m with a 4% antisite disorder on the B cations. Magnetic measurements give signs of 2D-antiferromagnetic behaviour with TN around 64 K. The Jahn-Teller distortion produced by Cu(2+) ions favours a crystallographic tetragonal distortion and consequently the in-plane super-superexchange antiferromagnetic interactions, J(90°), are favoured over the in-plane J(180°) antiferromagnetic exchange interactions. Both, J and J' magnetic interactions have been evaluated according to a Heisenberg antiferromagnetic rectangular model using an approximation to Curie's law in powers of J/T, being |J| around 10 times stronger than |J'|.

  15. Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor

    Science.gov (United States)

    Branny, Artur; Kumar, Santosh; Proux, Raphaël; Gerardot, Brian D

    2017-01-01

    An outstanding challenge in quantum photonics is scalability, which requires positioning of single quantum emitters in a deterministic fashion. Site positioning progress has been made in established platforms including defects in diamond and self-assembled quantum dots, albeit often with compromised coherence and optical quality. The emergence of single quantum emitters in layered transition metal dichalcogenide semiconductors offers new opportunities to construct a scalable quantum architecture. Here, using nanoscale strain engineering, we deterministically achieve a two-dimensional lattice of quantum emitters in an atomically thin semiconductor. We create point-like strain perturbations in mono- and bi-layer WSe2 which locally modify the band-gap, leading to efficient funnelling of excitons towards isolated strain-tuned quantum emitters that exhibit high-purity single photon emission. We achieve near unity emitter creation probability and a mean positioning accuracy of 120±32 nm, which may be improved with further optimization of the nanopillar dimensions. PMID:28530219

  16. Deterministic strain-induced arrays of quantum emitters in a two-dimensional semiconductor

    Science.gov (United States)

    Branny, Artur; Kumar, Santosh; Proux, Raphaël; Gerardot, Brian D.

    2017-05-01

    An outstanding challenge in quantum photonics is scalability, which requires positioning of single quantum emitters in a deterministic fashion. Site positioning progress has been made in established platforms including defects in diamond and self-assembled quantum dots, albeit often with compromised coherence and optical quality. The emergence of single quantum emitters in layered transition metal dichalcogenide semiconductors offers new opportunities to construct a scalable quantum architecture. Here, using nanoscale strain engineering, we deterministically achieve a two-dimensional lattice of quantum emitters in an atomically thin semiconductor. We create point-like strain perturbations in mono- and bi-layer WSe2 which locally modify the band-gap, leading to efficient funnelling of excitons towards isolated strain-tuned quantum emitters that exhibit high-purity single photon emission. We achieve near unity emitter creation probability and a mean positioning accuracy of 120+/-32 nm, which may be improved with further optimization of the nanopillar dimensions.

  17. Probing quantum discord in a Heisenberg dimer compound.

    Science.gov (United States)

    Chakraborty, Tanmoy; Singh, Harkirat; Singh, Sourabh; Gopal, Radha Krishna; Mitra, Chiranjib

    2013-10-23

    A quantitative estimation of quantum discord is performed for a Heisenberg spin 1/2 dimer compound (NH4CuPO4, H2O) by means of experimental magnetic and thermal measurements. Magnetic susceptibility and specific heat data were collected for NH4CuPO4, H2O and analyzed within the framework of the Heisenberg isolated dimer model. Internal energy as a function of temperature is obtained by integrating the specific heat versus temperature data. Subsequently, quantum discord, total correlations and spin-spin correlation function are quantified from susceptibility and internal energy and plotted as a function of temperature. Violation of Bell's inequality is also tested for NH4CuPO4, H2O via both experimental susceptibility and specific heat data signifying the presence of entanglement.

  18. Quantum correlations and coherence in spin-1 Heisenberg chains

    Science.gov (United States)

    Malvezzi, A. L.; Karpat, G.; ćakmak, B.; Fanchini, F. F.; Debarba, T.; Vianna, R. O.

    2016-05-01

    We explore quantum and classical correlations along with coherence in the ground states of spin-1 Heisenberg chains, namely the one-dimensional XXZ model and the one-dimensional bilinear biquadratic model, with the techniques of density matrix renormalization group theory. Exploiting the tools of quantum information theory, that is, by studying quantum discord, quantum mutual information, and three recently introduced coherence measures in the reduced density matrix of two nearest neighbor spins in the bulk, we investigate the quantum phase transitions and special symmetry points in these models. We point out the relative strengths and weaknesses of correlation and coherence measures as figures of merit to witness the quantum phase transitions and symmetry points in the considered spin-1 Heisenberg chains. In particular, we demonstrate that, as none of the studied measures can detect the infinite-order Kosterlitz-Thouless transition in the XXZ model, they appear to be able to signal the existence of the same type of transition in the biliear biquadratic model. However, we argue that what is actually detected by the measures here is the SU(3) symmetry point of the model rather than the infinite-order quantum phase transition. Moreover, we show in the XXZ model that examining even single site coherence can be sufficient to spotlight the second-order phase transition and the SU(2) symmetry point.

  19. Quantum Monte Carlo Study of Random Antiferromagnetic Heisenberg Chain

    OpenAIRE

    Todo, Synge; Kato, Kiyoshi; Takayama, Hajime

    1998-01-01

    Effects of randomness on the spin-1/2 and 1 antiferromagnetic Heisenberg chains are studied using the quantum Monte Carlo method with the continuous-time loop algorithm. We precisely calculated the uniform susceptibility, string order parameter, spatial and temporal correlation length, and the dynamical exponent, and obtained a phase diagram. The generalization of the continuous-time loop algorithm for the systems with higher-S spins is also presented.

  20. Type-I integrable quantum impurities in the Heisenberg model

    CERN Document Server

    Doikou, Anastasia

    2013-01-01

    Type-I quantum impurities are investigated in the context of the integrable Heisenberg model. This type of defects is associated to the (q)-harmonic oscillator algebra. The transmission matrices associated to this particular type of defects are computed via the Bethe ansatz methodology for the XXX model, as well as for the critical and non-critical XXZ spin chain. In the attractive regime of the critical XXZ spin chain the transmission amplitudes for the breathers are also identified.

  1. Decay of transverse correlations in quantum Heisenberg models

    Energy Technology Data Exchange (ETDEWEB)

    Björnberg, Jakob E., E-mail: jakob.bjornberg@gmail.com, E-mail: daniel@ueltschi.org [Department of Mathematical Sciences, Chalmers and University of Gothenburg, 41296 Göteborg (Sweden); Ueltschi, Daniel, E-mail: jakob.bjornberg@gmail.com, E-mail: daniel@ueltschi.org [Department of Mathematics, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2015-04-15

    We study a class of quantum spin systems that include the S=1/2 Heisenberg and XY-models and prove that two-point correlations exhibit exponential decay in the presence of a transverse magnetic field. The field is not necessarily constant, it may be random, and it points in the same direction. Our proof is entirely probabilistic and it relies on a random loop representations of the correlation functions, on stochastic domination and on first-passage percolation.

  2. Type-I integrable quantum impurities in the Heisenberg model

    Energy Technology Data Exchange (ETDEWEB)

    Doikou, Anastasia, E-mail: adoikou@upatras.gr

    2013-12-21

    Type-I quantum impurities are investigated in the context of the integrable Heisenberg model. This type of defects is associated to the (q)-harmonic oscillator algebra. The transmission matrices associated to this particular type of defects are computed via the Bethe ansatz methodology for the XXX model, as well as for the critical and non-critical XXZ spin chain. In the attractive regime of the critical XXZ spin chain the transmission amplitudes for the breathers are also identified.

  3. Entropy Squeezing in the Quantum Heisenberg XY Spin Chains

    Institute of Scientific and Technical Information of China (English)

    CHANG Ping; SHAO Bin; ZOU Jian

    2009-01-01

    The time evolution of entropy squeezing for the two-qubit XYZ Heisenberg model in an external uniform magnetic field is investigated in the language of quantum information.The effect of different parameters such as magnetic field and anisotropy parameter on the properties of entropy squeezing and variance squeezing are discussed.It is shown that magnetic field and anisotropy parameter can enhance the entropy squeezing.

  4. Entanglement of Two-Qubit Quantum Heisenberg XYZ Chain

    Institute of Scientific and Technical Information of China (English)

    惠小强; 郝三如; 陈文学; 岳瑞宏

    2002-01-01

    We derive the analytic expression of the concurrence in the quantum Heisenberg XY Z model and discuss the influence of parameters J, △ and Γ on the concurrence. By choosing different values of Γ and △, we obtain the XX, XY, XXX and XXZ chains. The concurrence decreases with increasing temperature. When entanglement. For the XXZ chain, when Γ→∞, the concurence will meet its maximum value Cmax= sinh(1/T)--cosh(1/T)@

  5. Quantum spin transistor with a Heisenberg spin chain

    Science.gov (United States)

    Marchukov, O. V.; Volosniev, A. G.; Valiente, M.; Petrosyan, D.; Zinner, N. T.

    2016-01-01

    Spin chains are paradigmatic systems for the studies of quantum phases and phase transitions, and for quantum information applications, including quantum computation and short-distance quantum communication. Here we propose and analyse a scheme for conditional state transfer in a Heisenberg XXZ spin chain which realizes a quantum spin transistor. In our scheme, the absence or presence of a control spin excitation in the central gate part of the spin chain results in either perfect transfer of an arbitrary state of a target spin between the weakly coupled input and output ports, or its complete blockade at the input port. We also discuss a possible proof-of-concept realization of the corresponding spin chain with a one-dimensional ensemble of cold atoms with strong contact interactions. Our scheme is generally applicable to various implementations of tunable spin chains, and it paves the way for the realization of integrated quantum logic elements. PMID:27721438

  6. Quantum spin transistor with a Heisenberg spin chain

    Science.gov (United States)

    Marchukov, O. V.; Volosniev, A. G.; Valiente, M.; Petrosyan, D.; Zinner, N. T.

    2016-10-01

    Spin chains are paradigmatic systems for the studies of quantum phases and phase transitions, and for quantum information applications, including quantum computation and short-distance quantum communication. Here we propose and analyse a scheme for conditional state transfer in a Heisenberg XXZ spin chain which realizes a quantum spin transistor. In our scheme, the absence or presence of a control spin excitation in the central gate part of the spin chain results in either perfect transfer of an arbitrary state of a target spin between the weakly coupled input and output ports, or its complete blockade at the input port. We also discuss a possible proof-of-concept realization of the corresponding spin chain with a one-dimensional ensemble of cold atoms with strong contact interactions. Our scheme is generally applicable to various implementations of tunable spin chains, and it paves the way for the realization of integrated quantum logic elements.

  7. Bipartite entanglement entropy in massive two-dimensional quantum field theory.

    Science.gov (United States)

    Doyon, Benjamin

    2009-01-23

    Recently, Cardy, Castro Alvaredo, and the author obtained the first exponential correction to saturation of the bipartite entanglement entropy at large region lengths in massive two-dimensional integrable quantum field theory. It depends only on the particle content of the model, and not on the way particles scatter. Based on general analyticity arguments for form factors, we propose that this result is universal, and holds for any massive two-dimensional model (also out of integrability). We suggest a link of this result with counting pair creations far in the past.

  8. A two-dimensional algebraic quantum liquid produced by an atomic simulator of the quantum Lifshitz model.

    Science.gov (United States)

    Po, Hoi Chun; Zhou, Qi

    2015-08-13

    Bosons have a natural instinct to condense at zero temperature. It is a long-standing challenge to create a high-dimensional quantum liquid that does not exhibit long-range order at the ground state, as either extreme experimental parameters or sophisticated designs of microscopic Hamiltonians are required for suppressing the condensation. Here we show that synthetic gauge fields for ultracold atoms, using either the Raman scheme or shaken lattices, provide physicists a simple and practical scheme to produce a two-dimensional algebraic quantum liquid at the ground state. This quantum liquid arises at a critical Lifshitz point, where a two-dimensional quartic dispersion emerges in the momentum space, and many fundamental properties of two-dimensional bosons are changed in its proximity. Such an ideal simulator of the quantum Lifshitz model allows experimentalists to directly visualize and explore the deconfinement transition of topological excitations, an intriguing phenomenon that is difficult to access in other systems.

  9. Quantum Hall effect in black phosphorus two-dimensional electron system.

    Science.gov (United States)

    Li, Likai; Yang, Fangyuan; Ye, Guo Jun; Zhang, Zuocheng; Zhu, Zengwei; Lou, Wenkai; Zhou, Xiaoying; Li, Liang; Watanabe, Kenji; Taniguchi, Takashi; Chang, Kai; Wang, Yayu; Chen, Xian Hui; Zhang, Yuanbo

    2016-07-01

    The development of new, high-quality functional materials has been at the forefront of condensed-matter research. The recent advent of two-dimensional black phosphorus has greatly enriched the materials base of two-dimensional electron systems (2DESs). Here, we report the observation of the integer quantum Hall effect in a high-quality black phosphorus 2DES. The high quality is achieved by embedding the black phosphorus 2DES in a van der Waals heterostructure close to a graphite back gate; the graphite gate screens the impurity potential in the 2DES and brings the carrier Hall mobility up to 6,000 cm(2) V(-1) s(-1). The exceptional mobility enabled us to observe the quantum Hall effect and to gain important information on the energetics of the spin-split Landau levels in black phosphorus. Our results set the stage for further study on quantum transport and device application in the ultrahigh mobility regime.

  10. The magnetic properties of a quasi-two-dimensional spin 1 easy axis Heisenberg antiferromagnet with competing interactions

    Energy Technology Data Exchange (ETDEWEB)

    Sousa, Griffith Mendonça A., E-mail: griffith_mas@hotmail.com; Pires, A.S.T.

    2014-03-15

    The Neel and collinear ordered phases of the two-dimensional S=1 antiferromagnet with next and next near neighbor exchange interactions and easy axis single ion anisotropy, on the square lattice, are studied at low temperature using a Modified Spin Wave Theory. We calculate the low-temperature quantities as a function of the temperature, frustration and anisotropy. We calculate also the phase diagram at T=0. We found a disordered phase separating the Neel and collinear phases. - Highlights: • The phase diagrams in zero temperature. • The critical temperature was studied as a function of frustration and D. • The sublattice magnetizations and the gap were studied.

  11. Heisenberg

    OpenAIRE

    Marques, Adílio Jorge; Departamento de Ciências Exatas, Biológicas e da Terra, Universidade Federal Fluminense

    2015-01-01

    Resenha do livro HeisenbergJosé Maria Filardo Bassalo e Francisco CarusoEditora Livraria da Física, São Paulo, 2014, 1a edição, 111 p.ISBN: 9788578612221http://dx.doi.org/10.5007/2175-7941.2015v32n1p291 Review of the book HeisenbergJosé Maria Filardo Bassalo e Francisco CarusoEditora Livraria da Física, São Paulo, 2014, 1a edição, 111 p.ISBN: 9788578612221http://dx.doi.org/10.5007/2175-7941.2015v32n1p291

  12. Nonlinear low-frequency electrostatic wave dynamics in a two-dimensional quantum plasma

    Energy Technology Data Exchange (ETDEWEB)

    Ghosh, Samiran, E-mail: sran_g@yahoo.com [Department of Applied Mathematics, University of Calcutta, 92, Acharya Prafulla Chandra Road, Kolkata-700 009 (India); Chakrabarti, Nikhil, E-mail: nikhil.chakrabarti@saha.ac.in [Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata-700064 (India)

    2016-08-15

    The problem of two-dimensional arbitrary amplitude low-frequency electrostatic oscillation in a quasi-neutral quantum plasma is solved exactly by elementary means. In such quantum plasmas we have treated electrons quantum mechanically and ions classically. The exact analytical solution of the nonlinear system exhibits the formation of dark and black solitons. Numerical simulation also predicts the possible periodic solution of the nonlinear system. Nonlinear analysis reveals that the system does have a bifurcation at a critical Mach number that depends on the angle of propagation of the wave. The small-amplitude limit leads to the formation of weakly nonlinear Kadomstev–Petviashvili solitons.

  13. On Relations between One-Dimensional Quantum and Two-Dimensional Classical Spin Systems

    Directory of Open Access Journals (Sweden)

    J. Hutchinson

    2015-01-01

    Full Text Available We exploit mappings between quantum and classical systems in order to obtain a class of two-dimensional classical systems characterised by long-range interactions and with critical properties equivalent to those of the class of one-dimensional quantum systems treated by the authors in a previous publication. In particular, we use three approaches: the Trotter-Suzuki mapping, the method of coherent states, and a calculation based on commuting the quantum Hamiltonian with the transfer matrix of a classical system. This enables us to establish universality of certain critical phenomena by extension from the results in the companion paper for the classical systems identified.

  14. Energy Spectra of Vortex Distributions in Two-Dimensional Quantum Turbulence

    Directory of Open Access Journals (Sweden)

    Ashton S. Bradley

    2012-10-01

    Full Text Available We theoretically explore key concepts of two-dimensional turbulence in a homogeneous compressible superfluid described by a dissipative two-dimensional Gross-Pitaeveskii equation. Such a fluid supports quantized vortices that have a size characterized by the healing length ξ. We show that, for the divergence-free portion of the superfluid velocity field, the kinetic-energy spectrum over wave number k may be decomposed into an ultraviolet regime (k≫ξ^{-1} having a universal k^{-3} scaling arising from the vortex core structure, and an infrared regime (k≪ξ^{-1} with a spectrum that arises purely from the configuration of the vortices. The Novikov power-law distribution of intervortex distances with exponent -1/3 for vortices of the same sign of circulation leads to an infrared kinetic-energy spectrum with a Kolmogorov k^{-5/3} power law, which is consistent with the existence of an inertial range. The presence of these k^{-3} and k^{-5/3} power laws, together with the constraint of continuity at the smallest configurational scale k≈ξ^{-1}, allows us to derive a new analytical expression for the Kolmogorov constant that we test against a numerical simulation of a forced homogeneous, compressible, two-dimensional superfluid. The numerical simulation corroborates our analysis of the spectral features of the kinetic-energy distribution, once we introduce the concept of a clustered fraction consisting of the fraction of vortices that have the same sign of circulation as their nearest neighboring vortices. Our analysis presents a new approach to understanding two-dimensional quantum turbulence and interpreting similarities and differences with classical two-dimensional turbulence, and suggests new methods to characterize vortex turbulence in two-dimensional quantum fluids via vortex position and circulation measurements.

  15. Thermal quantum discord in Heisenberg models with Dzyaloshinski-Moriya interaction

    Institute of Scientific and Technical Information of China (English)

    Wang Lin-Cheng; Yan Jun-Yan; Yi Xue-Xi

    2011-01-01

    We study the quantum discord of the bipartite Heisenberg model with the Dzyaloshinski-Moriya(DM)interaction in thermal equilibrium state and discuss the effect of the DM interaction on the quantum discord.The quantum entanglement of the system is also discussed and compared with quantum discord. Our results show that the quantum discord may reveal more properties of the system than quantum entanglement and the DM interaction may play an important role in the Heisenberg model.

  16. Quantification of quantum discord in a antiferromagnetic Heisenberg compound

    Energy Technology Data Exchange (ETDEWEB)

    Singh, H., E-mail: chiranjib@iiserkol.ac.in; Chakraborty, T., E-mail: chiranjib@iiserkol.ac.in; Mitra, C., E-mail: chiranjib@iiserkol.ac.in [Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, Mohanpur -741252, Nadia, West Bengal (India)

    2014-04-24

    An experimental quantification of concurrence and quantum discord from heat capacity (C{sub p}) measurement performed over a solid state system has been reported. In this work, thermodynamic measurements were performed on copper nitrate (CN, Cu(NO{sub 3}){sub 2}⋅2.5H{sub 2}O) single crystals which is an alternating antiferromagnet Heisenberg spin 1/2 system. CN being a weak dimerized antiferromagnet is an ideal system to investigate correlations between spins. The theoretical expressions were used to obtain concurrence and quantum discord curves as a function of temperature from heat capacity data of a real macroscopic system, CN.

  17. Heisenberg double of supersymmetric algebras for noncommutative quantum field theory

    Science.gov (United States)

    Kirchanov, V. S.

    2013-09-01

    The ground work is laid for the construction of a Heisenberg superdouble in the form of a smash product of a standard Poincaré-Lie quantum-operator superalgebra with coalgebra and its double Lie spatial superalgebra with coalgebra, which are Hopf algebras and a Hopf modular algebra, respectively. Deformation of the superalgebras is realized by Drinfeld twists for the shift and supershift operators. As a result, an extended algebra is obtained, containing a non(anti)commutative superspace and quantum-group generators.

  18. Interactions of a Charged Particle with Parallel Two-Dimensional Quantum Electron Gases

    Institute of Scientific and Technical Information of China (English)

    LI Chun-Zhi; SONG Yuan-Hong; WANG You-Nian

    2008-01-01

    @@ By using the linearized quantum hydrodynamic (QHD) theory, electronic excitations induced by a charged particle moving between or over two parallel two-dimensional quantum electron gases (2DQEG) are investigated. The calculation shows that the influence of the quantum effects on the interaction process should be taken into account. Including the quantum statistical and quantum diffraction effects, the general expressions of the induced potential and the stopping power are obtained. Our simulation results indicate that a V-shaped oscillatory wake potential exists in the electron gases during the test charge intrusion. Meanwhile, double peaks will occur in the stopping power when the distance of two surfaces is smaller and the test charge gets closer to any one of the two sheets.

  19. Emergent chiral spin liquid: fractional quantum Hall effect in a kagome Heisenberg model.

    Science.gov (United States)

    Gong, Shou-Shu; Zhu, Wei; Sheng, D N

    2014-09-10

    The fractional quantum Hall effect (FQHE) realized in two-dimensional electron systems under a magnetic field is one of the most remarkable discoveries in condensed matter physics. Interestingly, it has been proposed that FQHE can also emerge in time-reversal invariant spin systems, known as the chiral spin liquid (CSL) characterized by the topological order and the emerging of the fractionalized quasiparticles. A CSL can naturally lead to the exotic superconductivity originating from the condense of anyonic quasiparticles. Although CSL was highly sought after for more than twenty years, it had never been found in a spin isotropic Heisenberg model or related materials. By developing a density-matrix renormalization group based method for adiabatically inserting flux, we discover a FQHE in a spin-½ isotropic kagome Heisenberg model. We identify this FQHE state as the long-sought CSL with a uniform chiral order spontaneously breaking time reversal symmetry, which is uniquely characterized by the half-integer quantized topological Chern number protected by a robust excitation gap. The CSL is found to be at the neighbor of the previously identified Z2 spin liquid, which may lead to an exotic quantum phase transition between two gapped topological spin liquids.

  20. Ultraviolet finiteness of Chiral Perturbation Theory for two-dimensional Quantum Electrodynamics

    CERN Document Server

    Paston, S A; Franke, V A

    2003-01-01

    We consider the perturbation theory in the fermion mass (chiral perturbation theory) for the two-dimensional quantum electrodynamics. With this aim, we rewrite the theory in the equivalent bosonic form in which the interaction is exponential and the fermion mass becomes the coupling constant. We reformulate the bosonic perturbation theory in the superpropagator language and analyze its ultraviolet behavior. We show that the boson Green's functions without vacuum loops remain finite in all orders of the perturbation theory in the fermion mass.

  1. Quantum Monte Carlo simulation of a two-dimensional Majorana lattice model

    Science.gov (United States)

    Hayata, Tomoya; Yamamoto, Arata

    2017-07-01

    We study interacting Majorana fermions in two dimensions as a low-energy effective model of a vortex lattice in two-dimensional time-reversal-invariant topological superconductors. For that purpose, we implement ab initio quantum Monte Carlo simulation to the Majorana fermion system in which the path-integral measure is given by a semipositive Pfaffian. We discuss spontaneous breaking of time-reversal symmetry at finite temperatures.

  2. The elusive Heisenberg limit in quantum-enhanced metrology

    Science.gov (United States)

    Demkowicz-Dobrzański, Rafał; Kołodyński, Jan; Guţă, Mădălin

    2012-01-01

    Quantum precision enhancement is of fundamental importance for the development of advanced metrological optical experiments, such as gravitational wave detection and frequency calibration with atomic clocks. Precision in these experiments is strongly limited by the 1/√N shot noise factor with N being the number of probes (photons, atoms) employed in the experiment. Quantum theory provides tools to overcome the bound by using entangled probes. In an idealized scenario this gives rise to the Heisenberg scaling of precision 1/N. Here we show that when decoherence is taken into account, the maximal possible quantum enhancement in the asymptotic limit of infinite N amounts generically to a constant factor rather than quadratic improvement. We provide efficient and intuitive tools for deriving the bounds based on the geometry of quantum channels and semi-definite programming. We apply these tools to derive bounds for models of decoherence relevant for metrological applications including: depolarization, dephasing, spontaneous emission and photon loss. PMID:22990859

  3. Hadamard NMR spectroscopy for two-dimensional quantum information processing and parallel search algorithms.

    Science.gov (United States)

    Gopinath, T; Kumar, Anil

    2006-12-01

    Hadamard spectroscopy has earlier been used to speed-up multi-dimensional NMR experiments. In this work, we speed-up the two-dimensional quantum computing scheme, by using Hadamard spectroscopy in the indirect dimension, resulting in a scheme which is faster and requires the Fourier transformation only in the direct dimension. Two and three qubit quantum gates are implemented with an extra observer qubit. We also use one-dimensional Hadamard spectroscopy for binary information storage by spatial encoding and implementation of a parallel search algorithm.

  4. Quantum spin-glass transition in the two-dimensional electron gas

    Indian Academy of Sciences (India)

    Subir Sachdev

    2002-02-01

    We discuss the possibility of spin-glass order in the vicinity of the unexpected metallic state of the two-dimensional electron gas in zero applied magnetic field. An average ferromagnetic moment may also be present, and the spin-glass order then resides in the plane orthogonal to the ferromagnetic moment. We argue that a quantum transition involving the destruction of the spin-glass order in an applied in-plane magnetic field offers a natural explanation of some features of recent magnetoconductance measurements. We present a quantum field theory for such a transition and compute its mean field properties.

  5. Unconventional critical activated scaling of two-dimensional quantum spin glasses

    Science.gov (United States)

    Matoz-Fernandez, D. A.; Romá, F.

    2016-07-01

    We study the critical behavior of two-dimensional short-range quantum spin glasses by numerical simulations. Using a parallel tempering algorithm, we calculate the Binder cumulant for the Ising spin glass in a transverse magnetic field with two different short-range bond distributions, the bimodal and the Gaussian ones. Through an exhaustive finite-size analysis, we show that the cumulant probably follows an unconventional activated scaling, which we interpret as new evidence supporting the hypothesis that the quantum critical behavior is governed by an infinite randomness fixed point.

  6. Two-dimensional distributed-phase-reference protocol for quantum key distribution

    DEFF Research Database (Denmark)

    Bacco, Davide; Christensen, Jesper Bjerge; Usuga Castaneda, Mario A.;

    2016-01-01

    Quantum key distribution (QKD) and quantum communication enable the secure exchange of information between remote parties. Currently, the distributed-phase-reference (DPR) protocols, which are based on weak coherent pulses, are among the most practical solutions for long-range QKD. During the last...... 10 years, long-distance fiber-based DPR systems have been successfully demonstrated, although fundamental obstacles such as intrinsic channel losses limit their performance. Here, we introduce the first two-dimensional DPR-QKD protocol in which information is encoded in the time and phase of weak...

  7. Three-body recombination in a quasi-two-dimensional quantum gas

    Science.gov (United States)

    Huang, Bo; Zenesini, Alessandro; Grimm, Rudolf

    2016-05-01

    Quantum three-body recombination in three-dimensional systems is influenced by a series of weakly bound trimers known as Efimov states, which are induced by short-range interactions and exhibit a discrete scaling symmetry. On the other hand, two-dimensional systems with contact interactions are characterized by continuous scale invariance and support no Efimov physics. This raises questions about the behaviour of three-body recombination in the transition from three to two dimensions. We use ultracold caesium atoms trapped in anisotropic potentials formed by a pair of counter-propagating laser beams to experimentally investigate three-body recombination in quasi-two-dimensional systems with tunable confinement and tunable interactions. In our recent experiments, we observed a smooth transition of the three-body recombination rate coefficient from a three-dimensional to a deeply quasi-two-dimensional system. A comparison between the results obtained near two Feshbach resonances indicates a universal behaviour of three-body recombination in the quasi-two-dimensional regime. Austrian Science Fund FWF within project P23106.

  8. Superconformal quantum mechanics via Wigner-Heisenberg algebra

    Energy Technology Data Exchange (ETDEWEB)

    Carrion, H.L. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)]|[Universidade Federal, Rio de Janeiro, RJ (Brazil). Inst. de Fisica; E-mail: hleny@cbpf.br; Rodrigues, R. de Lima [Paraiba Univ., Cajazeiras, PB (Brazil). Dep. de Ciencias Exatas e da Natureza]. E-mail: rafael@df.ufcg.edu.br

    2004-03-01

    We show the natural relation between the Wigner Hamiltonian and the conformal Hamiltonian. It is presented a model in (super)conformal quantum mechanics with (super)conformal symmetry in the Wigner-Heisenberg algebra picture [x,p{sub x}]=i(1+cP) (P being the parity operator). In this context, the energy spectrum, the Casimir operator, creation and annihilation operators are defined. This superconformal Hamiltonian is similar to the super-Hamiltonian of the Calogero model and it is also an extension of the super-Hamiltonian for the Dirac Oscillator. (author)

  9. Thermal quantum discord in the Heisenberg chain with impurity

    Energy Technology Data Exchange (ETDEWEB)

    Gong, Jia-Min, E-mail: jmgong@yeah.net; Hui, Zhan-Qiang

    2014-07-01

    We study thermal quantum discord (TQD) in the Heisenberg chain with spin site or magnetic impurity. The former one of which may induce inhomogeneous exchange interactions between the neighboring spins, while the latter one may model a spin chain with nonuniform magnetic field. In contrast to one's traditional understanding, we found that the spin impurity can be used to enhance the TQD greatly for all the bipartition schemes of the chain, while the magnetic impurity located on one spin can make the TQD between the other two spins approaching its maximum 1 for the antiferromagnetic chain.

  10. The field-induced laws of thermodynamic properties in the two-dimensional spin-1 ferromagnetic Heisenberg model with the exchange and single-ion anisotropies

    Energy Technology Data Exchange (ETDEWEB)

    Pu Qiurong [Department of Physics, College of Physics and Electronic Engineering, Guangzhou University, Guangzhou 510006 (China); Chen Yuan, E-mail: newbayren@163.com [Department of Physics, College of Physics and Electronic Engineering, Guangzhou University, Guangzhou 510006 (China)

    2013-02-01

    Green's function method is applied to investigate the two-dimensional spin-1 ferromagnetic Heisenberg model with the exchange and single-ion anisotropies. In the presence of the magnetic field, the effects of the anisotropies and field on the thermodynamic properties are obtained within the random phase approximation combining with Anderson-Callen approximation. The field-induced laws are found for the thermodynamic properties. Field dependences of heights of the susceptibility maximum and specific heat maximum fit well to power laws. The linear increase at high fields is shown for positions of the susceptibility maximum and specific heat maximum. A power law at low fields occurs for the position of the susceptibility maximum. At the positions of the maxima, the magnetization and internal energy display the power-law increase and linear decrease with the field, respectively. The exponents of the power laws are dependent of the anisotropies, as well as the slopes of the linear laws. Our results do not support the 2/3 power law which was obtained by the Landau theory.

  11. Extraordinary behaviors in a two-dimensional decoherent alternative quantum walk

    Science.gov (United States)

    Chen, Tian; Zhang, Xiangdong

    2016-07-01

    We reveal the quantum and classical behaviors of the two-dimensional (2D) alternative quantum walk (AQW) in the presence of decoherence. For different kinds of decoherence, the analytic expressions for the moments of position distribution of the AQW are obtained. Taking the broken line noise and coin decoherence as examples of decoherence, we find that when decoherence emerges in only one direction, the anisotropic position distribution pattern appears, and not all the motions of the walker exhibit the transition from quantum to classical behaviors. Considering the effect of decoherence, we reveal the anisotropic correlations between the x (y ) position of the 2D walker and the state of the coin in 2D AQWs.

  12. Tunable band topology reflected by fractional quantum Hall States in two-dimensional lattices.

    Science.gov (United States)

    Wang, Dong; Liu, Zhao; Cao, Junpeng; Fan, Heng

    2013-11-01

    Two-dimensional lattice models subjected to an external effective magnetic field can form nontrivial band topologies characterized by nonzero integer band Chern numbers. In this Letter, we investigate such a lattice model originating from the Hofstadter model and demonstrate that the band topology transitions can be realized by simply introducing tunable longer-range hopping. The rich phase diagram of band Chern numbers is obtained for the simple rational flux density and a classification of phases is presented. In the presence of interactions, the existence of fractional quantum Hall states in both |C| = 1 and |C| > 1 bands is confirmed, which can reflect the band topologies in different phases. In contrast, when our model reduces to a one-dimensional lattice, the ground states are crucially different from fractional quantum Hall states. Our results may provide insights into the study of new fractional quantum Hall states and experimental realizations of various topological phases in optical lattices.

  13. Interior design of a two-dimensional semiclassical black hole: Quantum transition across the singularity

    CERN Document Server

    Levanony, Dana

    2010-01-01

    We study the internal structure of a two-dimensional dilatonic evaporating black hole, based on the CGHS model. At the semiclassical level, a (weak) spacelike singularity was previously found to develop inside the black hole. We employ here a simplified quantum formulation of spacetime dynamics in the neighborhood of this singularity, using a minisuperspace-like approach. Quantum evolution is found to be regular and well-defined at the semiclassical singularity. A well-localized initial wave-packet propagating towards the singularity bounces off the latter and retains its well-localized form. Our simplified quantum treatment thus suggests that spacetime may extend semiclassically beyond the singularity, and also signifies the specific extension.

  14. Evidence of two-dimensional quantum Wigner Crystal in a zero magnetic field

    Science.gov (United States)

    Huang, Jian; Pfeiffer, Loren; West, Ken

    2014-03-01

    In disorder-dominated cases, Anderson localization occurs as a result of destructive interference effects caused by (short-ranged) random disorders. On the other hand, in interaction-dominated scenarios, striking manifestations of quantum physics emerge in response to strong inter-particle Coulomb energy (EC). The most prominent interaction-driven effect is the Wigner crystallization (WC) of electrons, an electron solid made up with spatially separated charges settling in a form of a lattice. The classical version of the crystallization, with the Debye temperature ΘD two-dimensional (2D) electrons on helium surfaces (EHS). However, the more desired quantum version with the Fermi energy EF <two-dimensional hole (2DH) systems in a genuine interaction-driven regime. A high resolution dc VI measurement reveals a pA level threshold transport accompanied by resistivity oscillations, indicating the coexistence of a pinned quantum WC with discrete edge filaments of unpinned carriers. NSF DMR 1105183

  15. Test of quantum thermalization in the two-dimensional transverse-field Ising model

    Science.gov (United States)

    Blaß, Benjamin; Rieger, Heiko

    2016-12-01

    We study the quantum relaxation of the two-dimensional transverse-field Ising model after global quenches with a real-time variational Monte Carlo method and address the question whether this non-integrable, two-dimensional system thermalizes or not. We consider both interaction quenches in the paramagnetic phase and field quenches in the ferromagnetic phase and compare the time-averaged probability distributions of non-conserved quantities like magnetization and correlation functions to the thermal distributions according to the canonical Gibbs ensemble obtained with quantum Monte Carlo simulations at temperatures defined by the excess energy in the system. We find that the occurrence of thermalization crucially depends on the quench parameters: While after the interaction quenches in the paramagnetic phase thermalization can be observed, our results for the field quenches in the ferromagnetic phase show clear deviations from the thermal system. These deviations increase with the quench strength and become especially clear comparing the shape of the thermal and the time-averaged distributions, the latter ones indicating that the system does not completely lose the memory of its initial state even for strong quenches. We discuss our results with respect to a recently formulated theorem on generalized thermalization in quantum systems.

  16. Quantum State Transfer in a Two-dimensional Regular Spin Lattice of Triangular Shape

    CERN Document Server

    Miki, Hiroshi; Vinet, Luc; Zhedanov, Alexei

    2012-01-01

    Quantum state transfer in a triangular domain of a two-dimensional, equally-spaced, spin lat- tice with non-homogeneous nearest-neighbor couplings is analyzed. An exact solution of the one- excitation dynamics is provided in terms of 2-variable Krawtchouk orthogonal polynomials that have been recently defined. The probability amplitude for an excitation to transit from one site to another is given. For some values of the parameters, perfect transfer is shown to take place from the apex of the lattice to the boundary hypotenuse.

  17. Modeling A.C. Electronic Transport through a Two-Dimensional Quantum Point Contact

    Energy Technology Data Exchange (ETDEWEB)

    Aronov, I.E.; Beletskii, N.N.; Berman, G.P.; Campbell, D.K.; Doolen, G.D.; Dudiy, S.V.

    1998-12-07

    We present the results on the a.c. transport of electrons moving through a two-dimensional (2D) semiconductor quantum point contact (QPC). We concentrate our attention on the characteristic properties of the high frequency admittance ({omega}{approximately}0 - 50 GHz), and on the oscillations of the admittance in the vicinity of the separatrix (when a channel opens or closes), in presence of the relaxation effects. The experimental verification of such oscillations in the admittance would be a strong confirmation of the semi-classical approach to the a.c. transport in a QPC, in the separatrix region.

  18. Characterizing classical periodic orbits from quantum Green's functions in two-dimensional integrable systems: Harmonic oscillators and quantum billiards

    Science.gov (United States)

    Chen, Y. F.; Tung, J. C.; Tuan, P. H.; Yu, Y. T.; Liang, H. C.; Huang, K. F.

    2017-01-01

    A general method is developed to characterize the family of classical periodic orbits from the quantum Green's function for the two-dimensional (2D) integrable systems. A decomposing formula related to the beta function is derived to link the quantum Green's function with the individual classical periodic orbits. The practicality of the developed formula is demonstrated by numerically analyzing the 2D commensurate harmonic oscillators and integrable quantum billiards. Numerical analyses reveal that the emergence of the classical features in quantum Green's functions principally comes from the superposition of the degenerate states for 2D harmonic oscillators. On the other hand, the damping factor in quantum Green's functions plays a critical role to display the classical features in mesoscopic regime for integrable quantum billiards, where the physical function of the damping factor is to lead to the coherent superposition of the nearly degenerate eigenstates.

  19. Nonequilibrium Phase Transition in a Two-Dimensional Driven Open Quantum System

    Directory of Open Access Journals (Sweden)

    G. Dagvadorj

    2015-11-01

    Full Text Available The Berezinskii-Kosterlitz-Thouless mechanism, in which a phase transition is mediated by the proliferation of topological defects, governs the critical behavior of a wide range of equilibrium two-dimensional systems with a continuous symmetry, ranging from spin systems to superconducting thin films and two-dimensional Bose fluids, such as liquid helium and ultracold atoms. We show here that this phenomenon is not restricted to thermal equilibrium, rather it survives more generally in a dissipative highly nonequilibrium system driven into a steady state. By considering a quantum fluid of polaritons of an experimentally relevant size, in the so-called optical parametric oscillator regime, we demonstrate that it indeed undergoes a phase transition associated with a vortex binding-unbinding mechanism. Yet, the exponent of the power-law decay of the first-order correlation function in the (algebraically ordered phase can exceed the equilibrium upper limit: this shows that the ordered phase of driven-dissipative systems can sustain a higher level of collective excitations before the order is destroyed by topological defects. Our work suggests that the macroscopic coherence phenomena, observed recently in interacting two-dimensional light-matter systems, result from a nonequilibrium phase transition of the Berezinskii-Kosterlitz-Thouless rather than the Bose-Einstein condensation type.

  20. Numerical study for the c-dependence of fractal dimension in two-dimensional quantum gravity

    CERN Document Server

    Kawamoto, N; Kawamoto, Noboru; Yotsuji, Kenji

    2002-01-01

    We numerically investigate the fractal structure of two-dimensional quantum gravity coupled to matter central charge c for $-2 \\leq c \\leq 1$. We reformulate Q-state Potts model into the model which can be identified as a weighted percolation cluster model and can make continuous change of Q, which relates c, on the dynamically triangulated lattice. The c-dependence of the critical coupling is measured from the percolation probability and susceptibility. The c-dependence of the string susceptibility of the quantum surface is evaluated and has very good agreement with the theoretical predictions. The c-dependence of the fractal dimension based on the finite size scaling hypothesis is measured and has excellent agreement with one of the theoretical predictions previously proposed except for the region near $c\\approx 1$.

  1. Bound states in optical absorption of semiconductor quantum wells containing a two-dimensional electron Gas

    Science.gov (United States)

    Huard; Cox; Saminadayar; Arnoult; Tatarenko

    2000-01-01

    The dependence of the optical absorption spectrum of a semiconductor quantum well on two-dimensional electron concentration n(e) is studied using CdTe samples. The trion peak (X-) seen at low n(e) evolves smoothly into the Fermi edge singularity at high n(e). The exciton peak (X) moves off to high energy, weakens, and disappears. The X,X- splitting is linear in n(e) and closely equal to the Fermi energy plus the trion binding energy. For Cd0.998Mn0.002Te quantum wells in a magnetic field, the X,X- splitting reflects unequal Fermi energies for M = +/-1/2 electrons. The data are explained by Hawrylak's theory of the many-body optical response including spin effects.

  2. Entanglement at a two-dimensional quantum critical point: a numerical linked-cluster expansion study.

    Science.gov (United States)

    Kallin, Ann B; Hyatt, Katharine; Singh, Rajiv R P; Melko, Roger G

    2013-03-29

    We develop a method to calculate the bipartite entanglement entropy of quantum models, in the thermodynamic limit, using a numerical linked-cluster expansion (NLCE) involving only rectangular clusters. It is based on exact diagonalization of all n×m rectangular clusters at the interface between entangled subsystems A and B. We use it to obtain the Renyi entanglement entropy of the two-dimensional transverse field Ising model, for arbitrary real Renyi index α. Extrapolating these results as a function of the order of the calculation, we obtain universal pieces of the entanglement entropy associated with lines and corners at the quantum critical point. They show NLCE to be one of the few methods capable of accurately calculating universal properties of arbitrary Renyi entropies at higher dimensional critical points.

  3. Two-dimensional distributed-phase-reference protocol for quantum key distribution

    Science.gov (United States)

    Bacco, Davide; Christensen, Jesper Bjerge; Castaneda, Mario A. Usuga; Ding, Yunhong; Forchhammer, Søren; Rottwitt, Karsten; Oxenløwe, Leif Katsuo

    2016-12-01

    Quantum key distribution (QKD) and quantum communication enable the secure exchange of information between remote parties. Currently, the distributed-phase-reference (DPR) protocols, which are based on weak coherent pulses, are among the most practical solutions for long-range QKD. During the last 10 years, long-distance fiber-based DPR systems have been successfully demonstrated, although fundamental obstacles such as intrinsic channel losses limit their performance. Here, we introduce the first two-dimensional DPR-QKD protocol in which information is encoded in the time and phase of weak coherent pulses. The ability of extracting two bits of information per detection event, enables a higher secret key rate in specific realistic network scenarios. Moreover, despite the use of more dimensions, the proposed protocol remains simple, practical, and fully integrable.

  4. Cavity quantum electrodynamics with many-body states of a two-dimensional electron gas.

    Science.gov (United States)

    Smolka, Stephan; Wuester, Wolf; Haupt, Florian; Faelt, Stefan; Wegscheider, Werner; Imamoglu, Ataç

    2014-10-17

    Light-matter interaction has played a central role in understanding as well as engineering new states of matter. Reversible coupling of excitons and photons enabled groundbreaking results in condensation and superfluidity of nonequilibrium quasiparticles with a photonic component. We investigated such cavity-polaritons in the presence of a high-mobility two-dimensional electron gas, exhibiting strongly correlated phases. When the cavity was on resonance with the Fermi level, we observed previously unknown many-body physics associated with a dynamical hole-scattering potential. In finite magnetic fields, polaritons show distinct signatures of integer and fractional quantum Hall ground states. Our results lay the groundwork for probing nonequilibrium dynamics of quantum Hall states and exploiting the electron density dependence of polariton splitting so as to obtain ultrastrong optical nonlinearities.

  5. Phase diagram and correlation functions of the two-dimensional dissipative quantum XY model

    Science.gov (United States)

    Hou, Changtao; Varma, Chandra M.

    2016-11-01

    The two-dimensional quantum XY model, with a Caldeira-Leggett form of dissipation, is applicable to the quantum-critical properties of diverse experimental systems, ranging from superconductor to insulator transitions, ferromagnetic and antiferromagnetic transitions in metals, to the loop-current order transition in cuprates. We solve the reexpression of this model in terms of orthogonal topological excitations, vortices, and a variety of instantons, by renormalization group methods. The calculations explain the extraordinary properties of the model discovered in Monte Carlo calculations: the product form of the quantum-critical fluctuations in space and time, a spatial correlation length proportional to the logarithm of the temporal correlation length near the transition from a disordered to a fully ordered state, and the occurrence of a phase with spatial order without temporal order. They are intimately related to the flow of the metric of time in relation to the metric of space, i.e., of the dynamical critical exponent z . These properties appear to be essential in understanding the strange metallic phase found in a variety of quantum-critical transitions as well as the accompanying high-temperature superconductivity.

  6. Mott glass phase in a diluted bilayer Heisenberg quantum antiferromagnet

    Science.gov (United States)

    Ma, Nv-Sen; Sandvik, Anders W.; Yao, Dao-Xin

    2015-09-01

    We use quantum Monte Carlo simulations to study a dimer-diluted S = 1/2 Heisenberg model on a bilayer square lattice with intralayer interaction J1 and interlayer interaction J2. Below the classical percolation threshold pc, the system has three phases reachable by tuning the interaction ratio g = J2/J1: a Néel ordered phase, a gapless quantum glass phase, and a gapped quantum paramagnetic phase. We present the ground-state phase diagram in the plane of dilution p and interaction ratio g. The quantum glass phase is certified to be of the gapless Mott glass type, having a uniform susceptibility vanishing at zero temperature T and following a stretched exponential form at T > 0; χu exp(-b/Tα) with α < 1. At the phase transition point from Neel ordered to Mott glass, we find that the critical exponents are different from those of the clean system described by the standard O(3) universality class in 2+1 dimensions.

  7. Pauli-Heisenberg Oscillations in Electron Quantum Transport.

    Science.gov (United States)

    Thibault, Karl; Gabelli, Julien; Lupien, Christian; Reulet, Bertrand

    2015-06-12

    We measure the current fluctuations emitted by a normal-metal-insulator-normal-metal tunnel junction with a very wide bandwidth, from 0.3 to 13 GHz, down to very low temperature T=35  mK. This allows us to perform the spectroscopy (i.e., measure the frequency dependence) of thermal noise (no dc bias, variable temperature) and shot noise (low temperature, variable dc voltage bias). Because of the very wide bandwidth of our measurement, we deduce the current-current correlator in the time domain. We observe the thermal decay of this correlator as well as its oscillations with a period h/eV, a direct consequence of the effect of the Pauli and Heisenberg principles in quantum electron transport.

  8. Epitaxial superconductor-semiconductor two-dimensional systems: platforms for quantum circuits (Conference Presentation)

    Science.gov (United States)

    Shabani, Javad

    2016-10-01

    Theory suggests that the interface between a one-dimensional semiconductor (Sm) with strong spin-orbit coupling and a superconductor (S) hosts Majorana modes with nontrivial topological properties. A key challenge in fabrication of such hybrid devices is forming highly transparent contacts between the active electrons in the semiconductor and the superconducting metal. Recently, it has been shown that a near perfect interface and a highly transparent contact can be achieved using epitaxial growth of aluminum on InAs nanowires. In this work, we present the first two-dimensional epitaxial superconductor-semiconductor material system that can serve as a platform for topological superconductivity. We show that our material system, Al-InAs, satisfies all the requirements necessary to reach into the topological superconducting regime by individual characterization of the semiconductor two dimensional electron system, superconductivity of Al and performance of S-Sm-S junctions. This exciting development might lead to a number of useful applications ranging from spintronics to quantum computing.

  9. Multifarious topological quantum phase transitions in two-dimensional topological superconductors

    Science.gov (United States)

    Liu, Xiao-Ping; Zhou, Yuan; Wang, Yi-Fei; Gong, Chang-De

    2016-06-01

    We study the two-dimensional topological superconductors of spinless fermions in a checkerboard-lattice Chern-insulator model. With the short-range p-wave superconducting pairing, multifarious topological quantum phase transitions have been found and several phases with high Chern numbers have been observed. We have established a rich phase diagram for these topological superconducting states. A finite-size checkerboard-lattice cylinder with a harmonic trap potential has been further investigated. Based upon the self-consistent numerical calculations of the Bogoliubov-de Gennes equations, various phase transitions have also been identified at different regions of the system. Multiple pairs of Majorana fermions are found to be well-separated and localized at the phase boundaries between the phases characterized by different Chern numbers.

  10. Theory of the vortex-clustering transition in a confined two-dimensional quantum fluid

    CERN Document Server

    Yu, Xiaoquan; Nian, Jun; Reeves, Matthew T; Bradley, Ashton S

    2016-01-01

    Clustering of like-sign vortices in a planar bounded domain is known to occur at negative temperature, a phenomenon that Onsager demonstrated to be a consequence of bounded phase space. In a confined superfluid, quantized vortices can support such an ordered phase, provided they evolve as an almost isolated subsystem containing sufficient energy. A detailed theoretical understanding of the statistical mechanics of such states thus requires a microcanonical approach. Here we develop an analytical theory of the vortex clustering transition in a neutral system of quantum vortices confined to a two-dimensional disk geometry, within the microcanonical ensemble. As the system energy increases above a critical value, the system develops global order via the emergence of a macroscopic dipole structure from the homogeneous phase of vortices, spontaneously breaking the Z2 symmetry associated with invariance under vortex circulation exchange, and the rotational SO(2) symmetry due to the disk geometry. The dipole structu...

  11. One- and Two-Dimensional Nuclear Magnetic Resonance Spectroscopy with a Diamond Quantum Sensor

    Science.gov (United States)

    Boss, J. M.; Chang, K.; Armijo, J.; Cujia, K.; Rosskopf, T.; Maze, J. R.; Degen, C. L.

    2016-05-01

    We report on Fourier spectroscopy experiments performed with near-surface nitrogen-vacancy centers in a diamond chip. By detecting the free precession of nuclear spins rather than applying a multipulse quantum sensing protocol, we are able to unambiguously identify the NMR species devoid of harmonics. We further show that, by engineering different Hamiltonians during free precession, the hyperfine coupling parameters as well as the nuclear Larmor frequency can be selectively measured with up to five digits of precision. The protocols can be combined to demonstrate two-dimensional Fourier spectroscopy. Presented techniques will be useful for mapping nuclear coordinates in molecules deposited on diamond sensor chips, en route to imaging their atomic structure.

  12. Magnetoelectronic transport of the two-dimensional electron gas in CdSe single quantum wells

    Indian Academy of Sciences (India)

    P K Ghosh; A Ghosal; D Chattopadhyay

    2009-02-01

    Hall mobility and magnetoresistance coefficient for the two-dimensional (2D) electron transport parallel to the heterojunction interfaces in a single quantum well of CdSe are calculated with a numerical iterative technique in the framework of Fermi–Dirac statistics. Lattice scatterings due to polar-mode longitudinal optic (LO) phonons, and acoustic phonons via deformation potential and piezoelectric couplings, are considered together with background and remote ionized impurity interactions. The parallel mode of piezoelectric scattering is found to contribute more than the perpendicular mode. We observe that the Hall mobility decreases with increasing temperature but increases with increasing channel width. The magnetoresistance coefficient is found to decrease with increasing temperature and increase with increasing magnetic field in the classical region.

  13. Donor-bound electron states in a two-dimensional quantum ring under uniform magnetic field

    Institute of Scientific and Technical Information of China (English)

    Jia Bo-Yong; Yu Zhong-Yuan; Liu Yu-Min; Han Li-Hong; Yao Wen-Jie; Feng Hao; Ye Han

    2011-01-01

    The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring.The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.

  14. Properties of two-dimensional electron gas containing self-organized quantum antidots

    Science.gov (United States)

    Vasilyev, Yu.; Suchalkin, S.; Zundel, M.; Heisenberg, D.; Eberl, K.; von Klitzing, K.

    1999-11-01

    A nonuniform two-dimensional electron gas in a heterojunction with inserted self-organized electrically inactive dots (acting as antidots) has been fabricated by molecular-beam epitaxy of AlGaAs/AlInAs/GaAs layer sequences. Transport measurements give the ratio of the transport mobility to the quantum mobility less than four, which suggests that the dominant scattering at low magnetic fields is the short-range scattering from the lateral potential of the antidots. Far-infrared cyclotron resonance (CR) spectra show an absorption mode as narrow as 0.5 cm-1 at high magnetic fields associated with the high-mobility electron gas formed between the antidot islands and confined in the lateral directions. The confinement energy of 14 cm-1 is derived from the CR spectra.

  15. Unbinding of mutually avoiding random walks and two-dimensional quantum gravity

    Science.gov (United States)

    Carlon, Enrico; Baiesi, Marco

    2004-12-01

    We analyze the unbinding transition for a two-dimensional lattice polymer in which the constituent strands are mutually avoiding random walks. At low temperatures the strands are bound and form a single self-avoiding walk. We show that unbinding in this model is a strong first order transition. The entropic exponents associated with denaturated loops and end-segment distributions show sharp differences at the transition point and in the high temperature phase. Their values can be deduced from some exact arguments relying on a conformal mapping of copolymer networks into a fluctuating geometry, i.e., in the presence of quantum gravity. An excellent agreement between analytical and numerical estimates is observed for all cases analyzed.

  16. Reflectance measurement of two-dimensional photonic crystal nanocavities with embedded quantum dots

    CERN Document Server

    Stumpf, Wolfgang C; Kojima, Takanori; Fujita, Masayuki; Tanaka, Yoshinori; Noda, Susumu

    2010-01-01

    The spectra of two-dimensional photonic crystal slab nanocavities with embedded InAs quantum dots are measured by photoluminescence and reflectance. In comparing the spectra taken by these two different methods, consistency with the nanocavities' resonant wavelengths is found. Furthermore, it is shown that the reflectance method can measure both active and passive cavities. Q-factors of nanocavities, whose resonant wavelengths range from 1280 to 1620 nm, are measured by the reflectance method in cross polarization. Experimentally, Q-factors decrease for longer wavelengths and the intensity, reflected by the nanocavities on resonance, becomes minimal around 1360 nm. The trend of the Q-factors is explained by the change of the slab thickness relative to the resonant wavelength, showing a good agreement between theory and experiment. The trend of reflected intensity by the nanocavities on resonance can be understood as effects that originate from the PC slab and the underlying air cladding thickness. In addition...

  17. Quantum Phase Transition in the Two-Dimensional Random Transverse-Field Ising Model

    Science.gov (United States)

    Pich, C.; Young, A. P.

    1998-03-01

    We study the quantum phase transition in the random transverse-field Ising model by Monte Carlo simulations. In one-dimension it has been established that this system has the following striking behavior: (i) the dynamical exponent is infinite, and (ii) the exponents for the divergence of the average and typical correlation lengths are different. An important issue is whether this behavior is special to one-dimension or whether similar behavior persists in higher dimensions. Here we attempt to answer this question by studies of the two-dimensional model. Our simulations use the Wolff cluster algorithm and the results are analyzed by anisotropic finite size scaling, paying particular attention to the Binder ratio of moments of the order parameter distribution and the distribution of the spin-spin correlation functions for various distances.

  18. Multifarious topological quantum phase transitions in two-dimensional topological superconductors

    Science.gov (United States)

    Liu, Xiao-Ping; Zhou, Yuan; Wang, Yi-Fei; Gong, Chang-De

    2016-01-01

    We study the two-dimensional topological superconductors of spinless fermions in a checkerboard-lattice Chern-insulator model. With the short-range p-wave superconducting pairing, multifarious topological quantum phase transitions have been found and several phases with high Chern numbers have been observed. We have established a rich phase diagram for these topological superconducting states. A finite-size checkerboard-lattice cylinder with a harmonic trap potential has been further investigated. Based upon the self-consistent numerical calculations of the Bogoliubov-de Gennes equations, various phase transitions have also been identified at different regions of the system. Multiple pairs of Majorana fermions are found to be well-separated and localized at the phase boundaries between the phases characterized by different Chern numbers. PMID:27329219

  19. Measurement of the quantum capacitance of two-dimensional vanadium dioxide films

    Science.gov (United States)

    Wu, Zhe; Knighton, Talbot; Tarquini, Vinicio; Huang, Jian; Sepúlveda, Nelson; Department of Physics; Astronomy, Wayne State University Collaboration; Department of Electrical; Computer Engineering, Michigan State University Collaboration

    2015-03-01

    With a homebuilt ac bridge, we have performed capacitance measurement of quasi two-dimensional vanadium dioxide films grown on silicon-dioxide/p-doped silicon substrate. The out-phase-signal, which corresponds to the resistivity variation, is superior to the four-terminal measurement result of the temperature dependence of the resistivity which varies by four orders of magnitude from 360K to 310K. The hysteretic behavior shows an overlap of two distinctive features that indicate a shifted structural transition relative to the Mott transition. In addition, the quantum capacitance is obtained through the in-phase signals so that d μ/dn, the inverse of the density of states, is determined as a function of temperature. This has resulted in a diverging compressibility below the critical temperature by four orders of magnitude, consistent with a Mott transition influenced by Peierls transition.

  20. Two-dimensional topological crystalline insulator phase in quantum wells of trivial insulators

    Science.gov (United States)

    Niu, Chengwang; Buhl, Patrick M.; Bihlmayer, Gustav; Wortmann, Daniel; Blügel, Stefan; Mokrousov, Yuriy

    2016-06-01

    The realization of two-dimensional (2D) topological insulators (TIs) in HgTe/CdTe quantum wells (QWs) has generated an explosion of research on TIs and novel topologically nontrivial phases. Here we predict, based on first-principles calculations, that the newly discovered 2D topological crystalline insulators (TCIs) phase exists even in the QWs of trivial insulators, e.g. (Sn/Pb)Te and Na(Cl/Br), with mirror Chern number {n}{{M}}=-2. Tunable nontrivial energy gaps ranging from 4 to 238 meV are obtained, guaranteeing further room-temperature observations and applications. The combined effect of strain and electrostatic interaction that can be engineered by the cladding layers leads to a band inversion, resulting in the phase transition from trivial insulator to 2D TCIs. Our work provides a new strategy for engineering topological states in 2D materials.

  1. Electrically controlled crossing of energy levels in quantum dots in two-dimensional topological insulators

    Energy Technology Data Exchange (ETDEWEB)

    Sukhanov, Aleksei A.

    2017-05-15

    We study the energy spectra of bound states in quantum dots (QDs) formed by an electrostatic potential in two-dimensional topological insulator (TI) and their transformation with changes in QD depth and radius. It is found that, unlike a trivial insulator, the energy difference between the levels of the ground state and first excited state can decrease with decreasing the radius and increasing the depth of the QD so that these levels intersect under some critical condition. The crossing of the levels results in unusual features of optical properties caused by intraceneter electron transitions. In particular, it leads to significant changes of light absorption due to electron transitions between such levels and to the transient electroluminescence induced by electrical tuning of QD and TI parameters. In the case of magnetic TIs, the polarization direction of the absorbed or emitted circularly polarized light is changed due to the level crossing.

  2. Size Effect of a Negatively Charged Exciton in a Two-Dimensional Quantum Dot

    Institute of Scientific and Technical Information of China (English)

    LIU Chao; XIE Wen-Fang

    2009-01-01

    In this paper we study a negatively charged exciton (NCE), which is trapped by a two-dimensional (2D) parabolic potential.By using matrix diagonalization techniques, the correlation energies of the low-lying states with L = O, 1, and 2 are calculated as a function of confinement strength.We find that the size effects of different states are different.This phenomenon can be explained as a hidden symmetry, which is originated purely from symmetry.Based on symmetry, the features of the low-lying states are discussed in the influence of the 2D parabolic potential well.It is found that the confinement may cause accidental degeneracies between levels with different low-excited states.It is shown that the effect of quantum confinement on the binding energy of the heavy hole is stronger than that of a light hole.

  3. A gate defined quantum dot on the two-dimensional transition metal dichalcogenide semiconductor WSe2.

    Science.gov (United States)

    Song, Xiang-Xiang; Liu, Di; Mosallanejad, Vahid; You, Jie; Han, Tian-Yi; Chen, Dian-Teng; Li, Hai-Ou; Cao, Gang; Xiao, Ming; Guo, Guang-Can; Guo, Guo-Ping

    2015-10-28

    Two-dimensional layered materials, such as transition metal dichalcogenides (TMDCs), are promising materials for future electronics owing to their unique electronic properties. With the presence of a band gap, atomically thin gate defined quantum dots (QDs) can be achieved on TMDCs. Herein, standard semiconductor fabrication techniques are used to demonstrate quantum confined structures on WSe2 with tunnel barriers defined by electric fields, therefore eliminating the edge states induced by etching steps, which commonly appear in gapless graphene QDs. Over 40 consecutive Coulomb diamonds with a charging energy of approximately 2 meV were observed, showing the formation of a QD, which is consistent with the simulations. The size of the QD could be tuned over a factor of 2 by changing the voltages applied to the top gates. These results shed light on a way to obtain smaller quantum dots on TMDCs with the same top gate geometry compared to traditional GaAs/AlGaAs heterostructures with further research.

  4. Two-dimensional quantum percolation with binary non-zero hopping integrals

    Science.gov (United States)

    Dillon Thomas, Brianna; Nakanishi, Hisao

    In a previous work [Dillon and Nakanishi, Eur.Phys.J B 87, 286 (2014)], we calculated the transmission coefficient of the two-dimensional quantum percolation problem and mapped out in detail the three regimes of localization, i.e., exponentially localized, power-law localized, and delocalized which had been proposed earlier [Islam and Nakanishi, Phys.Rev. E 77, 061109 (2008)]. We now consider a variation on quantum percolation in which the hopping integral (Vdiluted) associated with bonds that connect to at least one diluted site is non-zero but a fraction of the hopping integral (Vfull=1) between non-diluted sites. We study the latter model by calculating quantities such as the transmission coefficient and the inverse participation ratio and find the original quantum percolation results to be stable over a wide range of energy. In particular, except in the immediate neighborhood of the band center (where increasing Vdiluted to just 0.02*Vfull appears to eliminate localization effects), increasing Vdiluted only shifts the boundaries between the 3 regimes but does not eliminate them until the Vdiluted reaches 20

  5. Monte carlo simulation study of the square lattice S=1/2 quantum heisenberg antiferromagnet

    CERN Document Server

    Kim, J K

    1999-01-01

    For the two dimensional S= 1/2 isotopic quantum Heisenberg antiferromagnet on a square lattice, we report our results of an extensive quantum Monte Carlo simulation for various physical observables such as the correlation length xi, the staggered magnetic susceptibility chi sub S sub T , the structure factor peak value S(Q), the internal energy epsilon, and the uniform susceptibility chi sub u. We find that chi sub S sub T approx chi sup 2 T and S(Q) approx xi sup 2 T sup 2 , in agreement with the predictions of the conventional theory but in disagreement with recent experiments. Our estimate of the spin stiffness constant rho sub s and spin wave velocity c, from the low temperature behavior of the chi sub u is shown to be consistent with the theoretical prediction of the low temperature behavior of the epsilon, and of the xi provided an additional correction up to T sup 2. However, our data are definitely inconsistent with the scenario of the crossover for the xi.

  6. Spatially correlated two-dimensional arrays of semiconductor and metal quantum dots in GaAs-based heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Nevedomskiy, V. N., E-mail: nevedom@mail.ioffe.ru; Bert, N. A.; Chaldyshev, V. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Preobrazhernskiy, V. V.; Putyato, M. A.; Semyagin, B. R. [Russian Academy of Sciences, Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

    2015-12-15

    A single molecular-beam epitaxy process is used to produce GaAs-based heterostructures containing two-dimensional arrays of InAs semiconductor quantum dots and AsSb metal quantum dots. The twodimensional array of AsSb metal quantum dots is formed by low-temperature epitaxy which provides a large excess of arsenic in the epitaxial GaAs layer. During the growth of subsequent layers at a higher temperature, excess arsenic forms nanoinclusions, i.e., metal quantum dots in the GaAs matrix. The two-dimensional array of such metal quantum dots is created by the δ doping of a low-temperature GaAs layer with antimony which serves as a precursor for the heterogeneous nucleation of metal quantum dots and accumulates in them with the formation of AsSb metal alloy. The two-dimensional array of InAs semiconductor quantum dots is formed via the Stranski–Krastanov mechanism at the GaAs surface. Between the arrays of metal and semiconductor quantum dots, a 3-nm-thick AlAs barrier layer is grown. The total spacing between the arrays of metal and semiconductor quantum dots is 10 nm. Electron microscopy of the structure shows that the arrangement of metal quantum dots and semiconductor quantum dots in the two-dimensional arrays is spatially correlated. The spatial correlation is apparently caused by elastic strain and stress fields produced by both AsSb metal and InAs semiconductor quantum dots in the GaAs matrix.

  7. Two-dimensional hole systems in indium-based quantum well heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Loher, Josef

    2016-08-01

    The complex spin-orbit interaction (SOI) of two-dimensional hole gas (2DHG) systems - the relativistic coupling of the hole spin degree of freedom to their movement in an electric field - is of fundamental interest in spin physics due to its key role for spin manipulation in spintronic devices. In this work, we were able to evaluate the tunability of Rashba-SOI-related parameters in the 2DHG system of InAlAs/InGaAs/InAs:Mn quantum well heterostructures experimentally by analyzing the hole density evolution of quantum interference effects at low magnetic fields. We achieved to cover a significant range of hole densities by the joint action of the variation of the manganese modulation doping concentration during molecular beam epitaxy and external field-effect-mediated manipulation of the 2D carrier density in Hall bar devices by a metallic topgate. Within these magnetotransport experiments, a reproducible phenomenon of remarkable robustness emerged in the transverse Hall magnetoresistivity of the indium 2DHG systems which are grown on a special InAlAs step-graded metamorphic buffer layer structure to compensate crystal lattice mismatch. As a consequence of the strain relaxation process, these material systems are characterized by anisotropic properties along different crystallographic directions. We identify a puzzling offset phenomenon in the zero-field Hall magnetoresistance and demonstrate it to be a universal effect in systems with spatially anisotropic transport properties.

  8. Atomistic Analysis of Room Temperature Quantum Coherence in Two-Dimensional CdSe Nanostructures.

    Science.gov (United States)

    Pal, Sougata; Nijjar, Parmeet; Frauenheim, Thomas; Prezhdo, Oleg V

    2017-03-02

    Recent experiments on CdSe nanoplatelets synthesized with precisely controlled thickness that eliminates ensemble disorder have allowed accurate measurement of quantum coherence at room temperature. Matching exactly the CdSe cores of the experimentally studied particles and considering several defects, we establish the atomistic origins of the loss of coherence between heavy and light hole excitations in two-dimensional CdSe and CdSe/CdZnS core/shell structures. The coherence times obtained using molecular dynamics based on tight-binding density functional theory are in excellent agreement with the measured values. We show that a long coherence time is a consequence of both small fluctuations in the energy gap between the excited state pair, which is much less than thermal energy, and a slow decay of correlation between the energies of the two states. Anionic defects at the core/shell interface have little effect on the coherence lifetime, while cationic defects strongly perturb the electronic structure, destroying the experimentally observed coherence. By coupling to the same phonon modes, the heavy and light holes synchronize their energy fluctuations, facilitating long-lived coherence. We further demonstrate that the electronic excitations are localized close to the surface of these narrow nanoscale systems, and therefore, they couple most strongly to surface acoustic phonons. The established features of electron-phonon coupling and the influence of defects, surfaces, and core/shell interfaces provide important insights into quantum coherence in nanoscale materials in general.

  9. Excited states of two-dimensional hydrogen atom in tilted magnetic field: Quantum chaos

    Science.gov (United States)

    Koval, Eugene A.; Koval, Oksana A.

    2017-09-01

    The aim of the current work is the research of the influence of a tilted magnetic field direction on the spectrum and the energy level spacing distribution of a two-dimensional (2D) hydrogen atom and of an exciton in GaAs/Al0.33Ga0.67As quantum well. It was discovered that the quantum chaos (QC) is initiated with an increasing angle α between the magnetic field direction and the normal to the atomic plane. It is characterized by the repulsion of levels leading to the eliminating of the shell structure and by changing the spectrum statistical properties. The statement about the initiation of chaos and its dominance over regular motion with increasing angle α is confirmed by the results of our calculations of the classical dynamics presented in this paper. The evolution of the spatial distribution of the square of the absolute value of the wave function at an increasing angle α was observed. The differences of calculated dependencies of energies for various excited states on the tilt angle at a wide range of the magnetic field strength were described.

  10. Polarized heat current generated by quantum pumping in two-dimensional topological insulators

    Science.gov (United States)

    Ronetti, F.; Carrega, M.; Ferraro, D.; Rech, J.; Jonckheere, T.; Martin, T.; Sassetti, M.

    2017-03-01

    We consider the transport properties of a two-dimensional topological insulator in a double quantum point contact geometry in the presence of a time-dependent external field. In the proposed setup an external gate is placed above a single constriction and it couples only with electrons belonging to the top edge. This asymmetric configuration and the presence of an ac signal allow for a quantum pumping mechanism, which, in turn, can generate finite heat and charge currents in an unbiased device configuration. A microscopic model for coupling with the external time-dependent gate potential is developed and the induced finite heat and charge currents are investigated. We demonstrate that in the noninteracting case, heat flow is associated with a single spin component, due to the helical nature of the edge states, and therefore a finite and polarized heat current is obtained in this configuration. The presence of e -e interchannel interactions strongly affects the current signal, lowering the degree of polarization of the system. Finally, we also show that separate heat and charge flows can be achieved, varying the amplitude of the external gate.

  11. Variational tensor network renormalization in imaginary time: Two-dimensional quantum compass model at finite temperature

    Science.gov (United States)

    Czarnik, Piotr; Dziarmaga, Jacek; Oleś, Andrzej M.

    2016-05-01

    Progress in describing thermodynamic phase transitions in quantum systems is obtained by noticing that the Gibbs operator e-β H for a two-dimensional (2D) lattice system with a Hamiltonian H can be represented by a three-dimensional tensor network, the third dimension being the imaginary time (inverse temperature) β . Coarse graining the network along β results in a 2D projected entangled-pair operator (PEPO) with a finite bond dimension D . The coarse graining is performed by a tree tensor network of isometries. The isometries are optimized variationally, taking into account full tensor environment, to maximize the accuracy of the PEPO. The algorithm is applied to the isotropic quantum compass model on an infinite square lattice near a symmetry-breaking phase transition at finite temperature. From the linear susceptibility in the symmetric phase and the order parameter in the symmetry-broken phase, the critical temperature is estimated at Tc=0.0606 (4 ) J , where J is the isotropic coupling constant between S =1/2 pseudospins.

  12. The Heisenberg Matrix Formulation of Quantum Field Theory

    CERN Document Server

    Brodsky, S J

    2002-01-01

    Heisenberg's matrix formulation of quantum mechanics can be generalized to relativistic systems by evolving in light-front time tau = t+z/c. The spectrum and wavefunctions of bound states, such as hadrons in quantum chromodynamics, can be obtained from matrix diagonalization of the light-front Hamiltonian on a finite dimensional light-front Fock basis defined using periodic boundary conditions in the light-front space coordinates. This method, discretized light-cone quantization (DLCQ), preserves the frame-independence of the front form even at finite resolution and particle number. Light-front quantization can also be used in the Hamiltonian form to construct an event generator for high energy physics reactions at the amplitude level. The light-front partition function, summed over exponentially-weighted light-front energies, has simple boost properties which may be useful for studies in heavy ion collisions. I also review recent work which shows that the structure functions measured in deep inelastic lepton...

  13. Laser driven intraband optical transitions in two-dimensional quantum dots and quantum rings

    Science.gov (United States)

    Barseghyan, M. G.; Kirakosyan, A. A.; Laroze, D.

    2017-01-01

    The intraband optical absorption have been investigated in the presence of hydrogenic donor impurity in GaAs/GaAlAs quantum dot and quantum ring in the intense laser field. The single electron energy spectrum and wave functions have been found using the effective mass approximation and exact diagonalization technique. Different selection rules are obtained for intraband transitions depending on the direction of incident light polarization. Due to the accidental degeneracy of the laser dressed impurity states the crossings of the curves of the threshold energies and the dipole matrix elements on laser field parameter have been observed. The intraband absorption coefficient is calculated for different locations of hydrogenic donor impurity and different values of intense laser field parameter. The obtained results show that the absorption spectrum can exhibit either a blue- or redshift depending on the impurity location, values of the laser field parameter and direction of incident light polarization. The obtained theoretical results indicate a novel opportunity to tune the performance of new devices, based on the quantum dots and quantum rings and to control their specific properties by means of intense laser and hydrogenic donor impurity.

  14. Tunable two-dimensional arrays of single Rydberg atoms for realizing quantum Ising models.

    Science.gov (United States)

    Labuhn, Henning; Barredo, Daniel; Ravets, Sylvain; de Léséleuc, Sylvain; Macrì, Tommaso; Lahaye, Thierry; Browaeys, Antoine

    2016-06-30

    Spin models are the prime example of simplified many-body Hamiltonians used to model complex, strongly correlated real-world materials. However, despite the simplified character of such models, their dynamics often cannot be simulated exactly on classical computers when the number of particles exceeds a few tens. For this reason, quantum simulation of spin Hamiltonians using the tools of atomic and molecular physics has become a very active field over the past years, using ultracold atoms or molecules in optical lattices, or trapped ions. All of these approaches have their own strengths and limitations. Here we report an alternative platform for the study of spin systems, using individual atoms trapped in tunable two-dimensional arrays of optical microtraps with arbitrary geometries, where filling fractions range from 60 to 100 per cent. When excited to high-energy Rydberg D states, the atoms undergo strong interactions whose anisotropic character opens the way to simulating exotic matter. We illustrate the versatility of our system by studying the dynamics of a quantum Ising-like spin-1/2 system in a transverse field with up to 30 spins, for a variety of geometries in one and two dimensions, and for a wide range of interaction strengths. For geometries where the anisotropy is expected to have small effects on the dynamics, we find excellent agreement with ab initio simulations of the spin-1/2 system, while for strongly anisotropic situations the multilevel structure of the D states has a measurable influence. Our findings establish arrays of single Rydberg atoms as a versatile platform for the study of quantum magnetism.

  15. Electronic transport in two-dimensional systems in the quantum hall regime

    Science.gov (United States)

    Tarquini, Vinicio

    The integer and the fractional quantum Hall effects are essential to the exploration of quantum matters characterized by topological phases. A quantum Hall system hosts one-dimensional (1D) chiral edge channels that manifest zero magnetoresistance, dissipationless due to the broken time reversal symmetry, and quantized Hall resistance vhe2 with v being the topological invariant (or Chern number). The 1-1 correspondence between the conducting gapless edge channels to the gapped incompressible bulk states is a defining character of a topological insulator (TI). Understanding this correspondence in real systems, especially the origin of its robustness (in terms of the limit of breakdown), is important both fundamentally and practically (i.e. in relation to spintronics). However, the breakdown mechanism, especially in light of the edge-bulk correlation, is still an open question. We adopt GaAs two-dimensional (2D) high-mobility hole systems confined in a 20 nm wide (100)-GaAs quantum wells and have perform transport measurement for a range of charge densities between 4 and 5 x 1010 cm -2 with a carrier mobility of 2 - 4 x 106 cm 2/V·s down to millikelvin temperatures. Systematic characterization of the 2D systems through Shubnikov-de Haas (SdH) oscillations yields an effective mass between 0.30 and 0.50me, in good agreement with the cyclotron resonance results. We then modify a regular Hall bar system into a unique anti-Hall bar geometry that provides an extra set of independent chiral edge channels without altering the topological invariant. We perform systematic measurement of quantum oscillations via chiral edges while simultaneously probing the bulk dynamics, through measuring across independent edges, in respond to the edge excitations. The edge-bulk correspondence reveals a non-equilibrium dynamical development of the incompressible bulk states that leads to a novel asymmetrical 1-0 Hall potential distribution. Moreover, probing the breakdown via inner and outer

  16. Experimental study of two-dimensional quantum Wigner solid in zero magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Jian [Department of Physics and Astronomy, Wayne State University, Detroit, MI 48201 (United States); Pfeiffer, L. N.; West, K. W. [Department of Electrical Engineering, Princeton University, Princeton, NJ 08544 (United States)

    2014-03-31

    At temperatures T → 0, strongly interacting two-dimensional (2D) electron systems manifest characteristic insulating behaviors that are key for understanding the nature of the ground state in light of the interplay between disorder and electron-electron interaction. In contrast to the hopping conductance demonstrated in the insulating side of the metal-to-insulator transition, the ultra-high quality 2D systems exhibit nonactivated T-dependence of the conductivity even for dilute carrier concentrations down to 7×10{sup 8} cm{sup −2}. The apparent metal-to-insulator transition (MIT) occurs for a large r{sub s} value around 40 for which a Wigner Crystalllization is expected. The magnetoresistance for a series of carrier densities in the vicinity of the transition exhibits a characteristic sign change in weak perpendicular magnetic field. Within the Wigner Crystallization regime (with r{sub s} > 40), we report an experimental observation of a characteristic nonlinear threshold behavior from a high-resolution dc dynamical response as an evidence for aWigner crystallization in high-purity GaAs 2D hole systems in zero magnetic field. The system under an increasing current drive exhibits voltage oscillations with negative differential resistance. They confirm the coexistence of a moving crystal along with striped edge states as observed for electrons on helium surfaces. Moreover, the threshold is well below the typical classical levels due to a different pinning and depinning mechanism that is possibly related to quantum processes.

  17. Experimental study of two-dimensional quantum Wigner solid in zero magnetic field

    Science.gov (United States)

    Huang, Jian; Pfeiffer, L. N.; West, K. W.

    2014-03-01

    At temperatures T → 0, strongly interacting two-dimensional (2D) electron systems manifest characteristic insulating behaviors that are key for understanding the nature of the ground state in light of the interplay between disorder and electron-electron interaction. In contrast to the hopping conductance demonstrated in the insulating side of the metal-to-insulator transition, the ultra-high quality 2D systems exhibit nonactivated T-dependence of the conductivity even for dilute carrier concentrations down to 7×108 cm-2. The apparent metal-to-insulator transition (MIT) occurs for a large rs value around 40 for which a Wigner Crystalllization is expected. The magnetoresistance for a series of carrier densities in the vicinity of the transition exhibits a characteristic sign change in weak perpendicular magnetic field. Within the Wigner Crystallization regime (with rs > 40), we report an experimental observation of a characteristic nonlinear threshold behavior from a high-resolution dc dynamical response as an evidence for aWigner crystallization in high-purity GaAs 2D hole systems in zero magnetic field. The system under an increasing current drive exhibits voltage oscillations with negative differential resistance. They confirm the coexistence of a moving crystal along with striped edge states as observed for electrons on helium surfaces. Moreover, the threshold is well below the typical classical levels due to a different pinning and depinning mechanism that is possibly related to quantum processes.

  18. Two-dimensional topological crystalline quantum spin Hall effect in transition metal intercalated compounds

    Science.gov (United States)

    Zhou, Jian; Jena, Puru

    2017-02-01

    While most of the two-dimensional (2D) topological crystalline insulators (TCIs) belong to group IV-VI narrow-band-gap semiconductors in a square lattice, in the present work we predict a TCI family based on transition metal intercalated compounds in a hexagonal lattice. First-principles calculations combined with a substrate-fixed globally optimal structural search technique show that a layer of Os prefers a uniform distribution between two graphene sheets. Band dispersion calculations reveal a Dirac point and a Dirac nodal ring near the Fermi level. The Dirac point is ascribed to the hybridization of e2 and e2* orbitals, and the Dirac ring is formed due to dispersion of s and e1* orbitals. Upon inclusion of spin-orbit coupling, these Dirac states open topologically nontrivial local band gaps, which are characterized by nonzero mirror Chern numbers. The quantum spin Hall effect is also observed by integrating the spin Berry curvature in the Brillouin zone. In contrast to the 2D group IV-VI TCIs whose band inversions at X and Y points are "locked" by C4 rotation symmetry, here the relative energy of two local band gaps can be manipulated by in-plane biaxial strains. Some other similar intercalation compounds are also shown to be topologically nontrivial. Our work extends the 2D TCI family into a hexagonal lattice composed of transition metals.

  19. Dynamic scaling of the restoration of rotational symmetry in Heisenberg quantum antiferromagnets

    Science.gov (United States)

    Weinberg, Phillip; Sandvik, Anders W.

    2017-08-01

    We apply imaginary-time evolution with the operator e-τ H to study relaxation dynamics of gapless quantum antiferromagnets described by the spin-rotation-invariant Heisenberg Hamiltonian H . Using quantum Monte Carlo simulations to obtain unbiased results, we propagate an initial state with maximal order parameter msz (the staggered magnetization) in the z spin direction and monitor the expectation value 〈ms〉 as a function of imaginary time τ . Results for different system sizes (lengths) L exhibit an initial essentially size independent relaxation of 〈ms〉 toward its value in the infinite-size spontaneously symmetry broken state, followed by a strongly size dependent final decay to zero when the O (3 ) rotational symmetry of the order parameter is restored. We develop a generic finite-size scaling theory that shows the relaxation time diverges asymptotically as Lz, where z is the dynamic exponent of the low-energy excitations. We use the scaling theory to develop a practical way of extracting the dynamic exponent from the numerical finite-size data, systematically eliminating scaling corrections. We apply the method to spin-1 /2 Heisenberg antiferromagnets on two different lattice geometries: the standard two-dimensional (2D) square lattice and a site-diluted 2D square lattice at the percolation threshold. In the 2D case we obtain z =2.001 (5 ) , which is consistent with the known value z =2 , while for the site-diluted lattice we find z =3.90 (1 ) or z =2.056 (8 ) Df , where Df=91 /48 is the fractal dimensionality of the percolating system. This is an improvement on previous estimates of z ≈3.7 . The scaling results also show a fundamental difference between the two cases; for the 2D square lattice, the data can be collapsed onto a common scaling function even when 〈ms〉 is relatively large, reflecting the Anderson tower of quantum rotor states with a common dynamic exponent z =2 . For the diluted 2D square lattice, the scaling works well only for

  20. Model analysis of magnetic susceptibility of Sr2IrO4 : A two-dimensional Jeff=1/2 Heisenberg system with competing interlayer couplings

    Science.gov (United States)

    Takayama, Tomohiro; Matsumoto, Akiyo; Jackeli, George; Takagi, Hidenori

    2016-12-01

    We report the analysis of magnetic susceptibility χ (T ) of Sr2IrO4 single crystal in the paramagnetic phase. We formulate the theoretical susceptibility based on isotropic Heisenberg antiferromagnetism incorporating the Dzyaloshinsky-Moriya interaction exactly, and include the interlayer couplings in a mean-field approximation. χ (T ) above TN was found to be well described by the model, indicating the predominant Heisenberg exchange consistent with the microscopic theory. The analysis points to a competition of nearest and next-nearest-neighbor interlayer couplings, which results in the up-up-down-down configuration of the in-plane canting moments identified by the diffraction experiments.

  1. Superfluid-insulator transition in a disordered two-dimensional quantum rotor model with random on-site interactions

    Science.gov (United States)

    An, Taeyang; Cha, Min-Chul

    2013-03-01

    We study the superfluid-insulator quantum phase transition in a disordered two-dimensional quantum rotor model with random on-site interactions in the presence of particle-hole symmetry. Via worm-algorithm Monte Carlo calculations of superfluid density and compressibility, we find the dynamical critical exponent z ~ 1 . 13 (2) and the correlation length critical exponent 1 / ν ~ 1 . 1 (1) . These exponents suggest that the insulating phase is a incompressible Mott glass rather than a Bose glass.

  2. The quantum vacuum in electromagnetic fields: From the Heisenberg-Euler effective action to vacuum birefringence

    CERN Document Server

    Karbstein, Felix

    2016-01-01

    The focus of these lectures is on the quantum vacuum subjected to classical electromagnetic fields. To this end we explicitly derive the renowned Heisenberg-Euler effective action in constant electromagnetic fields in a rather pedagogical and easy to conceive way. As an application, we use it to study vacuum birefringence constituting one of the most promising optical signatures of quantum vacuum nonlinearity.

  3. Beyond Uncertainty Heisenberg, Quantum Physics, and The Bomb

    CERN Document Server

    Cassidy, David C

    2010-01-01

    Award winning biographer revisits the controversial life of this well known German physicist to shed new light on troubling questions. What can we learn about the relationship of scientific research to state power from Heisenberg's role in Nazi Germany?

  4. Phenol-benzene complexation dynamics: quantum chemistry calculation, molecular dynamics simulations, and two dimensional IR spectroscopy.

    Science.gov (United States)

    Kwac, Kijeong; Lee, Chewook; Jung, Yousung; Han, Jaebeom; Kwak, Kyungwon; Zheng, Junrong; Fayer, M D; Cho, Minhaeng

    2006-12-28

    Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene/CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared vibrational echo spectrum as a function of time, which directly displays the formation and dissociation of the complex through the growth of off-diagonal peaks, and the linear absorption spectrum, which displays two hydroxyl stretch peaks, one for the complex and one for the free phenol. The results of the simulations are compared to previously reported experimental data and are found to be in quite reasonable agreement. The electronic structure calculations show that the complex is T shaped. The classical potential used for the phenol-benzene interaction in the MD simulations is in good accord with the highest level of the electronic structure calculations. A variety of other features is extracted from the simulations including the relationship between the structure and the projection of the electric field on the hydroxyl group. The fluctuating electric field is used to determine the hydroxyl stretch frequency-frequency correlation function (FFCF). The simulations are also used to examine the number distribution of benzene and CCl4 molecules in the first solvent shell around the phenol. It is found that the distribution is not that of the solvent mole fraction of benzene. There are substantial probabilities of finding a phenol in either a pure benzene environment or a pure CCl4 environment. A conjecture is made that relates the FFCF to the local number of benzene molecules in phenol's first solvent shell.

  5. Theory of the vortex-clustering transition in a confined two-dimensional quantum fluid

    Science.gov (United States)

    Yu, Xiaoquan; Billam, Thomas P.; Nian, Jun; Reeves, Matthew T.; Bradley, Ashton S.

    2016-08-01

    Clustering of like-sign vortices in a planar bounded domain is known to occur at negative temperature, a phenomenon that Onsager demonstrated to be a consequence of bounded phase space. In a confined superfluid, quantized vortices can support such an ordered phase, provided they evolve as an almost isolated subsystem containing sufficient energy. A detailed theoretical understanding of the statistical mechanics of such states thus requires a microcanonical approach. Here we develop an analytical theory of the vortex clustering transition in a neutral system of quantum vortices confined to a two-dimensional disk geometry, within the microcanonical ensemble. The choice of ensemble is essential for identifying the correct thermodynamic limit of the system, enabling a rigorous description of clustering in the language of critical phenomena. As the system energy increases above a critical value, the system develops global order via the emergence of a macroscopic dipole structure from the homogeneous phase of vortices, spontaneously breaking the Z2 symmetry associated with invariance under vortex circulation exchange, and the rotational SO (2 ) symmetry due to the disk geometry. The dipole structure emerges characterized by the continuous growth of the macroscopic dipole moment which serves as a global order parameter, resembling a continuous phase transition. The critical temperature of the transition, and the critical exponent associated with the dipole moment, are obtained exactly within mean-field theory. The clustering transition is shown to be distinct from the final state reached at high energy, known as supercondensation. The dipole moment develops via two macroscopic vortex clusters and the cluster locations are found analytically, both near the clustering transition and in the supercondensation limit. The microcanonical theory shows excellent agreement with Monte Carlo simulations, and signatures of the transition are apparent even for a modest system of 100

  6. Low-Lying States of the A+B-A+B- Coulomb Systems in Two-Dimensional Quantum Dots

    Institute of Scientific and Technical Information of China (English)

    XIE Wen-Fang

    2001-01-01

    The features of the low-lying spectra of four-body A+B-A+B- systems have been deduced based on symmetry. Using the method of few-body physics, we calculate the energy spectra of A + B- A + B- systems in a harmonic quantum dot. We find that the biexciton in a two-dimensional quantum dot may have other bound excited states and the quantum mechanical symmetry plays a crucialrole in determining the energy levels and structures of the low-lying states.

  7. Quantum-Wave Equation and Heisenberg Inequalities of Covariant Quantum Gravity

    Directory of Open Access Journals (Sweden)

    Claudio Cremaschini

    2017-07-01

    Full Text Available Key aspects of the manifestly-covariant theory of quantum gravity (Cremaschini and Tessarotto 2015–2017 are investigated. These refer, first, to the establishment of the four-scalar, manifestly-covariant evolution quantum wave equation, denoted as covariant quantum gravity (CQG wave equation, which advances the quantum state ψ associated with a prescribed background space-time. In this paper, the CQG-wave equation is proved to follow at once by means of a Hamilton–Jacobi quantization of the classical variational tensor field g ≡ g μ ν and its conjugate momentum, referred to as (canonical g-quantization. The same equation is also shown to be variational and to follow from a synchronous variational principle identified here with the quantum Hamilton variational principle. The corresponding quantum hydrodynamic equations are then obtained upon introducing the Madelung representation for ψ , which provides an equivalent statistical interpretation of the CQG-wave equation. Finally, the quantum state ψ is proven to fulfill generalized Heisenberg inequalities, relating the statistical measurement errors of quantum observables. These are shown to be represented in terms of the standard deviations of the metric tensor g ≡ g μ ν and its quantum conjugate momentum operator.

  8. Degenerate ground states and multiple bifurcations in a two-dimensional q-state quantum Potts model.

    Science.gov (United States)

    Dai, Yan-Wei; Cho, Sam Young; Batchelor, Murray T; Zhou, Huan-Qiang

    2014-06-01

    We numerically investigate the two-dimensional q-state quantum Potts model on the infinite square lattice by using the infinite projected entangled-pair state (iPEPS) algorithm. We show that the quantum fidelity, defined as an overlap measurement between an arbitrary reference state and the iPEPS ground state of the system, can detect q-fold degenerate ground states for the Z_{q} broken-symmetry phase. Accordingly, a multiple bifurcation of the quantum ground-state fidelity is shown to occur as the transverse magnetic field varies from the symmetry phase to the broken-symmetry phase, which means that a multiple-bifurcation point corresponds to a critical point. A (dis)continuous behavior of quantum fidelity at phase transition points characterizes a (dis)continuous phase transition. Similar to the characteristic behavior of the quantum fidelity, the magnetizations, as order parameters, obtained from the degenerate ground states exhibit multiple bifurcation at critical points. Each order parameter is also explicitly demonstrated to transform under the Z_{q} subgroup of the symmetry group of the Hamiltonian. We find that the q-state quantum Potts model on the square lattice undergoes a discontinuous (first-order) phase transition for q=3 and q=4 and a continuous phase transition for q=2 (the two-dimensional quantum transverse Ising model).

  9. An Approach to Loop Quantum Cosmology Through Integrable Discrete Heisenberg Spin Chains

    CERN Document Server

    Dantas, Christine C

    2012-01-01

    The quantum evolution equation of Loop Quantum Cosmology (LQC) -- the quantum Hamiltonian constraint -- is a difference equation. We relate the LQC constraint equation in vacuum Bianchi I separable (locally rotationally symmetric) models with an integrable differential-difference nonlinear Schr\\"odinger type equation, which in turn is known to be associated with integrable, discrete Heisenberg spin chain models in condensed matter physics. We illustrate the similarity between both systems with a simple constraint in the linear regime.

  10. Towards photonic quantum simulation of ground states of frustrated Heisenberg spin systems.

    Science.gov (United States)

    Ma, Xiao-song; Dakić, Borivoje; Kropatschek, Sebastian; Naylor, William; Chan, Yang-hao; Gong, Zhe-xuan; Duan, Lu-ming; Zeilinger, Anton; Walther, Philip

    2014-01-07

    Photonic quantum simulators are promising candidates for providing insight into other small- to medium-sized quantum systems. Recent experiments have shown that photonic quantum systems have the advantage to exploit quantum interference for the quantum simulation of the ground state of Heisenberg spin systems. Here we experimentally characterize this quantum interference at a tuneable beam splitter and further investigate the measurement-induced interactions of a simulated four-spin system by comparing the entanglement dynamics using pairwise concurrence. We also study theoretically a four-site square lattice with next-nearest neighbor interactions and a six-site checkerboard lattice, which might be in reach of current technology.

  11. Trapping photon-dressed Dirac electrons in a quantum dot studied by coherent two dimensional photon echo spectroscopy

    Science.gov (United States)

    Roslyak, O.; Gumbs, Godfrey; Mukamel, S.

    2012-05-01

    We study the localization of dressed Dirac electrons in a cylindrical quantum dot (QD) formed on monolayer and bilayer graphene by spatially different potential profiles. Short lived excitonic states which are too broad to be resolved in linear spectroscopy are revealed by cross peaks in the photon-echo nonlinear technique. Signatures of the dynamic gap in the two-dimensional spectra are discussed. The effect of the Coulomb induced exciton-exciton scattering and the formation of biexciton molecules are demonstrated.

  12. Meron-cluster simulation of the quantum antiferromagnetic Heisenberg model in a magnetic field in one- and two-dimensions

    Directory of Open Access Journals (Sweden)

    G. Palma

    2015-06-01

    Full Text Available Motivated by the numerical simulation of systems which display quantum phase transitions, we present a novel application of the meron-cluster algorithm to simulate the quantum antiferromagnetic Heisenberg model coupled to an external uniform magnetic field both in one and in two dimensions. In the infinite volume limit and at zero temperature we found numerical evidence that supports a quantum phase transition very close to the critical values B_c=2 and B_c = 4 for the system in one and two dimensions, respectively. For the one dimensional system, we have compared the numerical data obtained with analytical predictions for the magnetization density as a function of the external field obtained by scaling-behaviour analysis and Bethe Ansatz techniques. Since there is no analytical solution for the two dimensional case, we have compared our results with the magnetization density obtained by scaling relations for small lattice sizes and with the approximated thermodynamical limit at zero temperature guessed by scaling relations. Moreover, we have compared the numerical data with other numerical simulations performed by using different algorithms in one and two dimensions, like the directed loop method. The numerical data obtained are in perfect agreement with all these previous results, which confirms that the meron-algorithm is reliable for quantum Monte Carlo simulations and applicable both in one and two dimensions. Finally, we have computed the integrated autocorrelation time to measure the efficiency of the meron algorithm in one dimension.

  13. Spin-Ice State of the Quantum Heisenberg Antiferromagnet on the Pyrochlore Lattice

    Science.gov (United States)

    Huang, Yuan; Chen, Kun; Deng, Youjin; Prokof'ev, Nikolay; Svistunov, Boris

    2016-04-01

    We study the low-temperature physics of the SU(2)-symmetric spin-1 /2 Heisenberg antiferromagnet on a pyrochlore lattice and find "fingerprint" evidence for the thermal spin-ice state in this frustrated quantum magnet. Our conclusions are based on the results of bold diagrammatic Monte Carlo simulations, with good convergence of the skeleton series down to the temperature T /J =1 /6 . The identification of the spin-ice state is done through a remarkably accurate microscopic correspondence for the static structure factor between the quantum Heisenberg, classical Heisenberg, and Ising models at all accessible temperatures, and the characteristic bowtie pattern with pinch points observed at T /J =1 /6 . The dynamic structure factor at real frequencies (obtained by the analytic continuation of numerical data) is consistent with diffusive spinon dynamics at the pinch points.

  14. Spin-Ice State of the Quantum Heisenberg Antiferromagnet on the Pyrochlore Lattice.

    Science.gov (United States)

    Huang, Yuan; Chen, Kun; Deng, Youjin; Prokof'ev, Nikolay; Svistunov, Boris

    2016-04-29

    We study the low-temperature physics of the SU(2)-symmetric spin-1/2 Heisenberg antiferromagnet on a pyrochlore lattice and find "fingerprint" evidence for the thermal spin-ice state in this frustrated quantum magnet. Our conclusions are based on the results of bold diagrammatic Monte Carlo simulations, with good convergence of the skeleton series down to the temperature T/J=1/6. The identification of the spin-ice state is done through a remarkably accurate microscopic correspondence for the static structure factor between the quantum Heisenberg, classical Heisenberg, and Ising models at all accessible temperatures, and the characteristic bowtie pattern with pinch points observed at T/J=1/6. The dynamic structure factor at real frequencies (obtained by the analytic continuation of numerical data) is consistent with diffusive spinon dynamics at the pinch points.

  15. Interaction-based quantum metrology showing scaling beyond the Heisenberg limit.

    Science.gov (United States)

    Napolitano, M; Koschorreck, M; Dubost, B; Behbood, N; Sewell, R J; Mitchell, M W

    2011-03-24

    Quantum metrology aims to use entanglement and other quantum resources to improve precision measurement. An interferometer using N independent particles to measure a parameter χ can achieve at best the standard quantum limit of sensitivity, δχ ∝ N(-1/2). However, using N entangled particles and exotic states, such an interferometer can in principle achieve the Heisenberg limit, δχ ∝ N(-1). Recent theoretical work has argued that interactions among particles may be a valuable resource for quantum metrology, allowing scaling beyond the Heisenberg limit. Specifically, a k-particle interaction will produce sensitivity δχ ∝ N(-k) with appropriate entangled states and δχ ∝ N(-(k-1/2)) even without entanglement. Here we demonstrate 'super-Heisenberg' scaling of δχ ∝ N(-3/2) in a nonlinear, non-destructive measurement of the magnetization of an atomic ensemble. We use fast optical nonlinearities to generate a pairwise photon-photon interaction (corresponding to k = 2) while preserving quantum-noise-limited performance. We observe super-Heisenberg scaling over two orders of magnitude in N, limited at large numbers by higher-order nonlinear effects, in good agreement with theory. For a measurement of limited duration, super-Heisenberg scaling allows the nonlinear measurement to overtake in sensitivity a comparable linear measurement with the same number of photons. In other situations, however, higher-order nonlinearities prevent this crossover from occurring, reflecting the subtle relationship between scaling and sensitivity in nonlinear systems. Our work shows that interparticle interactions can improve sensitivity in a quantum-limited measurement, and experimentally demonstrates a new resource for quantum metrology.

  16. Emergence of a two-dimensional macrospin liquid in a highly frustrated three-dimensional quantum magnet

    Science.gov (United States)

    Sikkenk, Tycho S.; Coester, Kris; Buhrandt, Stefan; Fritz, Lars; Schmidt, Kai P.

    2017-02-01

    The classical Ising model on the frustrated three-dimensional (3D) swedenborgite lattice has disordered spin liquid ground states for all ratios of inter- and intraplanar couplings. Quantum fluctuations due to a transverse field give rise to several exotic phenomena. In the limit of weakly coupled kagome layers we find a 3D version of disorder by disorder degeneracy lifting. For large out-of-plane couplings one-dimensional macrospins are formed, which realize a disordered macrospin liquid phase on an emerging two-dimensional triangular lattice. We speculate about a possibly exotic version of quantum criticality that connects the polarized phase to the macrospin liquid.

  17. Quantum mechanical treatment of a constrained particle on two dimensional sphere

    Science.gov (United States)

    Jahangiri, L.; Panahi, H.

    2016-12-01

    In this work, we study the motion of a particle on two dimensional sphere. By writing the Schrodinger equation, we obtain the wave function and energy spectra for three dimensional harmonic oscillator potential plus trigonometric Rosen-Morse non-central potential. By letting three special cases for intertwining operator, we investigate the energy spectra and wave functions for Smorodinsky-Winternitz potential model.

  18. Quantum-corrected two-dimensional Horava-Lifshitz black hole entropy

    CERN Document Server

    Anacleto, M A; Brito, F A; Mota-Silva, J C

    2015-01-01

    In this paper we focus on the Halmiton-Jacobi method to determine the temperature and the entropy of a two-dimensional Horava-Lifshitz black hole by using the generalized uncertainty principles (GUP). We also address the product of horizons, mainly concerning the event, Cauchy, cosmological and virtual horizons.

  19. Quantum-Corrected Two-Dimensional Horava-Lifshitz Black Hole Entropy

    Directory of Open Access Journals (Sweden)

    M. A. Anacleto

    2016-01-01

    Full Text Available We focus on the Hamilton-Jacobi method to determine several thermodynamic quantities such as temperature, entropy, and specific heat of two-dimensional Horava-Lifshitz black holes by using the generalized uncertainty principles (GUP. We also address the product of horizons, mainly concerning the event, Cauchy, and cosmological and virtual horizons.

  20. Coherent electron focusing with quantum point contacts in a two-dimensional electron gas

    NARCIS (Netherlands)

    Houten, H. van; Beenakker, C.W.J.; Williamson, J.G.; Broekaart, M.E.I.; Loosdrecht, P.H.M. van; Wees, B.J. van; Mooij, J.E.; Foxon, C.T.; Harris, J.J.

    1989-01-01

    Transverse electron focusing in a two-dimensional electron gas is investigated experimentally and theoretically for the first time. A split Schottky gate on top of a GaAs-AlxGa1–xAs heterostructure defines two point contacts of variable width, which are used as injector and collector of ballistic el

  1. Two new integrable cases of two-dimensional quantum mechanics with a magnetic field

    Science.gov (United States)

    Marikhin, V. G.

    2016-04-01

    Two integrable cases of two-dimensional Schrödinger equation with a magnetic field are proposed. Using the polar coordinates and the symmetrical gauge, we will obtain solutions of these equations through biconfluent and confluent Heun functions. The quantization rules will be derived for both systems under consideration.

  2. On the Lorentz symmetry breaking effects on a Dirac neutral particle inside a two-dimensional quantum ring

    Science.gov (United States)

    Bakke, K.; Belich, H.

    2014-07-01

    We study the effects of the Lorentz symmetry violation in the nonrelativistic quantum dynamics of a spin-1/2 neutral particle interacting with external fields confined to a two-dimensional quantum ring (W.-C. Tan, J.C. Inkson, Semicond. Sci. Technol. 11, 1635 (1996)). We show a possible scenario for the Lorentz symmetry breaking that permits us to make an analogy with the Landau-Aharonov-Casher system (M. Ericsson, E. Sjöqvist, Phys. Rev. A 65, 013607 (2001)), where a change in the angular frequency characteristic of the confinement of a quantum particle to a two-dimensional ring is obtained. Then, we show that an upper bound for the Lorentz symmetry breaking parameters may be set up. Besides, we analyse another possible scenario of the Lorentz symmetry violation by showing the presence of an analogue of the Coulomb potential. We obtain the bound states solutions to the Schrödinger-Pauli equation and discuss a quantum effect characterized by the dependence of the angular frequency on the quantum numbers of the system.

  3. Exact diagonalization study of the spin-1 two-dimensional J{sub 1}–J{sub 3} Heisenberg model on a triangular lattice

    Energy Technology Data Exchange (ETDEWEB)

    Rubin, P., E-mail: rubin@fi.tartu.ee; Sherman, A.

    2014-11-07

    The spin-1 Heisenberg model on a triangular lattice with the ferromagnetic nearest-neighbor and antiferromagnetic third-nearest-neighbor exchange interactions, J{sub 1}=−(1−p)J and J{sub 2}=pJ, J>0(0≤p≤1), is studied with the use of the SPINPACK code. This model is applicable for the description of the magnetic properties of NiGa{sub 2}S{sub 4}. The ground, low-lying excited state energies and spin-spin correlation functions have been found for lattices with N=16 and N=20 sites with the periodic boundary conditions. These results are in qualitative agreement with earlier authors' results obtained with Mori's projection operator technique. - Highlights: • The S=1J{sub 1}–J{sub 3} Heisenberg model on a triangular lattice is studied. • The ferromagnetic nearest and AF 3rd-nearest-neighbor couplings are considered. • The exact diagonalization study of finite lattices was done. • The SPINPACK code using Lanczos' method is used for calculations. • The obtained results are in agreement with those obtained by Mori's approach.

  4. Quantum Spectra and Classical Orbits in Two-Dimensional Equilateral Triangular Billiards

    Institute of Scientific and Technical Information of China (English)

    LIN Sheng-Lu; GAO Feng; HONG Zheng-Pin; DU Meng-Li

    2005-01-01

    @@ We study the correspondence between quantum spectra and classical orbits in the equilateral triangular billiards. The eigenstates of such systems are not separable functions of two variables even though the problem is exactlysolvable. We calculate the Fourier transform of a quantum spectral function and find that the positions of thepeaks match well with the lengths of the classical orbits. This is another example showing that the quantum spectral function provides a bridge between quantum and classical mechanics.

  5. Construction of two-dimensional quantum field models through Longo-Witten endomorphisms

    CERN Document Server

    Tanimoto, Yoh

    2013-01-01

    We present a procedure to construct families of local, massive and interacting Haag-Kastler nets on the two-dimensional spacetime through an operator-algebraic method. An existence proof of local observable is given without relying on modular nuclearity. By a similar technique, another family of wedge-local nets is constructed using certain endomorphisms of conformal nets recently studied by Longo and Witten.

  6. Disordered phase of the two-dimensional J{sub 1}–J{sub 2} Heisenberg antiferromagnet with S=1 on a square lattice

    Energy Technology Data Exchange (ETDEWEB)

    Pires, A.S.T. [Departamento de Fisica, Universidade Federal de Minas Gerais, Belo Horizonte, MG, CP 702, 30123-970 (Brazil); Lapa, R.S., E-mail: rodrigophc@gmail.com [Departamento de Fisica, Universidade Federal de Minas Gerais, Belo Horizonte, MG, CP 702, 30123-970 (Brazil)

    2013-08-15

    We study the disordered phase of the J{sub 1}–J{sub 2} frustrated Heisenberg antiferromagnet with spin S=1 on a square lattice using a SU(3) Schwinger boson representation. In the approximation of Bose condensation and in a mean-field treatment of the four-operator terms, we calculate the gap as a function of J{sub 1}/J{sub 2}, and the quadrupole static structure factor at zero temperature. Our results indicate the existence of a nematic state in the paramagnetic phase. - Highlights: ► The disordered phase is studied. ► The energy gap in the paramagnetic phase is calculated. ► The static spin structure factor is calculated. ► The static quadrupole structure factor is calculated. ► The ground state energy is calculated.

  7. K-theory, cyclic cohomology and pairings for quantum Heisenberg manifolds

    DEFF Research Database (Denmark)

    Gabriel, Olivier

    2013-01-01

    The C*-algebras called quantum Heisenberg manifolds (QHMs) were introduced by Rieffel in 1989 as strict deformation quantizations of Heisenberg manifolds. It was later shown that they are also examples of generalized crossed products. In this article, we compute the pairings of K-theory and cyclic...... cohomology on the QHM. Combining these calculations with other results proved elsewhere, we also determine the periodic cyclic homology and cohomology of these algebras, and obtain explicit bases of the periodic cyclic cohomology of the QHM. We further isolate bases of periodic cyclic homology, expressed...

  8. Influence of Non-Uniform Magnetic Field on Quantum Teleportation in Heisenberg XY Model

    Institute of Scientific and Technical Information of China (English)

    SHAO Bin; YANG Tie-jian; ZHAO Yue-hong; ZOU Jian

    2007-01-01

    By considering the intrinsic decoherence, the validity of quantum teleportation of a two-qubit 1D Heisenberg XY chain in a non-uniform external magnetic field is studied. The fidelity as the measurement of a possible quantum teleportation is calculated and the effects of the non-uniform magnetic field and the intrinsic decoherence are discussed. It is found that anti-parallel magnetic field is more favorable for teleportation and the fidelity is suppressed by the intrinsic decoherence.

  9. Two-dimensional MAS NMR correlation protocols involving double-quantum filtering of quadrupolar spin-pairs.

    Science.gov (United States)

    Edén, Mattias

    2010-05-01

    Three two-dimensional (2D) NMR homonuclear correlation techniques invoking double-quantum (2Q) filtration of the central transitions of half-integer spins are evaluated numerically and experimentally. They correlate directly detected single-quantum (1Q) coherences in the t(2) domain with either of 1Q, two-spin 2Q or single-spin multiple-quantum coherence-evolutions in the indirect (t(1)) dimension. We employ experimental (23)Na and (27)Al NMR on sodium sulfite and the natural mineral sillimanite (SiAl(2)O(5)), in conjunction with simulated 2D spectra from pairs of dipolar-recoupled spins-3/2 and 5/2 at different external magnetic fields, to compare the correlation strategies from the viewpoints of 2D spectral resolution, signal sensitivity, implementational aspects and their relative merits for establishing internuclear proximities and quadrupolar tensor orientations.

  10. Effects of light on quantum phases and topological properties of two-dimensional Metal-organic frameworks

    Science.gov (United States)

    Wang, Yunhua; Liu, Yulan; Wang, Biao

    2017-01-01

    Periodically driven nontrivial quantum states open another door to engineer topological phases in solid systems by light. Here we show, based on the Floquet-Bloch theory, that the on-resonant linearly and circularly polarized infrared light brings in the exotic Floquet quantum spin Hall state and half-metal in two-dimensional Metal-organic frameworks (2D MOFs) because of the unbroken and broken time-reversal symmetry, respectively. We also observe that the off-resonant light triggers topological quantum phase transitions and induces semimetals with pseudospin-1 Dirac-Weyl fermions via the photon-dressed topological band structures of 2D MOFs. This work paves a way to design light-controlled spintronics and optoelectronics based on 2D MOFs. PMID:28134315

  11. Effects of light on quantum phases and topological properties of two-dimensional Metal-organic frameworks

    Science.gov (United States)

    Wang, Yunhua; Liu, Yulan; Wang, Biao

    2017-01-01

    Periodically driven nontrivial quantum states open another door to engineer topological phases in solid systems by light. Here we show, based on the Floquet-Bloch theory, that the on-resonant linearly and circularly polarized infrared light brings in the exotic Floquet quantum spin Hall state and half-metal in two-dimensional Metal-organic frameworks (2D MOFs) because of the unbroken and broken time-reversal symmetry, respectively. We also observe that the off-resonant light triggers topological quantum phase transitions and induces semimetals with pseudospin-1 Dirac-Weyl fermions via the photon-dressed topological band structures of 2D MOFs. This work paves a way to design light-controlled spintronics and optoelectronics based on 2D MOFs.

  12. Size-Dependent Biexciton Quantum Yields and Carrier Dynamics of Quasi-Two-Dimensional Core/Shell Nanoplatelets.

    Science.gov (United States)

    Ma, Xuedan; Diroll, Benjamin T; Cho, Wooje; Fedin, Igor; Schaller, Richard D; Talapin, Dmitri V; Gray, Stephen K; Wiederrecht, Gary P; Gosztola, David J

    2017-09-05

    Quasi-two-dimensional nanoplatelets (NPLs) possess fundamentally different excitonic properties from zero-dimensional quantum dots. We study lateral size-dependent photon emission statistics and carrier dynamics of individual NPLs using second-order photon correlation (g((2))(τ)) spectroscopy and photoluminescence (PL) intensity-dependent lifetime analysis. Room-temperature radiative lifetimes of NPLs can be derived from maximum PL intensity periods in PL time traces. It first decreases with NPL lateral size and then stays constant, deviating from the electric dipole approximation. Analysis of the PL time traces further reveals that the single exciton quantum yield in NPLs decreases with NPL lateral size and increases with protecting shell thickness, indicating the importance of surface passivation on NPL emission quality. Second-order photon correlation (g((2))(τ)) studies of single NPLs show that the biexciton quantum yield is strongly dependent on the lateral size and single exciton quantum yield of the NPLs. In large NPLs with unity single exciton quantum yield, the corresponding biexciton quantum yield can reach unity. These findings reveal that by careful growth control and core-shell material engineering, NPLs can be of great potential for light amplification and integrated quantum photonic applications.

  13. The quantum spectral analysis of the two-dimensional annular billiard system

    Institute of Scientific and Technical Information of China (English)

    Zhang Yan-Hui; Zhang Ji-Ouan; Xu Xue-You; Lin Sheng-Lu

    2009-01-01

    Based on the extended closed-orbit theory together with spectral analysis, this paper studies the correspondence between quantum mechanics and the classical counterpart in a two-dimeusional annular billiard. The results demonstrate that the Fourier-transformed quantum spectra are in very good accordance with the lengths of the classical ballistic trajectories, whereas spectral strength is intimately associated with the shapes of possible open orbits connecting arbitrary two points in the annular cavity. This approach facilitates an intuitive understanding of basic quantum features such as quantum interference, locations of the wavefunctions, and allows quantitative calculations in the range of high energies, where full quantum calculations may become impractical in general. This treatment provides a thread to explore the properties of microjunction transport and even quantum chaos under the much more general system.

  14. Low-temperature Spin-Ice State of Quantum Heisenberg Magnets on Pyrochlore Lattice

    Science.gov (United States)

    Huang, Yuan; Chen, Kun; Deng, Youjin; Prokof'ev, Nikolay; Svistunov, Boris

    We establish that the isotropic spin-1/2 Heisenberg antiferromagnet on pyrochlore lattice enters a spin-ice state at low, but finite, temperature. Our conclusions are based on results of the bold diagrammatic Monte Carlo simulations that demonstrate good convergence of the skeleton series down to temperature T = J/6. The ``smoking gun'' identification of the spin-ice state is done through a remarkably accurate microscopic correspondence for static spin-spin correlation function between the quantum Heisenberg and classical Heisenberg/Ising models at all accessible temperatures. In particular, at T/J = 1/6, the momentum dependence shows a characteristic bow-tie pattern with pinch points. By numerical analytical continuation method, we also obtain the dynamic structure factor at real frequencies, showing a diffusive spinon dynamics at pinch points and spin wave continuum along the nodal lines.?

  15. Loop equations and Virasoro constraints in non-perturbative two-dimensional quantum gravity

    Energy Technology Data Exchange (ETDEWEB)

    Dijkgraaf, R.; Verlinde, H. (Princeton Univ., NJ (USA). Joseph Henry Labs.); Verlinde, E. (Institute for Advanced Study, Princeton, NJ (USA). School of Natural Sciences)

    1991-01-21

    We give a derivation of the loop equation for two-dimensional gravity from the KdV equations and the string equation of the one-matrix model. We find that the loop equation is equivalent to an infinite set of linear constraints on the square root of the partition function satisfying the Virasoro algebra. We give an interpretation of these equations in topological gravity and discuss their extension to multi-matrix models. For the multi-critical models the loop equation naturally singles out the operators corresponding to the primary fields of the minimal models. (orig.).

  16. Loop Equations and Virasoro Constraints in Non-Perturbative Two-Dimensional Quantum Gravity

    Science.gov (United States)

    Dijkgraaf, Robbert; Verlinde, Herman; Verlinde, Erik

    We give a derivation of the loop equation for two-dimensional gravity from the KdV equations and the string equation of the one-matrix model. We find that the loop equation is equivalent to an infinite set of linear constraints on the square root of the partition function satisfying the Virasoro algebra. We give an interpretation of these equations in topological gravity and discuss their extension to multi-matrix models. For the multi-critical models the loop equation naturally singles out the operators corresponding to the primary fields of the minimal models.

  17. Spin-Orbit Splitting in Semiconductor Quantum Dots with a Two-Dimensional Ring Model

    Institute of Scientific and Technical Information of China (English)

    FENG Jun-Sheng; LIU Zheng

    2009-01-01

    We present a theoretical study of the energy levels with two-dimensional ring confining potential in the presence of the Rashba spin-orbit interaction.The features of some low-lying states in various strengths of the Rashba spin-orbit interaction are investigated.The Rashba spin-orbit splitting can also be influenced by the width of the potential barrier.The computed results show that the spin-polarized electronic states can be more easily achieved in a weakly confined dot when the confinement strength for the Rashba spin-orbit interaction is larger than a critical value.

  18. Plasmons in a free-standing nanorod with a two-dimensional parabolic quantum well caused bv surface states

    Institute of Scientific and Technical Information of China (English)

    Song Ya-Feng; Lü Yan-Wu; Wen Wei; Liu Xiang-Lin; Yang Shao-Yan; Zhu Qin-Sheng; Wang Zhan-Guo

    2012-01-01

    The collective charge density excitations in a free-standing nanorod with a two-dimensional parabolic quantum well are investigated within the framework of Bohm-Pine's random-phase approximation in the two-subband model.The new simplified analytical expressions of the Coulomb interaction matrix elements and dielectric functions are derived and numerically discussed.In addition,the electron density and temperature dependences of dispersion features are also investigated.We find that in the two-dimensional parabolic quantum well,the intrasubband upper branch is coupled with the intersubband mode,which is quite different from other quasi-one-dimensional systems like a cylindrical quantum wire with an infinite rectangular potential.In addition,we also find that higher temperature results in the intersubband mode(with an energy of 12 meV(~3 THz))becoming totally damped,which agrees well with the experimental results of Raman scattering in the literature.These interesting properties may provide useful references to the design of free-standing nanorod based devices.

  19. 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.

  20. Topology Change and the Emergence of Geometry in Two Dimensional Causal Quantum Gravity

    NARCIS (Netherlands)

    Westra, W.

    2007-01-01

    Despite many attempts, gravity has vigorously resisted a unification with the laws of quantum mechanics. Besides a plethora of technical issues, one is also faced with many interesting conceptual problems. The study of quantum gravity in lower dimensional models ameliorates the technical difficultie

  1. Variational study of the quantum phase transition in the bilayer Heisenberg model with bosonic RVB wavefunction.

    Science.gov (United States)

    Liao, Haijun; Li, Tao

    2011-11-30

    We study the ground state phase diagram of the bilayer Heisenberg model on a square lattice with a bosonic resonating valence bond (RVB) wavefunction. The wavefunction has the form of a Gutzwiller projected Schwinger boson mean-field ground state and involves two variational parameters. We find the wavefunction provides an accurate description of the system on both sides of the quantum phase transition. In particular, through the analysis of the spin structure factor, ground state fidelity susceptibility and the Binder moment ratio Q(2), a continuous transition from the antiferromagnetic ordered state to the quantum disordered state is found at the critical coupling of α(c) = J(⊥)/J(∥) ≈ 2.62, in good agreement with the result of quantum Monte Carlo simulation. The critical exponent estimated from the finite size scaling analysis (1/ν ≈ 1.4) is consistent with that of the classical 3D Heisenberg universality class.

  2. Hilbert-Schmidt Geometry of n-Level Jakobczyk-Siennicki Two-Dimensional Quantum Systems

    CERN Document Server

    Slater, P B

    2005-01-01

    Jakobczyk and Siennicki studied two-dimensional sections of a set of Bloch vectors corresponding to n x n density matrices of two-qubit systems (that is, the case n=4). They found essentially five different types of (nontrivial) separability regimes. We compute the Euclidean/Hilbert-Schmidt (HS) separability probabilities assigned to these regimes, and conduct parallel two-dimensional section analyses for the cases n=6,8,9 and 10. We obtain a very wide variety of exact HS-probabilities. For n>6, the probabilities are those of having a partial positive transpose (PPT). For the n=6 case, we also obtain biseparability probabilities; in the n=8,9 instances, bi-PPT probabilities; and for n=8, tri-PPT probabilities. By far, the most frequently recorded probability for n>4 is Pi/4 = 0.785398$. We also conduct a number of related analyses, pertaining to the (one-dimensional) boundaries (both exterior and interior) of the separability and PPT domains, and discuss some exact calculations pertaining to the 9-dimensional...

  3. Lorentz contraction of the equal-time Bethe-Salpeter amplitude in two-dimensional massless quantum electrodynamics

    Energy Technology Data Exchange (ETDEWEB)

    Radozycki, Tomasz [Cardinal Stefan Wyszynski University, Faculty of Mathematics and Natural Sciences, College of Sciences, Warsaw (Poland)

    2015-09-15

    The Lorentz transformation properties of the equal-time bound-state Bethe-Salpeter amplitude in the two-dimensional massless quantum electrodynamics (the so-called Schwinger model) are considered. It is shown that while boosting a bound state (a 'meson') this amplitude is subject to approximate Lorentz contraction. The effect is exact for large separations of constituent particles ('quarks'), while for small distances the deviation is more significant. For this phenomenon to appear, the full function, i.e. with the inclusion of all instanton contributions, has to be considered. The amplitude in each separate topological sector does not exhibit such properties. (orig.)

  4. Lorentz contraction of the equal-time Bethe–Salpeter amplitude in two-dimensional massless quantum electrodynamics

    Energy Technology Data Exchange (ETDEWEB)

    Radożycki, Tomasz, E-mail: t.radozycki@uksw.edu.pl [Faculty of Mathematics and Natural Sciences, College of Sciences, Cardinal Stefan Wyszyński University, Wóycickiego 1/3, 01-938, Warsaw (Poland)

    2015-09-24

    The Lorentz transformation properties of the equal-time bound-state Bethe–Salpeter amplitude in the two-dimensional massless quantum electrodynamics (the so-called Schwinger model) are considered. It is shown that while boosting a bound state (a ‘meson’) this amplitude is subject to approximate Lorentz contraction. The effect is exact for large separations of constituent particles (‘quarks’), while for small distances the deviation is more significant. For this phenomenon to appear, the full function, i.e. with the inclusion of all instanton contributions, has to be considered. The amplitude in each separate topological sector does not exhibit such properties.

  5. Fingerprints of field-induced Berezinskii-Kosterlitz-Thouless transition in quasi-two-dimensional S=1/2 Heisenberg magnets Cu(en)(H2O)2SO4 and Cu(tn)Cl2

    Science.gov (United States)

    Baranová, Lucia; Orendáčová, Alžbeta; Čižmár, Erik; Tarasenko, Róbert; Tkáč, Vladimír; Orendáč, Martin; Feher, Alexander

    2016-04-01

    Organo-metallic compounds Cu(en)(H2O)2SO4 (en=C2H8N2) and Cu(tn)Cl2 (tn=C3H10N2) representing S=1/2 quasi-two-dimensional Heisenberg antiferromagnets with an effective intra-layer exchange coupling J/kB≈3 K, have been examined by specific heat measurements at temperatures down to nominally 50 mK and magnetic fields up to 14 T. A comparative analysis of magnetic specific heat in zero magnetic field revealed nearly identical contribution of short-range magnetic correlations and significant differences were observed at lowest temperatures. A phase transition to long-range order was observed in Cu(en)(H2O)2SO4 at TC=0.9 K while hidden in Cu(tn)Cl2. A response of both compounds to the application of magnetic field has rather universal features characteristic for a field-induced Berezinskii-Kosterlitz-Thouless transition theoretically predicted for ideal two-dimensional magnets.

  6. Quantum Poincare Section of a Two-Dimensional hamiltonian in a Coherent State Representation

    Institute of Scientific and Technical Information of China (English)

    金迎新; 贺凯芬

    2002-01-01

    We study the quantum behaviour of a quasi-integrable Hamiltonian. The unperturbed Hamiltonian displays degeneracies of energy levels, which become avoided crossings under a nonintegrable perturbation. In this twodimensional system, the quantum Poincaré section plot is constructed in the coherent state representation with the restriction that the centres of the wavepackets are confined at the classical surface of constant energy. It is found that the quantum Poincaré section plot obtained in this way provides an evident counterpart of the classical system.

  7. 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.

  8. Two-dimensional models as testing ground for principles and concepts of local quantum physics

    Science.gov (United States)

    Schroer, Bert

    2006-02-01

    In the past two-dimensional models of QFT have served as theoretical laboratories for testing new concepts under mathematically controllable condition. In more recent times low-dimensional models (e.g., chiral models, factorizing models) often have been treated by special recipes in a way which sometimes led to a loss of unity of QFT. In the present work, I try to counteract this apartheid tendency by reviewing past results within the setting of the general principles of QFT. To this I add two new ideas: (1) a modular interpretation of the chiral model Diff( S)-covariance with a close connection to the recently formulated local covariance principle for QFT in curved spacetime and (2) a derivation of the chiral model temperature duality from a suitable operator formulation of the angular Wick rotation (in analogy to the Nelson-Symanzik duality in the Ostertwalder-Schrader setting) for rational chiral theories. The SL (2, Z) modular Verlinde relation is a special case of this thermal duality and (within the family of rational models) the matrix S appearing in the thermal duality relation becomes identified with the statistics character matrix S. The relevant angular "Euclideanization" is done in the setting of the Tomita-Takesaki modular formalism of operator algebras. I find it appropriate to dedicate this work to the memory of J.A. Swieca with whom I shared the interest in two-dimensional models as a testing ground for QFT for more than one decade. This is a significantly extended version of an "Encyclopedia of Mathematical Physics" contribution hep-th/0502125.

  9. Two-dimensional models as testing ground for principles and concepts of local quantum physics

    Energy Technology Data Exchange (ETDEWEB)

    Schroer, Bert [FU Berlin (Germany). Institut fuer Theoretische Physik

    2005-04-15

    In the past two-dimensional models of QFT have served as theoretical laboratories for testing new concepts under mathematically controllable condition. In more recent times low-dimensional models (e.g. chiral models, factoring models) often have been treated by special recipes in a way which sometimes led to a loss of unity of QFT. In the present work I try to counteract this apartheid tendency by reviewing past results within the setting of the general principles of QFT. To this I add two new ideas: (1) a modular interpretation of the chiral model Diff(S)-covariance with a close connection to the recently formulated local covariance principle for QFT in curved spacetime and (2) a derivation of the chiral model temperature duality from a suitable operator formulation of the angular Wick rotation (in analogy to the Nelson-Symanzik duality in the Ostertwalder-Schrader setting) for rational chiral theories. The SL(2,Z) modular Verlinde relation is a special case of this thermal duality and (within the family of rational models) the matrix S appearing in the thermal duality relation becomes identified with the statistics character matrix S. The relevant angular 'Euclideanization' is done in the setting of the Tomita-Takesaki modular formalism of operator algebras. I find it appropriate to dedicate this work to the memory of J. A. Swieca with whom I shared the interest in two-dimensional models as a testing ground for QFT for more than one decade. This is a significantly extended version of an 'Encyclopedia of Mathematical Physics' contribution hep-th/0502125. (author)

  10. Liquid-Gated High Mobility and Quantum Oscillation of the Two-Dimensional Electron Gas at an Oxide Interface.

    Science.gov (United States)

    Zeng, Shengwei; Lü, Weiming; Huang, Zhen; Liu, Zhiqi; Han, Kun; Gopinadhan, Kalon; Li, Changjian; Guo, Rui; Zhou, Wenxiong; Ma, Haijiao Harsan; Jian, Linke; Venkatesan, Thirumalai; Ariando

    2016-04-26

    Electric field effect in electronic double layer transistor (EDLT) configuration with ionic liquids as the dielectric materials is a powerful means of exploring various properties in different materials. Here, we demonstrate the modulation of electrical transport properties and extremely high mobility of two-dimensional electron gas at LaAlO3/SrTiO3 (LAO/STO) interface through ionic liquid-assisted electric field effect. With a change of the gate voltages, the depletion of charge carrier and the resultant enhancement of electron mobility up to 19 380 cm(2)/(V s) are realized, leading to quantum oscillations of the conductivity at the LAO/STO interface. The present results suggest that high-mobility oxide interfaces, which exhibit quantum phenomena, could be obtained by ionic liquid-assisted field effect.

  11. Two Dimensional Effective Electron Mass at the Fermi Level in Quantum Wells of III-V, Ternary and Quaternary Semiconductors.

    Science.gov (United States)

    Chakrabarti, S; Chatterjee, B; Debbarma, S; Ghatak, K P

    2015-09-01

    In this paper we study the influence of strong electric field on the two dimensional (2D)effective electron mass (EEM) at the Fermi level in quantum wells of III-V, ternary and quaternary semiconductors within the framework of k x p formalism by formulating a new 2D electron energy spectrum. It appears taking quantum wells of InSb, InAs, Hg(1-x)Cd(x)Te and In(1-x)Ga(x)As(1-y)P(y) lattice matched to InP as examples that the EEM increases with decreasing film thickness, increasing electric field and increases with increasing surface electron concentration exhibiting spikey oscillations because of the crossing over of the Fermi level by the quantized level in quantum wells and the quantized oscillation occurs when the Fermi energy touches the sub-band energy. The electric field makes the mass quantum number dependent and the oscillatory mass introduces quantum number dependent mass anisotropy in addition to energy. The EEM increases with decreasing alloy composition where the variations are totally band structure dependent. Under certain limiting conditions all the results for all the cases get simplified into the well-known parabolic energy bands and thus confirming the compatibility test. The content of this paper finds three applications in the fields of nano-science and technology.

  12. Entanglement in the quantum one-dimensional integer spin S Heisenberg antiferromagnet

    Science.gov (United States)

    Lima, L. S.

    2017-10-01

    We use the modified spin wave theory of Takahashi to study the entanglement entropy in the quantum one-dimensional integer spin Heisenberg antiferromagnet. We calculate the entanglement entropy of this spin system that is well known to be a quantum wire, in the classical limit (N → ∞). We obtain a decreasing the entanglement entropy with the temperature and we obtain none change in the entanglement in the point Δ = 1 at T = 0 where the system presents a quantum phase transition from a gapless phase in the spectrum Δ < 1 to a gapped phase Δ ≥ 1.

  13. Quantum dots and etch-induced depletion of a silicon two-dimensional electron gas

    Science.gov (United States)

    Klein, L. J.; Lewis, K. L. M.; Slinker, K. A.; Goswami, Srijit; van der Weide, D. W.; Blick, R. H.; Mooney, P. M.; Chu, J. O.; Coppersmith, S. N.; Friesen, Mark; Eriksson, M. A.

    2006-01-01

    The controlled depletion of electrons in semiconductors is the basis for numerous devices. Reactive-ion etching provides an effective technique for fabricating both classical and quantum devices. However, Fermi-level pinning must be carefully considered in the development of small devices, such as quantum dots. Because of depletion, the electrical size of the device is reduced in comparison with its physical dimension. To investigate this issue in modulation-doped silicon single-electron transistors, we fabricate several types of devices in silicon-germanium heterostructures using two different etches, CF4 and SF6. We estimate the depletion width associated with each etch by two methods: (i) conductance measurements in etched wires of decreasing thickness (to determine the onset of depletion), and (ii) capacitance measurements of quantum dots (to estimate the size of the active region). We find that the SF6 etch causes a much smaller depletion width, making it more suitable for device fabrication.

  14. Quantum limit for two-dimensional resolution of two incoherent optical point sources

    CERN Document Server

    Ang, Shan Zheng; Tsang, Mankei

    2016-01-01

    We obtain the multiple-parameter quantum Cram\\'er-Rao bound for estimating the Cartesian components of the centroid and separation of two incoherent optical point sources using an imaging system with finite spatial bandwidth. Under quite general and realistic assumptions on the point-spread function of the imaging system, and for weak source strengths, we show that the Cram\\'er-Rao bounds for the x and y components of the separation are independent of the values of those components, which may be well-below the conventional Rayleigh resolution limit. We also propose two linear optics-based measurement methods that approach the quantum bound for the estimation of the Cartesian components of the separation once the centroid has been located. One of the methods is an interferometric scheme that approaches the quantum bound for sub-Rayleigh separations. The other method uses fiber coupling to attain the bound regardless of the distance between the two sources.

  15. Two-Dimensional GaAs/AlGaAs Multiple Quantum Well Spatial Light Modulators

    Institute of Scientific and Technical Information of China (English)

    Qin Wang; Jan Borglind; Smilja Becanovic; Stéphane Junique; Daniel (A)gren; Bertrand Noharet; Linda H(o)glund; Olof (O)berg; Erik Petrini; Jan Y. Andersson; Hedda Malm

    2003-01-01

    Multiple quantum well spatial light modulators with 128x128 array in 38μm pitch are fabricated using two pproaches, one with an attachment of an optical substrate and another one without. These two fabrication processes are described and compared.

  16. Two-dimensional time-dependent quantum-mechanical scattering event

    Energy Technology Data Exchange (ETDEWEB)

    Galbraith, I.; Ching, Y.S.; Abraham, E.

    1984-01-01

    Nonrelativistic quantum-mechanical scattering in two dimensions is studied numerically by integrating the time-dependent Schroedinger equation. A partial-wave analysis is used to discuss the numerical results. A potential barrier, a square well and a single slit are considered as the scattering potentials.

  17. Quantum ratchet effects induced by terahertz radiation in GaN-based two-dimensional structures

    NARCIS (Netherlands)

    Weber, W.; Golub, L. E.; Danilov, S. N.; Karch, J.; Reitmaier, C.; Wittmann, B.; Bel' kov, V. V.; Ivchenko, E. L.; Kvon, Z. D.; Vinh, N. Q.; van der Meer, A. F. G.; Murdin, B.; Ganichev, S. D.

    2008-01-01

    Photogalvanic effects are observed and investigated in wurtzite (0001)-oriented GaN/AlGaN low-dimensional structures excited by terahertz radiation. The structures are shown to represent linear quantum ratchets. Experimental and theoretical analysis exhibits that the observed photocurrents are relat

  18. Quantum ratchet effects induced by terahertz radiation in GaN-based two-dimensional structures

    Science.gov (United States)

    Weber, W.; Golub, L. E.; Danilov, S. N.; Karch, J.; Reitmaier, C.; Wittmann, B.; Bel'Kov, V. V.; Ivchenko, E. L.; Kvon, Z. D.; Vinh, N. Q.; van der Meer, A. F. G.; Murdin, B.; Ganichev, S. D.

    2008-06-01

    Photogalvanic effects are observed and investigated in wurtzite (0001)-oriented GaN/AlGaN low-dimensional structures excited by terahertz radiation. The structures are shown to represent linear quantum ratchets. Experimental and theoretical analysis exhibits that the observed photocurrents are related to the lack of an inversion center in the GaN-based heterojunctions.

  19. Generalized Heisenberg Algebras, SUSYQM and Degeneracies: Infinite Well and Morse Potential

    Directory of Open Access Journals (Sweden)

    Véronique Hussin

    2011-03-01

    Full Text Available We consider classical and quantum one and two-dimensional systems with ladder operators that satisfy generalized Heisenberg algebras. In the classical case, this construction is related to the existence of closed trajectories. In particular, we apply these results to the infinite well and Morse potentials. We discuss how the degeneracies of the permutation symmetry of quantum two-dimensional systems can be explained using products of ladder operators. These products satisfy interesting commutation relations. The two-dimensional Morse quantum system is also related to a generalized two-dimensional Morse supersymmetric model. Arithmetical or accidental degeneracies of such system are shown to be associated to additional supersymmetry.

  20. Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal

    Energy Technology Data Exchange (ETDEWEB)

    Wosnitza, J; Ignatchik, O; Bergk, B [Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden-Rossendorf, D-01314 Dresden (Germany); Gvozdikov, V M [Max-Planck-Institut fuer Physik komplexer Systeme, D-01187 Dresden (Germany); Hagel, J [Institut fuer Festkoerperphysik, Technische Universitaet Dresden, D-01062 Dresden (Germany); Meeson, P J [H H Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom); Schlueter, J A [Materials Science Division, Argonne National Laboratory, Argonne, IL 60439 (United States); Davis, H; Winter, R W; Gard, G L [Department of Chemistry, Portland State University, Portland, OR 97207 (United States)], E-mail: J.Wosnitza@fzd.de

    2008-08-15

    We report on an anomalous behavior of the spin-splitting zeros in the de Haas-van Alphen (dHvA) signal of a quasi-two-dimensional organic superconductor. The zeros as well as the angular dependence of the amplitude of the second harmonic deviate remarkably from the standard Lifshitz-Kosevich (LK) prediction. In contrast, the angular dependence of the fundamental dHvA amplitude as well as the spin-splitting zeros of the Shubnikov-de Haas (SdH) signal follow the LK theory. We can explain this behavior of the dHvA signal by small chemical-potential (CP) oscillations and find a very good agreement between theory and experiment. A detailed wave-shape analysis of the dHvA oscillations corroborates the existence of an oscillating CP. We discuss the absence of the above spin-zero effect in the SdH signal and argue that in {beta}-prime-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} it can be explained by an incoherent variable range hopping interlayer transport which is insensitive to the small CP oscillations.

  1. Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal.

    Energy Technology Data Exchange (ETDEWEB)

    Wosnitza, J.; Gvozdikov, V. M.; Hagel, J.; Meeson, P. J.; Schlueter, J. A.; Ignatchick, O.; Winter, R. W.; Gard, G. L.; Davis, H.; Bergk, B.; Materials Science Division; Technische Univ. Dresden; Max-Planck Inst. Phys. Complex Systems; Univ. Bristol; Portland State Univ.

    2008-01-01

    We report on an anomalous behavior of the spin-splitting zeros in the de Haas-van Alphen (dHvA) signal of a quasi-two-dimensional organic superconductor. The zeros as well as the angular dependence of the amplitude of the second harmonic deviate remarkably from the standard Lifshitz-Kosevich (LK) prediction. In contrast, the angular dependence of the fundamental dHvA amplitude as well as the spin-splitting zeros of the Shubnikov-de Haas (SdH) signal follow the LK theory. We can explain this behavior of the dHvA signal by small chemical-potential (CP) oscillations and find a very good agreement between theory and experiment. A detailed wave-shape analysis of the dHvA oscillations corroborates the existence of an oscillating CP. We discuss the absence of the above spin-zero effect in the SdH signal and argue that in {beta}{double_prime}-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} it can be explained by an incoherent variable range hopping interlayer transport which is insensitive to the small CP oscillations.

  2. Two-dimensional models as testing ground for principles and concepts of local quantum physics

    CERN Document Server

    Schrör, B

    2005-01-01

    In the past two-dimensional models of QFT have served as theoretical laboratories for testing new concepts under mathematically controllable condition. In more recent times low-dimensional models (e.g. chiral models, factorizing models) often have been treated by special recipes in a way which sometimes led to a loss of unity of QFT. In the present work I try to counteract this apartheid tendency by reviewing past results within the setting of the general principles of QFT. To this I add two new ideas: a derivation of the chiral model temperature duality from a suitable operator formulation of the angular Wick rotation (in analogy to the Nelson-Symanzik duality in the Ostertwalder-Schrader setting) and a modular interpretation of the chiral model Diff(S)-covariance with a close connection to the recently formulated local covariance principle for QFT in curved spacetime. As a special case of the thermal duality, the SL(2,Z) modular Verlinde relation is thus a consequence of the principles of thermal QFT togeth...

  3. Ground-state properties of two-dimensional quantum fluid helium and hydrogen mixtures

    CERN Document Server

    Um, C I; Oh, H G

    1998-01-01

    Using a variational Jastrow wavefunction extended to include a three-body correlation function and a hypernetted chain scheme with the contributions of elementary diagrams, we analyze the ground-state energies and the structural properties of two-dimensional H- sup 4 He and H sub 2 - sup 4 He mixtures. The mixtures are in equilibrium at a lower density compared to a pure sup 4 He system because of the large zero-point energies of the hydrogen atom and molecule. We evaluate the lowering of the ground-state energies as a function of the impurity concentration and total density of mixtures. Comparing the result with boson sup 3 He- sup 4 He mixtures, we show that the shifts of energy mainly come from the difference of the zero-point energies of the impurities rather than from the interatomic potentials.We also analyze the enthalpies to study the miscibility and conclude that boson-boson mixtures are completely phase separated in their equilibria.

  4. Generation of Entanglement, Measure of Multipartite Entanglement in Fermionic Systems and Quantum Discord in Bipartite Systems and Heisenberg Chains

    CERN Document Server

    Lari, Behzad

    2011-01-01

    This is a thesis submitted to university of Pune, India, for the Ph.D. degree. This work deals with entanglement production in two qubit, two qutrit and three qubit systems, entanglement in indistinguishable fermionic systems, quantum discord in a Heisenberg chain and geometric measure of quantum discord in an arbitrary state of a bipartite quantum system.

  5. On Heisenberg Uncertainty Relationship, Its Extension, and the Quantum Issue of Wave-Particle Duality

    Science.gov (United States)

    Putz, Mihai V.

    2010-01-01

    Within the path integral Feynman formulation of quantum mechanics, the fundamental Heisenberg Uncertainty Relationship (HUR) is analyzed in terms of the quantum fluctuation influence on coordinate and momentum estimations. While introducing specific particle and wave representations, as well as their ratio, in quantifying the wave-to-particle quantum information, the basic HUR is recovered in a close analytical manner for a large range of observable particle-wave Copenhagen duality, although with the dominant wave manifestation, while registering its progressive modification with the factor 1-n2, in terms of magnitude n∈[0,1]. of the quantum fluctuation, for the free quantum evolution around the exact wave-particle equivalence. The practical implications of the present particle-to-wave ratio as well as of the free-evolution quantum picture are discussed for experimental implementation, broken symmetry and the electronic localization function. PMID:21152325

  6. On Heisenberg Uncertainty Relationship, Its Extension, and the Quantum Issue of Wave-Particle Duality

    Directory of Open Access Journals (Sweden)

    Mihai V. Putz

    2010-10-01

    Full Text Available Within the path integral Feynman formulation of quantum mechanics, the fundamental Heisenberg Uncertainty Relationship (HUR is analyzed in terms of the quantum fluctuation influence on coordinate and momentum estimations. While introducing specific particle and wave representations, as well as their ratio, in quantifying the wave-to-particle quantum information, the basic HUR is recovered in a close analytical manner for a large range of observable particle-wave Copenhagen duality, although with the dominant wave manifestation, while registering its progressive modification with the factor √1-n2, in terms of magnitude n ε [0,1] of the quantum fluctuation, for the free quantum evolution around the exact wave-particle equivalence. The practical implications of the present particle-to-wave ratio as well as of the free-evolution quantum picture are discussed for experimental implementation, broken symmetry and the electronic localization function.

  7. General model for a entanglement-enhanced composed quantum game on a two-dimensional lattice

    CERN Document Server

    Miszczak, Jarosław Adam; Sładkowski, Jan

    2013-01-01

    We introduce a method of analyzing entanglement enhanced quantum games on regular lattices of agents. Our method is valid for setups with periodic and non-periodic boundary conditions. To demonstrate our approach we study two different types games, namely the prisoner's dilemma game and a cooperative Parrondo's game. In both cases we obtain results showing, that entanglement is a crucial resource necessary for the agents to achieve positive capital gain.

  8. Quantum critical response function in quasi-two-dimensional itinerant antiferromagnets

    Science.gov (United States)

    Varma, C. M.; Zhu, Lijun; Schröder, Almut

    2015-10-01

    We reexamine the experimental results for the magnetic response function χ''(q ,E ,T ) for q around the antiferromagnetic vectors Q , in the quantum-critical region, obtained by inelastic neutron scattering, on an Fe-based superconductor and on a heavy-fermion compound. The motivation is to compare the results with a recent theory, which shows that the fluctuations in a generic antiferromagnetic model for itinerant fermions map to those in the universality class of the dissipative quantum-XY model. The quantum-critical fluctuations in this model, in a range of parameters, are given by the correlations of spatial and temporal topological defects. The theory predicts a χ''(q ,E ,T ) (i) which is a separable function of (q -Q ) and of (E ,T ) , (ii) at criticality, the energy-dependent part is ∝tanh(E /2 T ) below a cutoff energy, (iii) the correlation time departs from its infinite value at criticality on the disordered side by an essential singularity, and (iv) the correlation length depends logarithmically on the correlation time, so that the dynamical critical exponent z is ∞ . The limited existing experimental results are found to be consistent with the first two unusual predictions from which the linear dependence of the resistivity on T and the T lnT dependence of the entropy also follow. More experiments are suggested, especially to test the theory of variations on the correlation time and length on the departure from criticality.

  9. Universal Quantum Criticality in the Metal-Insulator Transition of Two-Dimensional Interacting Dirac Electrons

    Science.gov (United States)

    Otsuka, Yuichi; Yunoki, Seiji; Sorella, Sandro

    2016-01-01

    The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.

  10. Effective mass theory of a two-dimensional quantum dot in the presence of magnetic field

    Indian Academy of Sciences (India)

    Himanshu Asnani; Raghu Mahajan; Praveen Pathak; Vijay A Singh

    2009-09-01

    The effective mass of electrons in low-dimensional semiconductors is position-dependent. The standard kinetic energy operator of quantum mechanics for this position-dependent mass is non-Hermitian and needs to be modified. This is achieved by imposing the BenDaniel–Duke (BDD) boundary condition. We have investigated the role of this boundary condition for semiconductor quantum dots (QDs) in one, two and three dimensions. In these systems the effective mass m i inside the dot of size R is different from the mass m o outside. Hence a crucial factor in determining the electronic spectrum is the mass discontinuity factor = /} . We have proposed a novel quantum scale, , which is a dimensionless parameter proportional to 220, where 0 represents the barrier height. We show both by numerical calculations and asymptotic analysis that the ground state energy and the surface charge density, (ρ()), can be large and dependent on . We also show that the dependence of the ground state energy on the size of the dot is infraquadratic. We also study the system in the presence of magnetic field . The BDD condition introduces a magnetic length-dependent term $(\\sqrt{\\hbar /eB})$ into and hence the ground state energy. We demonstrate that the significance of BDD condition is pronounced at large and large magnetic fields. In many cases the results using the BDD condition is significantly different from the non-Hermitian treatment of the problem.

  11. Efficient Blue Electroluminescence Using Quantum-Confined Two-Dimensional Perovskites.

    Science.gov (United States)

    Kumar, Sudhir; Jagielski, Jakub; Yakunin, Sergii; Rice, Peter; Chiu, Yu-Cheng; Wang, Mingchao; Nedelcu, Georgian; Kim, Yeongin; Lin, Shangchao; Santos, Elton J G; Kovalenko, Maksym V; Shih, Chih-Jen

    2016-10-03

    Solution-processed hybrid organic-inorganic lead halide perovskites are emerging as one of the most promising candidates for low-cost light-emitting diodes (LEDs). However, due to a small exciton binding energy, it is not yet possible to achieve an efficient electroluminescence within the blue wavelength region at room temperature, as is necessary for full-spectrum light sources. Here, we demonstrate efficient blue LEDs based on the colloidal, quantum-confined 2D perovskites, with precisely controlled stacking down to one-unit-cell thickness (n = 1). A variety of low-k organic host compounds are used to disperse the 2D perovskites, effectively creating a matrix of the dielectric quantum wells, which significantly boosts the exciton binding energy by the dielectric confinement effect. Through the Förster resonance energy transfer, the excitons down-convert and recombine radiatively in the 2D perovskites. We report room-temperature pure green (n = 7-10), sky blue (n = 5), pure blue (n = 3), and deep blue (n = 1) electroluminescence, with record-high external quantum efficiencies in the green-to-blue wavelength region.

  12. Universal Quantum Criticality in the Metal-Insulator Transition of Two-Dimensional Interacting Dirac Electrons

    Directory of Open Access Journals (Sweden)

    Yuichi Otsuka

    2016-03-01

    Full Text Available The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.

  13. Solitons and nonlinear waves along quantum vortex filaments under the low-temperature two-dimensional local induction approximation

    Science.gov (United States)

    Van Gorder, Robert A.

    2016-05-01

    Very recent experimental work has demonstrated the existence of Kelvin waves along quantized vortex filaments in superfluid helium. The possible configurations and motions of such filaments is of great physical interest, and Svistunov previously obtained a Hamiltonian formulation for the dynamics of quantum vortex filaments in the low-temperature limit under the assumption that the vortex filament is essentially aligned along one axis, resulting in a two-dimensional (2D) problem. It is standard to approximate the dynamics of thin filaments by employing the local induction approximation (LIA), and we show that by putting the two-dimensional LIA into correspondence with the first equation in the integrable Wadati-Konno-Ichikawa-Schimizu (WKIS) hierarchy, we immediately obtain solutions to the two-dimensional LIA, such as helix, planar, and self-similar solutions. These solutions are obtained in a rather direct manner from the WKIS equation and then mapped into the 2D-LIA framework. Furthermore, the approach can be coupled to existing inverse scattering transform results from the literature in order to obtain solitary wave solutions including the analog of the Hasimoto one-soliton for the 2D-LIA. One large benefit of the approach is that the correspondence between the 2D-LIA and the WKIS allows us to systematically obtain vortex filament solutions directly in the Cartesian coordinate frame without the need to solve back from curvature and torsion. Implications of the results for the physics of experimentally studied solitary waves, Kelvin waves, and postvortex reconnection events are mentioned.

  14. Quantum entanglement and quantum phase transition under dissipation in the anisoropic Heisenberg xxz model with the Dzyaloshinskii-Moriya interaction

    Directory of Open Access Journals (Sweden)

    R Afzali

    2013-03-01

    Full Text Available   Because the key issue in quantum information and quantum computing is entanglement, the investigation of the effects of environment, as a source of quantum dissipation, and interaction between environment and system on entanglement and quantum phase transition is important. In this paper, we consider two-qubit system in the anisotropic Heisenberg XXZ model with the Dzyaloshinskii-moriya interaction, and accompanied quantum dissipation. Using Lindblad dynamics, the coupling effect and also temperature effect on concurrence, as a measure of entanglement of system, is obtained. The role of DM interaction parameters in the evolution of entanglement is investigated. Furthermore, using derivative of concurrence, the effects of dissipation and DM interaction parameter on quantum phase transition are obtained. It should be noted that spin-orbit interaction or DM parameter intensively influence the process of impressments of dissipation on entanglement measure and quantum phase transition. The current research is very important in the topics of nanometric systems.

  15. Two-dimensional spin liquids with Z2 topological order in an array of quantum wires

    Science.gov (United States)

    Patel, Aavishkar A.; Chowdhury, Debanjan

    2016-11-01

    Insulating Z2 spin liquids are a phase of matter with bulk anyonic quasiparticle excitations and ground-state degeneracies on manifolds with nontrivial topology. We construct a time-reversal symmetric Z2 spin liquid in two spatial dimensions using an array of quantum wires. We identify the anyons as kinks in the appropriate Luttinger-liquid description, compute their mutual statistics, and construct local operators that transport these quasiparticles. We also present a construction of a fractionalized Fermi liquid (FL*) by coupling the spin sector of the Z2 spin liquid to a Fermi liquid via a Kondo-like coupling.

  16. Entanglement and quantum phase transition in the Heisenberg-Ising model

    Institute of Scientific and Technical Information of China (English)

    Tan Xiao-Dong; Jin Bai-Qi; Gao Wei

    2013-01-01

    We use the quantum renormalization-group (QRG) method to study the entanglement and quantum phase transition (QPT) in the one-dimensional spin-l/2 Heisenberg-Ising model [Lieb E,Schultz T and Mattis D 1961 Ann.Phys.(N.Y.)16 407].We find the quantum phase boundary of this model by investigating the evolution of concurrence in terms of QRG iterations.We also investigate the scaling behavior of the system close to the quantum critical point,which shows that the minimum value of the first derivative of concurrence and the position of the minimum scale with an exponent of the system size.Also,the first derivative of concurrence between two blocks diverges at the quantum critical point,which is directly associated with the divergence of the correlation length.

  17. Strong equivalence principle in polymer quantum mechanics and deformed Heisenberg algebra

    Science.gov (United States)

    Kajuri, Nirmalya

    2016-10-01

    The strong equivalence principle (SEP) states that the description of a physical system in a gravitational field is indistinguishable from the description of the same system at rest in an accelerating frame. While this statement holds true in both general relativity and ordinary quantum mechanics, one expects it to fail when quantum gravity corrections are taken into account. In this paper we investigate the possible failure of the SEP in two quantum gravity inspired modifications of quantum mechanics—polymer quantum mechanics and deformed Heisenberg algebra. We find that the SEP fails to hold in both these theories. We estimate the deviation from SEP and find in both cases that it is too small to be measured in present day experiments.

  18. Strong Equivalence Principle in Polymer Quantum Mechanics and deformed Heisenberg Algebra

    CERN Document Server

    Kajuri, Nirmalya

    2016-01-01

    The Strong equivalence Principle (SEP) states that the description of a physical system in a gravitational field is indistinguishable from the description of the same system at rest in an accelerating frame. While this statement holds true in both General Relativity and ordinary Quantum Mechanics, one expects it to fail when quantum gravity corrections are taken into account. In this paper we investigate the possible failure of the SEP in two Quantum Gravity inspired modifications of Quantum Mechanics - Polymer Quantum Mechanics and deformed Heisenberg Algebra. We find that the SEP fails to hold in both these theories. We estimate the deviation from SEP and find in both cases that it is too small to be measured in present day experiments.

  19. Quantum Teleportation via Completely Anisotropic Heisenberg Chain in Inhomogeneous Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    FU Cheng-Hua; HU Zhan-Ning

    2013-01-01

    The quantum teleportation with the entangled thermal state is investigated based on the completely anisotropic Heisenberg chain in the presence of the externally inhomogeneous magnetic field.The effects of the anisotropy and magnetic field for the quantum fidefity are studied in detail.The zero temperature limit and the features of the nonzero temperature for this nonclassical fidelity are obtained.We find that the quantum teleportation demands more stringent conditions than the thermal entanglement of the resource by investigating the threshold temperature of the thermal concurrence and the critical temperature of the maximal teleportation fidelity.The useful quantum teleportation should avoid the point of the phase transition of the system and the anisotropy of the chain and the external magnetic field can control the applicability of the resource in the quantum teleportation.

  20. Thermal Entangled Quantum Refrigerator Working with Three-Qubit Heisenberg XX Model

    Institute of Scientific and Technical Information of China (English)

    郑洁; 何济洲; 何弦

    2011-01-01

    An entangled quantum refrigerator working with a three-qubit one-dimensional isotropic Heisenberg XX model in a constant external magnetic field is constructed in this paper. Based on the quantum first law of thermodynamics, the expressions for several basic thermodynamic quantities such as the heat transferred, the net work and the coefficient of performance are derived. Moreover, the influence of the thermal entanglement on the basic thermodynamic quantities is investigated. Several interesting features of the variation of the basic thermodynamic quantities with the thermal entanglement in zero and nonzero magnetic field are obtained.

  1. Binding energies of trions and biexcitons in two-dimensional semiconductors from diffusion quantum Monte Carlo calculations

    Science.gov (United States)

    Szyniszewski, M.; Mostaani, E.; Drummond, N. D.; Fal'ko, V. I.

    2017-02-01

    Excitonic effects play a particularly important role in the optoelectronic behavior of two-dimensional (2D) semiconductors. To facilitate the interpretation of experimental photoabsorption and photoluminescence spectra we provide statistically exact diffusion quantum Monte Carlo binding-energy data for Mott-Wannier models of excitons, trions, and biexcitons in 2D semiconductors. We also provide contact pair densities to allow a description of contact (exchange) interactions between charge carriers using first-order perturbation theory. Our data indicate that the binding energy of a trion is generally larger than that of a biexciton in 2D semiconductors. We provide interpolation formulas giving the binding energy and contact density of 2D semiconductors as functions of the electron and hole effective masses and the in-plane polarizability.

  2. Experimental apparatus for quantum simulation with two-dimensional 9Be + Coulomb crystals

    Science.gov (United States)

    Pyka, Karsten; Ball, Harrison; McRae, Terry; Edmunds, Claire; Lee, Michael W.; Henderson, Samuel; Biercuk, Michael J.; Quantum Control Lab Team

    2015-03-01

    We report on the development of a new experimental setup designed for Quantum Simulation studies at a computationally relevant scale using laser-cooled 9Be + ion-crystals in a Penning trap. The trap geometry is optimized using numerical calculations for trapping large ion crystals with enhanced optical access and reduced anharmonic perturbations. Separate loading and spectroscopy zones prevent long term drifts of the trapping parameters due to contamination of the trap electrodes with Be deposits. Our customized superconducting magnet provides a homogenous (dB/B telecom wavelength fiber laser systems in the IR via nonlinear conversion. Our new approach employs high-efficiency telecom modulators and mode-selecting cavities to generate multiple beamlines from a single Sum-frequency-Generation step. Ultimately, this newly developed setup will allow for studies of many-body spin systems with tuneable interaction strength from infinite-range to nearest-neighbour type interaction.

  3. Two-Dimensional Dirac Fermions in a Topological Insulator: Transport in the Quantum Limit

    Energy Technology Data Exchange (ETDEWEB)

    Analytis, J.G.; /SIMES, Stanford /SLAC /Stanford U., Geballe Lab /Stanford U., Appl. Phys. Dept.; McDonald, R.D.; /Los Alamos; Riggs, S.C.; /Natl. High Mag. Field Lab.; Chu, J.-H.; /SIMES, Stanford /SLAC /Stanford U., Geballe Lab /Stanford U., Appl. Phys. Dept.; Boebinger, G.S.; /Natl. High Mag. Field Lab.; Fisher, I.R.; /SIMES, Stanford /SLAC /Stanford U., Geballe Lab /Stanford U., Appl. Phys. Dept.

    2011-08-12

    Pulsed magnetic fields of up to 55T are used to investigate the transport properties of the topological insulator Bi{sub 2}Se{sub 3} in the extreme quantum limit. For samples with a bulk carrier density of n = 2.9 x 10{sup 16} cm{sup -3}, the lowest Landau level of the bulk 3D Fermi surface is reached by a field of 4T. For fields well beyond this limit, Shubnikov-de Haas oscillations arising from quantization of the 2D surface state are observed, with the {nu} = 1 Landau level attained by a field of {approx} 35T. These measurements reveal the presence of additional oscillations which occur at fields corresponding to simple rational fractions of the integer Landau indices.

  4. Quantum anomaly, universal relations, and breathing mode of a two-dimensional Fermi gas.

    Science.gov (United States)

    Hofmann, Johannes

    2012-05-01

    In this Letter, we show that the classical SO(2,1) symmetry of a harmonically trapped Fermi gas in two dimensions is broken by quantum effects. The anomalous correction to the symmetry algebra is given by a two-body operator that is well known as the contact. Taking into account this modification, we are able to derive the virial theorem for the system and a universal relation for the pressure of a homogeneous gas. The existence of an undamped breathing mode is associated with the classical symmetry. We provide an estimate for the anomalous frequency shift of this oscillation at zero temperature and compare the result with a recent experiment by [E. Vogt et al., Phys. Rev. Lett. 108, 070404 (2012)]. Discrepancies are attributed to finite temperature effects.

  5. Shear viscosity at the Ising-nematic quantum critical point in two dimensional metals

    CERN Document Server

    Patel, Aavishkar A; Sachdev, Subir

    2016-01-01

    In a strongly interacting quantum liquid without quasiparticles, general scaling arguments imply that the dimensionless ratio $(k_B /\\hbar)\\, \\eta/s$, where $\\eta$ is the shear viscosity and $s$ is the entropy density, is a universal number. We compute the shear viscosity of the Ising-nematic critical point of metals in spatial dimension $d=2$ by an expansion below $d=5/2$. The anisotropy associated with directions parallel and normal to the Fermi surface leads to a violation of the scaling expectations: $\\eta$ scales in the same manner as a chiral conductivity, and the ratio $\\eta/s$ diverges as $T^{-2/z}$, where $z$ is the dynamic critical exponent for fermionic excitations dispersing normal to the Fermi surface.

  6. Unconventional phases in quantum spin and pseudospin systems in two dimensional and three dimensional lattices

    Science.gov (United States)

    Xu, Cenke

    Several examples of quantum spin systems and pseudo spin systems have been studied, and unconventional states of matters and phase transitions have been realized in all these systems under consideration. In the p +/- ip superconductor Josephson lattice and the p--band cold atomic system trapped in optical lattices, novel phases which behave similarly to 1+1 dimensional systems are realized, despite the fact that the real physical systems are in two or three dimensional spaces. For instance, by employing a spin-wave analysis together with a new duality transformation, we establish the existence and stability of a novel gapless "critical phase", which we refer to as a "bond algebraic liquid". This novel critical phase is analogous to the 1+1 dimensional algebraic boson liquid phase. The reason for the novel physics is that there is a quasilocal gauge symmetry in the effective low energy Hamiltonian. In a spin-1 system on the kagome lattice, and a hard-core boson system on the honeycomb lattice, the low energy physics is controlled by two components of compact U(1) gauge symmetries that emerge at low energy. Making use of the confinement nature of the 2+1 dimensional compact gauge theories and the powerful duality between gauge theories and height field theories, the crystalline phase diagrams are studied for both systems, and the transitions to other phases are also considered. These phase diagrams might be accessible in strongly correlated materials, or atomic systems in optical lattices. A novel quantum ground state of matter is realized in a bosonic model on three dimensional fcc lattice with emergent low energy excitations. The novel phase obtained is a stable gapless boson liquid phase, with algebraic boson density correlations. The stability of this phase is protected against the instanton effect and superfluidity by self-duality and large gauge symmetries on both sides of the duality. The gapless collective excitations of this phase closely resemble the

  7. Quantum Fractals: From Heisenberg's Uncertainty to Barnsley's Fractality

    Science.gov (United States)

    Jadczyk, Arkadiusz

    2014-07-01

    This book brings together two concepts. The first is over a hundred years old -- the "quantum", while the second, "fractals", is newer, achieving popularity after the pioneering work of Benoit Mandelbrot. Both areas of research are expanding dramatically day by day. It is somewhat amazing that quantum theory, in spite of its age, is still a boiling mystery as we see in some quotes from recent publications addressed to non-expert readers:...

  8. Spiral versus modulated collinear phases in the quantum axial next-nearest-neighbor Heisenberg model

    Science.gov (United States)

    Oitmaa, J.; Singh, R. R. P.

    2016-12-01

    Motivated by the discovery of spiral and modulated collinear phases in several magnetic materials, we investigate the magnetic properties of Heisenberg spin S =1 /2 antiferromagnets in two and three dimensions, with frustration arising from second-neighbor couplings in one axial direction [the axial next-nearest-neighbor Heisenberg (ANNNH) model]. Our results clearly demonstrate the presence of an incommensurate spiral phase at T =0 in two dimensions, extending to finite temperatures in three dimensions. The crossover between Néel and spiral order occurs at a value of the frustration parameter considerably above the classical value 0.25, a sign of substantial quantum fluctuations. We also investigate a possible modulated collinear phase with a wavelength of four lattice spacings and find that it has substantially higher energy and hence is not realized in the model.

  9. High-field studies of quantum oscillations in quasi-two-dimensional organic metals

    Science.gov (United States)

    Sandhu, Pravindrajit

    frequencies in the dHvA signal is found to be a quantum mechanical effect arising from differences in field dependence of the states in the two partially occupied bands near the Fermi level.

  10. Andreev reflection and bound state formation in a ballistic two-dimensional electron gas probed by a quantum point contact

    Science.gov (United States)

    Irie, Hiroshi; Todt, Clemens; Kumada, Norio; Harada, Yuichi; Sugiyama, Hiroki; Akazaki, Tatsushi; Muraki, Koji

    2016-10-01

    We study coherent transport and bound state formation of Bogoliubov quasiparticles in a high-mobility I n0.75G a0.25As two-dimensional electron gas (2DEG) coupled to a superconducting Nb electrode by means of a quantum point contact (QPC) as a tunable single-mode probe. Below the superconducting critical temperature of Nb, the QPC shows a single-channel conductance greater than the conductance quantum 2 e2/h at zero bias, which indicates the presence of Andreev-reflected quasiparticles, time-reversed states of the injected electron, returning back through the QPC. The marked sensitivity of the conductance enhancement to voltage bias and perpendicular magnetic field suggests a mechanism analogous to reflectionless tunneling—a hallmark of phase-coherent transport, with the boundary of the 2DEG cavity playing the role of scatterers. When the QPC transmission is reduced to the tunneling regime, the differential conductance vs bias voltage probes the single-particle density of states in the proximity area. Measured conductance spectra show a double peak within the superconducting gap of Nb, demonstrating the formation of Andreev bound states in the 2DEG. Both of these results, obtained in the open and closed geometries, underpin the coherent nature of quasiparticles, i.e., phase-coherent Andreev reflection at the InGaAs/Nb interface and coherent propagation in the ballistic 2DEG.

  11. Two-dimensional double-quantum spectroscopy: peak shapes as a sensitive probe of carrier interactions in quantum wells

    CERN Document Server

    Tollerud, Jonathan O

    2016-01-01

    We identify carrier scattering at densities below which it has previously been observed in semiconductor quantum wells. These effects are evident in the peakshapes of 2D double-quantum spectra, which change as a function of excitation density. At high excitation densities ($\\geq 10^{9}$ carriers/,cm$^{-2}$) we observe untilted peaks similar to those reported in previous experiments. At low excitation densities (<$10^{8}$ carriers cm$^{-2}$) we observe narrower, tilted peaks. Using a simple simulation, we show that tilted peak-shapes are expected in double-quantum spectra when inhomogeneous broadening is much larger than homogeneous broadening, and that fast pure-decoherence of the double-quantum coherence can obscure this peak tilt. These results show that carrier interactions are important at lower densities than previously expected, and that the `natural' double-quantum peakshapes are hidden by carrier interactions at the excitation densities typically used. Furthermore, these results demonstrate that an...

  12. Quantum spin-1 anisotropic ferromagnetic Heisenberg model in a crystal field: a variational approach.

    Science.gov (United States)

    Carvalho, D C; Plascak, J A; Castro, L M

    2013-09-01

    A variational approach based on Bogoliubov inequality for the free energy is employed in order to treat the quantum spin-1 anisotropic ferromagnetic Heisenberg model in the presence of a crystal field. Within the Bogoliubov scheme an improved pair approximation has been used. The temperature-dependent thermodynamic functions have been obtained and provide much better results than the previous simple mean-field scheme. In one dimension, which is still nonintegrable for quantum spin-1, we get the exact results in the classical limit, or near-exact results in the quantum case, for the free energy, magnetization, and quadrupole moment, as well for the transition temperature. In two and three dimensions the corresponding global phase diagrams have been obtained as a function of the parameters of the Hamiltonian. First-order transition lines, second-order transition lines, tricritical and tetracritical points, and critical endpoints have been located through the analysis of the minimum of the Helmholtz free energy and a Landau-like expansion in the approximated free energy. Only first-order quantum transitions have been found at zero temperature. Limiting cases, such as isotropic Heisenberg, Blume-Capel, and Ising models, have been analyzed and compared to previous results obtained from other analytical approaches as well as from Monte Carlo simulations.

  13. Quantum vs Classical Magnetization Plateaus of S=1/2 Frustrated Heisenberg Chains

    Science.gov (United States)

    Hida, Kazuo; Affleck, Ian

    2005-06-01

    The competition between quantum and classical magnetization plateaus of S=1/2 frustrated Heisenberg chains with modified exchange couplings is investigated. The conventional S=1/2 frustrated Heisenberg chain is known to exhibit a 3-fold degenerate \\uparrow\\downarrow\\uparrow-type classical plateau at 1/3 of the saturation magnetization accompanied by the spontaneous Z3 translational symmetry breakdown. The stability of this plateau phase against period 3 exchange modulation which favors the \\bullet\\hskip -1pt-\\hskip -1pt\\bullet \\uparrow-type quantum plateau state (\\bullet\\hskip -1pt-\\hskip -1pt\\bullet = singlet dimer) is studied by bosonization, renormalization group and numerical diagonalization methods. The ground state phase diagram and the spin configuration in each phase are numerically determined. The translationally invariant Valence Bond Solid-type model with 4-spin and third neighbor interactions, which has the exact \\bullet\\hskip -1pt-\\hskip -1pt\\bullet \\uparrow-type quantum plateau state, is also presented. The phase transition to the classical \\uparrow\\downarrow\\uparrow-type ground state is also observed by varying the strength of 4-spin and third neighbor interactions. The relation between these two types of models with quantum plateau states is discussed.

  14. Critical spin dynamics of the 2D quantum Heisenberg antiferromagnets Sr2CuO2Cl2 and Sr2Cu3O4Cl2.

    Science.gov (United States)

    Kim, Y J; Birgeneau, R J; Chou, F C; Erwin, R W; Kastner, M A

    2001-04-02

    We report a neutron scattering study of the long-wavelength dynamic spin correlations in the model two-dimensional S = 1/2 square lattice Heisenberg antiferromagnets Sr2CuO2Cl2 and Sr2Cu3O4Cl2. The characteristic energy scale, omega(0)(T/J), is determined by measuring the quasielastic peak width in the paramagnetic phase over a wide range of temperature ( 0.2 less similarT/J less similar0.7). The obtained values for omega(0)(T/J) agree quantitatively between the two compounds and also with values deduced from quantum Monte Carlo simulations. The combined data show scaling behavior, omega approximately xi(-z), over the entire temperature range with z = 1.0(1), in agreement with dynamic scaling theory.

  15. Engineered two-dimensional Ising interactions in a trapped-ion quantum simulator with hundreds of spins.

    Science.gov (United States)

    Britton, Joseph W; Sawyer, Brian C; Keith, Adam C; Wang, C-C Joseph; Freericks, James K; Uys, Hermann; Biercuk, Michael J; Bollinger, John J

    2012-04-25

    The presence of long-range quantum spin correlations underlies a variety of physical phenomena in condensed-matter systems, potentially including high-temperature superconductivity. However, many properties of exotic, strongly correlated spin systems, such as spin liquids, have proved difficult to study, in part because calculations involving N-body entanglement become intractable for as few as N ≈ 30 particles. Feynman predicted that a quantum simulator--a special-purpose 'analogue' processor built using quantum bits (qubits)--would be inherently suited to solving such problems. In the context of quantum magnetism, a number of experiments have demonstrated the feasibility of this approach, but simulations allowing controlled, tunable interactions between spins localized on two- or three-dimensional lattices of more than a few tens of qubits have yet to be demonstrated, in part because of the technical challenge of realizing large-scale qubit arrays. Here we demonstrate a variable-range Ising-type spin-spin interaction, J(i,j), on a naturally occurring, two-dimensional triangular crystal lattice of hundreds of spin-half particles (beryllium ions stored in a Penning trap). This is a computationally relevant scale more than an order of magnitude larger than previous experiments. We show that a spin-dependent optical dipole force can produce an antiferromagnetic interaction J(i,j) proportional variant d(-a)(i,j), where 0 ≤ a ≤ 3 and d(i,j) is the distance between spin pairs. These power laws correspond physically to infinite-range (a = 0), Coulomb-like (a = 1), monopole-dipole (a = 2) and dipole-dipole (a = 3) couplings. Experimentally, we demonstrate excellent agreement with a theory for 0.05 ≲ a ≲ 1.4. This demonstration, coupled with the high spin count, excellent quantum control and low technical complexity of the Penning trap, brings within reach the simulation of otherwise computationally intractable problems in quantum magnetism.

  16. Critical behavior of the site diluted quantum anisotropic Heisenberg model in two dimensions

    Science.gov (United States)

    Lima, L. S.; Pires, A. S. T.; Costa, B. V.

    2015-11-01

    In this work we use the Self Consistent Harmonic Approximation and Quantum Monte Carlo technique to study the Quantum XY on a two dimensional square lattice in the presence of nonmagnetic impurities. In particular we discuss how site disorder changes the Berezinskii-Kosterlitz-Thouless transition temperature, TBKT. This temperature is determined as a function of the nonmagnetic density. Our results are consistent with an anomalous behavior of TBKT at a concentration close to the site percolation threshold. We interpret the results as due to a competition between the confining of vortices and quantum fluctuations, or due to finite size effects.

  17. Renormalization of the global quantum correlation and monogamy relation in the anisotropic Heisenberg XXZ model

    Science.gov (United States)

    Qin, Meng; Ren, Zhong-Zhou; Zhang, Xin

    2016-01-01

    In this study, the global quantum correlation, monogamy relation and quantum phase transition of the Heisenberg XXZ model are investigated by the method of quantum renormalization group. We obtain, analytically, the expressions of the global negativity, the global measurement-induced disturbance and the monogamy relation for the system. The result shows that for a three-site block state, the partial transpose of an asymmetric block can get stronger entanglement than that of the symmetric one. The residual entanglement and the difference of the monogamy relation of measurement-induced disturbance show a scaling behavior with the size of the system becoming large. Moreover, the monogamy nature of entanglement measured by negativity exists in the model, while the nonclassical correlation quantified by measurement-induced disturbance violates the monogamy relation and demonstrates polygamy.

  18. Geometric Quantum Discord in the Heisenberg XX Model with Three-Spin Interactions

    Science.gov (United States)

    Xie, Yu-Xia; Liu, Jing; Sun, Yu-Hang

    2017-02-01

    Quantum discord is a resource for quantum information processing tasks, and seeking flexible ways to control it is of practical significance. We investigate the trace distance, Bures distance, and Hellinger distance geometric quantum discords (GQDs) for thermal states of the Heisenberg XX chain with three-spin interactions. The results show that both the XZX + YZY and XZY - YZX types of three-spin interactions can be used to enhance evidently the GQDs for the boundary spins of the chain. The optimal strengths of three-spin interactions for which the maximum enhancement of the GQDs are achieved are strongly dependent on the GQD measures we adopted and the number of spins in the chain.

  19. Einstein-Heisenberg Consistency Condition Interplay with Cosmological Constant Prediction in Resummed Quantum Gravity

    CERN Document Server

    Ward, B F L

    2015-01-01

    We argue that our recent success in using our resummed quantum gravity approach to Einstein's general theory of relativity, in the context of the Planck scale cosmology formulation of Bonanno and Reuter, to estimate the value of the cosmological constant \\Lambda supports the use of quantum mechanical consistency requirements to constrain the main uncertainty in that very promising result. This main uncertainty, which is due to the uncertainty in the value of the time t_{\\text{tr}} at which the transition from the Planck scale cosmology to the FRW model occurs, is shown to be reduced, by requiring consistency between the Heisenberg uncertainty principle and the known properties of the solutions of Einstein's equations, from four orders of magnitude to the level of a factor of {\\cal O}(10). This lends more credibility to the over-all resummed quantum gravity approach itself, in general, and to our estimate of $\\Lambda$ in particular.

  20. Geometric Quantum Discord in the Heisenberg XX Model with Three-Spin Interactions

    Science.gov (United States)

    Xie, Yu-Xia; Liu, Jing; Sun, Yu-Hang

    2016-11-01

    Quantum discord is a resource for quantum information processing tasks, and seeking flexible ways to control it is of practical significance. We investigate the trace distance, Bures distance, and Hellinger distance geometric quantum discords (GQDs) for thermal states of the Heisenberg XX chain with three-spin interactions. The results show that both the XZX + YZY and XZY -YZX types of three-spin interactions can be used to enhance evidently the GQDs for the boundary spins of the chain. The optimal strengths of three-spin interactions for which the maximum enhancement of the GQDs are achieved are strongly dependent on the GQD measures we adopted and the number of spins in the chain.

  1. Phase diagram and spin correlations of the Kitaev-Heisenberg model: Importance of quantum effects

    Science.gov (United States)

    Gotfryd, Dorota; Rusnačko, Juraj; Wohlfeld, Krzysztof; Jackeli, George; Chaloupka, Jiří; Oleś, Andrzej M.

    2017-01-01

    We explore the phase diagram of the Kitaev-Heisenberg model with nearest neighbor interactions on the honeycomb lattice using the exact diagonalization of finite systems combined with the cluster mean field approximation, and supplemented by the insights from analytic approaches: the linear spin-wave and second-order perturbation theories. This study confirms that by varying the balance between the Heisenberg and Kitaev term, frustrated exchange interactions stabilize in this model either one of four phases with magnetic long range order: Néel phase, ferromagnetic phase, and two other phases with coexisting antiferromagnetic and ferromagnetic bonds, zigzag and stripy phase, or one of two distinct spin-liquid phases. Out of these latter disordered phases, the one with ferromagnetic Kitaev interactions has a substantially broader range of stability as the neighboring competing ordered phases, ferromagnetic and stripy, have very weak quantum fluctuations. Focusing on the quantum spin-liquid phases, we study spatial spin correlations and dynamic spin structure factor of the model by the exact diagonalization technique, and discuss the evolution of gapped low-energy spin response across the quantum phase transitions between the disordered spin liquid and phases with long range magnetic order.

  2. Enhancing the geometric quantum discord in the Heisenberg XX chain by Dzyaloshinsky–Moriya interaction

    Energy Technology Data Exchange (ETDEWEB)

    Gong, Jia-Min, E-mail: jmgong@yeah.net [School of Electronic Engineering, Xi' an University of Posts and Telecommunications, Xi' an 710121 (China); Tang, Qi [School of Electronic Engineering, Xi' an University of Posts and Telecommunications, Xi' an 710121 (China); Sun, Yu-Hang [School of Science, Xi' an University of Posts and Telecommunications, Xi' an 710121 (China); Qiao, Lin [School of Electronic Engineering, Xi' an University of Posts and Telecommunications, Xi' an 710121 (China)

    2015-03-15

    We studied the trace distance, the Hellinger distance, and the Bures distance geometric quantum discords (GQDs) for a two-spin Heisenberg XX chain with the Dzyaloshinsky–Moriya (DM) interaction and the external magnetic fields. We found that considerable enhancement of the GQDs can be achieved by introducing the DM interaction, and their maxima were obtained when the strength of the DM interaction approaches infinity. The external magnetic fields and the increase of the temperature can also enhance the GQDs to some extent during certain specific parameter regions.

  3. Quantum phase transitions in the Heisenberg J1-J2 triangular antiferromagnet in a magnetic field

    Science.gov (United States)

    Ye, Mengxing; Chubukov, Andrey V.

    2017-01-01

    We present the zero-temperature phase diagram of a Heisenberg antiferromagnet on a frustrated triangular lattice with nearest-neighbor (J1) and next-nearest-neighbor (J2) interactions, in a magnetic field. We show that the classical model has an accidental degeneracy for all J2/J1 and all fields, but the degeneracy is lifted by quantum fluctuations. We show that at large spin S , for J2/J11 , the transition remains first order, with a finite hysteresis width, but for S =1 /2 and, possibly, S =1 , there appears a new intermediate phase without a quasiclassical long-range order.

  4. Quantum entanglement in trimer spin-1/2 Heisenberg chains with antiferromagnetic coupling

    CERN Document Server

    Del Cima, O M; da Silva, S L L

    2015-01-01

    The quantum entanglement measure is determined, for the first time, for antiferromagnetic trimer spin-1/2 Heisenberg chains. The physical quantity proposed to measure the entanglement is the distance between states by adopting the Hilbert-Schmidt norm. The method is applied to the new magnetic Cu(II) trimer system, 2b.3CuCl_2.2H_2O, and to the trinuclear Cu(II) halide salt, (3MAP)_2Cu_2Cl_8. The decoherence temperature, above which the entanglement is suppressed, is determined for the both systems. A correlation among their decoherence temperatures and their respective exchange coupling constants is established.

  5. Heisenberg-limited quantum sensing and metrology with superpositions of twin-Fock states

    Science.gov (United States)

    Gerry, Christopher C.; Mimih, Jihane

    2011-03-01

    We discuss the prospects of performing Heisenberg-limited quantum sensing and metrology using a Mach-Zehnder interferometer with input states that are superpositions of twin-Fock states and where photon number parity measurements are made on one of the output beams of the interferometer. This study is motivated by the experimental challenge of producing twin-Fock states on opposite sides of a beam splitter. We focus on the use of the so-called pair coherent states for this purpose and discuss a possible mechanism for generating them. We also discuss the prospect of using other superstitions of twin-Fock states, for the purpose of interferometry.

  6. The effects of two-dimensional bifurcations and quantum beats in a system of combined atomic force and scanning tunneling microscopes with quantum dots

    Science.gov (United States)

    Zhukovsky, V. Ch.; Krevchik, V. D.; Semenov, M. B.; Krevchik, P. V.; Zaytsev, R. V.; Egorov, I. A.

    2016-11-01

    The field and temperature dependence of the probability of two-dimensional dissipative tunneling is studied in the framework of one-instanton approximation for a model double-well oscillator potential in an external electric field at finite temperature with account for the influence of two local phonon modes for quantum dots in a system of a combined atomic force and a scanning tunneling microscope. It is demonstrated that in the mode of synchronous parallel transfer of tunneling particles from the cantilever tip to the quantum dot the two local phonon modes result in the occurrence of two stable peaks in the curve of the 2D dissipative tunneling probability as a function of the field. Qualitative comparison of the theoretical curve in the limit of weak dissociation and the experimental current-voltage characteristic for quantum dots that grow from colloidal gold under a cantilever tip at the initial stage of quantum-dot formation when the quantum dot size does not exceed 10 nm is performed. It is established that one of the two stable peaks that correspond to interaction of tunneling particles with two local phonon modes in the temperature dependence of the 2D dissipative tunneling probability can be split in two, which corresponds to the tunneling channel interference mechanism. It is found that the theoretically predicted and experimentally observed mode of quantum beats occurs near the bifurcation point.

  7. Enhanced quantum efficiency from a mosaic of two dimensional MoS2 formed onto aminosilane functionalised substrates

    Science.gov (United States)

    Wang, Yichao; Della Gaspera, Enrico; Carey, Benjamin J.; Atkin, Paul; Berean, Kyle J.; Clark, Rhiannon M.; Cole, Ivan S.; Xu, Zai-Quan; Zhang, Yupeng; Bao, Qiaoliang; Ou, Jian Zhen; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2016-06-01

    Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4]2- anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications.Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of

  8. A naive matrix-model approach to two-dimensional quantum gravity coupled to matter of arbitrary central charge

    CERN Document Server

    Brézin, E

    1992-01-01

    In the usual matrix-model approach to random discretized two-dimensional manifolds, one introduces n Ising spins on each cell, i.e. a discrete version of 2D quantum gravity coupled to matter with a central charge n/2. The matrix-model consists then of an integral over $2^{n}$ matrices, which we are unable to solve for $n>1$. However for a fixed genus we can expand in the cosmological constant g for arbitrary values of n, and a simple minded analysis of the series yields for n=0,1 and 2 the expected results for the exponent $\\gamma_{string}$ with an amazing precision given the small number of terms that we considered. We then proceed to larger values of n. Simple tests of universality are successfully applied; for instance we obtain the same exponents for n=3 or for one Ising model coupled to a one dimensional target space. The calculations are easily extended to states Potts models, through an integration over $q^{n}$ matrices. We see no sign of the tachyonic instability of the theory, but we have only consid...

  9. Magnetic breakdown phenomenon in quasi-two-dimensional organic conductors: A quantum model inspired by a realistic band structure

    Science.gov (United States)

    Kim, Ju H.; Han, S. Y.; Brooks, J. S.

    1999-08-01

    We investigate the phenomenon of magnetic breakdown in quasi-two-dimensional organic conductors such as α-(ET)2KHg(SCN)4 and κ-(ET)2Cu(NCS)2 by constructing a tight-binding model based on a realistic band structure which is derived from the crystallographic data. We solve the model numerically to compute the magnetic field dependence of the magnetization and show that the present model accounts naturally for the experimentally observed magnetization oscillation frequencies that are forbidden in the semiclassical picture. The computed values of the fundamental and magnetic breakdown frequencies with no adjustable parameters are close to the experimentally measured values. For completeness, we carry out the computation for both canonical (fixed number of particles) and grand canonical (fixed chemical potential) ensembles, and show that the forbidden frequencies appear in both cases. Hence, the appearance of anomalous frequencies in the de Haas-van Alphen effect has a quantum-mechanical origin and arises from the interplay of electronic states from two partially occupied bands near the Fermi energy as a function of magnetic field. We also compute the temperature dependence of the magnetization and apply ad hoc the Lifshitz-Kosevich analysis to the amplitudes of the Fourier components at moderately high temperatures. This yields effective mass values for α-(ET)2KHg(SCN)4 in good agreement with experimental values.

  10. Effect of phase transition on quantum transport in group-IV two-dimensional U-shape device

    Energy Technology Data Exchange (ETDEWEB)

    Sadi, Mohammad Abdullah; Gupta, Gaurav, E-mail: a0089293@nus.edu.sg; Liang, Gengchiau [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore)

    2014-10-21

    The effect of phase-transition from the quantum-spin-hall to the band-insulator phase on the transport through a three-terminal U-shape spin-separator has been computationally investigated via non-equilibrium green function formalism. Two-dimensional group-IV elements have been comprehensively appraised as the device material. The device separates the unpolarized current injected at the source-terminal into nearly 100% spin-polarized currents of the opposite polarities at the two drain terminals. The phase-transition activated by the electric-field orthogonal to the device is shown to extensively influence the current magnitude and its spin-polarization, and the effect is stronger for materials with smaller intrinsic spin-orbit coupling. Moreover, the device length and the area under field are shown to critically affect the device characteristics on phase change. It is shown that the same device can be operated as a spin-filter by inducing phase-transition selectively in the channel. The results are important for designing spin-devices from Group-IV monolayers.

  11. A benchmark study of the two-dimensional Hubbard model with auxiliary-field quantum Monte Carlo method

    CERN Document Server

    Qin, Mingpu; Zhang, Shiwei

    2016-01-01

    Ground state properties of the Hubbard model on a two-dimensional square lattice are studied by the auxiliary-field quantum Monte Carlo method. Accurate results for energy, double occupancy, effective hopping, magnetization, and momentum distribution are calculated for interaction strengths of U/t from 2 to 8, for a range of densities including half-filling and n = 0.3, 0.5, 0.6, 0.75, and 0.875. At half-filling, the results are numerically exact. Away from half-filling, the constrained path Monte Carlo method is employed to control the sign problem. Our results are obtained with several advances in the computational algorithm, which are described in detail. We discuss the advantages of generalized Hartree-Fock trial wave functions and its connection to pairing wave functions, as well as the interplay with different forms of Hubbard-Stratonovich decompositions. We study the use of different twist angle sets when applying the twist averaged boundary conditions. We propose the use of quasi-random sequences, whi...

  12. Enhanced quantum efficiency from a mosaic of two dimensional MoS2 formed onto aminosilane functionalised substrates.

    Science.gov (United States)

    Wang, Yichao; Della Gaspera, Enrico; Carey, Benjamin J; Atkin, Paul; Berean, Kyle J; Clark, Rhiannon M; Cole, Ivan S; Xu, Zai-Quan; Zhang, Yupeng; Bao, Qiaoliang; Ou, Jian Zhen; Daeneke, Torben; Kalantar-Zadeh, Kourosh

    2016-06-16

    Developing scalable methods of growing two dimensional molybdenum disulphide (2D MoS2) with strong optical properties, on any desired substrates, is a necessary step towards industrial uptake of this material for optical applications. In this study, Si/SiO2 substrates were functionalised using self-assembled monolayers of three different aminosilanes with various numbers of amine groups and molecular lengths as underlayers for enhancing the adherence of the molybdenum precursor. The tetrahedral [MoS4](2-) anion groups from the molybdenum precursor were bonded on these silanised Si/SiO2 substrates afterwards. The substrates were then treated with a combined thermolysis and sulphurisation step. The results showed that silanisation of the substrates using the longest chains and the largest number of amine groups provided a good foundation to grow quasi 2D MoS2 made from adjacent flakes in a mosaic formation. Microscopy and spectroscopy investigations revealed that these quasi 2D MoS2 formed using this long chain aminosilane resulted in flakes with lateral dimensions in micron and submicron ranges composed of adjoining MoS2 pieces of 20 to 60 nm in lateral dimensions, dominantly made of 3 to 5 MoS2 fundamental layers. The obtained quasi 2D MoS2 shows a high internal quantum efficiency of 2.6% associated with the quantum confinement effect and high stoichiometry of the adjoining nanoflakes that form the structure of the sheets. The synthesis technique in this study is reliable and facile and offers a procedure to form large, scalable and patternable quasi 2D MoS2 sheets on various substrates with enhanced optical properties for practical applications.

  13. Renormalization of trace distance and multipartite entanglement close to the quantum phase transitions of one- and two-dimensional spin-chain systems

    Science.gov (United States)

    Wu, Wei; Xu, Jing-Bo

    2016-08-01

    We investigate the quantum phase transitions of spin systems in one and two dimensions by employing trace distance and multipartite entanglement along with the real-space quantum renormalization group method. As illustration examples, a one-dimensional and a two-dimensional XY models are considered. It is shown that the quantum phase transitions of these spin-chain systems can be revealed by the singular behaviors of the first derivatives of renormalized trace distance and multipartite entanglement in the thermodynamics limit. Moreover, we find that the renormalized trace distance and multipartite entanglement obey certain universal exponential-type scaling laws in the vicinity of the quantum critical points.

  14. Effects of anisotropy and magnetic fields on the specific heat of a quasi-two-dimensional Boltzmann gas in an elliptical parabolic quantum dot

    Institute of Scientific and Technical Information of China (English)

    Zhai Zhi-Yuan; Li Yu-Qi; Pan Xiao-Yin

    2012-01-01

    We investigate the effects due to anisotropy and magnetic field interaction for a quasi-two-dimensional Boltzmann gas in an elliptical parabolic quantum dot.The specific heat is studied with varying temperature,anisotropy,and magnetic field strength.The cases without and with the inclusion of the spin Zeeman interaction are considered.

  15. Exact matrix product solutions in the Heisenberg picture of an open quantum spin chain

    Energy Technology Data Exchange (ETDEWEB)

    Clark, S R; Jaksch, D [Centre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, Singapore 117543 (Singapore); Prior, J [Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Hartmann, M J [Technische Universitaet Muenchen, Physik Department I, James Franck Strasse, 85748 Garching (Germany); Plenio, M B [Institute for Mathematical Sciences, Imperial College London, SW7 2PG (United Kingdom)], E-mail: s.clark@physics.ox.ac.uk

    2010-02-15

    In recent work, Hartmann et al (2009 Phys. Rev. Lett. 102 057202) demonstrated that the classical simulation of the dynamics of open 1D quantum systems with matrix product algorithms can often be dramatically improved by performing time evolution in the Heisenberg picture. For a closed system this was exemplified by an exact matrix product operator (MPO) solution of the time-evolved creation operator of a quadratic fermi chain with a matrix dimension of just two. In this work, we show that this exact solution can be significantly generalized to include the case of an open quadratic fermi chain subjected to master equation evolution with Lindblad operators that are linear in the fermionic operators. Remarkably even in this open system the time evolution of operators continues to be described by MPOs with the same fixed dimension as that required by the solution of a coherent quadratic fermi chain for all times. Through the use of matrix product algorithms the dynamical behaviour of operators in this non-equilibrium open quantum system can be computed with a cost that is linear in the system size. We present some simple numerical examples that highlight how useful this might be for the more detailed study of open system dynamics. Given that Heisenberg picture simulations have been demonstrated to offer significant accuracy improvements for other open systems that are not exactly solvable, our work also provides further insight into how and why this advantage arises.

  16. A quantum fidelity study of the anisotropic next-nearest-neighbour triangular lattice Heisenberg model.

    Science.gov (United States)

    Thesberg, Mischa; Sørensen, Erik S

    2014-10-22

    Ground- and excited-state quantum fidelities in combination with generalized quantum fidelity susceptibilites, obtained from exact diagonalizations, are used to explore the phase diagram of the anisotropic next-nearest-neighbour triangular Heisenberg model. Specifically, the J'-J2 plane of this model, which connects the J1-J2 chain and the anisotropic triangular lattice Heisenberg model, is explored using these quantities. Through the use of a quantum fidelity associated with the first excited-state, in addition to the conventional ground-state fidelity, the BKT-type transition and Majumdar-Ghosh point of the J1-J2 chain (J'=0) are found to extend into the J'-J2 plane and connect with points on the J2=0 axis thereby forming bounded regions in the phase diagram. These bounded regions are then explored through the generalized quantum fidelity susceptibilities χρ, χ₁₂₀°, χD and χCAF which are associated with the spin stiffness, 120° spiral order parameter, dimer order parameter and collinear antiferromagnetic order parameter respectively. These quantities are believed to be extremely sensitive to the underlying phase and are thus well suited for finite-size studies. Analysis of the fidelity susceptibilities suggests that the J', J2≪J phase of the anisotropic triangular model is either a collinear antiferromagnet or possibly a gapless disordered phase that is directly connected to the Luttinger phase of the J1-J2 chain. Furthermore, the outer region is dominated by incommensurate spiral physics as well as dimer order.

  17. Mesoscopic quantum interference experiments in InGaAs and GaAs two-dimensional systems

    Science.gov (United States)

    Ren, Shaola

    The study of quantum interference in solid-state systems yields insight in fundamental properties of mesoscopic systems. Electron quantum interference constitutes an important method to explore mesoscopic physics and quantum decoherence. This dissertation focuses on two-dimensional (2D) electron systems in delta-Si doped n-type In0:64Ga0:36As/In 0:45Al0:55As, 2D hole systems in Si-doped p-type GaAs/Al 0:35Ga0:65As and C-doped p-type GaAs/Al0:24Ga 0:76As heterostructures. The low temperature experiments study the magnetotransport of nano- and micro-scale lithographically defined devices fabricated on the heterostructures. These devices include a single ring interferometer and a ring interferometer array in 2D electron system, Hall bar geometries and narrow wires in 2D hole systems. The single ring interferometer yields pronounced Aharonov-Bohm (AB) oscillations with magnetic flux periodicity of h/e over a wide range of magnetic field. The periodicity was confirmed by Fourier transformation of the oscillations. The AB oscillation amplitude shows a quasi-periodic modulation over applied magnetic field due to local magnetic flux threading through the interferometer arms. Further study of current and temperature dependence of the amplitude of the oscillations indicates that the Thouless energy forms the measure of excitation energies giving quantum decoherence. An in-plane magnetic field was applied to the single ring interferometer to study the Berry's phase and the Aharonov-Casher effect. The ring interferometer array yields both AB oscillations and Altshuler-Aronov-Spivak (AAS) oscillations, the latter with magnetic flux periodicity of h/2e. The AAS oscillations require time-reversal symmetry and hence can be used to qualify time-reversal symmetry breaking. More importantly, the fundamental mesoscopic dephasing length associated with time-reversal symmetry breaking under applied magnetic field, an effective magnetic length, can be obtained by the analysis of the AAS

  18. Quantum and thermal phase transitions in a bosonic atom-molecule mixture in a two-dimensional optical lattice

    Science.gov (United States)

    de Forges de Parny, L.; Rousseau, V. G.

    2017-01-01

    We study the ground state and the thermal phase diagram of a two-species Bose-Hubbard model, with U(1 ) ×Z2 symmetry, describing atoms and molecules on a two-dimensional optical lattice interacting via a Feshbach resonance. Using quantum Monte Carlo simulations and mean-field theory, we show that the conversion between the two species, coherently coupling the atomic and molecular states, has a crucial impact on the Mott-superfluid transition and stabilizes an insulating phase with a gap controlled by the conversion term—the Feshbach insulator—instead of a standard Mott-insulating phase. Depending on the detuning between atoms and molecules, this model exhibits three phases: the Feshbach insulator, a molecular condensate coexisting with noncondensed atoms, and a mixed atomic-molecular condensate. Employing finite-size scaling analysis, we observe three-dimensional (3D) X Y (3D Ising) transition when U(1 ) (Z2) symmetry is broken, whereas the transition is first order when both U(1 ) and Z2 symmetries are spontaneously broken. The finite-temperature phase diagram is also discussed. The thermal disappearance of the molecular superfluid leads to a Berezinskii-Kosterlitz-Thouless transition with unusual universal jump in the superfluid density. The loss of the quasi-long-range coherence of the mixed atomic and molecular superfluid is more subtle since only atoms exhibit conventional Berezinskii-Kosterlitz-Thouless criticality. We also observe a signal compatible with a classical first-order transition between the mixed superfluid and the normal Bose liquid at low temperature.

  19. A continuum approximation for the excitations of the (1,1,...,1 interface in the quantum Heisenberg model

    Directory of Open Access Journals (Sweden)

    Oscar Bolina

    2000-07-01

    Full Text Available It is shown that, with an appropriate scaling, the energy of low-lying excitations of the (1, 1,...,1 interface in the d-dimensional quantum Heisenberg model are given by the spectrum of the (d-1-dimensional Laplacian on a suitable domain.

  20. Onset of quantum criticality in the topological-to-nematic transition in a two-dimensional electron gas at filling factor ν =5 /2

    Science.gov (United States)

    Schreiber, K. A.; Samkharadze, N.; Gardner, G. C.; Biswas, Rudro R.; Manfra, M. J.; Csáthy, G. A.

    2017-07-01

    Under hydrostatic pressure, the ground state of a two-dimensional electron gas at ν =5 /2 changes from a fractional quantum Hall state to the stripe phase. By measuring the energy gap of the fractional quantum Hall state and of the onset temperature of the stripe phase, we mapped out a phase diagram of these competing phases in the pressure-temperature plane. Our data highlight the dichotomy of two descriptions of the half-filled Landau level near the quantum critical point: one based on electrons and another on composite fermions.

  1. Stapp`s quantum dualism: The James/Heisenberg model of consciousness

    Energy Technology Data Exchange (ETDEWEB)

    Noyes, H.P.

    1994-02-18

    Henry Stapp attempts to resolve the Cartesian dilemma by introducing what the author would characterize as an ontological dualism between mind and matter. His model for mind comes from William James` description of conscious events and for matter from Werner Heisenberg`s ontological model for quantum events (wave function collapse). His demonstration of the isomorphism between the two types of events is successful, but in the author`s opinion fails to establish a monistic, scientific theory. The author traces Stapp`s failure to his adamant rejection of arbitrariness, or `randomness`. This makes it impossible for him (or for Bohr and Pauli before him) to understand the power of Darwin`s explanation of biology, let along the triumphs of modern `neo-Darwinism`. The author notes that the point at issue is a modern version of the unresolved opposition between Leucippus and Democritus on one side and Epicurus on the other. Stapp`s views are contrasted with recent discussions of consciousness by two eminent biologists: Crick and Edelman. They locate the problem firmly in the context of natural selection on the surface of the earth. Their approaches provide a sound basis for further scientific work. The author briefly examines the connection between this scientific (rather than ontological) framework and the new fundamental theory based on bit-strings and the combinatorial hierarchy.

  2. Quantum Disordered State without Frustration in the Double Layer Heisenberg Antiferromagnet —Dimer Expansion and Projector Monte Carlo Study—

    Science.gov (United States)

    Hida, Kazuo

    1992-03-01

    The quantum disordered state (QDOS) of the spin 1/2 double layer square lattice Heisenberg antiferromagnet is studied. Using the dimer expansion from the limit of the large interlayer coupling J', the staggered susceptibility χ, the antiferromagnetic structure factor Sπ and the antiferromagnetic correlation length ξ are calculated up to the 6-th order in the intralayer coupling J. The ratio analysis shows that the QDOS becomes unstable against the Néel ordering at J'/J≃2.56. The critical exponents are not inconsistent with the universality class of the 3-dimensional classical Heisenberg model, suggesting that our QDOS corresponds to that expected in the 2-dimensional square lattice Heisenberg antiferromagnet with unphysically small spin (<0.276). The results of the projector Monte Carlo simulation also confirms the dimer expansion results.

  3. Translation of waves along quantum vortex filaments in the low-temperature two-dimensional local induction approximation

    Energy Technology Data Exchange (ETDEWEB)

    Van Gorder, Robert A., E-mail: Robert.VanGorder@maths.ox.ac.uk [Mathematical Institute, University of Oxford, Andrew Wiles Building, Radcliffe Observatory Quarter, Woodstock Road, Oxford OX2 6GG (United Kingdom)

    2015-09-15

    In a recent paper, we give a study of the purely rotational motion of general stationary states in the two-dimensional local induction approximation (2D-LIA) governing superfluid turbulence in the low-temperature limit [B. Svistunov, “Superfluid turbulence in the low-temperature limit,” Phys. Rev. B 52, 3647 (1995)]. Such results demonstrated that variety of stationary configurations are possible from vortex filaments exhibiting purely rotational motion in addition to commonly discussed configurations such as helical or planar states. However, the filaments (or, more properly, waves along these filaments) can also exhibit translational motion along the axis of orientation. In contrast to the study on vortex configurations for purely rotational stationary states, the present paper considers non-stationary states which exhibit a combination of rotation and translational motions. These solutions can essentially be described as waves or disturbances which ride along straight vortex filament lines. As expected from our previous work, there are a number of types of structures that can be obtained under the 2D-LIA. We focus on non-stationary states, as stationary states exhibiting translation will essentially take the form of solutions studied in [R. A. Van Gorder, “General rotating quantum vortex filaments in the low-temperature Svistunov model of the local induction approximation,” Phys. Fluids 26, 065105 (2014)], with the difference being translation along the reference axis, so that qualitative appearance of the solution geometry will be the same (even if there are quantitative differences). We discuss a wide variety of general properties of these non-stationary solutions and derive cases in which they reduce to known stationary states. We obtain various routes to Kelvin waves along vortex filaments and demonstrate that if the phase and amplitude of a disturbance both propagate with the same wave speed, then Kelvin waves will result. We also consider the self

  4. Intrinsic Energies of Two-dimensional Heisenberg Magnets and Ferromagnetic Single-walled Nanotubes%二维磁性系统和准一维磁性纳米管的内能

    Institute of Scientific and Technical Information of China (English)

    米斌周; 冯翠菊; 祁云平; 丁东; 薛永红

    2015-01-01

    Intrinsic energy of two⁃dimensional square lattice single⁃ion anisotropic Heisenberg ferromagnets, antiferromagnets, and ferromagnetic single⁃walled nanotubes are calculated with many⁃body Green’ s function method in quantum statistical theory. Calculated results of ferromagnets and antiferromagnets are compared. Between zero temperature and phase transition point, including zero temperature, anti⁃ferromagnetic energy is always lower than that of ferromagnetic energy. Calculation method of intrinsic energy in this paper is applicable not only to ferromagnetic system, but also suitable for antiferromagnetic system and ferrimagnetic system, as well as ferromagnetic single⁃walled nanotubes. Intrinsic energies are greatly lower than classical energies, which shows that transverse correlation effect is important.%采用量子统计理论的多体格林函数法计算二维单离子各向异性海森伯铁磁体、反铁磁体以及单壁铁磁纳米管的内能,对比铁磁体和反铁磁体的结果。在相同的参量下,反铁磁能量总是低于相应的铁磁能量(相变点除外)。由于反铁磁能量随温度上升的速度较铁磁能量快,当温度升高到居里点TC和奈尔点TN时( TC =TN ),铁磁能量和反铁磁能量相等。横向关联效应对系统内能的影响较大,不能忽略。

  5. Gapless chiral spin liquid in a kagome Heisenberg model

    Science.gov (United States)

    Bieri, Samuel; Messio, Laura; Bernu, Bernard; Lhuillier, Claire

    2015-08-01

    Motivated by recent experiments on the Heisenberg S =1 /2 quantum spin liquid candidate material kapellasite, we classify all possible chiral (time-reversal symmetry breaking) spin liquids with fermionic spinons on the kagome lattice. We obtain the phase diagram for the physically relevant extended Heisenberg model, comparing the energies of a wide range of microscopic variational wave functions. We propose that, at low temperature, kapellasite exhibits a gapless chiral spin liquid phase with spinon Fermi surfaces. This two-dimensional state inherits many properties of the nearby one-dimensional phase of decoupled antiferromagnetic spin chains, but also shows some remarkable differences. We discuss the spin structure factors and other physical properties.

  6. Anomalous curie response of impurities in quantum-critical spin-1/2 Heisenberg antiferromagnets.

    Science.gov (United States)

    Höglund, Kaj H; Sandvik, Anders W

    2007-07-13

    We consider a magnetic impurity in two different S=1/2 Heisenberg bilayer antiferromagnets at their respective critical interlayer couplings separating Néel and disordered ground states. We calculate the impurity susceptibility using a quantum Monte Carlo method. With intralayer couplings in only one of the layers (Kondo lattice), we observe an anomalous Curie constant C*, as predicted on the basis of field-theoretical work [S. Sachdev, Science 286, 2479 (1999)10.1126/science.286.5449.2479]. The value C* = 0.262 +/- 0.002 is larger than the normal Curie constant C=S(S+1)/3. Our low-temperature results for a symmetric bilayer are consistent with a universal C*.

  7. Constructive interference between disordered couplings enhances multiparty entanglement in quantum Heisenberg spin glass models

    Science.gov (United States)

    Mishra, Utkarsh; Rakshit, Debraj; Prabhu, R.; Sen(De, Aditi; Sen, Ujjwal

    2016-08-01

    Disordered systems form one of the centrestages of research in many body sciences and lead to a plethora of interesting phenomena and applications. A paradigmatic disordered system consists of a one-dimensional array of quantum spin-1/2 particles, governed by the Heisenberg spin glass Hamiltonian with natural or engineered quenched disordered couplings in an external magnetic field. These systems allow disorder-induced enhancement for bipartite and multipartite observables. Here we show that simultaneous application of independent quenched disorders results in disorder-induced enhancement, while the same is absent with individual application of the same disorders. We term the phenomenon as constructive interference and the corresponding parameter stretches as the Venus regions. Interestingly, it has only been observed for multiparty entanglement and is absent for the single- and two-party physical quantities.

  8. Heisenberg scaling of time-limited quantum metrology with realistic decoherence

    Science.gov (United States)

    Hardy, Maxime; Coish, William A.

    2012-02-01

    The prospect of using entanglement to improve various metrology tasks is one of the most promising avenues for a near-term real-world benefit from genuine quantum phenomena [1]. However, in the standard scenario, history-independent Markovian dephasing removes the quantum advantage [2]. We revisit the problem of quantum metrology using the model of trapped ions subject to non-Markovian phase damping decoherence caused by Gaussian noise with finite correlation length and time (a slight generalization of the model used in Ref. [3]). Assuming a fixed available measurement time shorter than the noise correlation time (the non-Markovian limit) and a noise source that is local in space, we recover Heisenberg scaling (˜1/N). This allows one to measure an ``instantaneous'' frequency to a higher precision than the time-averaged noise amplitude and moreover to a higher precision than classically allowed. Interestingly, for this protocol we show that the optimal number of measurements to be performed within the measurement time is three. [4pt] [1] V. Giovannetti, S. Lloyd, and L. Maccone Nature Photonics 5, 222 (2011) [2] S. F. Huelga et al. Phys. Rev. Lett. 79, 3865 (1997 [3] T. Monz et al. Phys. Rev. Lett. 106, 130506 (2011)

  9. Trapped-ion quantum simulation of tunable-range Heisenberg chains

    Energy Technology Data Exchange (ETDEWEB)

    Grass, Tobias [ICFO-Institut de Ciencies Fotoniques, Castelldefels, Barcelona (Spain); Lewenstein, Maciej [ICFO-Institut de Ciencies Fotoniques, Castelldefels, Barcelona (Spain); ICREA-Institucio Catalana de Recerca i Estudis Avancats, Barcelona (Spain)

    2014-12-01

    Quantum-optical techniques allow for generating controllable spin-spin interactions between ions, making trapped ions an ideal quantum simulator of Heisenberg chains. A single parameter, the detuning of the Raman coupling, allows to switch between ferromagnetic and antiferromagnetic chains, and to modify the range of the interactions. On the antiferromagnetic side, the system can be tuned from an extreme long-range limit, in which any pair of ions interacts with almost equal strength, to interactions with a decay. By exact diagonalization, we study how a system of up to 20 ions behaves upon tuning the interactions. We find that it undergoes a transition from a dimerized state with extremely short-ranged correlations towards a state with quasi long-range order, that is, algebraically decaying correlations. The dynamical evolution of the system after a local quench is shown to strongly vary in the two regimes: While in the dimerized limit, the excitation remains localized for long times, propagating spinons characterize the dynamics of the quasi-long-range ordered system. Taking a look onto the ferromagnetic side of the system, we demonstrate the feasibility of witnessing non-locality of quantum correlations by measuring two-particle correlators. (orig.)

  10. Investigations of the Quantum Correlation in Two-Qubit Heisenberg XYZ Model with Decoherence

    Science.gov (United States)

    Guo-Hui, Yang

    2016-12-01

    Quantum correlation dynamics in an anisotropic Heisenberg XYZ model under decoherence is investigated with the use of concurrence C and quantum discord (QD). With the Werner state as the initial state, we discuss the influence of mixture degree r on the dynamics. There are some difference between the time evolution behaviors of these two correlation measures with different value of r. For 0 ≤ r ≤ 1/3, there exists quantum discord but no entanglement; For 1/3

  11. Quantum entanglement and criticality of the antiferromagnetic Heisenberg model in an external field.

    Science.gov (United States)

    Liu, Guang-Hua; Li, Ruo-Yan; Tian, Guang-Shan

    2012-06-27

    By Lanczos exact diagonalization and the infinite time-evolving block decimation (iTEBD) technique, the two-site entanglement as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization in the antiferromagnetic Heisenberg (AFH) model under an external field are investigated. With increasing external field, the small size system shows some distinct upward magnetization stairsteps, accompanied synchronously with some downward two-site entanglement stairsteps. In the thermodynamic limit, the two-site entanglement, as well as the bipartite entanglement, the ground state energy, the nearest-neighbor correlations, and the magnetization are calculated, and the critical magnetic field h(c) = 2.0 is determined exactly. Our numerical results show that the quantum entanglement is sensitive to the subtle changing of the ground state, and can be used to describe the magnetization and quantum phase transition. Based on the discontinuous behavior of the first-order derivative of the entanglement entropy and fidelity per site, we think that the quantum phase transition in this model should belong to the second-order category. Furthermore, in the magnon existence region (h entanglement which can be described by a free bosonic field theory is observed, and the central charge c is determined to be 1.

  12. Magnon-induced nuclear relaxation in the quantum critical region of a Heisenberg linear chain

    Science.gov (United States)

    Hoch, M. J. R.

    2017-07-01

    The low-temperature properties of spin-1/2 one-dimensional (1D) Heisenberg antiferromagnetic (HAF) chains which have relatively small exchange couplings between the spins can be tuned using laboratory-scale magnetic fields. Magnetization measurements, made as a function of temperature, provide phase diagrams for these systems and establish the quantum critical point (QCP). The evolution of the spin dynamics behavior with temperature and applied field in the quantum critical (QC) region, near the QCP, is of particular interest and has been experimentally investigated in a number of 1D HAFs using neutron scattering and nuclear magnetic resonance as the preferred techniques. In the QC phase both quantum and thermal spin fluctuations are present. As a result of extended spin correlations in the chains, magnon excitations are important at finite temperatures. An expression for the NMR spin-lattice relaxation rate 1 /T1 of probe nuclei in the QC phase of 1D HAFs is obtained by considering Raman scattering processes which induce nuclear spin flips. The relaxation rate expression, which involves the temperature and the chemical potential, predicts scaling behavior of 1 /T1 consistent with recent experimental findings for quasi-1D HAF systems. A simple relationship between 1 /T1 and the deviation of the magnetization from saturation (MS-M ) is predicted for the QC region.

  13. Energies and wave functions of an off-centre donor in hemispherical quantum dot: Two-dimensional finite difference approach and ritz variational principle

    Energy Technology Data Exchange (ETDEWEB)

    Nakra Mohajer, Soukaina; El Harouny, El Hassan [Laboratoire de Physique de la Matière Condensée, Département de Physique, Faculté des Sciences, Université Abdelmalek Essaadi, B.P. 2121 M’Hannech II, 93030 Tétouan (Morocco); Ibral, Asmaa [Equipe d’Optique et Electronique du Solide, Département de Physique, Faculté des Sciences, Université Chouaïb Doukkali, B. P. 20 El Jadida Principale, El Jadida (Morocco); Laboratoire d’Instrumentation, Mesure et Contrôle, Département de Physique, Faculté des Sciences, Université Chouaïb Doukkali, B. P. 20 El Jadida Principale, El Jadida (Morocco); El Khamkhami, Jamal [Laboratoire de Physique de la Matière Condensée, Département de Physique, Faculté des Sciences, Université Abdelmalek Essaadi, B.P. 2121 M’Hannech II, 93030 Tétouan (Morocco); and others

    2016-09-15

    Eigenvalues equation solutions of a hydrogen-like donor impurity, confined in a hemispherical quantum dot deposited on a wetting layer and capped by an insulating matrix, are determined in the framework of the effective mass approximation. Conduction band alignments at interfaces between quantum dot and surrounding materials are described by infinite height barriers. Ground and excited states energies and wave functions are determined analytically and via one-dimensional finite difference approach in case of an on-center donor. Donor impurity is then moved from center to pole of hemispherical quantum dot and eigenvalues equation is solved via Ritz variational principle, using a trial wave function where Coulomb attraction between electron and ionized donor is taken into account, and by two-dimensional finite difference approach. Numerical codes developed enable access to variations of donor total energy, binding energy, Coulomb correlation parameter, spatial extension and radial probability density with respect to hemisphere radius and impurity position inside the quantum dot.

  14. Growth optimization and characterization of high mobility two-dimensional electron systems in AlAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Dasgupta, Shivaji

    2009-02-15

    In this work two-dimensional electron systems (2DESs) based on AlAs/AlGaAs heterostructures doped with Si are investigated. The electrons are confined in AlAs quantum wells (QWs) sandwiched between AlGaAs buffers. Analytical calculations and simulations for AlAs QWs are presented in the first chapter. The results show a cross-over width, above which the wide (001)-oriented QWs show double valley occupancy and wide (110)-oriented QWs show single valley occupancy. We solve the Schroedinger equation analytically for anisotropic masses. The solution shows the orientation dependence of the elliptical cyclotron orbit due to the anisotropic mass. We also present an introduction to the Landau level crossings based on g{sup *}m{sup *} product. In the next chapter, we present experimental results for the double-valley (001)-oriented AlAs QWs. We present the different structures of the deep AlAs QWs along with the low temperature magnetotransport data for these QWs. Thereafter, we present the results on shallow AlAs QWs. We achieved a mobility of 4.2 x 10{sup 5} cm{sup 2}/Vs at 330 mK for the deep backside doped AlAs QW. For the shallow QWs, we achieved a mobility of2.3 x 10{sup 5} cm{sup 2}/Vs at 330 mK, for a density of 2.9 x 10{sup 11} cm{sup -2}. From the magneto-transport data, we see evidence of the double-valley occupation for the (001)-oriented AlAs wide QWs. In the next chapter, we present experimental results for the single-valley (110)-oriented AlAs QWs. We deduced the donor binding energy and the doping efficiency for this facet from a doping series of double-sided doped QWs. Thereafter, we designed different structures for the (110)-oriented AlAs QWs, which we present along with their respective low temperature magneto-transport data. We measured one of the double-sided doped AlAs QWs at very high magnetic fields and low temperatures, down to 60 mK. At the end of the chapter, we present a spike feature observed in the magneto-transport data of these QWs. This

  15. Exact Realization of a Quantum-Dimer Model in Heisenberg Antiferromagnets on a Diamond-Like Decorated Lattice

    Science.gov (United States)

    Hirose, Yuhei; Oguchi, Akihide; Fukumoto, Yoshiyuki

    2016-09-01

    We study Heisenberg antiferromagnets on a diamond-like decorated square lattice perturbed by further neighbor couplings. The second-order effective Hamiltonian is calculated and the resultant Hamiltonian is found to be a square-lattice quantum-dimer model with a finite hopping amplitude and no repulsion, which suggests the stabilization of the plaquette phase. Our recipe for constructing quantum-dimer models can be adopted for other lattices and provides a route for the experimental realization of quantum-dimer models.

  16. Rotational Heisenberg Inequalities

    OpenAIRE

    Bréchet, Sylvain; Reuse, François; Maschke, Klaus; Ansermet, Jean-Philippe

    2015-01-01

    Since their discovery in 1927, the Heisenberg Inequalities have become an icon of quantum mechanics. Often inappropriately referred to as the Uncertainty Principle, these inequalities relating the standard deviations of the position and momentum observables to Planck's constant are one of the cornerstones of the quantum formalism even if the physical interpretation of quantum mechanics remains still open to controversy nowadays. The Heisenberg Inequalities governing translational motion are w...

  17. Heisenberg's observability principle

    OpenAIRE

    Wolff, JE

    2014-01-01

    Werner Heisenberg's 1925 paper ‘Quantum-theoretical re-interpretation of kinematic and mechanical relations’ marks the beginning of quantum mechanics. Heisenberg famously claims that the paper is based on the idea that the new quantum mechanics should be ‘founded exclusively upon relationships between quantities which in principle are observable’. My paper is an attempt to understand this observability principle, and to see whether its employment is philosophically defensible. Against interpr...

  18. Spin transport of the frustrated quasi-two-dimensional XY-like antiferromagnet

    Science.gov (United States)

    Lima, L. S.

    2017-01-01

    We use the Self Consistent Harmonic Approximation together with the Kubo formalism of the Linear Response Theory to study the spin transport in the two-dimensional frustrated Heisenberg antiferromagnet in a square lattice with easy-plane ion single anisotropy. The regular part of the spin conductivity σreg(ω) is determined for several values of the critical ion single parameter Dc, that separates the low D region from the large D quantum paramagnetic phase. We have obtained an abrupt change in the spin conductivity in the discontinuity points of the graphic Dc vs. η, where the system presents a quantum phase transition.

  19. Quantum correlations in a two-qubit anisotropic Heisenberg XYZ chain with uniform magnetic field

    Science.gov (United States)

    Li, Lei; Yang, Guo-Hui

    2014-07-01

    Quantum correlations in an anisotropic Heisenberg XYZ chain is investigated by use of concurrence C and measurement-induced disturbance (MID). We show that the behaviors of the MID are remarkably different from the concurrence. Firstly, it is shown that there is a revival phenomenon in the concurrence but not in the MID, which is suitable for both the ground state case and the finite temperature case. Based on the analysis of the ground-state C and MID structures, we illustrate the reason why the ground-state MID does not show a revival phenomenon in detail. Then we explore different effects of the external and self parameters on entanglement and MID behaviors. It can be shown that the region of MID is evidently larger than the case of concurrence, and that the concurrence signals a quantum phase transition even at finite T while MID does not. Cases where the concurrence finally maintains one nonzero constant value regardless of the value of the variable B for a constant Jz, while MID decreases monotonously to zero with increasing B. We also show that if B can take a proper range of values, the concurrence decreases with the improvement of the anisotropic parameter γ, whereas an opposite effect for MID behaviors is presented.

  20. Decay dynamics of quantum dots influenced by the local density of optical states of two-dimensional photonic crystal membranes

    DEFF Research Database (Denmark)

    Julsgaard, Brian; Johansen, Jeppe; Stobbe, Søren

    2008-01-01

    We have performed time-resolved spectroscopy on InAs quantum dot ensembles in photonic crystal membranes. The influence of the photonic crystal is investigated by varying the lattice constant systematically. We observe a strong slow down of the quantum dots’ spontaneous emission rates as the two-...... the bandgap in good agreement with local density of states calculations.......We have performed time-resolved spectroscopy on InAs quantum dot ensembles in photonic crystal membranes. The influence of the photonic crystal is investigated by varying the lattice constant systematically. We observe a strong slow down of the quantum dots’ spontaneous emission rates as the two...

  1. The diagonal and off-diagonal AC conductivity of two-dimensional electron gases with contactless Corbino geometry in the quantum Hall regime

    DEFF Research Database (Denmark)

    Petersen, Christian Leth; Hansen, Ole Per

    1996-01-01

    We have investigated the AC conductivity elements in the quantum Hall regime of two-dimensional electron gases coupled capacitively to electrodes with Corbino geometry. The samples are GaAlAs/GaAs single heterostructures, and the measurements are made at low frequencies, up to 20 kHz. The diagonal...... conductivity is derived from magnetocapacitance measurements. It increases with increasing frequency according to a power law at integer filling factors. The exponent of the power law depends on both temperature and filling factor. Ratios between Hall conductivities at different filling factors are obtained...

  2. Indirect exchange interaction between magnetic impurities in the two-dimensional topological insulator based on CdTe/HgTe/CdTe quantum wells

    Science.gov (United States)

    Kurilovich, P. D.; Kurilovich, V. D.; Burmistrov, I. S.

    2016-10-01

    We study indirect exchange interaction between magnetic impurities in the (001) CdTe/HgTe/CdTe symmetric quantum well. We consider low temperatures and the case of the chemical potential placed in the energy gap of the two-dimensional quasiparticle spectrum. We find that the indirect exchange interaction is suppressed exponentially with the distance between magnetic impurities. The presence of inversion asymmetry results in oscillations of the indirect exchange interaction with the distance and generates additional terms which are noninvariant under rotations in the (001) plane. The indirect exchange interaction matrix has complicated structure with some terms proportional to the sign of the energy gap.

  3. Quantum-spin-liquid states in the two-dimensional kagome antiferromagnets ZnxCu4-x(OD)6Cl2.

    Science.gov (United States)

    Lee, S-H; Kikuchi, H; Qiu, Y; Lake, B; Huang, Q; Habicht, K; Kiefer, K

    2007-11-01

    A three-dimensional system of interacting spins typically develops static long-range order when it is cooled. If the spins are quantum (S=1/2), however, novel quantum paramagnetic states may appear. The most highly sought state among them is the resonating-valence-bond state, in which every pair of neighbouring quantum spins forms an entangled spin singlet (valence bonds) and these singlets are quantum mechanically resonating among themselves. Here we provide an experimental indication for such quantum paramagnetic states existing in frustrated antiferromagnets, Zn(x)Cu(4-x)(OD)(6)Cl(2), where the S=1/2 magnetic Cu2+ moments form layers of a two-dimensional kagome lattice. We find that in Cu(4)(OD)(6)Cl(2), where distorted kagome planes are weakly coupled, a dispersionless excitation mode appears in the magnetic excitation spectrum below approximately 20 K, whose characteristics resemble those of quantum spin singlets in a solid state, known as a valence-bond solid, that breaks translational symmetry. Doping with non-magnetic Zn2+ ions reduces the distortion of the kagome lattice, and weakens the interplane coupling but also dilutes the magnetic occupancy of the kagome lattice. The valence-bond-solid state is suppressed, and for ZnCu(3)(OD)(6)Cl(2), where the kagome planes are undistorted and 90% occupied by the Cu2+ ions, the low-energy spin fluctuations become featureless.

  4. 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

    2016-10-01

    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.

  5. Heisenberg's First Paper

    Science.gov (United States)

    Cassidy, David C.

    1978-01-01

    Describes some of the discussion, correspondances and assumptions of Heisenberg. Includes clarifying and defending his explanation of the anomalous Zeeman Effect to the Quantum Physicists of his time. (GA)

  6. The Heisenberg-Weyl algebra on the circle and a related quantum mechanical model for hindered rotation.

    Science.gov (United States)

    Kouri, Donald J; Markovich, Thomas; Maxwell, Nicholas; Bodmann, Bernhard G

    2009-07-02

    We discuss a periodic variant of the Heisenberg-Weyl algebra, associated with the group of translations and modulations on the circle. Our study of uncertainty minimizers leads to a periodic version of canonical coherent states. Unlike the canonical, Cartesian case, there are states for which the uncertainty product associated with the generators of the algebra vanishes. Next, we explore the supersymmetric (SUSY) quantum mechanical setting for the uncertainty-minimizing states and interpret them as leading to a family of "hindered rotors". Finally, we present a standard quantum mechanical treatment of one of these hindered rotor systems, including numerically generated eigenstates and energies.

  7. Hadamard States and Two-dimensional Gravity

    CERN Document Server

    Salehi, H

    2001-01-01

    We have used a two-dimensional analog of the Hadamard state-condition to study the local constraints on the two-point function of a linear quantum field conformally coupled to a two-dimensional gravitational background. We develop a dynamical model in which the determination of the state of the quantum field is essentially related to the determination of a conformal frame. A particular conformal frame is then introduced in which a two-dimensional gravitational equation is established.

  8. Semiclassical initial value representation for the quantum propagator in the Heisenberg interaction representation

    Science.gov (United States)

    Petersen, Jakob; Pollak, Eli

    2015-12-01

    One of the challenges facing on-the-fly ab initio semiclassical time evolution is the large expense needed to converge the computation. In this paper, we suggest that a significant saving in computational effort may be achieved by employing a semiclassical initial value representation (SCIVR) of the quantum propagator based on the Heisenberg interaction representation. We formulate and test numerically a modification and simplification of the previous semiclassical interaction representation of Shao and Makri [J. Chem. Phys. 113, 3681 (2000)]. The formulation is based on the wavefunction form of the semiclassical propagation instead of the operator form, and so is simpler and cheaper to implement. The semiclassical interaction representation has the advantage that the phase and prefactor vary relatively slowly as compared to the "standard" SCIVR methods. This improves its convergence properties significantly. Using a one-dimensional model system, the approximation is compared with Herman-Kluk's frozen Gaussian and Heller's thawed Gaussian approximations. The convergence properties of the interaction representation approach are shown to be favorable and indicate that the interaction representation is a viable way of incorporating on-the-fly force field information within a semiclassical framework.

  9. Semiclassical initial value representation for the quantum propagator in the Heisenberg interaction representation

    Energy Technology Data Exchange (ETDEWEB)

    Petersen, Jakob; Pollak, Eli, E-mail: eli.pollak@weizmann.ac.il [Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovot (Israel)

    2015-12-14

    One of the challenges facing on-the-fly ab initio semiclassical time evolution is the large expense needed to converge the computation. In this paper, we suggest that a significant saving in computational effort may be achieved by employing a semiclassical initial value representation (SCIVR) of the quantum propagator based on the Heisenberg interaction representation. We formulate and test numerically a modification and simplification of the previous semiclassical interaction representation of Shao and Makri [J. Chem. Phys. 113, 3681 (2000)]. The formulation is based on the wavefunction form of the semiclassical propagation instead of the operator form, and so is simpler and cheaper to implement. The semiclassical interaction representation has the advantage that the phase and prefactor vary relatively slowly as compared to the “standard” SCIVR methods. This improves its convergence properties significantly. Using a one-dimensional model system, the approximation is compared with Herman-Kluk’s frozen Gaussian and Heller’s thawed Gaussian approximations. The convergence properties of the interaction representation approach are shown to be favorable and indicate that the interaction representation is a viable way of incorporating on-the-fly force field information within a semiclassical framework.

  10. Semiclassical initial value representation for the quantum propagator in the Heisenberg interaction representation.

    Science.gov (United States)

    Petersen, Jakob; Pollak, Eli

    2015-12-14

    One of the challenges facing on-the-fly ab initio semiclassical time evolution is the large expense needed to converge the computation. In this paper, we suggest that a significant saving in computational effort may be achieved by employing a semiclassical initial value representation (SCIVR) of the quantum propagator based on the Heisenberg interaction representation. We formulate and test numerically a modification and simplification of the previous semiclassical interaction representation of Shao and Makri [J. Chem. Phys. 113, 3681 (2000)]. The formulation is based on the wavefunction form of the semiclassical propagation instead of the operator form, and so is simpler and cheaper to implement. The semiclassical interaction representation has the advantage that the phase and prefactor vary relatively slowly as compared to the "standard" SCIVR methods. This improves its convergence properties significantly. Using a one-dimensional model system, the approximation is compared with Herman-Kluk's frozen Gaussian and Heller's thawed Gaussian approximations. The convergence properties of the interaction representation approach are shown to be favorable and indicate that the interaction representation is a viable way of incorporating on-the-fly force field information within a semiclassical framework.

  11. Quantum Dense Coding About a Two-Qubit Heisenberg XYZ Model

    Science.gov (United States)

    Xu, Hui-Yun; Yang, Guo-Hui

    2017-09-01

    By taking into account the nonuniform magnetic field, the quantum dense coding with thermal entangled states of a two-qubit anisotropic Heisenberg XYZ chain are investigated in detail. We mainly show the different properties about the dense coding capacity ( χ) with the changes of different parameters. It is found that dense coding capacity χ can be enhanced by decreasing the magnetic field B, the degree of inhomogeneity b and temperature T, or increasing the coupling constant along z-axis J z . In addition, we also find χ remains the stable value as the change of the anisotropy of the XY plane Δ in a certain temperature condition. Through studying different parameters effect on χ, it presents that we can properly turn the values of B, b, J z , Δ or adjust the temperature T to obtain a valid dense coding capacity ( χ satisfies χ > 1). Moreover, the temperature plays a key role in adjusting the value of dense coding capacity χ. The valid dense coding capacity could be always obtained in the lower temperature-limit case.

  12. The anisotropic quantum spin-1/2 Heisenberg antiferromagnet in the presence of a longitudinal field on a bcc lattice

    Energy Technology Data Exchange (ETDEWEB)

    Neto, Minos A., E-mail: minos@pq.cnpq.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); Roberto Viana, J., E-mail: vianafisica@bol.com.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); Ricardo de Sousa, J., E-mail: jsousa@edu.ufam.br [Departamento de Fisica, Universidade Federal do Amazonas, 3000, Japiim, Manaus, 69077-000 AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, Manaus, 69077-000 AM (Brazil)

    2012-08-15

    In this work we study the critical behavior of the quantum spin-1/2 anisotropic Heisenberg antiferromagnet in the presence of a longitudinal field on a body centered cubic (bcc) lattice as a function of temperature, anisotropy parameter ({Delta}) and magnetic field (H), where {Delta}=0 and 1 correspond the isotropic Heisenberg and Ising models, respectively. We use the framework of the differential operator technique in the effective-field theory with finite cluster of N=4 spins (EFT-4). The staggered m{sub s}=(m{sub A}-m{sub B})/2 and total m=(m{sub A}+m{sub B})/2 magnetizations are numerically calculated, where in the limit of m{sub s}{yields}0 the critical line T{sub N}(H,{Delta}) is obtained. The phase diagram in the T-H plane is discussed as a function of the parameter {Delta} for all values of H Element-Of [0,H{sub c}({Delta})], where H{sub c}({Delta}) correspond the critical field (T{sub N}=0). Special focus is given in the low temperature region, where a reentrant behavior is observed around of H=H{sub c}({Delta}){>=}H{sub c}({Delta}=1)=8J in the Ising limit, results in accordance with Monte Carlo simulation, and also was observed for all values of {Delta} Element-Of [0,1]. This reentrant behavior increases with increase of the anisotropy parameter {Delta}. In the limit of low field, our results for the Heisenberg limit are compared with series expansion values. - Highlights: Black-Right-Pointing-Pointer In the lat decade there has been a great interest in the physics of the quantum phase transition in spins system. Black-Right-Pointing-Pointer Effective-field theory in cluster with N=4 spins is generalized to treat the quantum spin-1/2 Heisenberg model. Black-Right-Pointing-Pointer We have obtained phase diagram at finite temperature for the quantum spin-1/2 antiferromagnet Heisenberg model as a bcc lattice.

  13. Near-field relaxation of a quantum emitter to two-dimensional semiconductors: Surface dissipation and exciton polaritons

    Science.gov (United States)

    Karanikolas, Vasilios D.; Marocico, Cristian A.; Eastham, Paul R.; Bradley, A. Louise

    2016-11-01

    The total spontaneous emission rate of a quantum emitter in the presence of an infinite MoS2 monolayer is enhanced by several orders of magnitude, compared to its free-space value, due to the excitation of surface exciton polariton modes and lossy modes. The spectral and distance dependence of the spontaneous emission rate are analyzed and the lossy surface wave, surface exciton polariton mode and radiative contributions are identified. The transverse magnetic and transverse electric exciton polariton modes can be excited for different emission frequencies of the quantum emitter, and their contributions to the total spontaneous emission rate are different. To calculate these different decay rates we use the non-Hermitian description of light-matter interactions, employing a Green's tensor formalism. The distance dependence follows different trends depending on the emission energy of the quantum emitter. For the case of the lossy surface waves, the distance dependence follows a z-n,n =2 ,3 ,4 , trend. When transverse magnetic exciton polariton modes are excited, they dominate and characterize the distance dependence of the spontaneous emission rate of a quantum emitter in the presence of the MoS2 layers. The interaction between a quantum emitter and a MoS2 superlattice is investigated, and we observe a splitting of the modes supported by the superlattice. Moreover, a blueshift of the peak values of the spontaneous emission rate of a quantum emitter is observed as the number of layers is increased. The field distribution profiles, created by a quantum emitter, are used to explain this behavior.

  14. Distance-dependent energy transfer between CdSe/CdS quantum dots and a two-dimensional semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Goodfellow, Kenneth M.; Vamivakas, A. Nick, E-mail: nick.vamivakas@rochester.edu [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Chakraborty, Chitraleema [Materials Science, University of Rochester, Rochester, New York 14627 (United States); Sowers, Kelly [Department of Chemistry, University of Rochester, Rochester, New York 14627 (United States); Waduge, Pradeep; Wanunu, Meni [Department of Physics, Northeastern University, Boston, Massachusetts 02115 (United States); Krauss, Todd [Institute of Optics, University of Rochester, Rochester, New York 14627 (United States); Department of Chemistry, University of Rochester, Rochester, New York 14627 (United States); Driscoll, Kristina [Department of Physics, Rochester Institute of Technology, Rochester, New York 14627 (United States)

    2016-01-11

    Atomically thin semiconductors, such as the transition metal dichalcogenides, show great potential for nanoscale photodetection, energy harvesting, and nanophotonics. Here, we investigate the efficiency of energy transfer between colloidal quantum dots with a cadmium selenide core and cadmium sulfide shell and monolayer molybdenum diselenide (MoSe{sub 2}). We show that MoSe{sub 2} effectively quenches the fluorescence of quantum dots when the two materials are in contact. We then separate the MoSe{sub 2} and quantum dots by inserting variable thickness hexagonal boron nitride (h-BN) spacers and show that the efficiency at which the MoSe{sub 2} quenches fluorescence decreases as the h-BN thickness is increased. For distances d, this trend can be modeled by a 1/d{sup 4} decay, in agreement with theory and recent studies involving graphene.

  15. Two-dimensional model colloids and nano wires: phase transitions, effects of external potentials and quantum effects

    Science.gov (United States)

    Franzrahe, K.; Henseler, P.; Ricci, A.; Strepp, W.; Sengupta, S.; Dreher, M.; Kircher, Chr.; Lohrer, M.; Quester, W.; Binder, K.; Nielaba, P.

    2005-07-01

    Quantum effects, structures and phase transitions in Nano-systems have been analyzed. An overview is given on the results of our computations on structural and elastic properties of model colloids, on phase transitions of model colloids in external fields, and on structural and electronic properties of stretched atomic wires.

  16. The Heisenberg Microscope: A Powerful Instructional Tool for Promoting Meta-Cognitive and Meta-Scientific Thinking on Quantum Mechanics and the "Nature of Science"

    Science.gov (United States)

    Hadzidaki, Pandora

    2008-01-01

    In this paper, we present a multi-dimensional study concerning Heisenberg's "gamma ray microscope", a thought experiment, which is intimately connected with the historical development of quantum mechanics (QM), and also with the most disputed interpretations of quantum theory. In this study: (a) we investigate how philosophers of science read and…

  17. The Heisenberg Microscope: A Powerful Instructional Tool for Promoting Meta-Cognitive and Meta-Scientific Thinking on Quantum Mechanics and the "Nature of Science"

    Science.gov (United States)

    Hadzidaki, Pandora

    2008-01-01

    In this paper, we present a multi-dimensional study concerning Heisenberg's "gamma ray microscope", a thought experiment, which is intimately connected with the historical development of quantum mechanics (QM), and also with the most disputed interpretations of quantum theory. In this study: (a) we investigate how philosophers of science read and…

  18. A matrix model for strings beyond the c=1 barrier: the spin-s Heisenberg model on random surfaces

    CERN Document Server

    Ambjorn, J; Sedrakyan, A

    2014-01-01

    We consider a spin-s Heisenberg model coupled to two-dimensional quantum gravity. We quantize the model using the Feynman path integral, summing over all possible two-dimensional geometries and spin configurations. We regularize this path integral by starting with the R-matrices defining the spin-s Heisenberg model on a regular 2d Manhattan lattice. 2d quantum gravity is included by defining the R-matrices on random Manhattan lattices and summing over these, in the same way as one sums over 2d geometries using random triangulations in non-critical string theory. We formulate a random matrix model where the partition function reproduces the annealed average of the spin-s Heisenberg model over all random Manhattan lattices. A technique is presented which reduces the random matrix integration in partition function to an integration over their eigenvalues.

  19. Two-dimensional transition metal dichalcogenides with a hexagonal lattice: Room-temperature quantum spin Hall insulators

    Science.gov (United States)

    Ma, Yandong; Kou, Liangzhi; Li, Xiao; Dai, Ying; Heine, Thomas

    2016-01-01

    So far, several transition metal dichalcogenide (TMDC)-based two-dimensional (2D) topological insulators (TIs) have been discovered, all of them based on a tetragonal lattice. However, in 2D crystals, the hexagonal rather than the tetragonal symmetry is the most common motif. Here, based on first principles calculations, we propose a class of stable 2D TMDCs of composition MX2(M =Mo ,W ;X =S ,Se ,Te ) with a hexagonal lattice. They are all in the same stability range as other 2D TMDC allotropes that have been demonstrated experimentally, and they are identified to be practical 2D TIs with large band gaps ranging from 41 to 198 meV, making them suitable for applications at room temperature. Besides, in contrast to tetragonal 2D TMDCs, their hexagonal lattice will greatly facilitate the integration of theses novel TI state van der Waals crystals with other hexagonal or honeycomb materials and thus provide a route for 2D material-based devices for wider nanoelectronic and spintronic applications. The nontrivial band gaps of both WS e2 and WT e2 2D crystals are 198 meV, which are larger than that in any previously reported TMDC-based TIs. These large band gaps entirely stem from the strong spin orbit coupling strength within the d orbitals of Mo/W atoms near the Fermi level. Our findings broaden the scientific and technological impact of both 2D TIs and TMDCs.

  20. Extracting trajectory equations of classical periodic orbits from the quantum eigenmodes in two-dimensional integrable billiards

    Science.gov (United States)

    Hsieh, Y. H.; Yu, Y. T.; Tuan, P. H.; Tung, J. C.; Huang, K. F.; Chen, Y. F.

    2017-02-01

    The trajectory equations for classical periodic orbits in the equilateral-triangular and circular billiards are systematically extracted from quantum stationary coherent states. The relationship between the phase factors of quantum stationary coherent states and the initial positions of classical periodic orbits is analytically derived. In addition, the stationary coherent states with noncoprime parametric numbers are shown to correspond to the multiple periodic orbits, which cannot be explicable in the one-particle picture. The stationary coherent states are further verified to be linked to the resonant modes that are generally observed in the experimental wave system excited by a localized and unidirectional source. The excellent agreement between the resonant modes and the stationary coherent states not only manifests the importance of classical features in experimental systems but also paves the way to manipulate the mesoscopic wave functions localized on the periodic orbits for applications.

  1. 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.

  2. Mid-Infrared Pulse Shaping and Two-Dimensional Spectroscopy of Open Quantum Systems in Liquid Solution

    Science.gov (United States)

    Ross, Matthew R.

    The primary focus of this work is the development of a mid-infrared pulse shaping system. The primary motivation for this system is for two-dimensional infrared (2DIR) spectroscopy, however, the mid-infrared pulse shaper also allows for more sophisticated spectroscopic experiments not previously attempted in the mid-infrared. Moreover, many can be implemented without changes or realignment of the optical setup. Example spectra are presented along with a discussion of capabilities and diagnostics. A second major project presented is 2DIR spectroscopy of iron pentacarbonyl, Fe(CO)5, a small metal carbonyl. This molecule undergoes Berry pseudorotation, a form of fluxtionality. This fast exchange of ligands mixes axial and equatorial modes and occurs on a timescale of picoseconds, too fast for NMR and other methods of measuring chemical structure and isomerization. Ultrafast chemical exchange spectroscopy, a measurement within 2DIR spectroscopy, is capable of resolving the time scales of this motion. We found that this process is affected by the solvent environment, specifically the solvent viscosity in alkanes and hydrogen bonding environments in alcohols. Lastly, a study is presented in which a series of synthetic metalloenzymes with a metal active site are studied by 2DIR spectroscopy. In this case a carbonyl is ligated to a copper-I atom in the active site, which then serves as our spectroscopic probe. We find, unexpectedly, that the shape of the carbonyl vibrational potential, as measured by the anharmonicity, is time-dependent. We attribute this to a geometrical rearrangement and are able to suggest that this effect is dependent on local site structure and dynamics and not significantly affected by electric potential near the peptide.

  3. Engineered two-dimensional Ising interactions in a trapped-ion quantum simulator with hundreds of spins

    CSIR Research Space (South Africa)

    Britton, JW

    2012-04-01

    Full Text Available apparatus, laser-cooled 9Be+ ions natu- rally form a stable 2D Coulomb crystal on a triangular lattice with 300 spins (Fig. 1). Each ion is spin-1/2 system (qubit) over which we exert high fidelity quantum control [26]. In this paper we demonstrate... as a function of the electric field intensity IR = ceo 2 jELj 2 = ceo2 jEU j 2 at the cen- ter of the laser beams. For qR = 4:8 and IR = 1 W/cm2 , Fo = 1:4 10 23 N. Stronger forces can be generated after experimental mod- ification to our...

  4. The Two-Dimensional MnO2/Graphene Interface: Half-metallicity and Quantum Anomalous Hall State

    KAUST Repository

    Gan, Liyong

    2015-10-07

    We explore the electronic properties of the MnO2/graphene interface by first-principles calculations, showing that MnO2 becomes half-metallic. MnO2 in the MnO2/graphene/MnO2 system provides time-reversal and inversion symmetry breaking. Spin splitting by proximity occurs at the Dirac points and a topologically nontrivial band gap is opened, enabling a quantum anomalous Hall state. The half-metallicity, spin splitting, and size of the band gap depend on the interfacial interaction, which can be tuned by strain engineering.

  5. Critical and reentrant behavior of the spin quantum 1/2 anisotropic Heisenberg antiferromagnet model with Dzyaloshinskii–Moriya interaction in a longitudinal magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Parente, Walter E.F.; Pacobahyba, J.T.M.; Araújo, Ijanílio G. [Departamento de Física, Universidade Federal de Roraima, BR 174, Km 12. Bairro Monte Cristo. CEP: 69300-000 Boa Vista, Roraima (Brazil); Neto, Minos A., E-mail: minos@pq.cnpq.br [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000, Manaus-AM (Brazil); Ricardo de Sousa, J. [Universidade Federal do Amazonas, Departamento de Física, 3000, Japiim, 69077-000, Manaus-AM (Brazil); National Institute of Science and Technology for Complex Systems, 3000, Japiim, 69077-000, Manaus-AM (Brazil); Akinci, Ümit [Department of Physics, Dokuz Eylül University, Tr-35160 Izmir (Turkey)

    2014-04-15

    In this paper we study the quantum spin-1/2 anisotropic Heisenberg antiferromagnet model in the presence of a Dzyaloshinskii–Moriya interaction (D) and a uniform longitudinal (H) magnetic field. Using the effective-field theory with a finite cluster N=2 spin (EFT-2) we calculate the phase diagrams in the H−T and D−T planes on a simple cubic lattice (z=6). We have only observed second order phase transitions for values between Δ∈[0,1], where the cases were analysed: Ising (Δ=1), anisotropic Heisenberg (Δ=0.6) and isotropic Heisenberg (Δ=0). - Highlights: • Anisotropic Heisenberg antiferromagnet on a simple cubic lattice. • Effective-field theory. • Dzyaloshinskii–Moriya interaction.

  6. Noncommutative perturbative quantum field theory: Wilson loop in two-dimensional Yang-Mills, and unitarity from string theory

    Science.gov (United States)

    Torrielli, Alessandro

    2003-01-01

    The results of our research on noncommutative perturbative quantum field theory and its relation to string theory are exposed with details. 1) We give an introduction to noncommutative quantum field theory and its derivation from open string theory in an antisymmetric background. 2) We perform a perturbative Wilson loop calculation for 2D NCYM. We compare the LCG results for the WML and the PV prescription. With WML the loop is well-defined and regular in the commutative limit. With PV the result is singular. This is intriguing: in the commutative theory their difference is related to topological excitations, moreover PV provides a point-like potential. 3) Commutative 2D YM exhibits an interplay between geometrical and U(N) gauge properties: in the exact expression of a Wilson loop with n windings a scaling intertwines n and N. In the NC case the interplay becomes tighter due to the merging of space-time and ``internal'' symmetries. Surprisingly, in our up to O(g^6) (and beyond) crossed graphs calculations the scaling we mentioned occurs for large n, N and theta. 4) We discuss the breakdown of perturbative unitarity of noncommutative electric-type QFT in the light of strings. We consider the analytic structure of string loop two-point functions suitably continuing them off-shell, and then study the Seiberg-Witten limit. In this way we pick up how the unphysical tachyonic branch cut appears in the NC field theory.

  7. Noncommutative perturbative quantum field theory Wilson loop in two-dimensional Yang-Mills, and unitarity from string theory

    CERN Document Server

    Torrielli, A

    2003-01-01

    The results of our research on noncommutative perturbative quantum field theory and its relation to string theory are exposed with details. 1) We give an introduction to noncommutative quantum field theory and its derivation from open string theory in an antisymmetric background. 2) We perform a perturbative Wilson loop calculation for 2D NCYM. We compare the LCG results for the WML and the PV prescription. With WML the loop is well-defined and regular in the commutative limit. With PV the result is singular. This is intriguing: in the commutative theory their difference is related to topological excitations, moreover PV provides a point-like potential. 3) Commutative 2D YM exhibits an interplay between geometrical and U(N) gauge properties: in the exact expression of a Wilson loop with n windings a scaling intertwines n and N. In the NC case the interplay becomes tighter due to the merging of space-time and ``internal'' symmetries. Surprisingly, in our up to O(g^6) (and beyond) crossed graphs calculations th...

  8. Two-dimensional rectangular tantalum carbide halides TaCX (X = Cl, Br, I): novel large-gap quantum spin Hall insulators

    Science.gov (United States)

    Zhou, Liujiang; Shi, Wujun; Sun, Yan; Shao, Bin; Felser, Claudia; Yan, Binghai; Frauenheim, Thomas

    2016-09-01

    Quantum spin Hall (QSH) insulates exist in special two-dimensional (2D) semiconductors, possessing the quantized spin-Hall conductance that are topologically protected from backscattering. Based on the first-principles calculations, we predict a novel family of QSH insulators in 2D tantalum carbide halides TaCX (X = Cl, Br, and I) with unique rectangular lattice and large direct energy gaps. The mechanism for 2D QSH effect originates from an intrinsic d-d band inversion in the process of chemical bonding. Further, stain and intrinsic electric field can be used to tune the electronic structure and enhance the energy gap. TaCX nanoribbon, which has the single-Dirac-cone edge states crossing the bulk band gap, exhibits a linear dispersion with a high Fermi velocity comparable to that of graphene. These 2D materials with considerable nontrivial gaps promise great application potential in the new generation of dissipationless electronics and spintronics.

  9. O2- -to-F- substitution on the quasi-two-dimensional quantum antiferromagnet (CuCl)LaNb2O7

    Science.gov (United States)

    Tassel, C.; Kobayashi, Y.; Mitsuoka, S.; Takeiri, F.; Ajiro, Y.; Kageyama, H.

    2011-09-01

    We present the preparation of the electron-doped quasi-two dimensional quantum antiferromagnet (CuCl)LaNb2O7 by two step-wise topochemical reactions. The first step involves a reductive fluorination of the insulating layered perovskite RbLaNb2O7 using polytetrafluoroethylene that allows electric conduction in the perovskite blocks. The product RbLaNb2O6F was then ion-exchanged with copper dichloride to yield (CuCl)LaNb2O6F. The synchrotron x-ray diffraction study indicates that the structure of the final compound is different from that of the pure (CuCl)LaNb2O7.

  10. Exchange enhancement of the electron g-factor in a two-dimensional semimetal in HgTe quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Bovkun, L. S., E-mail: bovkun@ipmras.ru; Krishtopenko, S. S.; Zholudev, M. S.; Ikonnikov, A. V.; Spirin, K. E. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Dvoretsky, S. A.; Mikhailov, N. N. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation); Teppe, F.; Knap, W. [Universite Montpellier II, Laboratoire Charles Coulomb (L2C), UMR CNRS 5221, GIS-TERALAB (France); Gavrilenko, V. I. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2015-12-15

    The exchange enhancement of the electron g-factor in perpendicular magnetic fields to 12 T in HgTe/CdHgTe quantum wells 20 nm wide with a semimetal band structure is studied. The electron effective mass and g-factor at the Fermi level are determined by analyzing the temperature dependence of the amplitude of Shubnikov–de Haas oscillation in weak fields and near odd Landau-level filling factors ν ≤ 9. The experimental values are compared with theoretical calculations performed in the one-electron approximation using the eight-band kp Hamiltonian. The found dependence of g-factor enhancement on the electron concentration is explained by changes in the contributions of hole- and electron-like states to exchange corrections to the Landau-level energies in the conduction band.

  11. Finite-temperature scaling close to Ising-nematic quantum critical points in two-dimensional metals

    Science.gov (United States)

    Punk, Matthias

    2016-11-01

    We study finite-temperature properties of metals close to an Ising-nematic quantum critical point in two spatial dimensions. In particular we show that at any finite temperature there is a regime where order parameter fluctuations are characterized by a dynamical critical exponent z =2 , in contrast to z =3 found at zero temperature. Our results are based on a simple Eliashberg-type approach, which gives rise to a boson self-energy proportional to Ω /γ (T ) at small momenta, where γ (T ) is the temperature dependent fermion scattering rate. These findings might shed some light on recent Monte Carlo simulations at finite temperature, where results consistent with z =2 were found.

  12. 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

  13. Heisenberg's wave packet reconsidered

    OpenAIRE

    Grabbe, J. Orlin

    2005-01-01

    This note shows that Heisenberg's choice for a wave function in his original paper on the uncertainty principle is simply a renormalized characteristic function of a stable distribution with certain restrictions on the parameters. Relaxing Heisenberg's restrictions leads to a more general formulation of the uncertainty principle. This reformulation shows quantum uncertainty can exist at a macroscopic level. These modifications also give rise to a new form of Schrodinger's wave equation as the...

  14. Magneto-thermoelectric effects in the two-dimensional electron gas of a HgTe quantum well due to THz laser heating by cyclotron resonance absorption

    Science.gov (United States)

    Pakmehr, Mehdi; Bruene, Christoph; Buhmann, Hartmut; Molenkamp, Laurens; McCombe, Bruce

    2015-03-01

    HgTe quantum wells (QWs) have shown a number of interesting phenomena over the past 20 years, most recently the first two-dimensional topological insulating state. We have studied thermoelectric photovoltages of 2D electrons in a 6.1 nm wide HgTe quantum well induced by cyclotron resonance absorption (B = 2 - 5 T) of a focused THz laser beam. We have estimated thermo-power coefficients by detailed analysis of the beam profile at the sample surface and the photovoltage signals developed across various contacts of a large Hall bar structure at a bath temperature of 1.6 K. We obtain reasonable values of the magneto-thermopower coefficients. Work at UB was supported by NSF DMR 1008138 and the Office of the Provost, and at the University of Wuerzburg by DARPA MESO Contract N6601-11-1-4105, by DFG Grant HA5893/4-1 within SPP 1666 and the Leibnitz Program, and the EU ERC-AG Program (Project 3-TOP.

  15. Fano resonance in the nonadiabatically pumped shot noise of a time-dependent quantum well in a two-dimensional electron gas and graphene

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Rui, E-mail: rzhu@scut.edu.cn; Dai, Jiao-Hua [Department of Physics, South China University of Technology, Guangzhou 510641 (China); Guo, Yong [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)

    2015-04-28

    Interference between different quantum paths can generate Fano resonance. One of the examples is transport through a quasibound state driven by a time-dependent scattering potential. Previously it is found that Fano resonance occurs as a result of energy matching in one-dimensional systems. In this work, we demonstrate that when transverse motion is present, Fano resonance occurs precisely at the wavevector matching situation. Using the Floquet scattering theory, we considered the transport properties of a nonadiabatic time-dependent well both in a two-dimensional electron gas and monolayer graphene structure. Dispersion of the quasibound state of a static quantum well is obtained with transverse motion present. We found that Fano resonance occurs when the wavevector in the transport direction of one of the Floquet sidebands is exactly identical to that of the quasibound state in the well at equilibrium and follows the dispersion pattern of the latter. To observe the Fano resonance phenomenon in the transmission spectrum, we also considered the pumped shot noise properties when time and spatial symmetry secures vanishing current in the considered configuration. Prominent Fano resonance is found in the differential pumped shot noise with respect to the reservoir Fermi energy.

  16. Proton transfer through hydrogen bonds in two-dimensional water layers: A theoretical study based on ab initio and quantum-classical simulations

    Energy Technology Data Exchange (ETDEWEB)

    Bankura, Arindam; Chandra, Amalendu, E-mail: amalen@iitk.ac.in [Department of Chemistry, Indian Institute of Technology, Kanpur 208016 (India)

    2015-01-28

    The dynamics of proton transfer (PT) through hydrogen bonds in a two-dimensional water layer confined between two graphene sheets at room temperature are investigated through ab initio and quantum-classical simulations. The excess proton is found to be mostly solvated as an Eigen cation where the hydronium ion donates three hydrogen bonds to the neighboring water molecules. In the solvation shell of the hydronium ion, the three coordinated water molecules with two donor hydrogen bonds are found to be properly presolvated to accept a proton. Although no hydrogen bond needs to be broken for transfer of a proton to such presolvated water molecules from the hydronium ion, the PT rate is still found to be not as fast as it is for one-dimensional chains. Here, the PT is slowed down as the probability of finding a water with two donor hydrogen bonds in the solvation shell of the hydronium ion is found to be only 25%-30%. The hydroxide ion is found to be solvated mainly as a complex anion where it accepts four H-bonds through its oxygen atom and the hydrogen atom of the hydroxide ion remains free all the time. Here, the presolvation of the hydroxide ion to accept a proton requires that one of its hydrogen bonds is broken and the proton comes from a neighboring water molecule with two acceptor and one donor hydrogen bonds. The coordination number reduction by breaking of a hydrogen bond is a slow process, and also the population of water molecules with two acceptor and one donor hydrogen bonds is only 20%-25% of the total number of water molecules. All these factors together tend to slow down the hydroxide ion migration rate in two-dimensional water layers compared to that in three-dimensional bulk water.

  17. Proton transfer through hydrogen bonds in two-dimensional water layers: A theoretical study based on ab initio and quantum-classical simulations

    Science.gov (United States)

    Bankura, Arindam; Chandra, Amalendu

    2015-01-01

    The dynamics of proton transfer (PT) through hydrogen bonds in a two-dimensional water layer confined between two graphene sheets at room temperature are investigated through ab initio and quantum-classical simulations. The excess proton is found to be mostly solvated as an Eigen cation where the hydronium ion donates three hydrogen bonds to the neighboring water molecules. In the solvation shell of the hydronium ion, the three coordinated water molecules with two donor hydrogen bonds are found to be properly presolvated to accept a proton. Although no hydrogen bond needs to be broken for transfer of a proton to such presolvated water molecules from the hydronium ion, the PT rate is still found to be not as fast as it is for one-dimensional chains. Here, the PT is slowed down as the probability of finding a water with two donor hydrogen bonds in the solvation shell of the hydronium ion is found to be only 25%-30%. The hydroxide ion is found to be solvated mainly as a complex anion where it accepts four H-bonds through its oxygen atom and the hydrogen atom of the hydroxide ion remains free all the time. Here, the presolvation of the hydroxide ion to accept a proton requires that one of its hydrogen bonds is broken and the proton comes from a neighboring water molecule with two acceptor and one donor hydrogen bonds. The coordination number reduction by breaking of a hydrogen bond is a slow process, and also the population of water molecules with two acceptor and one donor hydrogen bonds is only 20%-25% of the total number of water molecules. All these factors together tend to slow down the hydroxide ion migration rate in two-dimensional water layers compared to that in three-dimensional bulk water.

  18. Quantum features in the spin dynamics of S=1/2 and 1 Heisenberg antiferromagnets in spite of long-range ordered phases

    DEFF Research Database (Denmark)

    Enderle, M.; Kiefer, K.; Klopperpieper, A.;

    2000-01-01

    Uniform S = 1 and 1/2 Heisenberg antiferromagnetic chains have a quantum singlet ground state which is an eigenstate of the total spin with S(tot) = 0. However, the 'internal' order of these ground states is quite different, and is reflected in gapless excitations in the S = 1/2 state, while the S...

  19. Quantum integrability and supersymmetric vacua

    OpenAIRE

    Nekrasov, Nikita A.; Shatashvili, Samson L.

    2009-01-01

    This is an announcement of some of the results of a longer paper where the supersymmetric vacua of two dimensional N=2 susy gauge theories with matter are shown to be in one-to-one correspondence with the eigenstates of integrable spin chain Hamiltonians. The correspondence between the Heisenberg spin chain and the two dimensional U(N) theory with fundamental hypermultiplets is reviewed in detail. We demonstrate the isomorphism of the equivariant quantum cohomology of the cotangent bundle to ...

  20. Susceptibility of the 2D spin-1 / 2 Heisenberg antiferromagnet with an impurity.

    Science.gov (United States)

    Höglund, Kaj H; Sandvik, Anders W

    2003-08-15

    We use a quantum Monte Carlo method (stochastic series expansion) to study the effects of a magnetic or nonmagnetic impurity on the magnetic susceptibility of the two-dimensional Heisenberg antiferromagnet. At low temperatures, we find a log-divergent contribution to the transverse susceptibility. We also introduce an effective few-spin model that can quantitatively capture the differences between magnetic and nonmagnetic impurities at high and intermediate temperatures.

  1. Quantum chaos for two-dimensional Sinai billiard%二维Sinai台球系统的量子混沌研究

    Institute of Scientific and Technical Information of China (English)

    秦陈陈; 杨双波

    2014-01-01

    We study the classical and quantum correspondence for a two-dimensional Sinai billiard system. By using the Stationary state expansion method and Gutzwiller’s periodic orbit theory, we analyze the quantum length spectrum obtained through the Fourier transformation of the quantum density of state for the Sinai billiard system, and by comparing the peak position with the length of the classical periodic orbit we find their excellent correspondence. We observe that some quantum states are localized near some short period orbits, forming the quantum scarred states or superscarred states. In this paper we also investigate the nearest-neighbor spacing distribution of levels for both concentric and nonconcentric Sinai billiard systems, and find that the concentric Sinai billiard system is nearintegrable, and for the nonconcentric Sinai billiard system withϑ=3π/8 its nearest-neighbor spacing distribution of levels transits from nearintegrable to the Wigner distribution as the distance between the two centers increases.%研究了二维Sinai台球系统的经典与量子的对应关系,运用定态展开法和Gutzwiller的周期轨道理论对Sinai台球系统的态密度经傅里叶变换得到的量子长度谱进行分析,并把量子长度谱中峰的位置与其所对应的经典体系的周期轨道长度做对比,发现两者之间存在很好的对应关系。观察到了一些量子态局域在短周期轨道附近形成量子scarred态或量子superscarred态。还研究了同心与非同心Sinai台球系统的能级最近邻间距分布,发现同心Sinai台球系统是近可积的,非同心Sinai台球系统在θ=3π/8下,随两中心间距离的增加,能级最近邻间距分布将由近可积向维格那分布过渡。

  2. Minimal length uncertainty relation and gravitational quantum well

    NARCIS (Netherlands)

    Brau, F.; Buisseret, F.

    2006-01-01

    The dynamics of a particle in a gravitational quantum well is studied in the context of nonrelativistic quantum mechanics with a particular deformation of a two-dimensional Heisenberg algebra. This deformation yields a new short-distance structure characterized by a finite minimal uncertainty in pos

  3. 大粒子数二维硬核玻色子系统的量子蒙特卡罗模拟%Simulation of two-dimensional many-particle hardcore bosons by using the quantum Monte Carlo method

    Institute of Scientific and Technical Information of China (English)

    许莹; 李晋斌

    2012-01-01

    采用随机级数展开的量子蒙特卡罗方法研究二维硬核的玻色-赫伯德模型的热力学性质.首先通过算符变换将模型映射成为二维反铁磁准海森伯模型.变换后的模型比通常的海森伯模型多一项,该项正比于系统的格点总数N,对于大粒子数的系统,该项使模拟耗时指数增加,所以难以计算大粒子数系统.采用非局域操作循环更新后,这个困难可以得到很好的解决,可使粒子数总数增大到几千个.研究结果表明,粒子数密度在0—0.5范围内增大时,能量呈递减趋势,并趋于某一定值,随着正方晶格系统尺度增大,能量也随之增大;正方晶格系统尺度一定时,能量和磁化强度随着温度的升高而增大,化学势的变化对能量和磁化强度没有影响,能量随着正方晶格系统尺度增大而增大,磁化强度却随之减小;正方晶格系统尺度一定时,化学势的增大对比热没有影响,随着温度的升高比热出现先增大后减小的趋势,最后趋于某个值,达到平衡,而正方晶格系统尺度越大,比热曲线增大部分的趋势越大,减小部分的趋势也更明显,参照朗道超流理论,本文模拟的能量和比热曲线趋势与朗道二流体模型下HeⅡ的理论研究一致;不同正方晶格系统尺度的影响不大,均匀磁化率倒数在0—0.5(J/k_B)的低温范围内有很小的波动,J为耦合能,k_B为玻尔兹曼常数,温度在0.5—2(J/k_B)的范围内,均匀磁化率的倒数随着温度的升高而增大,且曲线的趋势显示了一种类似近藤行为.%In this paper,the stochastic series expansion quantum Monte Carlo method is employed to investigate the thermodynamic properties of hardcore Bose-Hubbard model in two-dimensional space.The two-dimensional hardcore Bose-Hubbard model can be mapped into the two-dimensional antiferromagnetic quasi-Heisenberg model under transform of bosonic operators.There is an additional term which is proportional

  4. Field-induced quantum criticality and universal temperature dependence of the magnetization of a spin-1/2 heisenberg chain.

    Science.gov (United States)

    Kono, Y; Sakakibara, T; Aoyama, C P; Hotta, C; Turnbull, M M; Landee, C P; Takano, Y

    2015-01-23

    High-precision dc magnetization measurements have been made on Cu(C4H4N2) (NO3)2 in magnetic fields up to 14.7 T, slightly above the saturation field Hs=13.97  T, in the temperature range from 0.08 to 15 K. The magnetization curve and differential susceptibility at the lowest temperature show excellent agreement with exact theoretical results for the spin-1/2 Heisenberg antiferromagnet in one dimension. A broad peak is observed in magnetization measured as a function of temperature, signaling a crossover to a low-temperature Tomonaga-Luttinger-liquid regime. With an increasing field, the peak moves gradually to lower temperatures, compressing the regime, and, at Hs, the magnetization exhibits a strong upturn. This quantum critical behavior of the magnetization and that of the specific heat withstand quantitative tests against theory, demonstrating that the material is a practically perfect one-dimensional spin-1/2 Heisenberg antiferromagnet.

  5. Influence of Intrinsic Decoherence on Entanglement in Two-Qubit Quantum Heisenberg XYZ Chain

    Institute of Scientific and Technical Information of China (English)

    SHAO Bin; ZENG Tian-Hai; ZOU Jian

    2005-01-01

    Taking the intrinsic decoherence effect into account, we investigate the time evolution of entanglement for two-qubit XYZ Heisenberg model in an external uniform magnetic field. Concurrence, the measurement of entanglement,is calculated. We show how the intrinsic decoherence modifies the time evolution of the entanglement and find that at short-time case, concurrence is oscillating as increasing magnetic field, which implies that entanglement may be enhanced or weakened in some time regions.

  6. Spin dynamics in high-mobility two-dimensional electron systems embedded in GaAs/AlGaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Griesbeck, Michael

    2012-11-22

    Since many years there has been great effort to explore the spin dynamics in low-dimensional electron systems embedded in GaAs/AlGaAs based heterostructures for the purpose of quantum computation and spintronics applications. Advances in technology allow for the design of high quality and well-defined two-dimensional electron systems (2DES), which are perfectly suited for the study of the underlying physics that govern the dynamics of the electron spin system. In this work, spin dynamics in high-mobility 2DES is studied by means of the all-optical time-resolved Kerr/Faraday rotation technique. In (001)-grown 2DES, a strong in-plane spin dephasing anisotropy is studied, resulting from the interference of comparable Rashba and Dresselhaus contributions to the spin-orbit field (SOF). The dependence of this anisotropy on parameters like the confinement length of the 2DES, the sample temperature, as well as the electron density is demonstrated. Furthermore, coherent spin dynamics of an ensemble of ballistically moving electrons is studied without and within an applied weak magnetic field perpendicular to the sample plane, which forces the electrons to move on cyclotron orbits. Finally, strongly anisotropic spin dynamics is investigated in symmetric (110)-grown 2DES, using the resonant spin amplification method. Here, extremely long out-of-plane spin dephasing times can be achieved, in consequence of the special symmetry of the Dresselhaus SOF.

  7. Quasi-two-dimensional Bose-Einstein condensation of spin triplets in the dimerized quantum magnet Ba2CuSi2O6Cl2

    Science.gov (United States)

    Okada, Makiko; Tanaka, Hidekazu; Kurita, Nobuyuki; Johmoto, Kohei; Uekusa, Hidehiro; Miyake, Atsushi; Tokunaga, Masashi; Nishimoto, Satoshi; Nakamura, Masaaki; Jaime, Marcelo; Radtke, Guillaume; Saúl, Andrés

    2016-09-01

    We synthesized single crystals of composition Ba2CuSi2O6Cl2 and investigated their quantum magnetic properties. The crystal structure is closely related to that of the quasi-two-dimensional (2D) dimerized magnet BaCuSi2O6 also known as Han purple. Ba2CuSi2O6Cl2 has a singlet ground state with an excitation gap of Δ /kB=20.8 K. The magnetization curves for two different field directions almost perfectly coincide when normalized by the g factor except for a small jump anomaly for a magnetic field perpendicular to the c axis. The magnetization curve with a nonlinear slope above the critical field is in excellent agreement with exact-diagonalization calculations based on a 2D coupled spin-dimer model. Individual exchange constants are also evaluated using density functional theory (DFT). The DFT results demonstrate a 2D exchange network and weak frustration between interdimer exchange interactions, supported by weak spin-lattice coupling implied from our magnetostriction data. The magnetic-field-induced spin ordering in Ba2CuSi2O6Cl2 is described as the quasi-2D Bose-Einstein condensation of triplets.

  8. Quantum soliton in 1D Heisenberg spin chains with Dzyaloshinsky-Moriya and next-nearest-neighbor interactions

    Science.gov (United States)

    Djoufack, Z. I.; Tala-Tebue, E.; Nguenang, J. P.; Kenfack-Jiotsa, A.

    2016-10-01

    We report in this work, an analytical study of quantum soliton in 1D Heisenberg spin chains with Dzyaloshinsky-Moriya Interaction (DMI) and Next-Nearest-Neighbor Interactions (NNNI). By means of the time-dependent Hartree approximation and the semi-discrete multiple-scale method, the equation of motion for the single-boson wave function is reduced to the nonlinear Schrödinger equation. It comes from this present study that the spectrum of the frequencies increases, its periodicity changes, in the presence of NNNI. The antisymmetric feature of the DMI was probed from the dispersion curve while changing the sign of the parameter controlling it. Five regions were identified in the dispersion spectrum, when the NNNI are taken into account instead of three as in the opposite case. In each of these regions, the quantum model can exhibit quantum stationary localized and stable bright or dark soliton solutions. In each region, we could set up quantum localized n-boson Hartree states as well as the analytical expression of their energy level, respectively. The accuracy of the analytical studies is confirmed by the excellent agreement with the numerical calculations, and it certifies the stability of the stationary quantum localized solitons solutions exhibited in each region. In addition, we found that the intensity of the localization of quantum localized n-boson Hartree states increases when the NNNI are considered. We also realized that the intensity of Hartree n-boson states corresponding to quantum discrete soliton states depend on the wave vector.

  9. Plaquette ordered phase and quantum phase diagram in the spin-1/2 J(1)-J(2) square Heisenberg model.

    Science.gov (United States)

    Gong, Shou-Shu; Zhu, Wei; Sheng, D N; Motrunich, Olexei I; Fisher, Matthew P A

    2014-07-11

    We study the spin-1/2 Heisenberg model on the square lattice with first- and second-neighbor antiferromagnetic interactions J(1) and J(2), which possesses a nonmagnetic region that has been debated for many years and might realize the interesting Z(2) spin liquid. We use the density matrix renormalization group approach with explicit implementation of SU(2) spin rotation symmetry and study the model accurately on open cylinders with different boundary conditions. With increasing J(2), we find a Néel phase and a plaquette valence-bond (PVB) phase with a finite spin gap. From the finite-size scaling of the magnetic order parameter, we estimate that the Néel order vanishes at J(2)/J(1)≃0.44. For 0.5two-dimensional limit. The dimer-dimer correlations reveal the s-wave character of the PVB order. For 0.44

  10. Bond Operator Mean Field Approach to the Magnetization Plateaux in Quantum Antiferromagnets —Application to the S=1/2 Coupled Dimerized Zigzag Heisenberg Chains—

    Science.gov (United States)

    Hida, Kazuo; Shiino, Masaru; Chen, Wei

    2004-06-01

    The magnetization plateaux in two dimensionally coupled S=1/2 dimerized zigzag Heisenberg chains are investigated by means of the bond operator mean field approximation. In the absence of the interchain coupling, this model is known to have a plateau at half of the saturation magnetization accompanied by the spontaneous translational symmetry breakdown. The parameter regime in which the plateau appears is reproduced well within the present approximation. In the presence of the interchain coupling, this plateau is shown to be suppressed. This result is also supported by the numerical diagonalization calculation.

  11. Origin of the anomalies the modified Heisenberg equation

    CERN Document Server

    Estève, J G

    2002-01-01

    The origin of the anomalies is analyzed. It is shown that they are due to the fact that the generators of the symmetry do not leave invariant the domain of definition of the Hamiltonian and then a term, normally forgotten in the Heisenberg equation, gives an extra contribution responsible for the non conservation of the charges. This explanation is equivalent to that of the Fujikawa in the path integral formalism. Finally, this approach is applied to the conformal symmetry breaking in two-dimensional quantum mechanics.

  12. Knight shifts around vacancies in the 2D Heisenberg model.

    Science.gov (United States)

    Anfuso, Fabrizio; Eggert, Sebastian

    2006-01-13

    The local response to a uniform field around vacancies in the two-dimensional spin-1/2 Heisenberg antiferromagnet is determined by numerical quantum Monte Carlo simulations as a function of temperature. It is possible to separate the Knight shifts into uniform and staggered contributions on the lattice which are analyzed and understood in detail. The contributions show interesting long- and short-range behavior that may be of relevance in NMR and susceptibility measurements. For more than one impurity, remarkable nonlinear enhancement and cancellation effects take place. We predict that the Curie impurity susceptibility will be observable for a random impurity concentration even in the thermodynamic limit.

  13. Classifying and assembling two-dimensional X-ray laser diffraction patterns of a single particle to reconstruct the three-dimensional diffraction intensity function: resolution limit due to the quantum noise

    Science.gov (United States)

    Tokuhisa, Atsushi; Taka, Junichiro; Kono, Hidetoshi; Go, Nobuhiro

    2012-01-01

    A new two-step algorithm is developed for reconstructing the three-dimensional diffraction intensity of a globular biological macromolecule from many experimentally measured quantum-noise-limited two-dimensional X-ray laser diffraction patterns, each for an unknown orientation. The first step is classification of the two-dimensional patterns into groups according to the similarity of direction of the incident X-rays with respect to the molecule and an averaging within each group to reduce the noise. The second step is detection of common intersecting circles between the signal-enhanced two-dimensional patterns to identify their mutual location in the three-dimensional wavenumber space. The newly developed algorithm enables one to detect a signal for classification in noisy experimental photon-count data with as low as ∼0.1 photons per effective pixel. The wavenumber of such a limiting pixel determines the attainable structural resolution. From this fact, the resolution limit due to the quantum noise attainable by this new method of analysis as well as two important experimental parameters, the number of two-dimensional patterns to be measured (the load for the detector) and the number of pairs of two-dimensional patterns to be analysed (the load for the computer), are derived as a function of the incident X-ray intensity and quantities characterizing the target molecule. PMID:22514069

  14. Frustrated diamond-chain quantum XXZ Heisenberg antiferromagnet in a magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Richter, Johannes, E-mail: Johannes.Richter@Physik.Uni-Magdeburg.DE [Institut für theoretische Physik, Otto-von-Guericke-Universität Magdeburg, P.O. Box 4120, D-39016 Magdeburg (Germany); Krupnitska, Olesia [Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, L' viv-11, 79011 (Ukraine); Krokhmalskii, Taras [Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, L' viv-11, 79011 (Ukraine); Department for Theoretical Physics, Ivan Franko National University of L' viv, 12 Drahomanov Street, L' viv-5, 79005 (Ukraine); Derzhko, Oleg [Institut für theoretische Physik, Otto-von-Guericke-Universität Magdeburg, P.O. Box 4120, D-39016 Magdeburg (Germany); Institute for Condensed Matter Physics, National Academy of Sciences of Ukraine, 1 Svientsitskii Street, L' viv-11, 79011 (Ukraine); Department for Theoretical Physics, Ivan Franko National University of L' viv, 12 Drahomanov Street, L' viv-5, 79005 (Ukraine); Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, I-34151 Trieste (Italy)

    2015-04-01

    We consider the antiferromagnetic spin-1/2 XXZ Heisenberg model on a frustrated diamond-chain lattice in a z- or x-aligned external magnetic field. We use the strong-coupling approach to elaborate an effective description in the low-temperature strong-field regime. The obtained effective models are spin-1/2 XY chains which are exactly solvable through the Jordan–Wigner fermionization. We perform exact-diagonalization studies of the magnetization curves to test the quality of the effective description. The results may have relevance for the description of the azurite spin-chain compound.

  15. Quantum simulating the frustrated Heisenberg model in a molecular dipolar crystal

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Yan-Li, E-mail: ylzhou@nudt.edu.cn [College of Science, National University of Defense Technology, 410073 Changsha (China); Ou, Bao-Quan [College of Science, National University of Defense Technology, 410073 Changsha (China); Wu, Wei [College of Science, National University of Defense Technology, 410073 Changsha (China); State Key Laboratory of High Performance Computing, National University of Defense Technology, 410073 Changsha (China)

    2015-10-23

    We study the simulation of spin models with polar molecules in a dipolar crystal. We employ a master equation approach to describe the dynamics of the system and to research the dissipation of the model. The reduced dynamics of the polar molecules lead to frustrated Heisenberg models with tuneable long-range interactions, via spin-dependent dipole–dipole interactions forces to the lattice vibrations. The influence of the lattice vibrations is calculated and analyzed in detail. - Highlights: • We simulate spin models with polar molecules in a dipolar crystal. • We employ a master equation to describe the dynamics of the system. • The influence of the lattice vibrations is calculated.

  16. Anisotropic Heisenberg model on hierarchical lattices with aperiodic interactions: a renormalization-group approach.

    Science.gov (United States)

    Branco, N S; de Sousa, J Ricardo; Ghosh, Angsula

    2008-03-01

    Using a real-space renormalization-group approximation, we study the anisotropic quantum Heisenberg model on hierarchical lattices, with interactions following aperiodic sequences. Three different sequences are considered, with relevant and irrelevant fluctuations, according to the Luck-Harris criterion. The phase diagram is discussed as a function of the anisotropy parameter Delta (such that Delta=0 and 1 correspond to the isotropic Heisenberg and Ising models, respectively). We find three different types of phase diagrams, with general characteristics: the isotropic Heisenberg plane is always an invariant one (as expected by symmetry arguments) and the critical behavior of the anisotropic Heisenberg model is governed by fixed points on the Ising-model plane. Our results for the isotropic Heisenberg model show that the relevance or irrelevance of aperiodic models, when compared to their uniform counterpart, is as predicted by the Harris-Luck criterion. A low-temperature renormalization-group procedure was applied to the classical isotropic Heisenberg model in two-dimensional hierarchical lattices: the relevance criterion is obtained, again in accordance with the Harris-Luck criterion.

  17. Quantum phase transition, universality, and scaling behaviors in the spin-1/2 Heisenberg model with ferromagnetic and antiferromagnetic competing interactions on a honeycomb lattice.

    Science.gov (United States)

    Huang, Yi-Zhen; Xi, Bin; Chen, Xi; Li, Wei; Wang, Zheng-Chuan; Su, Gang

    2016-06-01

    The quantum phase transition, scaling behaviors, and thermodynamics in the spin-1/2 quantum Heisenberg model with antiferromagnetic coupling J>0 in the armchair direction and ferromagnetic interaction J^{'}Heisenberg O(3) universality. A zero magnetization plateau is observed in the dimerized phase, whose width decreases with increasing α. A phase diagram in the coupling ratio α-magnetic field h plane is obtained, where four phases, including dimerized, stripe, canted stripe, and polarized, are identified. It is also unveiled that the temperature dependence of the specific heat C(T) for different α's intersects precisely at one point, similar to that of liquid ^{3}He under different pressures and several magnetic compounds under various magnetic fields. The scaling behaviors of Q_{2}, ρ, and C(T) are carefully analyzed. The susceptibility is compared with the experimental data to give the magnetic parameters of both compounds.

  18. Antiferromagnetic Heisenberg model on the icosahedron: influence of connectivity and the transition from the classical to the quantum limit.

    Science.gov (United States)

    Konstantinidis, N P

    2015-02-25

    The antiferromagnetic Heisenberg model on the icosahedron presents unconventional properties at the classical and quantum level, which originate in the frustrated nature of the interactions between the spins. Here we examine the importance of the connectivity of the icosahedron for the appearance of a magnetization discontinuity as a function of an external field which separates two families of lowest energy configurations. We also investigate the transition from the classical to the quantum limit. The influence of connectivity on the magnetic properties is revealed by considering the cluster as being made up of a closed strip of a triangular lattice with two additional spins attached. The classical magnetization discontinuity is shown to evolve continuously from the discontinuity effected by these two spins when they are uncoupled to the cluster. In the second part the transition from the classical to the quantum limit is examined by focusing on the low energy spectrum, taking fully into account the spatial and the spin symmetry of the model in the characterization of the states. A symmetry analysis of the highly degenerate lowest energy classical manifold identifies as its direct fingerprint the low energy quantum states for spin magnitude as low as s = 1, with the latter following a tower of states behavior which relates to the icosahedron having a structure reminiscent of a depleted triangular lattice. The classical character of the AHM for small s is also detected on the ground state energy and correlation functions. On the other hand the classical magnetization discontinuity in a field eventually disappears for small s, after a weak reentrant behavior.

  19. SU (N ) Heisenberg model with multicolumn representations

    Science.gov (United States)

    Okubo, Tsuyoshi; Harada, Kenji; Lou, Jie; Kawashima, Naoki

    2015-10-01

    The SU (N ) symmetric antiferromagnetic Heisenberg model with multicolumn representations on the two-dimensional square lattice is investigated by quantum Monte Carlo simulations. For the representation of a Young diagram with two columns, we confirm that a valence-bond solid (VBS) order appears as soon as the Néel order disappears at N =10 , indicating no intermediate phase. In the case of the representation with three columns, there is no evidence for either the Néel or the VBS ordering for N ≥15 . This is actually consistent with the large-N theory, which predicts that the VBS state immediately follows the Néel state, because the expected spontaneous order is too weak to be detected.

  20. Quantum chaos in the Heisenberg spin chain: The effect of Dzyaloshinskii-Moriya interaction

    Science.gov (United States)

    Vahedi, J.; Ashouri, A.; Mahdavifar, S.

    2016-10-01

    Using one-dimensional spin-1/2 systems as prototypes of quantum many-body systems, we study the emergence of quantum chaos. The main purpose of this work is to answer the following question: how the spin-orbit interaction, as a pure quantum interaction, may lead to the onset of quantum chaos? We consider the three integrable spin-1/2 systems: the Ising, the XX, and the XXZ limits and analyze whether quantum chaos develops or not after the addition of the Dzyaloshinskii-Moriya interaction. We find that depending on the strength of the anisotropy parameter, the answer is positive for the XXZ and Ising models, whereas no such evidence is observed for the XX model. We also discuss the relationship between quantum chaos and thermalization.

  1. Two-dimensional calculus

    CERN Document Server

    Osserman, Robert

    2011-01-01

    The basic component of several-variable calculus, two-dimensional calculus is vital to mastery of the broader field. This extensive treatment of the subject offers the advantage of a thorough integration of linear algebra and materials, which aids readers in the development of geometric intuition. An introductory chapter presents background information on vectors in the plane, plane curves, and functions of two variables. Subsequent chapters address differentiation, transformations, and integration. Each chapter concludes with problem sets, and answers to selected exercises appear at the end o

  2. Two dimensional vernier

    Science.gov (United States)

    Juday, Richard D. (Inventor)

    1992-01-01

    A two-dimensional vernier scale is disclosed utilizing a cartesian grid on one plate member with a polar grid on an overlying transparent plate member. The polar grid has multiple concentric circles at a fractional spacing of the spacing of the cartesian grid lines. By locating the center of the polar grid on a location on the cartesian grid, interpolation can be made of both the X and Y fractional relationship to the cartesian grid by noting which circles coincide with a cartesian grid line for the X and Y direction.

  3. Computational quantum chemistry for single Heisenberg spin couplings made simple: just one spin flip required.

    Science.gov (United States)

    Mayhall, Nicholas J; Head-Gordon, Martin

    2014-10-07

    We highlight a simple strategy for computing the magnetic coupling constants, J, for a complex containing two multiradical centers. On the assumption that the system follows Heisenberg Hamiltonian physics, J is obtained from a spin-flip electronic structure calculation where only a single electron is excited (and spin-flipped), from the single reference with maximum Ŝz, M, to the M - 1 manifold, regardless of the number of unpaired electrons, 2M, on the radical centers. In an active space picture involving 2M orbitals, only one β electron is required, together with only one α hole. While this observation is extremely simple, the reduction in the number of essential configurations from exponential in M to only linear provides dramatic computational benefits. This (M, M - 1) strategy for evaluating J is an unambiguous, spin-pure, wave function theory counterpart of the various projected broken symmetry density functional theory schemes, and likewise gives explicit energies for each possible spin-state that enable evaluation of properties. The approach is illustrated on five complexes with varying numbers of unpaired electrons, for which one spin-flip calculations are used to compute J. Some implications for further development of spin-flip methods are discussed.

  4. Computational quantum chemistry for single Heisenberg spin couplings made simple: Just one spin flip required

    Energy Technology Data Exchange (ETDEWEB)

    Mayhall, Nicholas J.; Head-Gordon, Martin, E-mail: mhg@cchem.berkeley.edu [Kenneth S. Pitzer Center for Theoretical Chemistry, Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2014-10-07

    We highlight a simple strategy for computing the magnetic coupling constants, J, for a complex containing two multiradical centers. On the assumption that the system follows Heisenberg Hamiltonian physics, J is obtained from a spin-flip electronic structure calculation where only a single electron is excited (and spin-flipped), from the single reference with maximum S{sup ^}{sub z}, M, to the M − 1 manifold, regardless of the number of unpaired electrons, 2M, on the radical centers. In an active space picture involving 2M orbitals, only one β electron is required, together with only one α hole. While this observation is extremely simple, the reduction in the number of essential configurations from exponential in M to only linear provides dramatic computational benefits. This (M, M − 1) strategy for evaluating J is an unambiguous, spin-pure, wave function theory counterpart of the various projected broken symmetry density functional theory schemes, and likewise gives explicit energies for each possible spin-state that enable evaluation of properties. The approach is illustrated on five complexes with varying numbers of unpaired electrons, for which one spin-flip calculations are used to compute J. Some implications for further development of spin-flip methods are discussed.

  5. Phase diagram of a two-dimensional liquid in GaAs/AlxGa1-xAs biased double quantum wells

    DEFF Research Database (Denmark)

    Timofeev, V. B.; Larionov, A. V.; Alessi, M. G.;

    2000-01-01

    densities, P, and temperatures, T. For increasing P or decreasing T, a sharp transition from two gases of photoexcited electrons and holes, spatially separated and confined in the two wells, to two two-dimensional (2D) liquids has been observed. The gas-to-2D-liquid transition is evidenced by a strong...

  6. Quantum breathers in Heisenberg ferromagnetic chains with Dzyaloshinsky-Moriya interaction.

    Science.gov (United States)

    Tang, Bing; Li, De-Jun; Tang, Yi

    2014-06-01

    We present an analytical study on quantum breathers in one-dimensional ferromagnetic XXZ chains with Dzyaloshinsky-Moriya interaction by means of the time-dependent Hartree approximation and the semidiscrete multiple-scale method. The stationary localized single-boson wave functions are obtained and these analytical solutions are checked by numerical simulations. With such stationary localized single-boson wave functions, we construct quantum breather states. Furthermore, the role of the Dzyaloshinsky-Moriya interaction is discussed.

  7. Quantum breathers in Heisenberg ferromagnetic chains with Dzyaloshinsky-Moriya interaction

    Energy Technology Data Exchange (ETDEWEB)

    Tang, Bing; Tang, Yi, E-mail: tangyii@hotmail.com [Department of Physics, Xiangtan University, Xiangtan 411105 (China); Li, De-Jun [College of Physics, Mechanical and Electrical Engineering, Jishou University, Jishou 416000 (China)

    2014-06-15

    We present an analytical study on quantum breathers in one-dimensional ferromagnetic XXZ chains with Dzyaloshinsky-Moriya interaction by means of the time-dependent Hartree approximation and the semidiscrete multiple-scale method. The stationary localized single-boson wave functions are obtained and these analytical solutions are checked by numerical simulations. With such stationary localized single-boson wave functions, we construct quantum breather states. Furthermore, the role of the Dzyaloshinsky-Moriya interaction is discussed.

  8. Modified Spin Wave Thoery of the Bilayer Square Lattice Frustrated Quantum Heisenberg Antiferromagnet

    OpenAIRE

    Hida, Kazuo

    1995-01-01

    The ground state of the square lattice bilayer quantum antiferromagnet with nearest and next-nearest neighbour intralayer interaction is studied by means of the modified spin wave method. For weak interlayer coupling, the ground state is found to be always magnetically ordered while the quantum disordered phase appear for large enough interlayer coupling. The properties of the disordered phase vary according to the strength of the frustration. In the regime of weak frustration, the disordered...

  9. Field-Induced Multiple Reentrant Quantum Phase Transitions in Randomly Dimerized Antiferromagnetic S=1/2 Heisenberg Chains

    Science.gov (United States)

    Hida, Kazuo

    2006-07-01

    The multiple reentrant quantum phase transitions in the S=1/2 antiferromagnetic Heisenberg chains with random bond alternation in the magnetic field are investigated by the density matrix renormalization group method combined with interchain mean field approximation. It is assumed that odd numbered bonds are antiferromagnetic with strength J and even numbered bonds can take the values JS and JW (JS > J > JW > 0) randomly with the probabilities p and 1- p, respectively. The pure version ( p=0 and 1) of this model has a spin gap but exhibits a field-induced antiferromagnetism in the presence of interchain coupling if Zeeman energy due to the magnetic field exceeds the spin gap. For 0 < p < 1, antiferromagnetism is induced by randomness at the small field region where the ground state is disordered due to the spin gap in the pure version. At the same time, this model exhibits randomness-induced plateaus at several values of magnetization. The antiferromagnetism is destroyed on the plateaus. As a consequence, we find a series of reentrant quantum phase transitions between transverse antiferromagnetic phases and disordered plateau phases with the increase of magnetic field for a moderate strength of interchain coupling. Above the main plateaus, the magnetization curve consists of a series of small plateaus and jumps between them. It is also found that antiferromagnetism is induced by infinitesimal interchain coupling at the jumps between the small plateaus. We conclude that this antiferromagnetism is supported by the mixing of low-lying excited states by the staggered interchain mean field even though the spin correlation function is short ranged in the ground state of each chain.

  10. Two-dimensional optical spectroscopy

    CERN Document Server

    Cho, Minhaeng

    2009-01-01

    Discusses the principles and applications of two-dimensional vibrational and optical spectroscopy techniques. This book provides an account of basic theory required for an understanding of two-dimensional vibrational and electronic spectroscopy.

  11. Experimentally determining the exchange parameters of quasi-two dimensional Heisenbert magnets

    Energy Technology Data Exchange (ETDEWEB)

    Singleton, John [Los Alamos National Laboratory; Sengupta, P [Los Alamos National Laboratory; Mcdonald, R D [Los Alamos National Laboratory; Cox, S [Los Alamos National Laboratory; Harrison, N [Los Alamos National Laboratory; Goddard, P A [UNIV OF OXFORD; Lancaster, T [UNIV OF OXFORD; Blundell, S J [UNIV OF OXFORD; Pratt, F L [RUTHERFORD APPLETON LAB; Manson, J L [EASTERN WASHINGTON UNIV; Southerland, H I [EASTERN WASHINGTON UNIV; Schlueter, J A [ANL

    2008-01-01

    Though long-range magnetic order cannot occur at temperatures T > 0 in a perfect two-dimensional (2D) Heisenberg magnet, real quasi-2D materials will invariably possess nonzero inter-plane coupling J{sub {perpendicular}} driving the system to order at elevated temperatures. This process can be studied using quantum Monte Carlo calculations. However, it is difficult to test the results of these calculations experimentally since for highly anisotropic materials in which the in-plane coupling is comparable with attainable magnetic fields J{sub {perpendicular}} is necessarily very small and inaccessible directly. In addition, because of the large anisotropy, the Neel temperatures are low and difficult to determine from thermodynamic measurements. Here, we present an elegant method of assessing the calculations via two independent experimental probes: pulsed-field magnetization in fields of up to 85 T, and muon-spin rotation.

  12. Quantum phase transition, universality, and scaling behaviors in the spin-1/2 Heisenberg model with ferromagnetic and antiferromagnetic competing interactions on a honeycomb lattice

    Science.gov (United States)

    Huang, Yi-Zhen; Xi, Bin; Chen, Xi; Li, Wei; Wang, Zheng-Chuan; Su, Gang

    2016-06-01

    The quantum phase transition, scaling behaviors, and thermodynamics in the spin-1/2 quantum Heisenberg model with antiferromagnetic coupling J >0 in the armchair direction and ferromagnetic interaction J'Monte Carlo method. By calculating the Binder ratio Q2 and spin stiffness ρ in two directions for various coupling ratios α =J'/J under different lattice sizes, we found that a quantum phase transition from the dimerized phase to the stripe phase occurs at the quantum critical point αc=-0.93 . Through the finite-size scaling analysis on Q2, ρx, and ρy, we determined the critical exponent related to the correlation length ν to be 0.7212(8), implying that this transition falls into a classical Heisenberg O(3) universality. A zero magnetization plateau is observed in the dimerized phase, whose width decreases with increasing α . A phase diagram in the coupling ratio α -magnetic field h plane is obtained, where four phases, including dimerized, stripe, canted stripe, and polarized, are identified. It is also unveiled that the temperature dependence of the specific heat C (T ) for different α 's intersects precisely at one point, similar to that of liquid 3He under different pressures and several magnetic compounds under various magnetic fields. The scaling behaviors of Q2, ρ , and C (T ) are carefully analyzed. The susceptibility is compared with the experimental data to give the magnetic parameters of both compounds.

  13. Generalised Heisenberg Relations

    OpenAIRE

    Brody, Dorje C.; Hughston, Lane P.

    1997-01-01

    A geometric framework for quantum statistical estimation is used to establish a series of higher order corrections to the Heisenberg uncertainty relations associated with pairs of canonically conjugate variables. These corrections can be expressed in terms of linear combinations of higher order cumulants for the distributions, and thus vanish for Gaussian distributions. Estimates for typical numerical values arising from these corrections are indicated in the case of a gamma distribution.

  14. Heisenberg's uncertainty principle

    OpenAIRE

    Busch, Paul; Heinonen, Teiko; Lahti, Pekka

    2007-01-01

    Heisenberg's uncertainty principle is usually taken to express a limitation of operational possibilities imposed by quantum mechanics. Here we demonstrate that the full content of this principle also includes its positive role as a condition ensuring that mutually exclusive experimental options can be reconciled if an appropriate trade-off is accepted. The uncertainty principle is shown to appear in three manifestations, in the form of uncertainty relations: for the widths of the position and...

  15. RANDOM ATTRACTORS FOR A STOCHASTIC HYDRODYNAMICAL EQUATION IN HEISENBERG PARAMAGNET

    Institute of Scientific and Technical Information of China (English)

    Guo Boling; Guo Chunxiao; Pu Xueke

    2011-01-01

    This article studies the asymptotic behaviors of the solution for a stochastic hydrodynamical equation in Heisenberg paramagnet in a two-dimensional periodic domain. We obtain the existence of random attractors in H1.

  16. Persistent entanglement in a class of eigenstates of quantum Heisenberg spin glasses

    Science.gov (United States)

    Kannawadi, Arun; Sharma, Auditya; Lakshminarayan, Arul

    2016-09-01

    The eigenstates of a quantum spin glass Hamiltonian with long-range interaction are examined from the point of view of localisation and entanglement. In particular, low particle sectors are examined and an anomalous family of eigenstates is found that is more delocalised but also has larger inter-spin entanglement. These are then identified as particle-added eigenstates from the one-particle sector. This motivates the introduction and the study of random promoted two-particle states, and it is shown that they may have large delocalisation such as generic random states and scale exactly like them. However, the entanglement as measured by two-spin concurrence displays different scaling with the total number of spins. This shows how for different classes of complex quantum states entanglement can be qualitatively different even if localisation measures such as participation ratio are not.

  17. Galilean quantum gravity with cosmological constant and the extended q-Heisenberg algebra

    OpenAIRE

    Papageorgiou, G; Schroers, B. J.

    2010-01-01

    We define a theory of Galilean gravity in 2+1 dimensions with cosmological constant as a Chern-Simons gauge theory of the doubly-extended Newton-Hooke group, extending our previous study of classical and quantum gravity in 2+1 dimensions in the Galilean limit. We exhibit an r-matrix which is compatible with our Chern-Simons action (in a sense to be defined) and show that the associated bi-algebra structure of the Newton-Hooke Lie algebra is that of the classical double of the extended Heisenb...

  18. Gapless line for the anisotropic Heisenberg spin-1/2 chain in a magnetic field and the quantum axial next-nearest-neighbor Ising chain

    OpenAIRE

    2003-01-01

    We study the anisotropic Heisenberg (XYZ) spin-1/2 chain placed in a magnetic field pointing along the x-axis. We use bosonization and a renormalization group analysis to show that the model has a non-trivial fixed point at a certain value of the XY anisotropy a and the magnetic field h. Hence, there is a line of critical points in the (a,h) plane on which the system is gapless, even though the Hamiltonian has no continuous symmetry. The quantum critical line corresponds to a spin-flop transi...

  19. Quantum transport in two dimensional electron gas/p-wave superconductor junction with Rashba spin–orbit coupling at the interface and in the normal layer

    Energy Technology Data Exchange (ETDEWEB)

    Mohammadkhani, R., E-mail: rmkhani@znu.ac.ir; Hassanloo, Gh.

    2014-11-01

    We have studied the tunneling conductance of a clean two dimensional electron gas/p- wave superconductor junction with Rashba spin–orbit coupling (RSOC) which is present in the normal layer and at the interface. Using the extended Blonder–Tinkham–Klapwijk formalism we have found that the subgap conductance peaks are shifted to a nonzero bias by RSOC at the interface which are the same as Ref. [1]. It is shown that for low insulating barrier and in the absence of the interface RSOC, the tunneling conductance decreases within energy gap with increasing of the RSOC in the normal layer while for high insulating barrier it enhances by increase of the RSOC. We have also shown that the RSOC inside the normal cannot affect the location of the subgap conductance peaks shifted by the interface RSOC.

  20. Anomalous spin excitation spectrum of the Heisenberg model in a magnetic field.

    Science.gov (United States)

    Syljuåsen, Olav F; Lee, Patrick A

    2002-05-20

    Making the assumption that high-energy fermions exist in the two dimensional spin- 1/2 Heisenberg antiferromagnet, we present predictions based on the pi-flux ansatz for the dynamic structure factor when the antiferromagnet is subject to a uniform magnetic field. The main result is the presence of gapped excitations in a momentum region near (pi,pi) with energy lower than that at (pi,pi). This is qualitatively different from spin-wave theory predictions and may be tested by experiments or by quantum Monte Carlo.

  1. Ground-state fidelity of the spin-1 Heisenberg chain with single ion anisotropy: quantum renormalization group and exact diagonalization approaches.

    Science.gov (United States)

    Langari, A; Pollmann, F; Siahatgar, M

    2013-10-09

    We study the phase diagram of the anisotropic spin-1 Heisenberg chain with single ion anisotropy (D) using a ground-state fidelity approach. The ground-state fidelity and its corresponding susceptibility are calculated within the quantum renormalization group scheme where we obtained the renormalization of fidelity preventing calculation of the ground state. Using this approach, the phase boundaries between the antiferromagnetic Néel, Haldane and large-D phases are obtained for the whole phase diagram, which justifies the application of quantum renormalization group to trace the symmetry-protected topological phases. In addition, we present numerical exact diagonalization (Lanczos) results in which we employ a recently introduced non-local order parameter to locate the transition from Haldane to large-D phase accurately.

  2. Thermal entangled quantum Otto engine based on the two qubits Heisenberg model with Dzyaloshinskii-Moriya interaction in an external magnetic field

    Science.gov (United States)

    Wang, Hao; Wu, Guoxing; Chen, Daojiong

    2012-07-01

    Based on the isotropic two spin-1/2 qubits Heisenberg model with Dzyaloshinskii-Moriya interaction in a constant external magnetic field, we have constructed the entangled quantum Otto engine. Expressions for the basic thermodynamic quantities, i.e. the amount of heat exchange, the net work output and the efficiency, are derived. The influence of thermal entanglement on these basic thermodynamic quantities is investigated. Moreover, some intriguing features and their qualitative explanations in zero and finite magnetic field are given. The validity of the second law of thermodynamics is confirmed in the system. The results obtained here have general significance and will be useful in increasing understanding of the performance of an entangled quantum engine.

  3. Heisenberg model and Rigged Configurations

    CERN Document Server

    Giri, Pulak Ranjan

    2015-01-01

    We show a correspondence of all the solutions of the spin-1/2 isotropic Heisenberg model for N=12 to the rigged configurations based on the comparison of the set of Takahashi quantum numbers in lexicographical order with the set of riggings of the rigged configurations in co-lexicographical order.

  4. Werner Heisenberg (1901-1976)

    OpenAIRE

    Todorov, Ivan

    2005-01-01

    A brief review of Heisenberg's life and work: participating in the youth movement in the aftermath of World War I, creating quantum mechanics, conflict with "deutsche Physik", involvement in "Hitler's Uranium Project", last illusions. Problems and dilemmas for scientists under a dictatorship - East and West.

  5. The Heisenberg antiferromagnet on the square-kagomé lattice

    Directory of Open Access Journals (Sweden)

    J. Richter

    2009-01-01

    Full Text Available We discuss the ground state, the low-lying excitations as well as high-field thermodynamics of the Heisenberg antiferromagnet on the two-dimensional square-kagomé lattice. This magnetic system belongs to the class of highly frustrated spin systems with an infinite non-trivial degeneracy of the classical ground state as it is also known for the Heisenberg antiferromagnet on the kagomé and on the star lattice. The quantum ground state of the spin-half system is a quantum paramagnet with a finite spin gap and with a large number of non-magnetic excitations within this gap. We also discuss the magnetization versus field curve that shows a plateaux as well as a macroscopic magnetization jump to saturation due to independent localized magnon states. These localized states are highly degenerate and lead to interesting features in the low-temperature thermodynamics at high magnetic fields such as an additional low-temperature peak in the specific heat and an enhanced magnetocaloric effect.

  6. Comment on “The two dimensional motion of a particle in an inverse square potential: Classical and quantum aspects” [J. Math. Phys. 54, 053509 (2013)

    Energy Technology Data Exchange (ETDEWEB)

    Bietenholz, Wolfgang, E-mail: wolbi@nucleares.unam.mx; Chryssomalakos, Chryssomalis, E-mail: chryss@nucleares.unam.mx; Salgado, Marcelo, E-mail: marcelo@nucleares.unam.mx [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, A.P. 70-543, México D.F. 04510, México (Mexico)

    2015-10-15

    We comment on a fatal flaw in the analysis contained in the work of Martínez-y-Romero et al., [J. Math. Phys. 54, 053509 (2013)], which concerns the motion of a point particle in an inverse square potential, and show that most conclusions reached there are wrong. In particular, the manifestly senseless claim that, in the attractive potential case, no bounded orbits exist for negative energies, is traced to a sign error. Several more mistakes, both in the classical and the quantum cases, are pointed out.

  7. Quantum and Transport Mobilities of a Two-Dimensional Electron Gas in the Presence of the Rashba Spin-Orbit Interaction

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A systematic theoretical approach is developed to study the electronic and transport properties of a twodimensional electron gas (2DEG) in the presence of spin-orbit interactions induced by the Rashba effect. The standard random-phase approximation is employed to calculate the screening length caused by electron-electron interaction in different transition channels. The quantum and transport mobilities in different spin branches are evaluated using the momentum-balance equation derived from the Boltzmann equation,in which the electron interactions with both the remote and background impurities are taken into account in an InAlAs/InGaAs heterojunction at low-temperatures.

  8. Periodic Two-Dimensional GaAs and InGaAs Quantum Rings Grown on GaAs (001) by Droplet Epitaxy.

    Science.gov (United States)

    Tung, Kar Hoo Patrick; Huang, Jian; Danner, Aaron

    2016-06-01

    Growth of ordered GaAs and InGaAs quantum rings (QRs) in a patterned SiO2 nanohole template by molecular beam epitaxy (MBE) using droplet epitaxy (DE) process is demonstrated. DE is an MBE growth technique used to fabricate quantum nanostructures of high crystal quality by supplying group III and group V elements in separate phases. In this work, ordered QRs grown on an ordered nanohole template are compared to self-assembled QRs grown with the same DE technique without the nanohole template. This study allows us to understand and compare the surface kinetics of Ga and InGa droplets when a template is present. It is found that template-grown GaAs QRs form clustered rings which can be attributed to low mobility of Ga droplets resulting in multiple nucleation sites for QR formation when As is supplied. However, the case of template-grown InGaAs QRs only one ring is formed per nanohole; no clustering is observed. The outer QR diameter is a close match to the nanohole template diameter. This can be attributed to more mobile InGa droplets, which coalesce from an Ostwald ripening to form a single large droplet before As is supplied. Thus, well-patterned InGaAs QRs are demonstrated and the kinetics of their growth are better understood which could potentially lead to improvements in the future devices that require the unique properties of patterned QRs.

  9. Effective mass of two-dimensional electrons in InGaAsN/GaAsSb type II quantum well by Shubnikov-de Haas oscillations

    Science.gov (United States)

    Kawamata, Shuichi; Hibino, Akira; Tanaka, Sho; Kawamura, Yuichi

    2016-10-01

    In order to develop optical devices for 2-3 μm wavelength regions, the InP-based InGaAs/GaAsSb type II multiple quantum well system has been investigated. By doping nitrogen into InGaAs layers, the system becomes effective in creating the optical devices with a longer wavelength. In this report, electrical transport properties are reported on the InGaAsN/GaAsSb type II system. The epitaxial layers with the single hetero or multiple quantum well structure on InP substrates are grown by the molecular beam epitaxy. The electrical resistance of samples with different nitrogen concentrations has been measured as a function of the magnetic field up to 9 Tesla at several temperatures between 2 and 6 K. The oscillation of the resistance due to the Shubnikov-de Haas (SdH) effect has been observed at each temperature. The effective mass is obtained from the temperature dependence of the amplitude of the SdH oscillations. The value of the effective mass increases from 0.048 for N = 0.0% to 0.062 for N = 1.2 and 1.5% as the nitrogen concentration increases. The mass enhancement occurs with corresponding to the reduction of the bandgap energy. These results are consistent with the band anticrossing model.

  10. Magneto-transport Spectroscopy of the First and Second Two-dimensional Subbands in Al0.25Ga0.75N/GaN Quantum Point Contacts

    Science.gov (United States)

    Lu, Fangchao; Tang, Ning; Shang, Liangliang; Guan, Hongming; Xu, Fujun; Ge, Weikun; Shen, Bo

    2017-01-01

    Magnetic transport spectroscopy is investigated in quantum point contacts (QPCs) fabricated in Al0.25Ga0.75N/GaN heterostructures. The magnetic field perpendicular to the two-dimensional electron gas (2DEG) is shown to depopulate the quasi-one-dimensional energy levels in the first two-dimensional (2D) subband faster than those in the second one. In GaN based heterostructures, the energy levels in the second 2D subband is generally concealed in the fast course of depletion and hence rarely detected. The perpendicular magnetic field facilitates the observation of the second 2D subband, and provides a method to study the properties of these energy levels. A careful analysis on the rate of the magnetic depletion with respect to the level index and confinement is carried out, from which the profile of the lateral confinement in GaN based QPCs is found to be triangular. The stability diagram at T shows the energy separation between the first and second 2D subband to be in the range of 32 to 42 meV. PMID:28225042

  11. Two-Dimensional NMR Lineshape Analysis

    Science.gov (United States)

    Waudby, Christopher A.; Ramos, Andres; Cabrita, Lisa D.; Christodoulou, John

    2016-04-01

    NMR titration experiments are a rich source of structural, mechanistic, thermodynamic and kinetic information on biomolecular interactions, which can be extracted through the quantitative analysis of resonance lineshapes. However, applications of such analyses are frequently limited by peak overlap inherent to complex biomolecular systems. Moreover, systematic errors may arise due to the analysis of two-dimensional data using theoretical frameworks developed for one-dimensional experiments. Here we introduce a more accurate and convenient method for the analysis of such data, based on the direct quantum mechanical simulation and fitting of entire two-dimensional experiments, which we implement in a new software tool, TITAN (TITration ANalysis). We expect the approach, which we demonstrate for a variety of protein-protein and protein-ligand interactions, to be particularly useful in providing information on multi-step or multi-component interactions.

  12. A two-dimensional Dirac fermion microscope

    Science.gov (United States)

    Bøggild, Peter; Caridad, José M.; Stampfer, Christoph; Calogero, Gaetano; Papior, Nick Rübner; Brandbyge, Mads

    2017-06-01

    The electron microscope has been a powerful, highly versatile workhorse in the fields of material and surface science, micro and nanotechnology, biology and geology, for nearly 80 years. The advent of two-dimensional materials opens new possibilities for realizing an analogy to electron microscopy in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2D electron guns, deflectors, tunable lenses and various detectors. The simulations show how simple objects can be imaged with well-controlled and collimated in-plane beams consisting of relativistic charge carriers. Finally, we discuss the potential of such microscopes for investigating edges, terminations and defects, as well as interfaces, including external nanoscale structures such as adsorbed molecules, nanoparticles or quantum dots.

  13. A two-dimensional Dirac fermion microscope.

    Science.gov (United States)

    Bøggild, Peter; Caridad, José M; Stampfer, Christoph; Calogero, Gaetano; Papior, Nick Rübner; Brandbyge, Mads

    2017-06-09

    The electron microscope has been a powerful, highly versatile workhorse in the fields of material and surface science, micro and nanotechnology, biology and geology, for nearly 80 years. The advent of two-dimensional materials opens new possibilities for realizing an analogy to electron microscopy in the solid state. Here we provide a perspective view on how a two-dimensional (2D) Dirac fermion-based microscope can be realistically implemented and operated, using graphene as a vacuum chamber for ballistic electrons. We use semiclassical simulations to propose concrete architectures and design rules of 2D electron guns, deflectors, tunable lenses and various detectors. The simulations show how simple objects can be imaged with well-controlled and collimated in-plane beams consisting of relativistic charge carriers. Finally, we discuss the potential of such microscopes for investigating edges, terminations and defects, as well as interfaces, including external nanoscale structures such as adsorbed molecules, nanoparticles or quantum dots.

  14. On the Heisenberg principle, namely on the information-disturbance trade-off in a quantum measurement

    OpenAIRE

    D'Ariano, Giacomo Mauro

    2002-01-01

    Common misconceptions on the Heisenberg principle are reviewed, and the original spirit of the principle is reestablished in terms of the trade-off between information retrieved by a measurement and disturbance on the measured system. After analyzing the possibility of probabilistically reversible measurements, along with erasure of information and undoing of disturbance, general information-disturbance trade-offs are presented, where the disturbance of the measurement is related to the possi...

  15. Berry phase in Heisenberg representation

    Science.gov (United States)

    Andreev, V. A.; Klimov, Andrei B.; Lerner, Peter B.

    1994-01-01

    We define the Berry phase for the Heisenberg operators. This definition is motivated by the calculation of the phase shifts by different techniques. These techniques are: the solution of the Heisenberg equations of motion, the solution of the Schrodinger equation in coherent-state representation, and the direct computation of the evolution operator. Our definition of the Berry phase in the Heisenberg representation is consistent with the underlying supersymmetry of the model in the following sense. The structural blocks of the Hamiltonians of supersymmetrical quantum mechanics ('superpairs') are connected by transformations which conserve the similarity in structure of the energy levels of superpairs. These transformations include transformation of phase of the creation-annihilation operators, which are generated by adiabatic cyclic evolution of the parameters of the system.

  16. Cosmological implications of Heisenberg's principle

    CERN Document Server

    Gonzalo, Julio A

    2015-01-01

    The aim of this book is to analyze the all important implications of Heisenberg's Uncertainty Principle for a finite universe with very large mass-energy content such as ours. The earlier and main contributors to the formulation of Quantum Mechanics are briefly reviewed regarding the formulation of Heisenberg's Principle. After discussing “indeterminacy” versus ”uncertainty”, the universal constants of physics are reviewed and Planck's units are given. Next, a novel set of units, Heisenberg–Lemaitre units, are defined in terms of the large finite mass of the universe. With the help of Heisenberg's principle, the time evolution of the finite zero-point energy for the universe is investigated quantitatively. Next, taking advantage of the rigorous solutions of Einstein's cosmological equation for a flat, open and mixed universe of finite mass, the most recent and accurate data on the “age” (to) and the expansion rate (Ho) of the universe and their implications are reconsidered.

  17. Efficient excitation of photoluminescence in a two-dimensional waveguide consisting of a quantum dot-polymer sandwich-type structure.

    Science.gov (United States)

    Suárez, I; Larrue, A; Rodríguez-Cantó, P J; Almuneau, G; Abargues, R; Chirvony, V S; Martínez-Pastor, J P

    2014-08-15

    In this Letter, we study a new kind of organic polymer waveguide numerically and experimentally by combining an ultrathin (10-50 nm) layer of compactly packed CdSe/ZnS core/shell colloidal quantum dots (QDs) sandwiched between two cladding poly(methyl methacrylate) (PMMA) layers. When a pumping laser beam is coupled into the waveguide edge, light is mostly confined around the QD layer, improving the efficiency of excitation. Moreover, the absence of losses in the claddings allows the propagation of the pumping laser beam along the entire waveguide length; hence, a high-intensity photoluminescence (PL) is produced. Furthermore, a novel fabrication technology is developed to pattern the PMMA into ridge structures by UV lithography in order to provide additional light confinement. The sandwich-type waveguide is analyzed in comparison to a similar one formed by a PMMA film homogeneously doped by the same QDs. A 100-fold enhancement in the waveguided PL is found for the sandwich-type case due to the higher concentration of QDs inside the waveguide.

  18. Quantum Oscillations in a Two-Dimensional Electron Gas at the Rocksalt/Zincblende Interface of PbTe/CdTe (111) Heterostructures.

    Science.gov (United States)

    Zhang, Bingpo; Lu, Ping; Liu, Henan; Jiao, Lin; Ye, Zhenyu; Jaime, M; Balakirev, F F; Yuan, Huiqiu; Wu, Huizhen; Pan, Wei; Zhang, Yong

    2015-07-08

    Quantum oscillations are observed in the 2DEG system at the interface of novel heterostructures, PbTe/CdTe (111), with nearly identical lattice parameters (a(PbTe) = 0.6462 nm, a(CdTe) = 0.648 nm) but very different lattice structures (PbTe: rock salt, CdTe: zinc blende). The 2DEG formation mechanism, a mismatch in the bonding configurations of the valence electrons at the interface, is uniquely different from the other known 2DEG systems. The aberration-corrected scanning transmission electron microscope (AC-STEM) characterization indicates an abrupt interface without cation interdiffusion due to a large miscibility gap between the two constituent materials. Electronic transport measurements under magnetic field up to 60 T, with the observation of Landau level filling factor ν = 1, unambiguously reveal a π Berry phase, suggesting the Dirac Fermion nature of the 2DEG at the heterostructure interface, and the PbTe/CdTe heterostructure being a new candidate for 2D topological crystalline insulators.

  19. The generalization of the Mermin-Wagner theorem and the possibility of long-range order in the isotropic discrete one-dimensional quantum Heisenberg model

    Energy Technology Data Exchange (ETDEWEB)

    Rudoy, Yu.G., E-mail: rudikar@mail.ru [Department of Theoretical Physics, People' s Friendship University of Russia, ul. Miklukho-Maclaya 6, 117981 Moscow (Russian Federation); Kotelnikova, O.A. [Department of Magnetism, Physical Faculty, Lomonosov Moscow State University, Vorobievy Gory, 119991 Moscow (Russian Federation)

    2012-10-15

    The problem of existence of long-range order in the isotropic quantum Heisenberg model on the D=1 lattice is reconsidered in view of the possibility of sufficiently slow decaying exchange interaction with infinite effective radius. It is shown that the macrosopic arguments given by Landau and Lifshitz and then supported microscopically by Mermin and Wagner fail for this case so that the non-zero spontaneous magnetization may yet exist. This result was anticipated by Thouless on the grounds of phenomenological analysis, and we give its microscopic foundation, which amounts to the generalization of Mermin-Wagner theorem for the case of the infinite second moment of the exchange interaction. Two well known in lattice statistics models - i.e., Kac-I and Kac-II - illustrate our results.

  20. Quantum-chemical analysis of thermodynamics of two-dimensional cluster formation of alpha-amino acids at the air/water interface.

    Science.gov (United States)

    Vysotsky, Yu B; Fomina, E S; Belyaeva, E A; Aksenenko, E V; Vollhardt, D; Miller, R

    2009-12-31

    The semiempirical quantum-chemical PM3 method is used to calculate the thermodynamic parameters of clusterization of the S-form of alpha-amino acids with the general composition C(n)H(2n+1)CHNH(2)COOH (n = 5-15) at 278 and 298 K. It is shown that six stable conformations of monomers exist, for which the thermodynamic parameters (enthalpy and Gibbs' energy) of the formation and absolute entropy are calculated. The correlation dependencies of the calculated parameters on the alkyl chain length are found to be linear. The structures of the monomers are used to build larger clusters (dimers, tetramers, hexamers). For all small clusters (comprised of two to six molecules), the thermodynamic parameters of formation and clusterization are calculated. It is shown that for tetramers and hexamers the enthalpy, entropy, and Gibbs' energy of clusterization are linearly dependent on the alkyl chain length, whereas for the dimers these dependencies are stepwise. The thermodynamic characteristics of clusterization of associates tilted by angles of 9 and 30 degrees with respect to the normal to the interface are calculated. It is shown that the 30 degrees angle orientation is more energetically advantageous for this class of compounds. The geometric parameters of the unit cell characteristic for the infinite 2D film which corresponds to the most advantageous conformation of the monomer were calculated using the PM3 parametrization to be a = 4.57-4.71 A and b = 5.67-5.75 A, with the angle between the axes theta = 100-103 degrees . These values agree well with the available experimental data. Spontaneous clusterization of alpha-amino acids at the air/water interface at 278 K takes place if the alkyl chain length exceeds 11-12 carbon atoms, whereas for 298 K this clusterization threshold corresponds to 13-14 carbon atoms in the alkyl chain, also in agreement with the experimental data.

  1. Quantum-chemical analysis of thermodynamics of two-dimensional cluster formation of racemic α-amino acids at the air/water interface.

    Science.gov (United States)

    Vysotsky, Yu B; Fomina, E S; Belyaeva, E A; Aksenenko, E V; Fainerman, V B; Vollhardt, D; Miller, R

    2011-03-17

    The quantum-chemical semiempiric PM3 method is used to calculate the thermodynamic parameters of clusterization for the racemic α-amino acids C(n)H(2n+1)CHNH(2)COOH with n=5-15 at 278 and 298 K. Possible relative orientations of the monomers in the heterochiral clusters are considered. It is shown that, for the racemic mixtures of α-amino acids, the formation of heterochiral 2D films is most energetically preferable with the alternating (rather than "checkered") packing of the enantiomers with opposite specific rotation. The two enantiomeric forms of α-amino acids in the heterochiral 2D clusters are tilted with respect to the normal to the q direction at angles of φ(1)=20° and φ(2) = 33°, whereas the single enantiomeric forms are oriented at an angle of δ=9° with respect to the normal to the p direction. It is shown that the heterochiral 2D film based on the α-amino acid structures oriented at the angle φ(2)=33° with respect to the normal to the q direction possesses a rectangular unit cell with the geometric parameters a = 4.62 Å and b = 10.70 Å and the tilt angle of the alkyl chain of the molecule with respect to the interface t(2)=35°, which is in good agreement with the X-ray structural data a=4.80 Å, b=9.67 Å, and t(2)=37°. The parameters of the lattice structure of monolayers formed by amphiphilic amino acids are shown to be determined by the "a" type of the intermolecular H-H interactions, whereas the tilt angle of the molecules with respect to the interface depends on the volume and the structure of the functional groups involved in the hydrophilic part of the molecule. Spontaneous clusterization of the racemic form of α-amino acids at the air/water interface at 278 K takes place if the alkyl chain length is equal or higher than 12-13 carbon atoms, whereas for 298 K this clusterization threshold corresponds to 14 carbon atoms in the hydrocarbon chain. These values agree with the experimental data. © 2011 American Chemical Society

  2. Binding energy of two-dimensional biexcitons

    DEFF Research Database (Denmark)

    Singh, Jai; Birkedal, Dan; Vadim, Lyssenko;

    1996-01-01

    Using a model structure for a two-dimensional (2D) biexciton confined in a quantum well, it is shown that the form of the Hamiltonian of the 2D biexciton reduces into that of an exciton. The binding energies and Bohr radii of a 2D biexciton in its various internal energy states are derived...... analytically using the fractional dimension approach. The ratio of the binding energy of a 2D biexciton to that of a 2D exciton is found to be 0.228, which agrees very well with the recent experimental value. The results of our approach are compared with those of earlier theories....

  3. Two-dimensional liquid chromatography

    DEFF Research Database (Denmark)

    Græsbøll, Rune

    of this thesis is on online comprehensive two-dimensional liquid chromatography (online LC×LC) with reverse phase in both dimensions (online RP×RP). Since online RP×RP has not been attempted before within this research group, a significant part of this thesis consists of knowledge and experience gained...

  4. Two dimensional unstable scar statistics.

    Energy Technology Data Exchange (ETDEWEB)

    Warne, Larry Kevin; Jorgenson, Roy Eberhardt; Kotulski, Joseph Daniel; Lee, Kelvin S. H. (ITT Industries/AES Los Angeles, CA)

    2006-12-01

    This report examines the localization of time harmonic high frequency modal fields in two dimensional cavities along periodic paths between opposing sides of the cavity. The cases where these orbits lead to unstable localized modes are known as scars. This paper examines the enhancements for these unstable orbits when the opposing mirrors are both convex and concave. In the latter case the construction includes the treatment of interior foci.

  5. Two-Dimensional Vernier Scale

    Science.gov (United States)

    Juday, Richard D.

    1992-01-01

    Modified vernier scale gives accurate two-dimensional coordinates from maps, drawings, or cathode-ray-tube displays. Movable circular overlay rests on fixed rectangular-grid overlay. Pitch of circles nine-tenths that of grid and, for greatest accuracy, radii of circles large compared with pitch of grid. Scale enables user to interpolate between finest divisions of regularly spaced rule simply by observing which mark on auxiliary vernier rule aligns with mark on primary rule.

  6. Renormalization of two-dimensional quantum electrodynamics

    Energy Technology Data Exchange (ETDEWEB)

    Casana S, Rodolfo; Dias, Sebastiao A

    1997-12-01

    The Schwinger model, when quantized in a gauge non-invariant way exhibits a dependence on a parameter {alpha} (the Jackiw-Rajaraman parameter) in a way which is analogous to the case involving chiral fermions (the chiral Schwinger model). For all values of a {alpha}1, there are divergences in the fermionic Green`s functions. We propose a regularization of the generating functional Z [{eta}, {eta}, J] and we use it to renormalize the theory to one loop level, in a semi-perturbative sense. At the end of the renormalization procedure we find an implicit dependence of {alpha} on the renormalization scale {mu}. (author) 26 refs.

  7. Multiple Quantum Coherences (MQ) NMR and Entanglement Dynamics in the Mixed-Three-Spin XXX Heisenberg Model with Single-Ion Anisotropy

    Science.gov (United States)

    Arian Zad, Hamid

    2016-12-01

    We analytically investigate Multiple Quantum (MQ) NMR dynamics in a mixed-three-spin (1/2,1,1/2) system with XXX Heisenberg model at the front of an external homogeneous magnetic field B. A single-ion anisotropy property ζ is considered for the spin-1. The intensities dependence of MQ NMR coherences on their orders (zeroth and second orders) for two pairs of spins (1,1/2) and (1/2,1/2) of the favorite tripartite system are obtained. It is also investigated dynamics of the pairwise quantum entanglement for the bipartite (sub)systems (1,1/2) and (1/2,1/2) permanently coupled by, respectively, coupling constants J}1 and J}2, by means of concurrence and fidelity. Then, some straightforward comparisons are done between these quantities and the intensities of MQ NMR coherences and ultimately some interesting results are reported. We also show that the time evolution of MQ coherences based on the reduced density matrix of the pair spins (1,1/2) is closely connected with the dynamics of the pairwise entanglement. Finally, we prove that one can introduce MQ coherence of the zeroth order corresponds to the pair spins (1,1/2) as an entanglement witness at some special time intervals.

  8. Field-Induced Quantum Phase Transitions in S = 1/2 J1-J2 Heisenberg Model on Square Lattice

    Science.gov (United States)

    Morita, Katsuhiro; Shibata, Naokazu

    2016-09-01

    We study the magnetic field dependence of the ground state of the S = 1/2 J1-J2 Heisenberg model on the square lattice by the density matrix renormalization group (DMRG) method. With the use of the sine-square deformation, we obtain eight different ground states including plaquette valence-bond crystal with a finite spin gap, transverse Néel, transverse stripe, 1/2 magnetization plateau with up-up-up-down (uuud), and three new states we named the Y-like, V-like, and Ψ states around J2/J1 = 0.55-0.6. The phase transitions from the transverse Néel (at J2/J1 = 0.55) and stripe (at J2/J1 = 0.6) states to the uuud and Y-like states, respectively, are discontinuous, as in the case of a spin flop.

  9. Order-disorder quantum phase transition in the quasi-one-dimensional spin-1/2 collinear antiferromagnetic Heisenberg model.

    Science.gov (United States)

    Rufo, Sabrina; Mendonça, Griffith; Plascak, J A; de Sousa, J Ricardo

    2013-09-01

    The ground-state properties of the quasi-one-dimensional spin-1/2 antiferromagnetic Heisenberg model is investigated by using a variational method. Spins on chains along the x direction are antiferromagnetically coupled with exchange J>0, while spins between chains in the y direction are coupled either ferromagnetically (J' 0). The staggered and the colinear antiferromagnetic magnetizations are computed and their dependence on the anisotropy parameter λ=|J'|/J is analyzed. It is found that an infinitesimal interchain coupling parameter is sufficient to stabilize a long-range order with either a staggered magnetization m_{s} (J' > 0) or a colinear antiferromagnetic magnetization m_{caf} (J' < 0), both behaving as ≃λ¹/² for λ → 0.

  10. Quantum crystals and spin chains

    Energy Technology Data Exchange (ETDEWEB)

    Dijkgraaf, Robbert [KdV Institute for Mathematics, University of Amsterdam, Plantage Muidergracht 24, 1018 TV Amsterdam (Netherlands); Institute for Theoretical Physics, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam (Netherlands); Orlando, Domenico [Institut de Physique, Universite de Neuchatel, Rue Breguet 1, CH-2000 Neuchatel (Switzerland); Reffert, Susanne [Institute for Theoretical Physics, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam (Netherlands)], E-mail: sreffert@gmail.com

    2009-04-21

    In this article, we discuss the quantum version of the melting crystal corner in one, two, and three dimensions, generalizing the treatment for the quantum dimer model. Using a mapping to spin chains we find that the two-dimensional case (growth of random partitions) is integrable and leads directly to the Hamiltonian of the Heisenberg XXZ ferromagnet. The three-dimensional case of the melting crystal corner is described in terms of a system of coupled XXZ spin chains. We give a conjecture for its mass gap and analyze the system numerically.

  11. Quantum crystals and spin chains

    Science.gov (United States)

    Dijkgraaf, Robbert; Orlando, Domenico; Reffert, Susanne

    2009-04-01

    In this article, we discuss the quantum version of the melting crystal corner in one, two, and three dimensions, generalizing the treatment for the quantum dimer model. Using a mapping to spin chains we find that the two-dimensional case (growth of random partitions) is integrable and leads directly to the Hamiltonian of the Heisenberg XXZ ferromagnet. The three-dimensional case of the melting crystal corner is described in terms of a system of coupled XXZ spin chains. We give a conjecture for its mass gap and analyze the system numerically.

  12. Calculation of generalized spin stiffness constant of strongly correlated doped quantum antiferromagnet on two-dimensional lattice and it's application to effective exchange constant for semi-itinerant systems

    Science.gov (United States)

    Bhattacharjee, Suraka; Chaudhury, Ranjan

    2016-11-01

    The generalized spin stiffness constant for a doped quantum antiferromagnet has been investigated both analytically and numerically as a function of doping concentration at zero temperature, based on the strongly correlated t-J model on two-dimensional square lattice. The nature of the theoretical dependence of the stiffness constant on doping shows a striking similarity with that of the effective exchange constant, obtained from the combination of other theoretical and experimental techniques in the low doping region. This correspondence once again establishes that spin stiffness can very well play the role of an effective exchange constant even in the strongly correlated semi-itinerant systems. Our theoretical plot of the stiffness constant against doping concentration in the whole doping region exhibits the various characteristic features like a possible crossover in the higher doping regions and persistence of short range ordering even for very high doping with the complete vanishing of spin stiffness occurring only close to 100% doping. Our results receive very good support from various other theoretical approaches and also brings out a few limitations of some of them. Our detailed analysis highlights the crucial importance of the study of spin stiffness for the proper understanding of magnetic correlations in a semi-itinerant magnetic system described by the strongly correlated t-J model. Moreover, our basic formalism can also be utilized for determination of the effective exchange constant and magnetic correlations for itinerant magnetic systems, in general in a novel way.

  13. Werner Heisenberg - Life and Work

    CERN Document Server

    2002-01-01

    Werner Heisenberg (centre) with Wolfgang Pauli (left) and Enrico Fermi on Lake Como, September 1927. An exhibition on the life and work of Werner Heisenberg will be on display in the Main Building (Mezzanine) at CERN from 1 - 23 July. The exhibition was produced by the University Archive of Leipzig University (Gerald Wiemers) and the Max-Planck-Institut für Physik in Munich (Helmut Rechenberg) to mark the centenary of Heisenberg's birth in 1901. German theoretical physicist Werner Karl Heisenberg (5 December 1901 - 1 February 1976) was one of the leading scientists of the 20th century. He carried out important work in nuclear and particle physics, but his most significant contribution was to the development of quantum mechanics. He is best known for his uncertainty principle, which restricts the accuracy with which some properties of atoms and particles - such as position and linear momentum - can be determined simultaneously. In 1932 he was awarded the Noble Prize in Physics 'for the creation of q...

  14. Werner Heisenberg - Life and Work

    CERN Multimedia

    2002-01-01

    Werner Heisenberg (centre) with Wolfgang Pauli and Enrico Fermi, 1927. An exhibition on the life and work of Werner Heisenberg will be on display in the Main Building (Mezzanine) at CERN from 1 - 30 July*. German theoretical physicist Werner Karl Heisenberg (1901 - 1976) was one of the leading scientists of the 20th century. Nobel Prize in Physics in 1932, his most significant contribution was to the development of quantum mechanics. He is best known for his uncertainty principle, which restricts the accuracy with which some properties of atoms and particles can be determined simultaneously. Heisenberg was a keen supporter of CERN, and was as the first chairman of CERN's Scientific Policy Committee in October 1954. A related celebration will take place in the TH Amphitheatre (4/3-006), on Thursday 18 July at 16:00. After an introduction from the Director-General Luciano Maiani, his daughter, Barbara Blum, his last postgraduate, Helmut Rechenberg and Valentin Telegdi will evoke memories of the life and work ...

  15. Two-dimensional liquid chromatography

    DEFF Research Database (Denmark)

    Græsbøll, Rune

    Two-dimensional liquid chromatography has received increasing interest due to the rise in demand for analysis of complex chemical mixtures. Separation of complex mixtures is hard to achieve as a simple consequence of the sheer number of analytes, as these samples might contain hundreds or even...... dimensions. As a consequence of the conclusions made within this thesis, the research group has, for the time being, decided against further development of online LC×LC systems, since it was not deemed ideal for the intended application, the analysis of the polar fraction of oil. Trap-and...

  16. Quantum quenches in the anisotropic spin- 1/2 Heisenberg chain: different approaches to many-body dynamics far from equilibrium

    Energy Technology Data Exchange (ETDEWEB)

    Barmettler, Peter; Gritsev, Vladimir [Department of Physics, University of Fribourg, CH-1700 Fribourg (Switzerland); Punk, Matthias [CPHT, Ecole Polytechnique, 91128 Palaiseau (France); Demler, Eugene [Department of Physics, Harvard University, Cambridge, MA 02138 (United States); Altman, Ehud, E-mail: peter.barmettler@cpht.polytechnique.f [Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100 (Israel)

    2010-05-15

    Recent experimental achievements in controlling ultracold gases in optical lattices open a new perspective on quantum many-body physics. In these experimental setups, it is possible to study coherent time evolution of isolated quantum systems. These dynamics reveal new physics beyond the low-energy properties that are usually relevant in solid-state many-body systems. In this paper, we study the time evolution of antiferromagnetic order in the Heisenberg chain after a sudden change of the anisotropy parameter, using various numerical and analytical methods. As a generic result, we find that the order parameter, which can show oscillatory or non-oscillatory dynamics, decays exponentially except for the effectively non-interacting case of the XX limit. For weakly ordered initial states, we also find evidence for an algebraic correction to the exponential law. The study is based on numerical simulations using a numerical matrix product method for infinite system sizes (iMPS), for which we provide a detailed description and an error analysis. Additionally, we investigate in detail the exactly solvable XX limit. These results are compared to approximative analytical approaches including an effective description by the XZ model as well as by mean-field, Luttinger-liquid and sine-Gordon theories. The comparison reveals which aspects of non-equilibrium dynamics can, as in equilibrium, be described by low-energy theories and which are the novel phenomena specific to quantum quench dynamics. The relevance of the energetically high part of the spectrum is illustrated by means of a full numerical diagonalization of the Hamiltonian.

  17. Clifford Algebras in Symplectic Geometry and Quantum Mechanics

    OpenAIRE

    Binz, Ernst; de Gosson, Maurice A.; Hiley, Basil J.

    2011-01-01

    The necessary appearance of Clifford algebras in the quantum description of fermions has prompted us to re-examine the fundamental role played by the quaternion Clifford algebra, C(0,2). This algebra is essentially the geometric algebra describing the rotational properties of space. Hidden within this algebra are symplectic structures with Heisenberg algebras at their core. This algebra also enables us to define a Poisson algebra of all homogeneous quadratic polynomials on a two-dimensional s...

  18. Quantum Monte Carlo simulations of fidelity at magnetic quantum phase transitions.

    Science.gov (United States)

    Schwandt, David; Alet, Fabien; Capponi, Sylvain

    2009-10-23

    When a system undergoes a quantum phase transition, the ground-state wave function shows a change of nature, which can be monitored using the fidelity concept. We introduce two quantum Monte Carlo schemes that allow the computation of fidelity and its susceptibility for large interacting many-body systems. These methods are illustrated on a two-dimensional Heisenberg model, where fidelity estimators show marked behavior at two successive quantum phase transitions. We also develop a scaling theory which relates the divergence of the fidelity susceptibility to the critical exponent of the correlation length. A good agreement is found with the numerical results.

  19. Two-dimensional capillary origami

    Energy Technology Data Exchange (ETDEWEB)

    Brubaker, N.D., E-mail: nbrubaker@math.arizona.edu; Lega, J., E-mail: lega@math.arizona.edu

    2016-01-08

    We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid. - Highlights: • Full solution set of the two-dimensional capillary origami problem. • Fluid does not necessarily wet the entire plate. • Global energy approach provides exact differential equations satisfied by minimizers. • Bifurcation diagrams highlight three different regimes. • Conditions for spontaneous encapsulation are identified.

  20. Teleportation via thermally entangled states of a two-qubit Heisenberg XXZ chain

    Institute of Scientific and Technical Information of China (English)

    QIN Meng; TAO Ying-Juan; TIAN Dong-Ping

    2008-01-01

    We investigate quantum teleportation as a tool to study the thermally entangled state of a twoqubit Heisenberg XXZ chain.Our work is mainly to investigate the characteristics of a Heisenberg XXZ chain and get some analytical results of the fully entangled fraction.We also consider the entanglement teleportation via a two-qubit Heisenberg XXZ chain.

  1. Quantum phase transitions and string orders in the spin-1/2 Heisenberg-Ising alternating chain with Dzyaloshinskii-Moriya interaction.

    Science.gov (United States)

    Liu, Guang-Hua; You, Wen-Long; Li, Wei; Su, Gang

    2015-04-29

    Quantum phase transitions (QPTs) and the ground-state phase diagram of the spin-1/2 Heisenberg-Ising alternating chain (HIAC) with uniform Dzyaloshinskii-Moriya (DM) interaction are investigated by a matrix-product-state (MPS) method. By calculating the odd- and even-string order parameters, we recognize two kinds of Haldane phases, i.e. the odd- and even-Haldane phases. Furthermore, doubly degenerate entanglement spectra on odd and even bonds are observed in odd- and even-Haldane phases, respectively. A rich phase diagram including four different phases, i.e. an antiferromagnetic (AF), AF stripe, odd- and even-Haldane phases, is obtained. These phases are found to be separated by continuous QPTs: the topological QPT between the odd- and even-Haldane phases is verified to be continuous and corresponds to conformal field theory with central charge c = 1; while the rest of the phase transitions in the phase diagram are found to be c = 1/2. We also revisit, with our MPS method, the exactly solvable case of HIAC model with DM interactions only on odd bonds and find that the even-Haldane phase disappears, but the other three phases, i.e. the AF, AF stripe and odd-Haldane phases, still remain in the phase diagram. We exhibit the evolution of the even-Haldane phase by tuning the DM interactions on the even bonds gradually.

  2. Two-dimensional capillary origami

    Science.gov (United States)

    Brubaker, N. D.; Lega, J.

    2016-01-01

    We describe a global approach to the problem of capillary origami that captures all unfolded equilibrium configurations in the two-dimensional setting where the drop is not required to fully wet the flexible plate. We provide bifurcation diagrams showing the level of encapsulation of each equilibrium configuration as a function of the volume of liquid that it contains, as well as plots representing the energy of each equilibrium branch. These diagrams indicate at what volume level the liquid drop ceases to be attached to the endpoints of the plate, which depends on the value of the contact angle. As in the case of pinned contact points, three different parameter regimes are identified, one of which predicts instantaneous encapsulation for small initial volumes of liquid.

  3. Two-dimensional cubic convolution.

    Science.gov (United States)

    Reichenbach, Stephen E; Geng, Frank

    2003-01-01

    The paper develops two-dimensional (2D), nonseparable, piecewise cubic convolution (PCC) for image interpolation. Traditionally, PCC has been implemented based on a one-dimensional (1D) derivation with a separable generalization to two dimensions. However, typical scenes and imaging systems are not separable, so the traditional approach is suboptimal. We develop a closed-form derivation for a two-parameter, 2D PCC kernel with support [-2,2] x [-2,2] that is constrained for continuity, smoothness, symmetry, and flat-field response. Our analyses, using several image models, including Markov random fields, demonstrate that the 2D PCC yields small improvements in interpolation fidelity over the traditional, separable approach. The constraints on the derivation can be relaxed to provide greater flexibility and performance.

  4. Prediction of large-gap quantum spin hall insulator and Rashba-Dresselhaus effect in two-dimensional g-TIA (A = N, P, As, and Sb) monolayer films

    Institute of Scientific and Technical Information of China (English)

    Xinru Li[1; Ying Dai[1; Yandong Ma[1; Wei Wei[1; Lin Yu[1; Baibiao Huang[2

    2015-01-01

    A new family of two-dimensional (2D) topological insulators (TIs) comprising g-TIA (A = N, P, As, and Sb) monolayers constructed by T1 and group-V elements is predicted by first-principles calculations and molecular-dynamics (MD) simulations. The geometric stability, band inversion, nontrivial edge states, and electric polarity are investigated to predict the large-gap quantum spin Hall insulator and Rashba-Dresselhaus effects. The MD results reveal that the g-T1A monolayers remain stable even at room temperature. The g-T1A (A = As, Sb) monolayers become TIs under the influence of strong spin-orbit couplings with large bulk bandgaps of 131 and 268 meV, respectively. A single band inversion is observed in each g-T1A (A = As, Sb) monolayer, indicating a nontrivial topological nature. Furthermore, the topological edge states are described by introducing a sufficiently wide zigzag-nanoribbon. A Dirac point in the middle of the bulk gap connects the valence- and conduction-band edges. The Fermi velocity near the Dirac point with a linear band dispersion is -0.51 × 106 m/s, which is comparable to that of many other 2D nanomaterials. More importantly, owing to the broken inversion symmetry normal to the plane of the g-T1A films, a promising Rashba-Dresselhaus effect with the parameter up to 0.85 eV-A is observed in the g-T1A (A = As, Sb) monolayers. Our findings regarding 2D topological g-T1A monolayers with room-temperature bandgaps, intriguing topological edge states, and a promising Rashba-Dresselhaus effect are of fundamental value and suggest potential applications in nanoelectronic devices.

  5. Modern or Anti-modern Science? Weimar Culture, Natural Science and the Heidegger-Heisenberg Exchange

    Science.gov (United States)

    Carson, Cathryn

    The following sections are included: * Weimar Culture and Scientific Rationality * Heidegger Read Historically * Science and Crisis * Quantum Mechanics and the Heidegger-Heisenberg Exchange * Conclusion * Acknowledgments

  6. Slave-Fermion Mean-Field Theory of Heisenberg Model

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    A nearly half-filled two-dimensional Heisenberg model is investigated. A slave-fermion method with fermions as the charge carriers and bosons as the spin carriers is proposed. The ground state shows antiferromagnetic long range order at T = 0. The spin-spin correlation and static susceptibility are also obtained.

  7. Classifying Two-dimensional Hyporeductive Triple Algebras

    CERN Document Server

    Issa, A Nourou

    2010-01-01

    Two-dimensional real hyporeductive triple algebras (h.t.a.) are investigated. A classification of such algebras is presented. As a consequence, a classification of two-dimensional real Lie triple algebras (i.e. generalized Lie triple systems) and two-dimensional real Bol algebras is given.

  8. Two-dimensional topological photonic systems

    Science.gov (United States)

    Sun, Xiao-Chen; He, Cheng; Liu, Xiao-Ping; Lu, Ming-Hui; Zhu, Shi-Ning; Chen, Yan-Feng

    2017-09-01

    The topological phase of matter, originally proposed and first demonstrated in fermionic electronic systems, has drawn considerable research attention in the past decades due to its robust transport of edge states and its potential with respect to future quantum information, communication, and computation. Recently, searching for such a unique material phase in bosonic systems has become a hot research topic worldwide. So far, many bosonic topological models and methods for realizing them have been discovered in photonic systems, acoustic systems, mechanical systems, etc. These discoveries have certainly yielded vast opportunities in designing material phases and related properties in the topological domain. In this review, we first focus on some of the representative photonic topological models and employ the underlying Dirac model to analyze the edge states and geometric phase. On the basis of these models, three common types of two-dimensional topological photonic systems are discussed: 1) photonic quantum Hall effect with broken time-reversal symmetry; 2) photonic topological insulator and the associated pseudo-time-reversal symmetry-protected mechanism; 3) time/space periodically modulated photonic Floquet topological insulator. Finally, we provide a summary and extension of this emerging field, including a brief introduction to the Weyl point in three-dimensional systems.

  9. Asymptotics for Two-dimensional Atoms

    DEFF Research Database (Denmark)

    Nam, Phan Thanh; Portmann, Fabian; Solovej, Jan Philip

    2012-01-01

    We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E^{\\TF}(\\lambd......We prove that the ground state energy of an atom confined to two dimensions with an infinitely heavy nucleus of charge $Z>0$ and $N$ quantum electrons of charge -1 is $E(N,Z)=-{1/2}Z^2\\ln Z+(E^{\\TF}(\\lambda)+{1/2}c^{\\rm H})Z^2+o(Z^2)$ when $Z\\to \\infty$ and $N/Z\\to \\lambda$, where $E......^{\\TF}(\\lambda)$ is given by a Thomas-Fermi type variational problem and $c^{\\rm H}\\approx -2.2339$ is an explicit constant. We also show that the radius of a two-dimensional neutral atom is unbounded when $Z\\to \\infty$, which is contrary to the expected behavior of three-dimensional atoms....

  10. Two-dimensional function photonic crystals

    CERN Document Server

    Wu, Xiang-Yao; Liu, Xiao-Jing; Liang, Yu

    2016-01-01

    In this paper, we have firstly proposed two-dimensional function photonic crystals, which the dielectric constants of medium columns are the functions of space coordinates $\\vec{r}$, it is different from the two-dimensional conventional photonic crystals constituting by the medium columns of dielectric constants are constants. We find the band gaps of two-dimensional function photonic crystals are different from the two-dimensional conventional photonic crystals, and when the functions form of dielectric constants are different, the band gaps structure should be changed, which can be designed into the appropriate band gaps structures by the two-dimensional function photonic crystals.

  11. Heisenberg algebra for noncommutative Landau problem

    Science.gov (United States)

    Li, Kang; Cao, Xiao-Hua; Wang, Dong-Yan

    2006-10-01

    The Landau problem on non-commutative quantum mechanics is studied, where the Heisenberg algebra and the Landau energy levels as well as the non-commutative angular momentum are constructed in detail in non-commutative space and non-commutative phase space respectively.

  12. Heisenberg algebra for noncommutative Landau problem

    Institute of Scientific and Technical Information of China (English)

    Li Kang; Cao Xiao-Hua; Wang Dong-Yan

    2006-01-01

    The Landau problem on non-commutative quantum mechanics is studied, where the Heisenberg algebra and the Landau energy levels as well as the non-commutative angular momentum are constructed in detail in non-commutative space and non-commutative phase space respectively.

  13. Two-dimensional gas of massless Dirac fermions in graphene.

    Science.gov (United States)

    Novoselov, K S; Geim, A K; Morozov, S V; Jiang, D; Katsnelson, M I; Grigorieva, I V; Dubonos, S V; Firsov, A A

    2005-11-10

    Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.

  14. [Two traditions in the scientific learning of the world. A case study of creation and reception of quantum mechanics over the period 1925-1927, on the bases of discussion between Werner Heisenberg and Albert Einstein].

    Science.gov (United States)

    Krajniak, Wiktor

    2014-01-01

    The purpose of this article is the analyses of discussion between Albert Einstein and Werner Heisenberg in the period 1925-1927. Their disputes, relating to the sources of scientific knowledge, its methods and the value of knowledge acquired in this way, are part of the characteristic for the European science discourse between rationalism and empirism. On the basis of some sources and literature on the subject, the epistemological positions of both scholars in the period were reconstructed. This episode, yet poorly known, is a unique example of scientific disputes, whose range covers a broad spectrum of methodological problems associated with the historical development of science. The conducted analysis sheds some light on the source of popularity of logical empirism in the first half of the 20th century. A particular emphasis is placed on the impact of the neopositivist ideas which reflect Heisenberg's research program, being the starting point for the Copenhagen interpretation of quantum mechanics. The main assumption of logical empirism, concerning acquisition of scientific knowledge only by means of empirical procedures and logical analysis of the language of science, in view of the voiced by Einstein arguments, bears little relationship with actual testing practices in the historical aspect of the development of science. The criticism of Heisenberg's program, carried out by Einstein, provided arguments for the main critics of the neopositivist ideal and contributed to the bankruptcy of the idea of logical empirism, thereby starting a period of critical rationalism prosperity, arising from criticism of neopositivism and alluding to Einstein's ideas.

  15. Tracking dynamics of two-dimensional continuous attractor neural networks

    Science.gov (United States)

    Fung, C. C. Alan; Wong, K. Y. Michael; Wu, Si

    2009-12-01

    We introduce an analytically solvable model of two-dimensional continuous attractor neural networks (CANNs). The synaptic input and the neuronal response form Gaussian bumps in the absence of external stimuli, and enable the network to track external stimuli by its translational displacement in the two-dimensional space. Basis functions of the two-dimensional quantum harmonic oscillator in polar coordinates are introduced to describe the distortion modes of the Gaussian bump. The perturbative method is applied to analyze its dynamics. Testing the method by considering the network behavior when the external stimulus abruptly changes its position, we obtain results of the reaction time and the amplitudes of various distortion modes, with excellent agreement with simulation results.

  16. On a general Heisenberg exchange effective Hamiltonian

    Energy Technology Data Exchange (ETDEWEB)

    Blanco, J.A.; Prida Pidal, V.M. [Dept. de Fisica, Oviedo Univ. (Spain)

    1995-07-01

    A general Heisenberg exchange effective Hamiltonian is deduced in a straightforward way from the elemental quantum mechanical principles for the case of magnetic ions with non-orbital degeneracy in a crystalline lattice. Expressions for the high order direct exchange coupling constants or parameters are presented. The meaning of this effective Hamiltonian is important because extracting information from the Heisenberg Hamiltonian is a difficult task and is however taken as the starting point for many quite profound investigations of magnetism in solids and therefore could play an important role in an introductory course to solid state physics. (author)

  17. Global geometric entanglement and quantum phase transition in three-leg spin-3/2 Heisenberg tubes

    Science.gov (United States)

    Chen, Ai Min; Su, Yao Heng; Xia, Cai-Juan; Cho, Sam Young

    2016-10-01

    Based on the tensor network representations, we have developed an efficient scheme to calculate the global geometric entanglement as a multipartite entanglement measure for the three-leg spin tubes. From the geometric entanglement, the phase diagram of a spin-3 / 2 isosceles triangle spin tube has been investigated varying the base interaction α. Two Berezinsky-Kosterlitz-Thouless phase transitions are estimated to be α c1 ≃ 0.68 and α c2 ≃ 3.85, respectively. Then, even though the spin tube is in gapless spin liquid phases for α α c2, the geometrical structure difference between the groundstate wavefunctions for the two regions is found to reflect the global geometric entanglement that contains bipartite and multipartite contributions. Further, the phase transition points from the von Neumann entropies and fidelity are consistent with that from the geometric entanglement. As a result, the global geometric entanglement can be used to explore a geometrical nature of quantum phases as well as an indicator for quantum phase transitions in many-body lattice systems.

  18. Spin gap and string order parameter in the ferromagnetic spiral staircase heisenberg ladder: a quantum Monte Carlo study.

    Science.gov (United States)

    Brünger, C; Assaad, F F; Capponi, S; Alet, F; Aristov, D N; Kiselev, M N

    2008-01-11

    We consider a spin-1/2 ladder with a ferromagnetic rung coupling J perpendicular and inequivalent chains. This model is obtained by a twist (theta) deformation of the ladder and interpolates between the isotropic ladder (theta=0) and the SU(2) ferromagnetic Kondo necklace model (theta = pi). We show that the ground state in the (theta, J perpendicular) plane has a finite string order parameter characterizing the Haldane phase. Twisting the chain introduces a new energy scale, which we interpret in terms of a Suhl-Nakamura interaction. As a consequence we observe a crossover in the scaling of the spin gap at weak coupling from delta/J parallel proportional, variant J perpendicular/J parallel for theta theta c. Those results are obtained on the basis of large scale quantum Monte Carlo calculations.

  19. Predicting Two-Dimensional Silicon Carbide Monolayers.

    Science.gov (United States)

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I

    2015-10-27

    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics.

  20. Topological defects in two-dimensional crystals

    OpenAIRE

    Chen, Yong; Qi, Wei-Kai

    2008-01-01

    By using topological current theory, we study the inner topological structure of the topological defects in two-dimensional (2D) crystal. We find that there are two elementary point defects topological current in two-dimensional crystal, one for dislocations and the other for disclinations. The topological quantization and evolution of topological defects in two-dimensional crystals are discussed. Finally, We compare our theory with Brownian-dynamics simulations in 2D Yukawa systems.

  1. Noncompact Heisenberg spin magnets from high-energy QCD; 1 Baxter Q-operator and Separation of Variables

    CERN Document Server

    Derkachov, S E; Manashov, A N

    2001-01-01

    We analyze a completely integrable two-dimensional quantum-mechanical model that emerged in the recent studies of the compound gluonic states in multi-color QCD at high energy. The model represents a generalization of the well-known homogenous Heisenberg spin magnet to infinite-dimensional representations of the SL(2,C) group and can be reformulated within the Quantum Inverse Scattering Method. Solving the Yang-Baxter equation, we obtain the R-matrix for the SL(2,C) representations of the principal series and discuss its properties. We explicitly construct the Baxter Q-operator for this model and show how it can be used to determine the energy spectrum. We apply Sklyanin's method of the Separated Variables to obtain an integral representation for the eigenfunctions of the Hamiltonian. We demonstrate that the language of Feynman diagrams supplemented with the method of uniqueness provide a powerful technique for analyzing the properties of the model.

  2. Computational Quantum Chemistry for Multiple-Site Heisenberg Spin Couplings Made Simple: Still Only One Spin-Flip Required.

    Science.gov (United States)

    Mayhall, Nicholas J; Head-Gordon, Martin

    2015-05-21

    We provide a simple procedure for using inexpensive ab initio calculations to compute exchange coupling constants, J(AB), for multiradical molecules containing both an arbitrary number of radical sites and an arbitrary number of unpaired electrons. For a system comprised of 2M unpaired electrons, one needs only to compute states having the Ŝ(z) quantum number M - 1. Conveniently, these are precisely the states that are accessed by the family of single spin-flip methods. Building an effective Hamiltonian with these states allows one to extract all of the J(AB) constants in the molecule. Unlike approaches based on density functional theory, this procedure relies on neither spin-contaminated states nor nonunique spin-projection formulas. A key benefit is that it is possible to obtain completely spin-pure exchange coupling constants with inexpensive ab initio calculations. A couple of examples are provided to illustrate the approach, including a 4-nickel cubane complex and a 6-chromium horseshoe complex with 18 entangled electrons.

  3. Level crossings in complex two-dimensional potentials

    Indian Academy of Sciences (India)

    Qing-Hai Wang

    2009-08-01

    Two-dimensional $\\mathcal{PT}$-symmetric quantum-mechanical systems with the complex cubic potential 12 = 2 + 2 + 2 and the complex Hénon–Heiles potential HH = 2 + 2 + (2 − 3/3) are investigated. Using numerical and perturbative methods, energy spectra are obtained to high levels. Although both potentials respect the $\\mathcal{PT}$ symmetry, the complex energy eigenvalues appear when level crossing happens between same parity eigenstates.

  4. Chronology Protection in Two-Dimensional Dilaton Gravity

    CERN Document Server

    Mishima, T; Mishima, Takashi; Nakamichi, Akika

    1994-01-01

    The global structure of 1 + 1 dimensional compact Universe is studied in two-dimensional model of dilaton gravity. First we give a classical solution corresponding to the spacetime in which a closed time-like curve appears, and show the instability of this spacetime due to the existence of matters. We also observe quantum version of such a spacetime having closed timelike curves never reappear unless the parameters are fine-tuned.

  5. Tricritical behavior in a two-dimensional field theory

    Science.gov (United States)

    Hamber, Herbert

    1980-05-01

    The critical behavior of a two-dimensional scalar Euclidean field theory with a potential term that allows for three minima is analyzed using an approximate position-space renormalization-group transformation on the equivalent quantum spin Hamiltonian. The global phase diagram shows a tricritical point separating a critical line from a line of first-order transitions. Other critical properties are examined, and good agreement is found with results on classical spin models belonging to the same universality class.

  6. Dynamical structure factors and excitation modes of the bilayer Heisenberg model

    Science.gov (United States)

    Lohöfer, M.; Coletta, T.; Joshi, D. G.; Assaad, F. F.; Vojta, M.; Wessel, S.; Mila, F.

    2015-12-01

    Using quantum Monte Carlo simulations along with higher-order spin-wave theory, bond-operator and strong-coupling expansions, we analyze the dynamical spin structure factor of the spin-half Heisenberg model on the square-lattice bilayer. We identify distinct contributions from the low-energy Goldstone modes in the magnetically ordered phase and the gapped triplon modes in the quantum disordered phase. In the antisymmetric (with respect to layer inversion) channel, the dynamical spin structure factor exhibits a continuous evolution of spectral features across the quantum phase transition, connecting the two types of modes. Instead, in the symmetric channel, we find a depletion of the spectral weight when moving from the ordered to the disordered phase. While the dynamical spin structure factor does not exhibit a well-defined distinct contribution from the amplitude (or Higgs) mode in the ordered phase, we identify an only marginally damped amplitude mode in the dynamical singlet structure factor, obtained from interlayer bond correlations, in the vicinity of the quantum critical point. These findings provide quantitative information in direct relation to possible neutron or light scattering experiments in a fundamental two-dimensional quantum-critical spin system.

  7. Strongly interacting two-dimensional Dirac fermions

    NARCIS (Netherlands)

    Lim, L.K.; Lazarides, A.; Hemmerich, Andreas; de Morais Smith, C.

    2009-01-01

    We show how strongly interacting two-dimensional Dirac fermions can be realized with ultracold atoms in a two-dimensional optical square lattice with an experimentally realistic, inherent gauge field, which breaks time reversal and inversion symmetries. We find remarkable phenomena in a temperature

  8. Topology optimization of two-dimensional waveguides

    DEFF Research Database (Denmark)

    Jensen, Jakob Søndergaard; Sigmund, Ole

    2003-01-01

    In this work we use the method of topology optimization to design two-dimensional waveguides with low transmission loss.......In this work we use the method of topology optimization to design two-dimensional waveguides with low transmission loss....

  9. Determination of Band-filling Change in the Two-dimensional Organic Conductor, τ-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y, (y ≤ 0.875) by the Quantum Oscillation of Magnetoresistance

    Science.gov (United States)

    Yoshino, Harukazu; Murata, Keizo; Nakanishi, Tsutomu; Li, Lin; Choi, Eun Sang; Graf, David; Brooks, James S.; Nogami, Yoshio; Papavassiliou, George C.

    2005-01-01

    The effect of thermal treatment on the transport properties is studied for a two-dimensional organic conductor τ-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y, (y ≤ 0.875). The temperature dependence of the electric resistivity below room temperature was found to be changed from metallic down to low temperature to semiconducting by heating up to 420 K. One of the two frequencies of Shubnikov--de Haas oscillations are found to be different between the non-heated and heated parts from a single crystal, while no evidence of structural change in X-ray photograph was observed. The present result clearly shows that nominal valence or band filling can be controlled by simple thermal treatment for the quasi-two-dimensional organic metal. The mechanism of the change in the band filling is discussed in terms of anion decomposition.

  10. Quantum spins and quasiperiodicity: a real space renormalization group approach.

    Science.gov (United States)

    Jagannathan, A

    2004-01-30

    We study the antiferromagnetic spin-1/2 Heisenberg model on a two-dimensional bipartite quasiperiodic structure, the octagonal tiling, the aperiodic equivalent of the square lattice for periodic systems. An approximate block spin renormalization scheme is described for this problem. The ground state energy and local staggered magnetizations for this system are calculated and compared with the results of a recent quantum Monte Carlo calculation for the tiling. It is conjectured that the ground state energy is exactly equal to that of the quantum antiferromagnet on the square lattice.

  11. Supersymmetry and the constants of motion of the two-dimensional isotropic harmonic oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Torres del Castillo, G.F. [Departamento de Fisica Matematica, Instituto de Ciencias, Universidad Autonoma de Puebla, 72570 Puebla (Mexico); Tepper G, T. [Escuela de Ciencias, Departamento de Fisica y Matematicas, Universidad de Las Americas-Puebla, Santa Catarina Martir, 72820 Cholula, Puebla (Mexico)

    2002-07-01

    It is shown that the constants of motion of the two-dimensional isotropic harmonic oscillator not related to the rotational invariance of the Hamiltonian can be derived using the ideas of supersymmetric quantum mechanics. (Author)

  12. Interaction of two-dimensional magnetoexcitons

    Science.gov (United States)

    Dumanov, E. V.; Podlesny, I. V.; Moskalenko, S. A.; Liberman, M. A.

    2017-04-01

    We study interaction of the two-dimensional magnetoexcitons with in-plane wave vector k→∥ = 0 , taking into account the influence of the excited Landau levels (ELLs) and of the external electric field perpendicular to the surface of the quantum well and parallel to the external magnetic field. It is shown that the account of the ELLs gives rise to the repulsion between the spinless magnetoexcitons with k→∥ = 0 in the Fock approximation, with the interaction constant g decreasing inverse proportional to the magnetic field strength B (g (0) ∼ 1 / B) . In the presence of the perpendicular electric field the Rashba spin-orbit coupling (RSOC), Zeeman splitting (ZS) and nonparabolicity of the heavy-hole dispersion law affect the Landau quantization of the electrons and holes. They move along the new cyclotron orbits, change their Coulomb interactions and cause the interaction between 2D magnetoexcitons with k→∥ = 0 . The changes of the Coulomb interactions caused by the electrons and by the holes moving with new cyclotron orbits are characterized by some coefficients, which in the absence of the electric field turn to be unity. The differences between these coefficients of the electron-hole pairs forming the magnetoexcitons determine their affinities to the interactions. The interactions between the homogeneous, semihomogeneous and heterogeneous magnetoexcitons forming the symmetric states with the same signs of their affinities are attractive whereas in the case of different sign affinities are repulsive. In the heterogeneous asymmetric states the interactions have opposite signs in comparison with the symmetric states. In all these cases the interaction constant g have the dependence g (0) 1 /√{ B} .

  13. Ground states, magnetization plateaus and bipartite entanglement of frustrated spin-1/2 Ising-Heisenberg and Heisenberg triangular tubes

    Science.gov (United States)

    Alécio, Raphael C.; Lyra, Marcelo L.; Strečka, Jozef

    2016-11-01

    The ground-state phase diagram, magnetization process and bipartite entanglement of the frustrated spin-1/2 Ising-Heisenberg and Heisenberg triangular tube (three-leg ladder) are investigated in a non-zero external magnetic field. The exact ground-state phase diagram of the spin-1/2 Ising-Heisenberg tube with Heisenberg intra-rung and Ising inter-rung couplings consists of six distinct gapped phases, which manifest themselves in a magnetization curve as intermediate plateaus at zero, one-third and two-thirds of the saturation magnetization. Four out of six available ground states exhibit quantum entanglement between two spins from the same triangular unit evidenced by a non-zero concurrence. Density-matrix renormalization group calculations are used in order to construct the ground-state phase diagram of the analogous but purely quantum spin-1/2 Heisenberg tube with Heisenberg intra- and inter-rung couplings, which consists of four gapped and three gapless phases. The Heisenberg tube shows a continuous change of the magnetization instead of a plateau at zero magnetization, while the intermediate one-third and two-thirds plateaus may be present or not in the zero-temperature magnetization curve.

  14. Study of the bilinear biquadratic Heisenberg model on a honeycomb lattice via Schwinger bosons

    Energy Technology Data Exchange (ETDEWEB)

    Moura, Antônio R., E-mail: antoniormoura.br@gmail.com [Universidade Federal de Uberlândia, Minas Gerais (Brazil); Pereira, Afrânio R. [Departamento de Física, Universidade Federal de Viçosa, 36570-000, Minas Gerais (Brazil)

    2013-09-15

    We analyze the biquadratic bilinear Heisenberg magnet on a honeycomb lattice via Schwinger boson formalism. Due to their vulnerability to quantum fluctuations, non-conventional lattices (kagome, triangular and honeycomb for example) have been cited as candidates to support spin liquid states. Such states without long range order at zero temperature are known in one-dimensional spin models but their existence in higher dimensional systems is still under debate. Biquadratic interaction is responsible for various possibilities and phases as it is well-founded for one-dimensional systems. Here we have used a bosonic representation to study the properties at zero and finite low temperatures of the biquadratic term in the two-dimensional hexagonal honeycomb lattice. The results show an ordered state at zero temperature but much more fragile than that of a square lattice; the behavior at finite low temperatures is in accordance with expectations. - Highlights: • We study the biquadric bilinear Heisenberg model on a honeycomb lattice. • We show the impossibility of a liquid spin state at zero temperature. • The order is weaker than the square lattice model. • The low energy excitations are relativistic Goldstone modes. • The results at finite temperatures agree with the Mermin–Wagner theorem.

  15. Realization of an Ultrasensitive Heisenberg-Limited Interferometer

    Science.gov (United States)

    2006-07-31

    used a Monte Carlo simulation program to examine the effect of losses on this highly nonlinear detection scheme, with its experimental imple...is below since many authors do not follow the 200 word limit 14. SUBJECT TERMS quantum optics, nonlinear optics, squeezed states, Heisenberg -limited...Programs 1001 N. Emmett St. P.O. Box 400195 Charlottesville, VA 22904 -4195 Realization of an Ultrasensitive Heisenberg -Limited Interferometer REPORT

  16. Chiral Kosterlitz-Thouless transition in the frustrated Heisenberg antiferromagnet on a pyrochlore slab.

    Science.gov (United States)

    Kawamura, Hikaru; Arimori, Takuya

    2002-02-18

    Ordering of the geometrically frustrated two-dimensional Heisenberg antiferromagnet on a pyrochlore slab is studied by Monte Carlo simulations. In contrast to the kagomé Heisenberg antiferromagnet, the model exhibits locally noncoplanar spin structures at low temperatures, bearing nontrivial chiral degrees of freedom. Under certain conditions, the model exhibits a novel Kosterlitz-Thouless-type transition at a finite temperature associated with these chiral degrees of freedom.

  17. Two Dimensional Plasmonic Cavities on Moire Surfaces

    Science.gov (United States)

    Balci, Sinan; Kocabas, Askin; Karabiyik, Mustafa; Kocabas, Coskun; Aydinli, Atilla

    2010-03-01

    We investigate surface plasmon polariton (SPP) cavitiy modes on two dimensional Moire surfaces in the visible spectrum. Two dimensional hexagonal Moire surface can be recorded on a photoresist layer using Interference lithography (IL). Two sequential exposures at slightly different angles in IL generate one dimensional Moire surfaces. Further sequential exposure for the same sample at slightly different angles after turning the sample 60 degrees around its own axis generates two dimensional hexagonal Moire cavity. Spectroscopic reflection measurements have shown plasmonic band gaps and cavity states at all the azimuthal angles (omnidirectional cavity and band gap formation) investigated. The plasmonic band gap edge and the cavity states energies show six fold symmetry on the two dimensional Moire surface as measured in reflection measurements.

  18. Two-dimensional function photonic crystals

    Science.gov (United States)

    Liu, Xiao-Jing; Liang, Yu; Ma, Ji; Zhang, Si-Qi; Li, Hong; Wu, Xiang-Yao; Wu, Yi-Heng

    2017-01-01

    In this paper, we have studied two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , that can become true easily by electro-optical effect and optical kerr effect. We calculated the band gap structures of TE and TM waves, and found the TE (TM) wave band gaps of function photonic crystals are wider (narrower) than the conventional photonic crystals. For the two-dimensional function photonic crystals, when the dielectric constant functions change, the band gaps numbers, width and position should be changed, and the band gap structures of two-dimensional function photonic crystals can be adjusted flexibly, the needed band gap structures can be designed by the two-dimensional function photonic crystals, and it can be of help to design optical devices.

  19. Two-Dimensional Planetary Surface Lander

    Science.gov (United States)

    Hemmati, H.; Sengupta, A.; Castillo, J.; McElrath, T.; Roberts, T.; Willis, P.

    2014-06-01

    A systems engineering study was conducted to leverage a new two-dimensional (2D) lander concept with a low per unit cost to enable scientific study at multiple locations with a single entry system as the delivery vehicle.

  20. Entangling qubits by Heisenberg spin exchange and anyon braiding

    Science.gov (United States)

    Zeuch, Daniel

    As the discovery of quantum mechanics signified a revolution in the world of physics more than one century ago, the notion of a quantum computer in 1981 marked the beginning of a drastic change of our understanding of information and computability. In a quantum computer, information is stored using quantum bits, or qubits, which are described by a quantum-mechanical superposition of the quantum states 0 and 1. Computation then proceeds by acting with unitary operations on these qubits. These operations are referred to as quantum logic gates, in analogy to classical computation where bits are acted on by classical logic gates. In order to perform universal quantum computation it is, in principle, sufficient to carry out single-qubit gates and two-qubit gates, where the former act on individual qubits and the latter, acting on two qubits, are used to entangle qubits with each other. The present thesis is divided into two main parts. In the first, we are concerned with spin-based quantum computation. In a spin-based quantum computer, qubits are encoded into the Hilbert space spanned by spin-1/2 particles, such as electron spins trapped in semiconductor quantum dots. For a suitable qubit encoding, turning on-and-off, or "pulsing,'' the isotropic Heisenberg exchange Hamiltonian JSi · Sj allows for universal quantum computation and it is this scheme, known as exchange-only quantum computation, which we focus on. In the second part of this thesis, we consider a topological quantum computer in which qubits are encoded using so-called Fibonacci anyons, exotic quasiparticle excitations that obey non-Abelian statistics, and which may emerge in certain two-dimensional topological systems such as fractional quantum-Hall states. Quantum gates can then be carried out by moving these particles around one another, a process that can be viewed as braiding their 2+1 dimensional worldlines. The subject of the present thesis is the development and theoretical understanding of

  1. Blockspin Cluster Algorithms for Quantum Spin Systems

    CERN Document Server

    Wiese, U J

    1992-01-01

    Cluster algorithms are developed for simulating quantum spin systems like the one- and two-dimensional Heisenberg ferro- and anti-ferromagnets. The corresponding two- and three-dimensional classical spin models with four-spin couplings are maped to blockspin models with two-blockspin interactions. Clusters of blockspins are updated collectively. The efficiency of the method is investigated in detail for one-dimensional spin chains. Then in most cases the new algorithms solve the problems of slowing down from which standard algorithms are suffering.

  2. HEISENBERG'S INEQUALITY AND LOGARITHMIC HEISENBERG'S INEQUALITY FOR AMBIGUITY FUNCTION

    Institute of Scientific and Technical Information of China (English)

    Tian Guji

    2000-01-01

    In this article we discuss the relation between Heisenberg's inequality and logarithmic Heisenberg's (entropy) inequality for ambiguity function. After building up a Heisenberg's inequality, we obtain a connection of variance with entropy by variational method. Using classical Taylor's expansion, we prove that the equality in Heisenberg's inequality holds if and only if the entropy of 2k - 1 order is equal to (2k - 1)!.

  3. Spin-1/2 Ising-Heisenberg model with the pair XYZ Heisenberg interaction and quartic Ising interactions as the exactly soluble zero-field eight-vertex model.

    Science.gov (United States)

    Strecka, Jozef; Canová, Lucia; Minami, Kazuhiko

    2009-05-01

    The spin-1/2 Ising-Heisenberg model with the pair XYZ Heisenberg interaction and quartic Ising interactions is exactly solved by establishing a precise mapping relationship with the corresponding zero-field (symmetric) eight-vertex model. It is shown that the Ising-Heisenberg model with the ferromagnetic Heisenberg interaction exhibits a striking critical behavior, which manifests itself through re-entrant phase transitions as well as continuously varying critical exponents. The changes in critical exponents are in accordance with the weak universality hypothesis in spite of a peculiar singular behavior that emerges at a quantum critical point of the infinite order, which occurs at the isotropic limit of the Heisenberg interaction. On the other hand, the Ising-Heisenberg model with the antiferromagnetic Heisenberg interaction surprisingly exhibits less significant changes in both critical temperatures and critical exponents upon varying the strength of the exchange anisotropy in the Heisenberg interaction.

  4. Dynamic creation of a topologically-ordered Hamiltonian using spin-pulse control in the Heisenberg model.

    Science.gov (United States)

    Tanamoto, Tetsufumi; Ono, Keiji; Liu, Yu-xi; Nori, Franco

    2015-06-17

    Hamiltonian engineering is an important approach for quantum information processing, when appropriate materials do not exist in nature or are unstable. So far there is no stable material for the Kitaev spin Hamiltonian with anisotropic interactions on a honeycomb lattice, which plays a crucial role in the realization of both Abelian and non-Abelian anyons. Here, we show two methods to dynamically realize the Kitaev spin Hamiltonian from the conventional Heisenberg spin Hamiltonian using pulse-control techniques based on the Baker-Campbell-Hausdorff (BCH) formula. In the first method, the Heisenberg interaction is changed into Ising interactions in the first process of the pulse sequence. In the next process of the first method, we transform them to a desirable anisotropic Kitaev spin Hamiltonian. In the second more efficient method, we show that if we carefully design two-dimensional pulses that vary depending on the qubit location, we can obtain the desired Hamiltonian in only one step of applying the BCH formula. As an example, we apply our methods to spin qubits based on quantum dots, in which the effects of both the spin-orbit interaction and the hyperfine interaction are estimated.

  5. Entanglement Entropy in Two-Dimensional String Theory.

    Science.gov (United States)

    Hartnoll, Sean A; Mazenc, Edward A

    2015-09-18

    To understand an emergent spacetime is to understand the emergence of locality. Entanglement entropy is a powerful diagnostic of locality, because locality leads to a large amount of short distance entanglement. Two-dimensional string theory is among the very simplest instances of an emergent spatial dimension. We compute the entanglement entropy in the large-N matrix quantum mechanics dual to two-dimensional string theory in the semiclassical limit of weak string coupling. We isolate a logarithmically large, but finite, contribution that corresponds to the short distance entanglement of the tachyon field in the emergent spacetime. From the spacetime point of view, the entanglement is regulated by a nonperturbative "graininess" of space.

  6. Topological states in two-dimensional hexagon lattice bilayers

    Science.gov (United States)

    Zhang, Ming-Ming; Xu, Lei; Zhang, Jun

    2016-10-01

    We investigate the topological states of the two-dimensional hexagon lattice bilayer. The system exhibits a quantum valley Hall (QVH) state when the interlayer interaction t⊥ is smaller than the nearest neighbor hopping energy t, and then translates to a trivial band insulator state when t⊥ / t > 1. Interestingly, the system is found to be a single-edge QVH state with t⊥ / t = 1. The topological phase transition also can be presented via changing bias voltage and sublattice potential in the system. The QVH states have different edge modes carrying valley current but no net charge current. The bias voltage and external electric field can be tuned easily in experiments, so the present results will provide potential application in valleytronics based on the two-dimensional hexagon lattice.

  7. On the critical behaviour of two-dimensional liquid crystals

    Directory of Open Access Journals (Sweden)

    A.l. Fariñas-Sánchez

    2010-01-01

    Full Text Available The Lebwohl-Lasher (LL model is the traditional model used to describe the nematic-isotropic transition of real liquid crystals. In this paper, we develop a numerical study of the temperature behaviour and of finite-size scaling of the two-dimensional (2D LL-model. We discuss two possible scenarios. In the first one, the 2D LL-model presents a phase transition similar to the topological transition appearing in the 2D XY-model. In the second one, the 2D LL-model does not exhibit any critical transition, but its low temperature behaviour is rather characterized by a crossover from a disordered phase to an ordered phase at zero temperature. We realize and discuss various comparisons with the 2D XY-model and the 2D Heisenberg model. Having added finite-size scaling behaviour of the order parameter and conformal mapping of order parameter profile to previous studies, we analyze the critical scaling of the probability distribution function, hyperscaling relations and stiffness order parameter and conclude that the second scenario (no critical transition is the most plausible.

  8. Two-dimensional Fourier transform ESR correlation spectroscopy

    Science.gov (United States)

    Gorcester, Jeff; Freed, Jack H.

    1988-04-01

    We describe our pulsed two-dimensional Fourier transform ESR experiment and demonstrate its applicabilty for the double resonance of motionally narrowed nitroxides. Multiple pulse irradiation of the entire nitroxide spectrum enables the correlation of two precessional periods, allowing observation of cross correlations between hyperfine lines introduced by magnetization transfer in the case of a three-pulse experiment (2D ELDOR), or coherence transfer in the case of a two-pulse experiment (COSY). Cross correlations are revealed by the presence of cross peaks which connect the autocorrelation lines appearing along the diagonal ω1=ω2. The amplitudes of these cross peaks are determined by the rates of magnetization transfer in the 2D ELDOR experiment. The density operator theory for the experiment is outlined and applied to the determination of Heisenberg exchange (HE) rates in 2,2,6,6-tetramethyl-4-piperidone-N-oxyl-d15 (PD-tempone) dissolved in toluene-d8. The quantitative accuracy of this experiment is established by comparison with the HE rate measured from the dependence of the spin echo T2 on nitroxide concentration.

  9. Interpolation by two-dimensional cubic convolution

    Science.gov (United States)

    Shi, Jiazheng; Reichenbach, Stephen E.

    2003-08-01

    This paper presents results of image interpolation with an improved method for two-dimensional cubic convolution. Convolution with a piecewise cubic is one of the most popular methods for image reconstruction, but the traditional approach uses a separable two-dimensional convolution kernel that is based on a one-dimensional derivation. The traditional, separable method is sub-optimal for the usual case of non-separable images. The improved method in this paper implements the most general non-separable, two-dimensional, piecewise-cubic interpolator with constraints for symmetry, continuity, and smoothness. The improved method of two-dimensional cubic convolution has three parameters that can be tuned to yield maximal fidelity for specific scene ensembles characterized by autocorrelation or power-spectrum. This paper illustrates examples for several scene models (a circular disk of parametric size, a square pulse with parametric rotation, and a Markov random field with parametric spatial detail) and actual images -- presenting the optimal parameters and the resulting fidelity for each model. In these examples, improved two-dimensional cubic convolution is superior to several other popular small-kernel interpolation methods.

  10. Heisenberg scaling of imaging resolution by coherent enhancement

    CERN Document Server

    McConnell, Robert; Yoder, Theodore J; Bruzewicz, Colin D; Chuang, Isaac L; Chiaverini, John; Sage, Jeremy M

    2016-01-01

    Classical imaging works by scattering photons from an object to be imaged, and achieves resolution scaling as $1/\\sqrt{t}$, with $t$ the imaging time. By contrast, the laws of quantum mechanics allow one to utilize quantum coherence to obtain imaging resolution that can scale as quickly as $1/t$ -- the so-called "Heisenberg limit." However, ambiguities in the obtained signal often preclude taking full advantage of this quantum enhancement, while imaging techniques designed to be unambiguous often lose this optimal Heisenberg scaling. Here, we demonstrate an imaging technique which combines unambiguous detection of the target with Heisenberg scaling of the resolution. We also demonstrate a binary search algorithm which can efficiently locate a coherent target using the technique, resolving a target trapped ion to within 3% of the $1/e^2$ diameter of the excitation beam.

  11. TWO-DIMENSIONAL TOPOLOGY OF COSMOLOGICAL REIONIZATION

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yougang; Xu, Yidong; Chen, Xuelei [Key Laboratory of Computational Astrophysics, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012 China (China); Park, Changbom [School of Physics, Korea Institute for Advanced Study, 85 Hoegiro, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of); Kim, Juhan, E-mail: wangyg@bao.ac.cn, E-mail: cbp@kias.re.kr [Center for Advanced Computation, Korea Institute for Advanced Study, 85 Hoegiro, Dongdaemun-gu, Seoul 130-722 (Korea, Republic of)

    2015-11-20

    We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two-dimensional genus curve for the early, middle, and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometre Array.

  12. Two dimensional topology of cosmological reionization

    CERN Document Server

    Wang, Yougang; Xu, Yidong; Chen, Xuelei; Kim, Juhan

    2015-01-01

    We study the two-dimensional topology of the 21-cm differential brightness temperature for two hydrodynamic radiative transfer simulations and two semi-numerical models. In each model, we calculate the two dimensional genus curve for the early, middle and late epochs of reionization. It is found that the genus curve depends strongly on the ionized fraction of hydrogen in each model. The genus curves are significantly different for different reionization scenarios even when the ionized faction is the same. We find that the two-dimensional topology analysis method is a useful tool to constrain the reionization models. Our method can be applied to the future observations such as those of the Square Kilometer Array.

  13. Magnetization process and collective excitations in the S=1/2 triangular-lattice Heisenberg antiferromagnet Ba3CoSb2O9.

    Science.gov (United States)

    Susuki, Takuya; Kurita, Nobuyuki; Tanaka, Takuya; Nojiri, Hiroyuki; Matsuo, Akira; Kindo, Koichi; Tanaka, Hidekazu

    2013-06-28

    We have performed high-field magnetization and electronic spin resonance (ESR) measurements on Ba3CoSb2O9 single crystals, which approximates the two-dimensional (2D) S=1/2 triangular-lattice Heisenberg antiferromagnet. For an applied magnetic field H parallel to the ab plane, the entire magnetization curve including the plateau at one-third of the saturation magnetization (Ms) is in excellent agreement with the results of theoretical calculations except a small step anomaly near (3/5)Ms, indicative of a theoretically undiscovered quantum phase transition. However, for H∥c, the magnetization curve exhibits a cusp near Ms/3 owing to the weak easy-plane anisotropy and the 2D quantum fluctuation. From a detailed analysis of the collective ESR modes observed in the ordered state, combined with the magnetization process, we have determined all the magnetic parameters including the interlayer and anisotropic exchange interactions.

  14. Two-dimensional x-ray diffraction

    CERN Document Server

    He, Bob B

    2009-01-01

    Written by one of the pioneers of 2D X-Ray Diffraction, this useful guide covers the fundamentals, experimental methods and applications of two-dimensional x-ray diffraction, including geometry convention, x-ray source and optics, two-dimensional detectors, diffraction data interpretation, and configurations for various applications, such as phase identification, texture, stress, microstructure analysis, crystallinity, thin film analysis and combinatorial screening. Experimental examples in materials research, pharmaceuticals, and forensics are also given. This presents a key resource to resea

  15. Matching Two-dimensional Gel Electrophoresis' Spots

    DEFF Research Database (Denmark)

    Dos Anjos, António; AL-Tam, Faroq; Shahbazkia, Hamid Reza

    2012-01-01

    This paper describes an approach for matching Two-Dimensional Electrophoresis (2-DE) gels' spots, involving the use of image registration. The number of false positive matches produced by the proposed approach is small, when compared to academic and commercial state-of-the-art approaches. This ar......This paper describes an approach for matching Two-Dimensional Electrophoresis (2-DE) gels' spots, involving the use of image registration. The number of false positive matches produced by the proposed approach is small, when compared to academic and commercial state-of-the-art approaches...

  16. Mobility anisotropy of two-dimensional semiconductors

    Science.gov (United States)

    Lang, Haifeng; Zhang, Shuqing; Liu, Zhirong

    2016-12-01

    The carrier mobility of anisotropic two-dimensional semiconductors under longitudinal acoustic phonon scattering was theoretically studied using deformation potential theory. Based on the Boltzmann equation with the relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was derived, showing that the influence of effective mass on mobility anisotropy is larger than those of deformation potential constant or elastic modulus. Parameters were collected for various anisotropic two-dimensional materials (black phosphorus, Hittorf's phosphorus, BC2N , MXene, TiS3, and GeCH3) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio is overestimated by the previously described method.

  17. Towards two-dimensional search engines

    OpenAIRE

    Ermann, Leonardo; Chepelianskii, Alexei D.; Shepelyansky, Dima L.

    2011-01-01

    We study the statistical properties of various directed networks using ranking of their nodes based on the dominant vectors of the Google matrix known as PageRank and CheiRank. On average PageRank orders nodes proportionally to a number of ingoing links, while CheiRank orders nodes proportionally to a number of outgoing links. In this way the ranking of nodes becomes two-dimensional that paves the way for development of two-dimensional search engines of new type. Statistical properties of inf...

  18. Two-dimensionally confined topological edge states in photonic crystals

    Science.gov (United States)

    Barik, Sabyasachi; Miyake, Hirokazu; DeGottardi, Wade; Waks, Edo; Hafezi, Mohammad

    2016-11-01

    We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three-dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.

  19. Two-Dimensionally Confined Topological Edge States in Photonic Crystals

    CERN Document Server

    Barik, Sabyasachi; DeGottardi, Wade; Waks, Edo; Hafezi, Mohammad

    2016-01-01

    We present an all-dielectric photonic crystal structure that supports two-dimensionally confined helical topological edge states. The topological properties of the system are controlled by the crystal parameters. An interface between two regions of differing band topologies gives rise to topological edge states confined in a dielectric slab that propagate around sharp corners without backscattering. Three dimensional finite-difference time-domain calculations show these edges to be confined in the out-of-plane direction by total internal reflection. Such nanoscale photonic crystal architectures could enable strong interactions between photonic edge states and quantum emitters.

  20. Electronic Transmission Properties of Two-Dimensional Quasi-Lattice

    Institute of Scientific and Technical Information of China (English)

    侯志林; 傅秀军; 刘有延

    2002-01-01

    In the framework of the tight binding model, the electronic transmission properties of two-dimensional Penrose lattices with free boundary conditions are studied using the generalized eigenfunction method (Phys. Rev. B 60(1999)13444). The electronic transmission coefficients for Penrose lattices with different sizes and widths are calculated, and the result shows strong energy dependence because of the quasiperiodic structure and quantum coherent effect. Around the Fermi level E = 0, there is an energy region with zero transmission amplitudes,which suggests that the studied systems are insulating. The spatial distributions of several typical electronic states with different transmission coefficients are plotted to display the propagation process.