WorldWideScience

Sample records for quantum phase transitions

  1. Understanding quantum phase transitions

    CERN Document Server

    Carr, Lincoln

    2010-01-01

    Quantum phase transitions (QPTs) offer wonderful examples of the radical macroscopic effects inherent in quantum physics: phase changes between different forms of matter driven by quantum rather than thermal fluctuations, typically at very low temperatures. QPTs provide new insight into outstanding problems such as high-temperature superconductivity and display fundamental aspects of quantum theory, such as strong correlations and entanglement. Over the last two decades, our understanding of QPTs has increased tremendously due to a plethora of experimental examples, powerful new numerical meth

  2. Entanglement, quantum phase transitions and quantum algorithms

    CERN Document Server

    Orus, R

    2006-01-01

    The work that we present in this thesis tries to be at the crossover of quantum information science, quantum many-body physics, and quantum field theory. We use tools from these three fields to analyze problems that arise in the interdisciplinary intersection. More concretely, in Chapter 1 we consider the irreversibility of renormalization group flows from a quantum information perspective by using majorization theory and conformal field theory. In Chapter 2 we compute the entanglement of a single copy of a bipartite quantum system for a variety of models by using techniques from conformal field theory and Toeplitz matrices. The entanglement entropy of the so-called Lipkin-Meshkov-Glick model is computed in Chapter 3, showing analogies with that of (1+1)-dimensional quantum systems. In Chapter 4 we apply the ideas of scaling of quantum correlations in quantum phase transitions to the study of quantum algorithms, focusing on Shor's factorization algorithm and quantum algorithms by adiabatic evolution solving a...

  3. Adiabatic quantum computation and quantum phase transitions

    CERN Document Server

    Latorre, J I; Latorre, Jose Ignacio; Orus, Roman

    2003-01-01

    We analyze the ground state entanglement in a quantum adiabatic evolution algorithm designed to solve the NP-complete Exact Cover problem. The entropy of entanglement seems to obey linear and universal scaling at the point where the mass gap becomes small, suggesting that the system passes near a quantum phase transition. Such a large scaling of entanglement suggests that the effective connectivity of the system diverges as the number of qubits goes to infinity and that this algorithm cannot be efficiently simulated by classical means. On the other hand, entanglement in Grover's algorithm is bounded by a constant.

  4. Quantum phase transitions in constrained Bose systems

    OpenAIRE

    Bonnes, Lars

    2011-01-01

    This doctoral thesis studies low dimensional quantum systems that can be realized in recent cold atom experiments. From the viewpoint of quantum statistical mechanics, the main emphasis is on the detailed study of the different quantum and thermal phases and their transitions using numerical methods, such as quantum Monte Carlo and the Tensor Network Renormalization Group. The first part of this work deals with a lattice Boson model subject to strong three-body losses. In a quantum-Zeno li...

  5. Dynamical quantum phase transitions (Review Article)

    Science.gov (United States)

    Zvyagin, A. A.

    2016-11-01

    During recent years the interest to dynamics of quantum systems has grown considerably. Quantum many body systems out of equilibrium often manifest behavior, different from the one predicted by standard statistical mechanics and thermodynamics in equilibrium. Since the dynamics of a many-body quantum system typically involve many excited eigenstates, with a non-thermal distribution, the time evolution of such a system provides an unique way for investigation of non-equilibrium quantum statistical mechanics. Last decade such new subjects like quantum quenches, thermalization, pre-thermalization, equilibration, generalized Gibbs ensemble, etc. are among the most attractive topics of investigation in modern quantum physics. One of the most interesting themes in the study of dynamics of quantum many-body systems out of equilibrium is connected with the recently proposed important concept of dynamical quantum phase transitions. During the last few years a great progress has been achieved in studying of those singularities in the time dependence of characteristics of quantum mechanical systems, in particular, in understanding how the quantum critical points of equilibrium thermodynamics affect their dynamical properties. Dynamical quantum phase transitions reveal universality, scaling, connection to the topology, and many other interesting features. Here we review the recent achievements of this quickly developing part of low-temperature quantum physics. The study of dynamical quantum phase transitions is especially important in context of their connection to the problem of the modern theory of quantum information, where namely non-equilibrium dynamics of many-body quantum system plays the major role.

  6. Conductor-insulator quantum phase transitions

    CERN Document Server

    Trivedi, Nandini; Valles, James M

    2012-01-01

    When many particles come together how do they organise themselves? And what destroys this organisation? Combining experiments and theory, this book describes intriguing quantum phases - metals, superconductors and insulators - and transitions between them.

  7. Quantum Phase Transitions in a Finite System

    CERN Document Server

    Leviatan, A

    2006-01-01

    A general procedure for studying finite-N effects in quantum phase transitions of finite systems is presented and applied to the critical-point dynamics of nuclei undergoing a shape-phase transition of second-order (continuous), and of first-order with an arbitrary barrier.

  8. Rescuing a Quantum Phase Transition with Quantum Noise

    Science.gov (United States)

    Zhang, Gu; Novais, E.; Baranger, Harold U.

    2017-02-01

    We show that placing a quantum system in contact with an environment can enhance non-Fermi-liquid correlations, rather than destroy quantum effects, as is typical. The system consists of two quantum dots in series with two leads; the highly resistive leads couple charge flow through the dots to the electromagnetic environment, the source of quantum noise. While the charge transport inhibits a quantum phase transition, the quantum noise reduces charge transport and restores the transition. We find a non-Fermi-liquid intermediate fixed point for all strengths of the noise. For strong noise, it is similar to the intermediate fixed point of the two-impurity Kondo model.

  9. Quantum phase transitions with dynamical flavors

    CERN Document Server

    Bea, Yago; Ramallo, Alfonso V

    2016-01-01

    We study the properties of a D6-brane probe in the ABJM background with smeared massless dynamical quarks in the Veneziano limit. Working at zero temperature and non-vanishing charge density, we show that the system undergoes a quantum phase transition in which the topology of the brane embedding changes from a black hole to a Minkowski embedding. In the unflavored background the phase transition is of second order and takes place when the charge density vanishes. We determine the corresponding critical exponents and show that the scaling behavior near the quantum critical point has multiplicative logarithmic corrections. In the background with dynamical quarks the phase transition is of first order and occurs at non-zero charge density. In this case we compute the discontinuity of several physical quantities as functions of the number $N_f$ of unquenched quarks of the background.

  10. Quantum phase transitions with dynamical flavors

    Science.gov (United States)

    Bea, Yago; Jokela, Niko; Ramallo, Alfonso V.

    2016-07-01

    We study the properties of a D6-brane probe in the Aharony-Bergman-Jafferis-Maldacena (ABJM) background with smeared massless dynamical quarks in the Veneziano limit. Working at zero temperature and nonvanishing charge density, we show that the system undergoes a quantum phase transition in which the topology of the brane embedding changes from a black hole to a Minkowski embedding. In the unflavored background the phase transition is of second order and takes place when the charge density vanishes. We determine the corresponding critical exponents and show that the scaling behavior near the quantum critical point has multiplicative logarithmic corrections. In the background with dynamical quarks the phase transition is of first order and occurs at nonzero charge density. In this case we compute the discontinuity of several physical quantities as functions of the number Nf of unquenched quarks of the background.

  11. Discord under the influence of a quantum phase transition

    Institute of Scientific and Technical Information of China (English)

    Wang Lin-cheng; Shen Jian; Yi Xue-Xi

    2011-01-01

    This paper studies the discord of a bipartite two-level system coupling to an XY spin-chain environment in a transverse field and investigates the relationship between the discord property and the environment's quantum phase transition. The results show that the quantum discord is also able to characterize the quantum phase transitions. We also discuss the difference between discord and entanglement, and show that quantum discord may reveal more general information than quantum entanglement for characterizing the environment's quantum phase transition.

  12. Phase Transition in Loop Quantum Gravity

    CERN Document Server

    Mäkelä, Jarmo

    2016-01-01

    We point out that with a specific counting of states loop quantum gravity implies that black holes perform a phase transition at a certain characteristic temperature $T_C$. In this phase transition the punctures of the spin network on the stretched horizon of the black hole jump, in effect, from the vacuum to the excited states. The characteristic temperature $T_C$ may be regarded as the lowest possible temperature of the hole. From the point of view of a distant observer at rest with respect to the hole the characteristic temperature $T_C$ corresponds to the Hawking temperature of the hole.

  13. Scaling of the local quantum uncertainty at quantum phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Coulamy, I.B.; Warnes, J.H.; Sarandy, M.S., E-mail: msarandy@if.uff.br; Saguia, A.

    2016-04-29

    We investigate the local quantum uncertainty (LQU) between a block of L qubits and one single qubit in a composite system of n qubits driven through a quantum phase transition (QPT). A first-order QPT is analytically considered through a Hamiltonian implementation of the quantum search. In the case of second-order QPTs, we consider the transverse-field Ising chain via a numerical analysis through density matrix renormalization group. For both cases, we compute the LQU for finite-sizes as a function of L and of the coupling parameter, analyzing its pronounced behavior at the QPT. - Highlights: • LQU is suitable for the analysis of block correlations. • LQU exhibits pronounced behavior at quantum phase transitions. • LQU exponentially saturates in the quantum search. • Concavity of LQU indicates criticality in the Ising chain.

  14. PT phase transition in multidimensional quantum systems

    CERN Document Server

    Bender, Carl M

    2012-01-01

    Non-Hermitian PT-symmetric quantum-mechanical Hamiltonians generally exhibit a phase transition that separates two parametric regions, (i) a region of unbroken PT symmetry in which the eigenvalues are all real, and (ii) a region of broken PT symmetry in which some of the eigenvalues are complex. This transition has recently been observed experimentally in a variety of physical systems. Until now, theoretical studies of the PT phase transition have generally been limited to one-dimensional models. Here, four nontrivial coupled PT-symmetric Hamiltonians, $H=p^2/2+x^2/2+q^2/2+y^2/2+igx^2y$, $H=p^2/2+x^2/2+q^2/2+y^2+igx^2y$, $H=p^2/2+x^2/2+q^2/2+y^2/2+r^2/2+z^2/2+igxyz$, and $H=p^2/2+x^2/2+q^2/2+y^2+r^2/2+3z^2/2+igxyz$ are examined. Based on extensive numerical studies, this paper conjectures that all four models exhibit a phase transition. The transitions are found to occur at $g\\approx 0.1$, $g\\approx 0.04$, $g\\approx 0.1$, and $g\\approx 0.05$. These results suggest that the PT phase transition is a robust phen...

  15. Exotic quantum phase transitions of strongly interacting topological insulators

    Science.gov (United States)

    Slagle, Kevin; You, Yi-Zhuang; Xu, Cenke

    2015-03-01

    Using determinant quantum Monte Carlo simulations, we demonstrate that an extended Hubbard model on a bilayer honeycomb lattice has two novel quantum phase transitions. The first is a quantum phase transition between the weakly interacting gapless Dirac fermion phase and a strongly interacting fully gapped and symmetric trivial phase, which cannot be described by the standard Gross-Neveu model. The second is a quantum critical point between a quantum spin Hall insulator with spin Sz conservation and the previously mentioned strongly interacting fully gapped phase. At the latter quantum critical point the single-particle excitations remain gapped, while spin and charge gaps both close. We argue that the first quantum phase transition is related to the Z16 classification of the topological superconductor 3He-B phase with interactions, while the second quantum phase transition is a topological phase transition described by a bosonic O (4 ) nonlinear sigma model field theory with a Θ term.

  16. Quantum Fisher information as signature of superradiant quantum phase transition

    CERN Document Server

    Wang, T L; Yang, W; Jin, G R; Lambert, N; Nori, F

    2013-01-01

    The single-mode Dicke model is well-known to undergo a quantum phase transition from the so-called normal phase to the supperradiant phase (hereinafter called the "superradiant quantum phase transition"). Normally, quantum phase transitions are closely related to the critical behavior of quantities such as entanglement, quantum fluctuations, and fidelity. In this paper, we study quantum Fisher information (QFI) of the field mode and that of the atoms in the ground state of the Dicke Hamiltonian. For finite and large enough number of atoms N, our numerical results show that near the critical atom-field coupling, the QFIs of the atomic and the field subsystems can surpass the classical limits, due to the appearance of nonclassical squeezed states. As the coupling increases far beyond the critical point, the two subsystems are in highly mixed states, which degrade the QFI and hence the ultimate phase sensitivity. In the thermodynamic limit, we present analytical results of the QFIs and their relationships with t...

  17. Quantum phase transition and entanglement in Li atom system

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    By use of the exact diagonalization method, the quantum phase transition and en- tanglement in a 6-Li atom system are studied. It is found that entanglement appears before the quantum phase transition and disappears after it in this exactly solvable quantum system. The present results show that the von Neumann entropy, as a measure of entanglement, may reveal the quantum phase transition in this model.

  18. Dynamical phase transitions in quantum mechanics

    Directory of Open Access Journals (Sweden)

    Rotter Ingrid

    2012-02-01

    Full Text Available The nucleus is described as an open many-body quantum system with a non-Hermitian Hamilton operator the eigenvalues of which are complex, in general. The eigenvalues may cross in the complex plane (exceptional points, the phases of the eigenfunctions are not rigid in approaching the crossing points and the widths bifurcate. By varying only one parameter, the eigenvalue trajectories usually avoid crossing and width bifurcation occurs at the critical value of avoided crossing. An analog spectroscopic redistribution takes place for discrete states below the particle decay threshold. By this means, a dynamical phase transition occurs in the many-level system starting at a critical value of the level density. Hence the properties of the low-lying nuclear states (described well by the shell model and those of highly excited nuclear states (described by random ensembles differ fundamentally from one another. The statement of Niels Bohr on the collective features of compound nucleus states at high level density is therefore not in contradiction to the shell-model description of nuclear (and atomic states at low level density. Dynamical phase transitions are observed experimentally in different quantum mechanical systems by varying one or two parameters.

  19. Nuclear Binding Near a Quantum Phase Transition

    Science.gov (United States)

    Elhatisari, Serdar; Li, Ning; Rokash, Alexander; Alarcón, Jose Manuel; Du, Dechuan; Klein, Nico; Lu, Bing-nan; Meißner, Ulf-G.; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A.; Lee, Dean; Rupak, Gautam

    2016-09-01

    How do protons and neutrons bind to form nuclei? This is the central question of ab initio nuclear structure theory. While the answer may seem as simple as the fact that nuclear forces are attractive, the full story is more complex and interesting. In this work we present numerical evidence from ab initio lattice simulations showing that nature is near a quantum phase transition, a zero-temperature transition driven by quantum fluctuations. Using lattice effective field theory, we perform Monte Carlo simulations for systems with up to twenty nucleons. For even and equal numbers of protons and neutrons, we discover a first-order transition at zero temperature from a Bose-condensed gas of alpha particles (4He nuclei) to a nuclear liquid. Whether one has an alpha-particle gas or nuclear liquid is determined by the strength of the alpha-alpha interactions, and we show that the alpha-alpha interactions depend on the strength and locality of the nucleon-nucleon interactions. This insight should be useful in improving calculations of nuclear structure and important astrophysical reactions involving alpha capture on nuclei. Our findings also provide a tool to probe the structure of alpha cluster states such as the Hoyle state responsible for the production of carbon in red giant stars and point to a connection between nuclear states and the universal physics of bosons at large scattering length.

  20. Nuclear binding near a quantum phase transition

    CERN Document Server

    Elhatisari, Serdar; Rokash, Alexander; Alarcón, Jose Manuel; Du, Dechuan; Klein, Nico; Lu, Bing-nan; Meißner, Ulf-G; Epelbaum, Evgeny; Krebs, Hermann; Lähde, Timo A; Lee, Dean; Rupak, Gautam

    2016-01-01

    How do protons and neutrons bind to form nuclei? This is the central question of ab initio nuclear structure theory. While the answer may seem as simple as the fact that nuclear forces are attractive, the full story is more complex and interesting. In this work we present numerical evidence from ab initio lattice simulations showing that nature is near a quantum phase transition, a zero-temperature transition driven by quantum fluctuations. Using lattice effective field theory, we perform Monte Carlo simulations for systems with up to twenty nucleons. For even and equal numbers of protons and neutrons, we discover a first-order transition at zero temperature from a Bose-condensed gas of alpha particles (4He nuclei) to a nuclear liquid. Whether one has an alpha-particle gas or nuclear liquid is determined by the strength of the alpha-alpha interactions, and we show that the alpha-alpha interactions depend on the strength and locality of the nucleon-nucleon interactions. The existence of the nearby first-order ...

  1. Topology-driven magnetic quantum phase transition in topological insulators.

    Science.gov (United States)

    Zhang, Jinsong; Chang, Cui-Zu; Tang, Peizhe; Zhang, Zuocheng; Feng, Xiao; Li, Kang; Wang, Li-Li; Chen, Xi; Liu, Chaoxing; Duan, Wenhui; He, Ke; Xue, Qi-Kun; Ma, Xucun; Wang, Yayu

    2013-03-29

    The breaking of time reversal symmetry in topological insulators may create previously unknown quantum effects. We observed a magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 topological insulator films grown by means of molecular beam epitaxy. Across the critical point, a topological quantum phase transition is revealed through both angle-resolved photoemission measurements and density functional theory calculations. We present strong evidence that the bulk band topology is the fundamental driving force for the magnetic quantum phase transition. The tunable topological and magnetic properties in this system are well suited for realizing the exotic topological quantum phenomena in magnetic topological insulators.

  2. Phase transitions in open quantum systems

    CERN Document Server

    Jung, C; Rotter, I

    1999-01-01

    We consider the behaviour of open quantum systems in dependence on the coupling to one decay channel by introducing the coupling parameter $\\alpha$ being proportional to the average degree of overlapping. Under critical conditions, a reorganization of the spectrum takes place which creates a bifurcation of the time scales with respect to the lifetimes of the resonance states. We derive analytically the conditions under which the reorganization process can be understood as a second-order phase transition and illustrate our results by numerical investigations. The conditions are fulfilled e.g. for a picket fence with equal coupling of the states to the continuum. Energy dependencies within the system are included. We consider also the generic case of an unfolded Gaussian Orthogonal Ensemble. In all these cases, the reorganization of the spectrum occurs at the critical value $\\alpha_{crit}$ of the control parameter globally over the whole energy range of the spectrum. All states act cooperatively.

  3. Emergence of Decoherence as Phenomenon in Quantum Phase Transition

    CERN Document Server

    Quan, H T; Liu, X F; Sun, C P

    2005-01-01

    We consider the intrinsic relation between the appearance of classicality of a quantum system and the occurrence of quantum phase transition (QPT) in the environment surrounding this system, and study in detail the novel mechanism of quantum decoherence based on QPT with a generalized Hepp-Coleman model where the quantum system is a two level system and the environment is the Ising spin chain interacting with the quantum system. It is discovered that, the quantum decoherence of the quantum system can be accompanied by the quantum critical phenomenon induced by the effective transverse back-action of the quantum system on the environment.

  4. Preon model and cosmological quantum-hyperchromodynamic phase transition

    Science.gov (United States)

    Nishimura, H.; Hayashi, Y.

    1987-05-01

    From the cosmological viewpoint, we investigate whether or not recent preon models are compatible with the picture of the first-order phase transition from the preon phase to the composite quark-lepton phase. It is shown that the current models accepting the 't Hooft anomaly-matching condition together with quantum hyperchromodynamics are consistent with the cosmological first-order phase transition.

  5. Optically induced phase transition of excitons in coupled quantum dots

    Institute of Scientific and Technical Information of China (English)

    Chen Zi-Dong

    2008-01-01

    The weak classical light excitations in many semiconductor quantum dots have been chosen as important solidstate quantum systems for processing quantum information and implementing quantum computing. For strong classical light we predict theoretically a novel phase transition as a function of magnitude of this classical light from the deformed to the normal phases in resonance case, and the essential features of criticality such as the scaling behaviour, critical exponent and universality are also present in this paper.

  6. Quantum Phase Transitions in Odd-Mass Nuclei

    CERN Document Server

    Leviatan, A; Iachello, F

    2011-01-01

    Quantum shape-phase transitions in odd-even nuclei are investigated in the framework of the interacting boson-fermion model. Classical and quantum analysis show that the presence of the odd fermion strongly influences the location and nature of the phase transition, especially near the critical point. Experimental evidence for the occurrence of spherical to axially-deformed transitions in odd-proton nuclei Pm, Eu and Tb (Z=61, 63, 65) is presented.

  7. Quantum decoherence of subcritical bubble in electroweak phase transition

    CERN Document Server

    Shiromizu, T

    1995-01-01

    In a weakly first order phase transition the typical scale of a subcritical bubble calculated in our previous papers turned out to be too small. At this scale quantum fluctuations may dominate and our previous classical result may be altered. So we examine the critical size of a subcritical bubble where quantum-to-classical transition occurs through quantum decoherence. We show that this critical size is almost equal to the typical scale which we previously obtained.

  8. Quantum phase transitions in Bose-Fermi systems

    CERN Document Server

    Petrellis, D; Iachello, F

    2011-01-01

    Quantum phase transitions in a system of N bosons with angular momentum L=0,2 (s,d) and a single fermion with angular momentum j are investigated both classically and quantum mechanically. It is shown that the presence of the odd fermion strongly influences the location and nature of the phase transition, especially the critical value of the control parameter at which the phase transition occurs. Experimental evidence for the U(5)-SU(3) (spherical to axially-deformed) transition in odd-even nuclei is presented.

  9. Integrability and Quantum Phase Transitions in Interacting Boson Models

    CERN Document Server

    Dukelsky, J; García-Ramos, J E; Pittel, S

    2003-01-01

    The exact solution of the boson pairing hamiltonian given by Richardson in the sixties is used to study the phenomena of level crossings and quantum phase transitions in the integrable regions of the sd and sdg interacting boson models.

  10. Quantum Monte Carlo simulation of topological phase transitions

    Science.gov (United States)

    Yamamoto, Arata; Kimura, Taro

    2016-12-01

    We study the electron-electron interaction effects on topological phase transitions by the ab initio quantum Monte Carlo simulation. We analyze two-dimensional class A topological insulators and three-dimensional Weyl semimetals with the long-range Coulomb interaction. The direct computation of the Chern number shows the electron-electron interaction modifies or extinguishes topological phase transitions.

  11. Quantum Monte Carlo simulation of topological phase transitions

    CERN Document Server

    Yamamoto, Arata

    2016-01-01

    We study the electron-electron interaction effects on topological phase transitions by the ab-initio quantum Monte Carlo simulation. We analyze two-dimensional class A topological insulators and three-dimensional Weyl semimetals with the long-range Coulomb interaction. The direct computation of the Chern number shows the electron-electron interaction modifies or extinguishes topological phase transitions.

  12. Non-equilibrium quantum phase transition via entanglement decoherence dynamics

    Science.gov (United States)

    Lin, Yu-Chen; Yang, Pei-Yun; Zhang, Wei-Min

    2016-01-01

    We investigate the decoherence dynamics of continuous variable entanglement as the system-environment coupling strength varies from the weak-coupling to the strong-coupling regimes. Due to the existence of localized modes in the strong-coupling regime, the system cannot approach equilibrium with its environment, which induces a nonequilibrium quantum phase transition. We analytically solve the entanglement decoherence dynamics for an arbitrary spectral density. The nonequilibrium quantum phase transition is demonstrated as the system-environment coupling strength varies for all the Ohmic-type spectral densities. The 3-D entanglement quantum phase diagram is obtained. PMID:27713556

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

    DEFF Research Database (Denmark)

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

    2005-01-01

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

  14. String theory, quantum phase transitions, and the emergent Fermi liquid.

    Science.gov (United States)

    Cubrović, Mihailo; Zaanen, Jan; Schalm, Koenraad

    2009-07-24

    A central problem in quantum condensed matter physics is the critical theory governing the zero-temperature quantum phase transition between strongly renormalized Fermi liquids as found in heavy fermion intermetallics and possibly in high-critical temperature superconductors. We found that the mathematics of string theory is capable of describing such fermionic quantum critical states. Using the anti-de Sitter/conformal field theory correspondence to relate fermionic quantum critical fields to a gravitational problem, we computed the spectral functions of fermions in the field theory. By increasing the fermion density away from the relativistic quantum critical point, a state emerges with all the features of the Fermi liquid.

  15. Quantum phase transition in a common metal.

    Science.gov (United States)

    Yeh, A; Soh, Yeong-Ah; Brooke, J; Aeppli, G; Rosenbaum, T F; Hayden, S M

    2002-10-03

    The classical theory of solids, based on the quantum mechanics of single electrons moving in periodic potentials, provides an excellent description of substances ranging from semiconducting silicon to superconducting aluminium. Over the last fifteen years, it has become increasingly clear that there are substances for which the conventional approach fails. Among these are certain rare earth compounds and transition metal oxides, including high-temperature superconductors. A common feature of these materials is complexity, in the sense that they have relatively large unit cells containing heterogeneous mixtures of atoms. Although many explanations have been put forward for their anomalous properties, it is still possible that the classical theory might suffice. Here we show that a very common chromium alloy has some of the same peculiarities as the more exotic materials, including a quantum critical point, a strongly temperature-dependent Hall resistance and evidence for a 'pseudogap'. This implies that complexity is not a prerequisite for unconventional behaviour. Moreover, it should simplify the general task of explaining anomalous properties because chromium is a relatively simple system in which to work out in quantitative detail the consequences of the conventional theory of solids.

  16. Quantum phase transitions with parity-symmetry breaking and hysteresis

    Science.gov (United States)

    Trenkwalder, A.; Spagnolli, G.; Semeghini, G.; Coop, S.; Landini, M.; Castilho, P.; Pezzè, L.; Modugno, G.; Inguscio, M.; Smerzi, A.; Fattori, M.

    2016-09-01

    Symmetry-breaking quantum phase transitions play a key role in several condensed matter, cosmology and nuclear physics theoretical models. Its observation in real systems is often hampered by finite temperatures and limited control of the system parameters. In this work we report, for the first time, the experimental observation of the full quantum phase diagram across a transition where the spatial parity symmetry is broken. Our system consists of an ultracold gas with tunable attractive interactions trapped in a spatially symmetric double-well potential. At a critical value of the interaction strength, we observe a continuous quantum phase transition where the gas spontaneously localizes in one well or the other, thus breaking the underlying symmetry of the system. Furthermore, we show the robustness of the asymmetric state against controlled energy mismatch between the two wells. This is the result of hysteresis associated with an additional discontinuous quantum phase transition that we fully characterize. Our results pave the way to the study of quantum critical phenomena at finite temperature, the investigation of macroscopic quantum tunnelling of the order parameter in the hysteretic regime and the production of strongly quantum entangled states at critical points.

  17. Dissipation-driven quantum phase transitions in collective spin systems

    Energy Technology Data Exchange (ETDEWEB)

    Morrison, S [Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria); Parkins, A S [Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand)], E-mail: smor161@aucklanduni.ac.nz

    2008-10-14

    We consider two different collective spin systems subjected to strong dissipation-on the same scale as interaction strengths and external fields-and show that either continuous or discontinuous dissipative quantum phase transitions can occur as the dissipation strength is varied. First, we consider a well-known model of cooperative resonance fluorescence that can exhibit a second-order quantum phase transition, and analyse the entanglement properties near the critical point. Next, we examine a dissipative version of the Lipkin-Meshkov-Glick interacting collective spin model, where we find that either first- or second-order quantum phase transitions can occur, depending only on the ratio of the interaction and external field parameters. We give detailed results and interpretation for the steady-state entanglement in the vicinity of the critical point, where it reaches a maximum. For the first-order transition we find that the semiclassical steady states exhibit a region of bistability. (fast track communication)

  18. Quantum Shape-Phase Transitions in Finite Nuclei

    CERN Document Server

    Leviatan, A

    2007-01-01

    Quantum shape-phase transitions in finite nuclei are considered in the framework of the interacting boson model. Critical-point Hamiltonians for first- and second-order transitions are identified by resolving them into intrinsic and collective parts. Suitable wave functions and finite-N estimates for observables at the critical-points are derived.

  19. Quantum Shape-Phase Transitions in Finite Nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Leviatan, A. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)

    2007-05-15

    Quantum shape-phase transitions in finite nuclei are considered in the framework of the interacting boson model. Critical-point Hamiltonians for first- and second-order transitions are identified by resolving them into intrinsic and collective parts. Suitable wave functions and finite-N estimates for observables at the critical-points are derived.

  20. Spin dynamics and spin freezing at ferromagnetic quantum phase transitions

    Science.gov (United States)

    Schmakat, P.; Wagner, M.; Ritz, R.; Bauer, A.; Brando, M.; Deppe, M.; Duncan, W.; Duvinage, C.; Franz, C.; Geibel, C.; Grosche, F. M.; Hirschberger, M.; Hradil, K.; Meven, M.; Neubauer, A.; Schulz, M.; Senyshyn, A.; Süllow, S.; Pedersen, B.; Böni, P.; Pfleiderer, C.

    2015-07-01

    We report selected experimental results on the spin dynamics and spin freezing at ferromagnetic quantum phase transitions to illustrate some of the most prominent escape routes by which ferromagnetic quantum criticality is avoided in real materials. In the transition metal Heusler compound Fe2TiSn we observe evidence for incipient ferromagnetic quantum criticality. High pressure studies in MnSi reveal empirical evidence for a topological non-Fermi liquid state without quantum criticality. Single crystals of the hexagonal Laves phase compound Nb1- y Fe2+ y provide evidence of a ferromagnetic to spin density wave transition as a function of slight compositional changes. Last but not least, neutron depolarisation imaging in CePd1- x Rh x underscore evidence taken from the bulk properties of the formation of a Kondo cluster glass.

  1. Quantum scaling in many-body systems an approach to quantum phase transitions

    CERN Document Server

    Continentino, Mucio

    2017-01-01

    Quantum phase transitions are strongly relevant in a number of fields, ranging from condensed matter to cold atom physics and quantum field theory. This book, now in its second edition, approaches the problem of quantum phase transitions from a new and unifying perspective. Topics addressed include the concepts of scale and time invariance and their significance for quantum criticality, as well as brand new chapters on superfluid and superconductor quantum critical points, and quantum first order transitions. The renormalisation group in real and momentum space is also established as the proper language to describe the behaviour of systems close to a quantum phase transition. These phenomena introduce a number of theoretical challenges which are of major importance for driving new experiments. Being strongly motivated and oriented towards understanding experimental results, this is an excellent text for graduates, as well as theorists, experimentalists and those with an interest in quantum criticality.

  2. Quantum correlation and quantum phase transition in the one-dimensional extended Ising model

    Science.gov (United States)

    Zhang, Xi-Zheng; Guo, Jin-Liang

    2017-09-01

    Quantum phase transitions can be understood in terms of Landau's symmetry-breaking theory. Following the discovery of the quantum Hall effect, a new kind of quantum phase can be classified according to topological rather than local order parameters. Both phases coexist for a class of exactly solvable quantum Ising models, for which the ground state energy density corresponds to a loop in a two-dimensional auxiliary space. Motivated by this we study quantum correlations, measured by entanglement and quantum discord, and critical behavior seen in the one-dimensional extended Ising model with short-range interaction. We show that the quantum discord exhibits distinctive behaviors when the system experiences different topological quantum phases denoted by different topological numbers. Quantum discords capability to detect a topological quantum phase transition is more reliable than that of entanglement at both zero and finite temperatures. In addition, by analyzing the divergent behaviors of quantum discord at the critical points, we find that the quantum phase transitions driven by different parameters of the model can also display distinctive critical behaviors, which provides a scheme to detect the topological quantum phase transition in practice.

  3. Partial dynamical symmetry at critical points of quantum phase transitions.

    Science.gov (United States)

    Leviatan, A

    2007-06-15

    We show that partial dynamical symmetries can occur at critical points of quantum phase transitions, in which case underlying competing symmetries are conserved exactly by a subset of states, and mix strongly in other states. Several types of partial dynamical symmetries are demonstrated with the example of critical-point Hamiltonians for first- and second-order transitions in the framework of the interacting boson model, whose dynamical symmetries correspond to different shape phases in nuclei.

  4. Quantum Phase Transitions in Conventional Matrix Product Systems

    Science.gov (United States)

    Zhu, Jing-Min; Huang, Fei; Chang, Yan

    2017-02-01

    For matrix product states(MPSs) of one-dimensional spin-1/2 chains, we investigate a new kind of conventional quantum phase transition(QPT). We find that the system has two different ferromagnetic phases; on the line of the two ferromagnetic phases coexisting equally, the system in the thermodynamic limit is in an isolated mediate-coupling state described by a paramagnetic state and is in the same state as the renormalization group fixed point state, the expectation values of the physical quantities are discontinuous, and any two spin blocks of the system have the same geometry quantum discord(GQD) within the range of open interval (0,0.25) and the same classical correlation(CC) within the range of open interval (0,0.75) compared to any phase having no any kind of correlation. We not only realize the control of QPTs but also realize the control of quantum correlation of quantum many-body systems on the critical line by adjusting the environment parameters, which may have potential application in quantum information fields and is helpful to comprehensively and deeply understand the quantum correlation, and the organization and structure of quantum correlation especially for long-range quantum correlation of quantum many-body systems.

  5. Quantum phase transitions in the noncommutative Dirac Oscillator

    CERN Document Server

    Panella, O

    2014-01-01

    We study the (2+1) dimensional Dirac oscillator in a homogeneous magnetic field in the non-commutative plane. It is shown that the effect of non-commutativity is twofold: $i$) momentum non commuting coordinates simply shift the critical value ($B_{\\text{cr}}$) of the magnetic field at which the well known left-right chiral quantum phase transition takes place (in the commuting phase); $ii$) non-commutativity in the space coordinates induces a new critical value of the magnetic field, $B_{\\text{cr}}^*$, where there is a second quantum phase transition (right-left), --this critical point disappears in the commutative limit--. The change in chirality associated with the magnitude of the magnetic field is examined in detail for both critical points. The phase transitions are described in terms of the magnetisation of the system. Possible applications to the physics of silicene and graphene are briefly discussed.

  6. Collectivity, Phase Transitions and Exceptional Points in Open Quantum Systems

    CERN Document Server

    Heiss, W D; Rotter, I

    1998-01-01

    Phase transitions in open quantum systems, which are associated with the formation of collective states of a large width and of trapped states with rather small widths, are related to exceptional points of the Hamiltonian. Exceptional points are the singularities of the spectrum and eigenfunctions, when they are considered as functions of a coupling parameter. In the present paper this parameter is the coupling strength to the continuum. It is shown that the positions of the exceptional points (their accumulation point in the thermodynamical limit) depend on the particular type and energy dependence of the coupling to the continuum in the same way as the transition point of the corresponding phase transition.

  7. Quantum phase transitions in low-dimensional optical lattices

    NARCIS (Netherlands)

    Di Liberto, M.F.

    2015-01-01

    In this thesis, we discuss quantum phase transitions in low-dimensional optical lattices, namely one- and two-dimensional lattices. The dimensional confinement is realized in experiments by suppressing the hopping in the extra dimensions through a deep potential barrier that prevents the atoms to tu

  8. Phase sensitive quantum interference on forbidden transition in ladder scheme

    CERN Document Server

    Koganov, Gennady A

    2014-01-01

    A three level ladder system is analyzed and the coherence of initially electric-dipole forbidden transition is calculated. Due to the presence of two laser fields the initially dipole forbidden transition becomes dynamically permitted due to ac Stark effect. It is shown that such transitions exhibit quantum-interference-related phenomena, such as electromagnetically induced transparency, gain without inversion and enhanced refractive index. Gain and dispersion characteristics of such transitions strongly depend upon the relative phase between the driving and the probe fields. Unlike allowed transitions, gain/absorption behavior of ac-Stark allowed transitions exhibit antisymmetric feature on the Rabi sidebands. It is found that absorption/gain spectra possess extremely narrow sub-natural resonances on these ac Stark allowed forbidden transitions. An interesting finding is simultaneous existence of gain and negative dispersion at Autler-Townes transition which may lead to both reduction of the group velocity a...

  9. Quantum coherence and quantum phase transition in the XY model with staggered Dzyaloshinsky-Moriya interaction

    Energy Technology Data Exchange (ETDEWEB)

    Hui, Ning-Ju [Department of Applied Physics, Xi' an University of Technology, Xi' an 710054 (China); Xu, Yang-Yang; Wang, Jicheng; Zhang, Yixin [Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, School of Science, Jiangnan University, Wuxi 214122 (China); Hu, Zheng-Da, E-mail: huyuanda1112@jiangnan.edu.cn [Jiangsu Provincial Research Center of Light Industrial Optoelectronic Engineering and Technology, School of Science, Jiangnan University, Wuxi 214122 (China)

    2017-04-01

    We investigate the properties of geometric quantum coherence in the XY spin-1/2 chain with staggered Dzyaloshinsky-Moriya interaction via the quantum renormalization-group approach. It is shown that the geometric quantum coherence and its coherence susceptibility are effective to detect the quantum phase transition. In the thermodynamic limit, the geometric quantum coherence exhibits a sudden jump. The coherence susceptibilities versus the anisotropy parameter and the Dzyaloshinsky-Moriya interaction are infinite and vanishing, respectively, illustrating the distinct roles of the anisotropy parameter and the Dzyaloshinsky-Moriya interaction in quantum phase transition. Moreover, we also explore the finite-size scaling behaviors of the coherence susceptibilities. For a finite-size chain, the coherence susceptibility versus the phase-transition parameter is always maximal at the critical point, indicating the dramatic quantum fluctuation. Besides, we show that the correlation length can be revealed by the scaling exponent for the coherence susceptibility versus the Dzyaloshinsky-Moriya interaction.

  10. Quantum coherence and quantum phase transition in the XY model with staggered Dzyaloshinsky-Moriya interaction

    Science.gov (United States)

    Hui, Ning-Ju; Xu, Yang-Yang; Wang, Jicheng; Zhang, Yixin; Hu, Zheng-Da

    2017-04-01

    We investigate the properties of geometric quantum coherence in the XY spin-1/2 chain with staggered Dzyaloshinsky-Moriya interaction via the quantum renormalization-group approach. It is shown that the geometric quantum coherence and its coherence susceptibility are effective to detect the quantum phase transition. In the thermodynamic limit, the geometric quantum coherence exhibits a sudden jump. The coherence susceptibilities versus the anisotropy parameter and the Dzyaloshinsky-Moriya interaction are infinite and vanishing, respectively, illustrating the distinct roles of the anisotropy parameter and the Dzyaloshinsky-Moriya interaction in quantum phase transition. Moreover, we also explore the finite-size scaling behaviors of the coherence susceptibilities. For a finite-size chain, the coherence susceptibility versus the phase-transition parameter is always maximal at the critical point, indicating the dramatic quantum fluctuation. Besides, we show that the correlation length can be revealed by the scaling exponent for the coherence susceptibility versus the Dzyaloshinsky-Moriya interaction.

  11. Absorbing State Phase Transition with Competing Quantum and Classical Fluctuations

    Science.gov (United States)

    Marcuzzi, Matteo; Buchhold, Michael; Diehl, Sebastian; Lesanovsky, Igor

    2016-06-01

    Stochastic processes with absorbing states feature examples of nonequilibrium universal phenomena. While the classical regime has been thoroughly investigated in the past, relatively little is known about the behavior of these nonequilibrium systems in the presence of quantum fluctuations. Here, we theoretically address such a scenario in an open quantum spin model which, in its classical limit, undergoes a directed percolation phase transition. By mapping the problem to a nonequilibrium field theory, we show that the introduction of quantum fluctuations stemming from coherent, rather than statistical, spin flips alters the nature of the transition such that it becomes first order. In the intermediate regime, where classical and quantum dynamics compete on equal terms, we highlight the presence of a bicritical point with universal features different from the directed percolation class in a low dimension. We finally propose how this physics could be explored within gases of interacting atoms excited to Rydberg states.

  12. Quantum phase transition of light as a control of the entanglement between interacting quantum dots

    NARCIS (Netherlands)

    Barragan, Angela; Vera-Ciro, Carlos; Mondragon-Shem, Ian

    We study coupled quantum dots arranged in a photonic crystal, interacting with light which undergoes a quantum phase transition. At the mean-field level for the infinite lattice, we compute the concurrence of the quantum dots as a measure of their entanglement. We find that this quantity smoothly

  13. Emergence of coherence and the dynamics of quantum phase transitions

    Science.gov (United States)

    Braun, Simon; Friesdorf, Mathis; Hodgman, Sean S.; Schreiber, Michael; Ronzheimer, Jens Philipp; Riera, Arnau; del Rey, Marco; Bloch, Immanuel; Eisert, Jens

    2015-01-01

    The dynamics of quantum phase transitions pose one of the most challenging problems in modern many-body physics. Here, we study a prototypical example in a clean and well-controlled ultracold atom setup by observing the emergence of coherence when crossing the Mott insulator to superfluid quantum phase transition. In the 1D Bose–Hubbard model, we find perfect agreement between experimental observations and numerical simulations for the resulting coherence length. We, thereby, perform a largely certified analog quantum simulation of this strongly correlated system reaching beyond the regime of free quasiparticles. Experimentally, we additionally explore the emergence of coherence in higher dimensions, where no classical simulations are available, as well as for negative temperatures. For intermediate quench velocities, we observe a power-law behavior of the coherence length, reminiscent of the Kibble–Zurek mechanism. However, we find nonuniversal exponents that cannot be captured by this mechanism or any other known model. PMID:25775515

  14. Benford's Law: Detection of Quantum Phase Transitions similarly as Earthquakes

    CERN Document Server

    De, Aditi Sen

    2011-01-01

    More than a century earlier, it was predicted that the first significant digit appearing in a data, be it from natural sciences or from some mathematical series, will be nonuniformly distributed, with the number one appearing with the highest frequency. This law goes by the name of Benford's law. It has been observed to hold for data from a huge variety of sources, ranging from earthquakes to infectious disease cases. Quantum phase transitions are cooperative phenomena where qualitative changes occur in physical quantities of a many-body system at zero temperature. We find that Benford's law can be applied to detect quantum phase transitions in a way that is very similar to how it can distinguish earthquakes from background noise. Being certainly of very different physical origins, seismic activity and quantum cooperative phenomena may therefore be detected by similar methods. The result may provide methods to overcome the limitations associated with precise measurements in experiments.

  15. Scaling and Universality at Dynamical Quantum Phase Transitions.

    Science.gov (United States)

    Heyl, Markus

    2015-10-02

    Dynamical quantum phase transitions (DQPTs) at critical times appear as nonanalyticities during nonequilibrium quantum real-time evolution. Although there is evidence for a close relationship between DQPTs and equilibrium phase transitions, a major challenge is still to connect to fundamental concepts such as scaling and universality. In this work, renormalization group transformations in complex parameter space are formulated for quantum quenches in Ising models showing that the DQPTs are critical points associated with unstable fixed points of equilibrium Ising models. Therefore, these DQPTs obey scaling and universality. On the basis of numerical simulations, signatures of these DQPTs in the dynamical buildup of spin correlations are found with an associated power-law scaling determined solely by the fixed point's universality class. An outlook is given on how to explore this dynamical scaling experimentally in systems of trapped ions.

  16. Quantum Phase Transitions in Anti-ferromagnetic Planar Cubic Lattices

    CERN Document Server

    Wellard, C J; Wellard, Cameron; Orus, Roman

    2004-01-01

    Motivated by its relation to an NP-hard problem we analyze the ground state properties of anti-ferromagnetic Ising-spin networks in planar cubic lattices under the action of homogeneous transverse and longitudinal magnetic fields. We consider different instances of the cubic geometry and find a set of quantum phase transitions for each one of the systems, which we characterize by means of entanglement behavior and majorization theory. Entanglement scaling at the critical region is in agreement with results arising from conformal symmetry, therefore even the simplest planar systems can display very large amounts of quantum correlation. No conclusion can be made as to the scaling behavior of the minimum energy gap, with the data allowing equally good fits to exponential and power law decays. Analysis of entanglement and especially of majorization instead of the energy spectrum proves to be a good way of detecting quantum phase transitions in highly frustrated configurations.

  17. Quantum phase transition induced by real-space topology

    Science.gov (United States)

    Li, C.; Zhang, G.; Lin, S.; Song, Z.

    2016-12-01

    A quantum phase transition (QPT), including both topological and symmetry breaking types, is usually induced by the change of global parameters, such as external fields or global coupling constants. In this work, we demonstrate the existence of QPT induced by the real-space topology of the system. We investigate the groundstate properties of the tight-binding model on a honeycomb lattice with the torus geometry based on exact results. It is shown that the ground state experiences a second-order QPT, exhibiting the scaling behavior, when the torus switches to a tube, which reveals the connection between quantum phase and the real-space topology of the system.

  18. Quantum phase transition induced by real-space topology.

    Science.gov (United States)

    Li, C; Zhang, G; Lin, S; Song, Z

    2016-12-22

    A quantum phase transition (QPT), including both topological and symmetry breaking types, is usually induced by the change of global parameters, such as external fields or global coupling constants. In this work, we demonstrate the existence of QPT induced by the real-space topology of the system. We investigate the groundstate properties of the tight-binding model on a honeycomb lattice with the torus geometry based on exact results. It is shown that the ground state experiences a second-order QPT, exhibiting the scaling behavior, when the torus switches to a tube, which reveals the connection between quantum phase and the real-space topology of the system.

  19. A Quantum Phase Transition in the Cosmic Ray Energy Distribution

    CERN Document Server

    Widom, A; Srivastava, Y

    2015-01-01

    We here argue that the "knee" of the cosmic ray energy distribution at $E_c \\sim 1$ PeV represents a second order phase transition of cosmic proportions. The discontinuity of the heat capacity per cosmic ray particle is given by $\\Delta c=0.450196\\ k_B$. However the idea of a deeper critical point singularity cannot be ruled out by present accuracy in neither theory nor experiment. The quantum phase transition consists of cosmic rays dominated by bosons for the low temperature phase E E_c$. The low temperature phase arises from those nuclei described by the usual and conventional collective boson models of nuclear physics. The high temperature phase is dominated by protons. The transition energy $E_c$ may be estimated in terms of the photo-disintegration of nuclei.

  20. Phase transition of light on complex quantum networks.

    Science.gov (United States)

    Halu, Arda; Garnerone, Silvano; Vezzani, Alessandro; Bianconi, Ginestra

    2013-02-01

    Recent advances in quantum optics and atomic physics allow for an unprecedented level of control over light-matter interactions, which can be exploited to investigate new physical phenomena. In this work we are interested in the role played by the topology of quantum networks describing coupled optical cavities and local atomic degrees of freedom. In particular, using a mean-field approximation, we study the phase diagram of the Jaynes-Cummings-Hubbard model on complex networks topologies, and we characterize the transition between a Mott-like phase of localized polaritons and a superfluid phase. We found that, for complex topologies, the phase diagram is nontrivial and well defined in the thermodynamic limit only if the hopping coefficient scales like the inverse of the maximal eigenvalue of the adjacency matrix of the network. Furthermore we provide numerical evidences that, for some complex network topologies, this scaling implies an asymptotically vanishing hopping coefficient in the limit of large network sizes. The latter result suggests the interesting possibility of observing quantum phase transitions of light on complex quantum networks even with very small couplings between the optical cavities.

  1. Quantum phase transition between cluster and antiferromagnetic states

    CERN Document Server

    Son, Wonmin; Fazio, Rosario; Hamma, Alioscia; Pascazio, Saverio; Vedral, Vlatko

    2011-01-01

    We study a Hamiltonian system describing a three spin-1/2 cluster-like interaction competing with an Ising-like exchange. We show that the ground state in the cluster phase possesses symmetry protected topological order. A continuous quantum phase transition occurs as result of the competition between the cluster and Ising terms. At the critical point the Hamiltonian is self-dual. The geometric entanglement is also studied. Our findings in one dimension corroborate the analysis of the two dimensional generalization of the system, indicating, at a mean field level, the presence of a direct transition between an antiferromagnetic and a valence bond solid ground state.

  2. Divergent thermopower without a quantum phase transition.

    Science.gov (United States)

    Limtragool, Kridsanaphong; Phillips, Philip W

    2014-08-22

    A general principle of modern statistical physics is that divergences of either thermodynamic or transport properties are only possible if the correlation length diverges. We show by explicit calculation that the thermopower in the quantum XY model d = 1 + 1 and the Kitaev model in d = 2 + 1 can (i) diverge even when the correlation length is finite and (ii) remain finite even when the correlation length diverges, thereby providing a counterexample to the standard paradigm. Two conditions are necessary: (i) the sign of the charge carriers and that of the group velocity must be uncorrelated and (ii) the current operator defined formally as the derivative of the Hamiltonian with respect to the gauge field does not describe a set of excitations that have a particle interpretation, as in strongly correlated electron matter. Recent experimental and theoretical findings on the divergent thermopower of a 2D electron gas are discussed in this context.

  3. Black holes as critical point of quantum phase transition.

    Science.gov (United States)

    Dvali, Gia; Gomez, Cesar

    We reformulate the quantum black hole portrait in the language of modern condensed matter physics. We show that black holes can be understood as a graviton Bose-Einstein condensate at the critical point of a quantum phase transition, identical to what has been observed in systems of cold atoms. The Bogoliubov modes that become degenerate and nearly gapless at this point are the holographic quantum degrees of freedom responsible for the black hole entropy and the information storage. They have no (semi)classical counterparts and become inaccessible in this limit. These findings indicate a deep connection between the seemingly remote systems and suggest a new quantum foundation of holography. They also open an intriguing possibility of simulating black hole information processing in table-top labs.

  4. Black holes as critical point of quantum phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Dvali, Gia [Arnold Sommerfeld Center for Theoretical Physics, Department fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, Muenchen (Germany); Max-Planck-Institut fuer Physik, Muenchen (Germany); CERN, Theory Department, Geneva 23 (Switzerland); New York University, Department of Physics, Center for Cosmology and Particle Physics, New York, NY (United States); Gomez, Cesar [Arnold Sommerfeld Center for Theoretical Physics, Department fuer Physik, Ludwig-Maximilians-Universitaet Muenchen, Muenchen (Germany); Universidad Autonoma de Madrid, Instituto de Fisica Teorica UAM-CSIC, C-XVI, Madrid (Spain)

    2014-02-15

    We reformulate the quantum black hole portrait in the language of modern condensed matter physics. We show that black holes can be understood as a graviton Bose-Einstein condensate at the critical point of a quantum phase transition, identical to what has been observed in systems of cold atoms. The Bogoliubov modes that become degenerate and nearly gapless at this point are the holographic quantum degrees of freedom responsible for the black hole entropy and the information storage. They have no (semi)classical counterparts and become inaccessible in this limit. These findings indicate a deep connection between the seemingly remote systems and suggest a new quantum foundation of holography. They also open an intriguing possibility of simulating black hole information processing in table-top labs. (orig.)

  5. Characterizing quantum phase transitions by single qubit operations

    CERN Document Server

    Giampaolo, S M; De Siena, S

    2006-01-01

    We introduce observable quantities, borrowing from concepts of quantum information theory, for the characterization of quantum phase transitions in spin systems. These observables are uniquely defined in terms of single spin unitary operations. We define the energy gap between the ground state and the state produced by the action of a single-qubit local gate. We show that this static quantity involves only single-site expectations and two-point correlation functions on the ground state. We then discuss a dynamical local observable defined as the acceleration of quantum state evolution after performing an instaneous single-qubit perturbation on the ground state. This quantity involves three-point correlations as well. We show that both the static and the dynamical observables detect and characterize completely quantum critical points in a class of spin systems.

  6. Black Holes as Critical Point of Quantum Phase Transition

    CERN Document Server

    Dvali, Gia

    2014-01-01

    We reformulate the quantum black hole portrait in the language of modern condensed matter physics. We show that black holes can be understood as a graviton Bose-Einstein condensate at the critical point of a quantum phase transition, identical to what has been observed in systems of cold atoms. The Bogoliubov modes that become degenerate and nearly gapless at this point are the holographic quantum degrees of freedom responsible for the black hole entropy and the information storage. They have no (semi)classical counterparts and become inaccessible in this limit. These findings indicate a deep connection between the seemingly remote systems and suggest a new quantum foundation of holography. They also open an intriguing possibility of simulating black hole information processing in table-top labs.

  7. Black holes as critical point of quantum phase transition

    Science.gov (United States)

    Dvali, Gia; Gomez, Cesar

    2014-02-01

    We reformulate the quantum black hole portrait in the language of modern condensed matter physics. We show that black holes can be understood as a graviton Bose-Einstein condensate at the critical point of a quantum phase transition, identical to what has been observed in systems of cold atoms. The Bogoliubov modes that become degenerate and nearly gapless at this point are the holographic quantum degrees of freedom responsible for the black hole entropy and the information storage. They have no (semi)classical counterparts and become inaccessible in this limit. These findings indicate a deep connection between the seemingly remote systems and suggest a new quantum foundation of holography. They also open an intriguing possibility of simulating black hole information processing in table-top labs.

  8. Exciton-driven quantum phase transitions in holography

    CERN Document Server

    Gubankova, E; Schalm, K; Zaanen, J

    2014-01-01

    We study phase transitions driven by fermionic double-trace deformations in gauge-gravity duality. Both the strength of the double trace deformation and the infrared conformal dimension/self-energy scaling of the quasiparticle can be used to decrease the critical temperature to zero, leading to a line of quantum critical points. The self-energy scaling is controlled indirectly through an applied magnetic field and the quantum phase transition naturally involves the condensation of a fermion bilinear which models the spin density wave in antiferromagnetic state. The nature of the quantum critical points depends on the parameters and we find either a BKT-type transition or one of two distinct second order transitions with non-mean field exponents. One of these is an anomalous branch where the order parameter of constituent non-Fermi liquid quasiparticles is enhanced by the magnetic field. Stabilization of ordered non-Fermi liquids by a strong magnetic field is observed in experiments with highly oriented pyroli...

  9. The Quantum Space Phase Transitions for Particles and Force Fields

    Directory of Open Access Journals (Sweden)

    Chung D.-Y.

    2006-07-01

    Full Text Available We introduce a phenomenological formalism in which the space structure is treated in terms of attachment space and detachment space. Attachment space attaches to an object, while detachment space detaches from the object. The combination of these spaces results in three quantum space phases: binary partition space, miscible space and binary lattice space. Binary lattice space consists of repetitive units of alternative attachment space and detachment space. In miscible space, attachment space is miscible to detachment space, and there is no separation between attachment space and detachment spaces. In binary partition space, detachment space and attachment space are in two separat continuous regions. The transition from wavefunction to the collapse of wavefuction under interference becomes the quantum space phase transition from binary lattice space to miscible space. At extremely conditions, the gauge boson force field undergoes a quantum space phase transition to a "hedge boson force field", consisting of a "vacuum" core surrounded by a hedge boson shell, like a bubble with boundary.

  10. 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.

  11. Excited-state quantum phase transition in the Rabi model

    Science.gov (United States)

    Puebla, Ricardo; Hwang, Myung-Joong; Plenio, Martin B.

    2016-08-01

    The Rabi model, a two-level atom coupled to a harmonic oscillator, can undergo a second-order quantum phase transition (QPT) [M.-J. Hwang et al., Phys. Rev. Lett. 115, 180404 (2015), 10.1103/PhysRevLett.115.180404]. Here we show that the Rabi QPT accompanies critical behavior in the higher-energy excited states, i.e., the excited-state QPT (ESQPT). We derive analytic expressions for the semiclassical density of states, which show a logarithmic divergence at a critical energy eigenvalue in the broken symmetry (superradiant) phase. Moreover, we find that the logarithmic singularities in the density of states lead to singularities in the relevant observables in the system such as photon number and atomic polarization. We corroborate our analytical semiclassical prediction of the ESQPT in the Rabi model with its numerically exact quantum mechanical solution.

  12. Quantum phases, supersolids and quantum phase transitions of interacting bosons in frustrated lattices

    Energy Technology Data Exchange (ETDEWEB)

    Ye, Jinwu, E-mail: jy306@ccs.msstate.edu [Beijing Key Laboratory for Terahertz Spectroscopy and Imaging, Key Laboratory of Terahertz Optoelectronics, Ministry of Education, Department of Physics, Capital Normal University, Beijing 100048 (China); Department of Physics and Astronomy, Mississippi State University, P.O. Box 5167, MS 39762 (United States); Chen, Yan, E-mail: yanchen99@gmail.com [Department of Physics, Surface Physics Laboratory (National Key Laboratory) and Lab of Advanced Materials, Fudan University, Shanghai (China)

    2013-04-11

    By using the dual vortex method (DVM), we develop systematically a simple and effective scheme to use the vortex degree of freedoms on dual lattices to characterize the symmetry breaking patterns of the boson insulating states in the direct lattices. Then we apply our scheme to study quantum phases and phase transitions in an extended boson Hubbard model slightly away from 1/3 (2/3) filling on frustrated lattices such as triangular and Kagome lattice. In a triangular lattice at 1/3, we find a X-CDW, a stripe CDW phase which was found previously by a density operator formalism (DOF). Most importantly, we also find a new CDW-VB phase which has both local CDW and local VB orders, in sharp contrast to a bubble CDW phase found previously by the DOF. In the Kagome lattice at 1/3, we find a VBS phase and a 6-fold CDW phase. Most importantly, we also identify a CDW-VB phase which has both local CDW and local VB orders which was found in previous QMC simulations. We also study several other phases which are not found by the DVM. By analyzing carefully the saddle point structures of the dual gauge fields in the translational symmetry breaking sides and pushing the effective actions slightly away from the commensurate filling f=1/3(2/3), we classified all the possible types of supersolids and analyze their stability conditions. In a triangular lattice, there are X-CDW supersolid, stripe CDW supersolid, but absence of any valence bond supersolid (VB-SS). There are also a new kind of supersolid: CDW-VB supersolid. In a Kagome lattice, there are 6-fold CDW supersolid, stripe CDW supersolid, but absence of any valence bond supersolid (VB-SS). There are also a new kind of supersolid: CDW-VB supersolid. We show that independent of the types of the SS, the quantum phase transitions from solids to supersolids driven by a chemical potential are in the same universality class as that from a Mott insulator to a superfluid, therefore have exact exponents z=2, ν=1/2, η=0 (with

  13. Polarons and Mobile Impurities Near a Quantum Phase Transition

    Science.gov (United States)

    Shadkhoo, Shahriar

    derives the effective Euclidean action from the classical equation of motion. We calculate the effective mass of the polaron in the model polar liquid at zero and finite temperatures. The self-trapping transition of this polaron turns out to be discontinuous in certain regions of the phase diagram. In order to systematically investigate the role of quantum fluctuations on the polaron properties, we adopt a quantum field theory which supports nearly-critical local modes: the quantum Landau-Brazovskii (QLB) model, which exhibits fluctuation-induced first order transition (weak crystallization). In the vicinity of the phase transition, the quantum fluctuations are strongly correlated; one can in principle tune the strength of these fluctuations, by adjusting the parameters close to or away from the transition point. Furthermore, sufficiently close to the transition, the theory accommodates "soliton'' solutions, signaling the nonlinear response of the system. Therefore, the model seems to be a promising candidate for studying the effects of strong quantum fluctuations and also failure of linear response theory, in the polaron problem. We observe that at zero temperature, and away from the Brazovskii transition where the linear response approximation is valid, the localization transition of the polaron is discontinuous. Upon enhancing fluctuations---of either thermal or quantum nature---the gap of the effective mass closes at distinct second-order critical points. Sufficiently close to the Brazovskii transition where the nonlinear contributions of the field are significantly large, a new state appears in addition to extended and self-trapped polarons: an impurity-induced soliton. We interpret this as the break-down of linear response, reminiscent of what we observe in a polar liquid. Quantum LB model has been proposed to be realizable in ultracold Bose gases in cavities. We thus discuss the experimental feasibility, and propose a setup which is believed to exhibit the

  14. Quantum Phase Transition in the Shape of Zr isotopes

    CERN Document Server

    Togashi, Tomoaki; Otsuka, Takaharu; Shimizu, Noritaka

    2016-01-01

    The rapid shape change in Zr isotopes near neutron number $N$=60 is identified to be caused by type II shell evolution associated with massive proton excitations to its $0g_{9/2}$ orbit, and is shown to be a quantum phase transition. Monte Carlo shell-model calculations are carried out for Zr isotopes of $N$=50-70 with many configurations spanned by eight proton orbits and eight neutron orbits. Energy levels and B(E2) values are obtained within a single framework in a good agreement with experiments, depicting various shapes in going from $N$=50 to 70. Novel coexistence of prolate and triaxial shapes is suggested.

  15. Quantum phase transitions about parity breaking in matrix product systems

    Institute of Scientific and Technical Information of China (English)

    ZHU Jing-Min

    2011-01-01

    According to our scheme to construct quantum phase transitions (QPTs) in spin chain systems with matrix product ground states, we first successfully combine matrix product state (MPS) QPTs with spontaneous symmetry breaking. For a concrete model, we take into account a kind of MPS QPTs accompanied by spontaneous parity breaking, though for either side of the critical point the GS is typically unique, and show that the kind of MPS QPTs occur only in the thermodynamic limit and are accompanied by the appearance of singularities, diverging correlation length, vanishing energy gap and the entanglement entropy of a half-infinite chain not only staying finite but also whose first derivative discontinuous.

  16. P T phase transition in multidimensional quantum systems

    Science.gov (United States)

    Bender, Carl M.; Weir, David J.

    2012-10-01

    Non-Hermitian P T-symmetric quantum-mechanical Hamiltonians generally exhibit a phase transition that separates two parametric regions, (i) a region of unbroken P T symmetry in which the eigenvalues are all real, and (ii) a region of broken P T symmetry in which some of the eigenvalues are complex. This transition has recently been observed experimentally in a variety of physical systems. Until now, theoretical studies of the P T phase transition have generally been limited to one-dimensional models. Here, four nontrivial coupled P T-symmetric Hamiltonians, H=\\textstyle {\\frac{1}{2}}p^2+\\textstyle {\\frac{1}{2}}x^2+\\textstyle {\\frac{1}{2}}q^2+\\textstyle {\\frac{1}{2}}y^2+igx^2y, H=\\textstyle {\\frac{1}{2}}p^2+\\textstyle {\\frac{1}{2}}x^2+\\textstyle {\\frac{1}{2}}q^2+y^2+igx^2y, H=\\textstyle {\\frac{1}{2}}p^2+\\textstyle {\\frac{1}{2}}x^2+\\textstyle {\\frac{1}{2}}q^2+\\textstyle {\\frac{1}{2}}y^2+\\textstyle {\\frac{1}{2}}r^2+\\textstyle {\\frac{1}{2}}z^2+igxyz, and H=\\textstyle {\\frac{1}{2}}p^2+ \\textstyle {\\frac{1}{2}}x^2+\\textstyle {\\frac{1}{2}}q^2+y^2+\\textstyle {\\frac{1}{2}}r^2+\\textstyle {\\frac{3}{2}}z^2+igxyz are examined. Based on extensive numerical studies, this paper conjectures that all four models exhibit a phase transition. The transitions are found to occur at g ≈ 0.1, g ≈ 0.04, g ≈ 0.1 and g ≈ 0.05. These results suggest that the P T phase transition is a robust phenomenon not limited to systems having one degree of freedom.

  17. Characterization of Quantum Phase Transition using Holographic Entanglement Entropy

    CERN Document Server

    Ling, Yi; Wu, Jian-Pin

    2016-01-01

    We investigate the holographic entanglement entropy (HEE) in Einstein-Maxwell-Dilaton theory. In this framework black brane solutions with vanishing entropy density in zero temperature limit have been constructed in the presence of Q-lattice structure. We find that the first order derivative of HEE with repsect to lattice parameters exhibits the maximization behavior near quantum critical points (QCPs), which coincides with the phenomenon observed in realistic condensed matter system. Our discovery in this letter extends our previous observation in arXiv:1502.03661 where HEE itself diagnoses the quantum phase transition (QPT) with local extremes. We propose that it would be a univeral feature that HEE or its derivatives with respect to system parameters can characterize QPT in a generic holographic system.

  18. New Dynamical Scaling Universality for Quantum Networks Across Adiabatic Quantum Phase Transitions

    Science.gov (United States)

    Acevedo, Oscar L.; Rodriguez, Ferney J.; Quiroga, Luis; Johnson, Neil F.; Rey, Ana M.

    2014-05-01

    We reveal universal dynamical scaling behavior across adiabatic quantum phase transitions in networks ranging from traditional spatial systems (Ising model) to fully connected ones (Dicke and Lipkin-Meshkov-Glick models). Our findings, which lie beyond traditional critical exponent analysis and adiabatic perturbation approximations, are applicable even where excitations have not yet stabilized and, hence, provide a time-resolved understanding of quantum phase transitions encompassing a wide range of adiabatic regimes. We show explicitly that even though two systems may traditionally belong to the same universality class, they can have very different adiabatic evolutions. This implies that more stringent conditions need to be imposed than at present, both for quantum simulations where one system is used to simulate the other and for adiabatic quantum computing schemes.

  19. Quantum phase transition of the transverse-field quantum Ising model on scale-free networks.

    Science.gov (United States)

    Yi, Hangmo

    2015-01-01

    I investigate the quantum phase transition of the transverse-field quantum Ising model in which nearest neighbors are defined according to the connectivity of scale-free networks. Using a continuous-time quantum Monte Carlo simulation method and the finite-size scaling analysis, I identify the quantum critical point and study its scaling characteristics. For the degree exponent λ=6, I obtain results that are consistent with the mean-field theory. For λ=4.5 and 4, however, the results suggest that the quantum critical point belongs to a non-mean-field universality class. Further simulations indicate that the quantum critical point remains mean-field-like if λ>5, but it continuously deviates from the mean-field theory as λ becomes smaller.

  20. Quantum phase transition of the transverse-field quantum Ising model on scale-free networks

    Science.gov (United States)

    Yi, Hangmo

    2015-01-01

    I investigate the quantum phase transition of the transverse-field quantum Ising model in which nearest neighbors are defined according to the connectivity of scale-free networks. Using a continuous-time quantum Monte Carlo simulation method and the finite-size scaling analysis, I identify the quantum critical point and study its scaling characteristics. For the degree exponent λ =6 , I obtain results that are consistent with the mean-field theory. For λ =4.5 and 4, however, the results suggest that the quantum critical point belongs to a non-mean-field universality class. Further simulations indicate that the quantum critical point remains mean-field-like if λ >5 , but it continuously deviates from the mean-field theory as λ becomes smaller.

  1. Quantum information entropy for one-dimensional system undergoing quantum phase transition

    Science.gov (United States)

    Xu-Dong, Song; Shi-Hai, Dong; Yu, Zhang

    2016-05-01

    Calculations of the quantum information entropy have been extended to a non-analytically solvable situation. Specifically, we have investigated the information entropy for a one-dimensional system with a schematic “Landau” potential in a numerical way. Particularly, it is found that the phase transitional behavior of the system can be well expressed by the evolution of quantum information entropy. The calculated results also indicate that the position entropy Sx and the momentum entropy Sp at the critical point of phase transition may vary with the mass parameter M but their sum remains as a constant independent of M for a given excited state. In addition, the entropy uncertainty relation is proven to be robust during the whole process of the phase transition. Project supported by the National Natural Science Foundation of China (Grant No. 11375005) and partially by 20150964-SIP-IPN, Mexico.

  2. Quantum Phase Transitions and Dimerized Phases in Frustrated Spin Ladder

    Institute of Scientific and Technical Information of China (English)

    WEN Rui; LIU Guang-Hua; TIAN Guang-Shan

    2011-01-01

    In this paper, we study the phase diagram of a frustrated spin ladder model by applying the bosonization technique and the density-matrix renormalization-group (DMRG) algorithm. Effect of the intra-chain next-nearestneighbor (NNN) super-exchange interaction is investigated in detail and the order parameters are calculated to detect the emergence of the dimerized phases. We find that the intra-chain NNN interaction plays a key role in inducing dimerized phases.

  3. Strain-induced topological quantum phase transition in phosphorene oxide

    Science.gov (United States)

    Kang, Seoung-Hun; Park, Jejune; Woo, Sungjong; Kwon, Young-Kyun

    Using ab initio density functional theory, we investigate the structural stability and electronic properties of phosphorene oxides (POx) with different oxygen compositions x. A variety of configurations are modeled and optimized geometrically to search for the equilibrium structure for each x value. Our electronic structure calculations on the equilibrium configuration obtained for each x reveal that the band gap tends to increase with the oxygen composition of x 0.5. We further explore the strain effect on the electronic structure of the fully oxidized phosphorene, PO, with x = 1. At a particular strain without spin-orbit coupling (SOC) is observed a band gap closure near the Γ point in the k space. We further find the strain in tandem with SOC induces an interesting band inversion with a reopened very small band gap (5 meV), and thus gives rise to a topological quantum phase transition from a normal insulator to a topological insulator. Such a topological phase transition is confirmed by the wave function analysis and the band topology identified by the Z2 invariant calculation.

  4. Universal Critical Behavior at a Phase Transition to Quantum Turbulence

    CERN Document Server

    Takahashi, Masahiro; Takeuchi, Kazumasa A

    2016-01-01

    Turbulence is one of the most prototypical phenomena of systems driven out of equilibrium. While turbulence has been studied mainly with classical fluids like water, considerable attention is now drawn to quantum turbulence (QT), observed in quantum fluids such as superfluid helium and Bose-Einstein condensates. A distinct feature of QT is that it consists of quantum vortices, by which turbulent circulation is quantized. Yet, under strong forcing, characteristic properties of developed classical turbulence such as Kolmogorov's law have also been identified in QT. Here, we study the opposite limit of weak forcing, i.e., the onset of QT, numerically, and find another set of universal scaling laws known for classical non-equilibrium systems. Specifically, we show that the transition belongs to the directed percolation universality class, known to arise generically in transitions into an absorbing state, including transitions to classical shear-flow turbulence after very recent studies. We argue that quantum vort...

  5. A magnetically induced quantum phase transition in holography

    CERN Document Server

    Gnecchi, A; Papadoulaki, O; Toldo, C

    2016-01-01

    We investigate quantum phase transitions in a 2+1 dimensional gauge theory at finite chemical potential $\\chi$ and magnetic field $B$. The gravity dual is based on 4D $\\mathcal{N}=2$ Fayet-Iliopoulos gauged supergravity and the solutions we consider---that are constructed analytically---are extremal, dyonic, asymptotically $AdS_4$ black-branes with a nontrivial radial profile for the scalar field. We discover a line of second order fixed points at $B=B_c(\\chi)$ between the dyonic black brane and an extremal "thermal gas" solution with a singularity of good-type, according to the acceptability criteria of Gubser [1]. The dual field theory is the ABJM theory [2] deformed by a triple trace operator $\\Phi^3$ and placed at finite charge and magnetic field. This line of fixed points might be useful in studying the various strongly interacting quantum critical phenomena such as the ones proposed to underlie the cuprate superconductors. We also find curious similarities between the behaviour of the VeV $\\langle \\Phi ...

  6. Cavity-assisted dynamical quantum phase transition in superconducting quantum simulators

    Science.gov (United States)

    Tian, Lin

    Coupling a quantum many-body system to a cavity can create bifurcation points in the phase diagram, where the many-body system switches between different phases. Here I will discuss the dynamical quantum phase transitions at the bifurcation points of a one-dimensional transverse field Ising model coupled to a cavity. The Ising model can be emulated with various types of superconducting qubits connected in a chain. With a time-dependent Bogoliubov method, we show that an infinitesimal quench of the driving field can cause gradual evolution of the transverse field on the Ising spins to pass through the quantum critical point. Our calculation shows that the cavity-induced nonlinearity plays an important role in the dynamics of this system. Quasiparticles can be excited in the Ising chain during this process, which results in the deviation of the system from its adiabatic ground state. This work is supported by the National Science Foundation under Award Number 0956064.

  7. Quantum phase transition, quantum fidelity and fidelity susceptibility in the Yang-Baxter system

    Science.gov (United States)

    Hu, Taotao; Yang, Qi; Xue, Kang; Wang, Gangcheng; Zhang, Yan; Li, Xiaodan; Ren, Hang

    2017-01-01

    In this paper, we investigate the ground-state fidelity and fidelity susceptibility in the many-body Yang-Baxter system and analyze their connections with quantum phase transition. The Yang-Baxter system was perturbed by a twist of e^{iφ} at each bond, where the parameter φ originates from the q-deformation of the braiding operator U with q = e^{-iφ} (Jimbo in Yang-Baxter equations in integrable systems, World Scientific, Singapore, 1990), and φ has a physical significance of magnetic flux (Badurek et al. in Phys. Rev. D 14:1177, 1976). We test the ground-state fidelity related by a small parameter variation φ which is a different term from the one used for driving the system toward a quantum phase transition. It shows that ground-state fidelity develops a sharp drop at the transition. The drop gets sharper as system size N increases. It has been verified that a sufficiently small value of φ used has no effect on the location of the critical point, but affects the value of F(gc,φ) . The smaller the twist φ, the more the value of F(gc,φ) is close to 0. In order to avoid the effect of the finite value of φ, we also calculate the fidelity susceptibility. Our results demonstrate that in the Yang-Baxter system, the quantum phase transition can be well characterized by the ground-state fidelity and fidelity susceptibility in a special way.

  8. Observation of the Quantum Anomalous Hall Insulator to Anderson Insulator Quantum Phase Transition and its Scaling Behavior

    Science.gov (United States)

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

    2016-09-01

    Fundamental insight into the nature of the quantum phase transition from a superconductor to an insulator in two dimensions, or from one plateau to the next or to an insulator in the quantum Hall effect, has been revealed through the study of its scaling behavior. Here, we report on the experimental observation of a quantum phase transition from a quantum-anomalous-Hall insulator to an Anderson insulator in a magnetic topological insulator by tuning the chemical potential. Our experiment demonstrates the existence of scaling behavior from which we extract the critical exponent for this quantum phase transition. We expect that our work will motivate much further investigation of many properties of quantum phase transition in this new context.

  9. Unconventional transformation of spin Dirac phase across a topological quantum phase transition.

    Science.gov (United States)

    Xu, Su-Yang; Neupane, Madhab; Belopolski, Ilya; Liu, Chang; Alidoust, Nasser; Bian, Guang; Jia, Shuang; Landolt, Gabriel; Slomski, Batosz; Dil, J Hugo; Shibayev, Pavel P; Basak, Susmita; Chang, Tay-Rong; Jeng, Horng-Tay; Cava, Robert J; Lin, Hsin; Bansil, Arun; Hasan, M Zahid

    2015-04-17

    The topology of a topological material can be encoded in its surface states. These surface states can only be removed by a bulk topological quantum phase transition into a trivial phase. Here we use photoemission spectroscopy to image the formation of protected surface states in a topological insulator as we chemically tune the system through a topological transition. Surprisingly, we discover an exotic spin-momentum locked, gapped surface state in the trivial phase that shares many important properties with the actual topological surface state in anticipation of the change of topology. Using a spin-resolved measurement, we show that apart from a surface bandgap these states develop spin textures similar to the topological surface states well before the transition. Our results offer a general paradigm for understanding how surface states in topological phases arise from a quantum phase transition and are suggestive for the future realization of Weyl arcs, condensed matter supersymmetry and other fascinating phenomena in the vicinity of a quantum criticality.

  10. Intrinsic Spin Hall Effect Induced by Quantum Phase Transition in HgCdTe Quantum Wells

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Wen; Chang, Kai; /Beijing, Inst. Semiconductors; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-19

    Spin Hall effect can be induced both by the extrinsic impurity scattering and by the intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. This difference gives a direct mechanism to experimentally distinguish the intrinsic spin Hall effect from the extrinsic one.

  11. 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.

  12. Quantum spin/valley Hall effect and topological insulator phase transitions in silicene

    KAUST Repository

    Tahir, M.

    2013-04-26

    We present a theoretical realization of quantum spin and quantum valley Hall effects in silicene. We show that combination of an electric field and intrinsic spin-orbit interaction leads to quantum phase transitions at the charge neutrality point. This phase transition from a two dimensional topological insulator to a trivial insulating state is accompanied by a quenching of the quantum spin Hall effect and the onset of a quantum valley Hall effect, providing a tool to experimentally tune the topological state of silicene. In contrast to graphene and other conventional topological insulators, the proposed effects in silicene are accessible to experiments.

  13. 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.

  14. Peculiar Quantum Phase Transitions and Hidden Supersymmetry in a Lipkin-Meshkov-Glick Model

    Institute of Scientific and Technical Information of China (English)

    CHEN Gang; LIANG Jiu-Qing

    2009-01-01

    In this paper we theoretically report an unconventional quantum phase transition of a simple Lipkin-Meshkov-Glick model: an interacting collective spin system without external magnetic field. It is shown that this model with integer-spin can exhibit a first-order quantum phase transition between different disordered phases, and more intriguingly, possesses a hidden supersymmetry at the critical point. However, for half-integer spin we predict another first-order quantum phase transition between two different long-range-ordered phases with a vanishing energy gap, which is induced by the destructive topological quantum interference between the intanton and anti-instanton tunneling paths and accompanies spontaneously breaking of supersymmetry at the same critical point. We also show that, when the total spin-value varies from half-integer to integer this model can exhibit an abrupt variation of Berry phase from π to zero.

  15. Decorated defect condensate, a window to unconventional quantum phase transitions in Weyl semimetals

    CERN Document Server

    You, Yizhi

    2016-01-01

    We investigate the unconventional quantum phase transitions in Weyl semimetals. The emergent boson fields, coupling with the Weyl fermion bilinears, contain a Wess-Zumino-Witten term or topological $\\Theta$ term inherited from the momentum space monopoles carried by Weyl points. Three types of unconventional quantum critical points will be studied in order: (1) The transition between two distinct symmetry breaking phases whose criticality is beyond Landau's paradigm. (2) The transition between a symmetry breaking state to a topological ordered state. (3) The transition between $3d$ topological order phase to trivial disordered phase whose criticality could be traced back to a $Z_2$ symmetry breaking transition in $4d$. The essence of these unconventional critical points lies in the fact that the topological defect of an order parameter carries either a nontrivial quantum number or a topological term so the condensation of the defects would either break some symmetry or give rise to a topological order phase w...

  16. 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.

  17. Effects of Quantum Correction on Dynamical Phase Transition in a Single Species Bosonic Josephson Junction

    Institute of Scientific and Technical Information of China (English)

    TIAN Jing; QIU Hai-Bo

    2013-01-01

    In this paper,by employing Bogliubov backreaction method,we investigate quantum correction effects on dynamical phase transition in a single species bosonic Josephson junction induced by increasing nonlinear interaction.Compared with mean field theory results,we find that the transition point is shifted.The dynamical phase transition is accompanied by a change of the entanglement entropy,which is found to reach a maximum at the transition point of the mean field theory.

  18. Computational studies of thermal and quantum phase transitions approached through non-equilibrium quenching

    Science.gov (United States)

    Liu, Cheng-Wei

    Phase transitions and their associated critical phenomena are of fundamental importance and play a crucial role in the development of statistical physics for both classical and quantum systems. Phase transitions embody diverse aspects of physics and also have numerous applications outside physics, e.g., in chemistry, biology, and combinatorial optimization problems in computer science. Many problems can be reduced to a system consisting of a large number of interacting agents, which under some circumstances (e.g., changes of external parameters) exhibit collective behavior; this type of scenario also underlies phase transitions. The theoretical understanding of equilibrium phase transitions was put on a solid footing with the establishment of the renormalization group. In contrast, non-equilibrium phase transition are relatively less understood and currently a very active research topic. One important milestone here is the Kibble-Zurek (KZ) mechanism, which provides a useful framework for describing a system with a transition point approached through a non-equilibrium quench process. I developed two efficient Monte Carlo techniques for studying phase transitions, one is for classical phase transition and the other is for quantum phase transitions, both are under the framework of KZ scaling. For classical phase transition, I develop a non-equilibrium quench (NEQ) simulation that can completely avoid the critical slowing down problem. For quantum phase transitions, I develop a new algorithm, named quasi-adiabatic quantum Monte Carlo (QAQMC) algorithm for studying quantum quenches. I demonstrate the utility of QAQMC quantum Ising model and obtain high-precision results at the transition point, in particular showing generalized dynamic scaling in the quantum system. To further extend the methods, I study more complex systems such as spin-glasses and random graphs. The techniques allow us to investigate the problems efficiently. From the classical perspective, using the

  19. Quantum Phase Transitions of Hard-Core Bosons on the Kagome Lattice

    Science.gov (United States)

    Isakov, S. V.; Melko, R. G.; Sengupta, K.; Wessel, S.; Kim, Yong Baek

    2006-03-01

    We study hard-core bosons with nearest-neighbor repulsion on the kagome lattice at different filling factors using quantum Monte Carlo simulations and a dual vortex theory. At half-filling, the ground state of the system is always a uniform superfluid in contrast to the case of the triangular lattice. There exists a quantum phase transition from a superfluid to a valence bond solid phase away from half-filling. The possibility of unusual quantum criticality is investigated.

  20. Universality of Holographic Phase Transitions and Holographic Quantum Liquids

    CERN Document Server

    Benincasa, Paolo

    2009-01-01

    We explore the phase structure for defect theories in full generality using the gauge/gravity correspondence. On the gravity side, the systems are constructed by introducing M (probe) D(p+4-2k)-branes in a background generated by N Dp-branes to obtain a codimension-k intersection. The dual gauge theory is a U(N) Supersymmetric Yang-Mills theory on a (1+p-k)-dimensional defect with both adjoint and fundamental degrees of freedom. We focus on the phase structure in the chemical potential versus temperature plane. We observe the existence of two universality classes for holographic gauge theories, which are identified by the order of the phase transition in the interior of the chemical potential/temperature plane. Specifically, all the sensible systems with no defect show a third order phase transition. Gauge theories on a defect with (p-1)-spatial directions are instead characterised by a second order phase transition. One can therefore state that the order of this phase transition is intimately related to the ...

  1. Nonequilibrium Quantum Criticality and Non-Markovian Environment: Critical Exponent of a Quantum Phase Transition

    Science.gov (United States)

    Nagy, D.; Domokos, P.

    2015-07-01

    We show that the critical exponent of a quantum phase transition in a damped-driven open system is determined by the spectral density function of the reservoir. We consider the open-system variant of the Dicke model, where the driven boson mode and also the large N spin couple to independent reservoirs at zero temperature. The critical exponent, which is 1 if there is no spin-bath coupling, decreases below 1 when the spin couples to a sub-Ohmic reservoir.

  2. Quantum phase transition in the Dzyaloshinskii-Moriya interaction with inhomogeneous magnetic field: Geometric approach

    Science.gov (United States)

    Najarbashi, G.; Seifi, B.

    2017-02-01

    In this paper, we generalize the results of Oh (Phys Lett A 373:644-647, 2009) to Dzyaloshinskii-Moriya model under non-uniform external magnetic field to investigate the relation between entanglement, geometric phase (or Berry phase) and quantum phase transition. We use quaternionic representation to relate the geometric phase to the quantum phase transition. For small values of DM parameter, the Berry phase is more appropriate than the concurrence measure, while for large values, the concurrence is a good indicator to show the phase transition. On the other hand, by increasing the DM interaction the phase transition occurs for large values of anisotropy parameter. In addition, for small values of magnetic field the concurrence measure is appropriate indicator for quantum phase transition, but for large values of magnetic field the Berry phase shows a sharp changes in the phase transition points. The results show that the Berry phase and concurrence form a complementary system from phase transition point of view.

  3. On Mean-Field Theory of Quantum Phase Transition in Granular Superconductors

    CERN Document Server

    Simkin, M V

    1996-01-01

    In previous work on quantum phase transition in granular superconductors, where mean-field theory was used, an assumption was made that the order parameter as a function of the mean field is a convex up function. Though this is not always the case in phase transitions, this assumption must be verified, what is done in this article.

  4. Pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons.

    Science.gov (United States)

    Haller, Elmar; Hart, Russell; Mark, Manfred J; Danzl, Johann G; Reichsöllner, Lukas; Gustavsson, Mattias; Dalmonte, Marcello; Pupillo, Guido; Nägerl, Hanns-Christoph

    2010-07-29

    Quantum many-body systems can have phase transitions even at zero temperature; fluctuations arising from Heisenberg's uncertainty principle, as opposed to thermal effects, drive the system from one phase to another. Typically, during the transition the relative strength of two competing terms in the system's Hamiltonian changes across a finite critical value. A well-known example is the Mott-Hubbard quantum phase transition from a superfluid to an insulating phase, which has been observed for weakly interacting bosonic atomic gases. However, for strongly interacting quantum systems confined to lower-dimensional geometry, a novel type of quantum phase transition may be induced and driven by an arbitrarily weak perturbation to the Hamiltonian. Here we observe such an effect--the sine-Gordon quantum phase transition from a superfluid Luttinger liquid to a Mott insulator--in a one-dimensional quantum gas of bosonic caesium atoms with tunable interactions. For sufficiently strong interactions, the transition is induced by adding an arbitrarily weak optical lattice commensurate with the atomic granularity, which leads to immediate pinning of the atoms. We map out the phase diagram and find that our measurements in the strongly interacting regime agree well with a quantum field description based on the exactly solvable sine-Gordon model. We trace the phase boundary all the way to the weakly interacting regime, where we find good agreement with the predictions of the one-dimensional Bose-Hubbard model. Our results open up the experimental study of quantum phase transitions, criticality and transport phenomena beyond Hubbard-type models in the context of ultracold gases.

  5. The Quantum Space Phase Transitions for Particles and Force Fields

    OpenAIRE

    Chung D.-Y.; Krasnoholovets V.

    2006-01-01

    We introduce a phenomenological formalism in which the space structure is treated in terms of attachment space and detachment space. Attachment space attaches to an object, while detachment space detaches from the object. The combination of these spaces results in three quantum space phases: binary partition space, miscible space and binary lattice space. Binary lattice space consists of repetitive units of alternative attachment space and detachment spac...

  6. Quantum phase transitions about parity breaking in matrix product systems%Quantum phase transitions about parity breaking in matrix product systems

    Institute of Scientific and Technical Information of China (English)

    ZHU Jing-Min

    2011-01-01

    According to our scheme to construct quantum phase transitions (QPTs) in spin chain systems with matrix product ground states, we first successfully combine matrix product state (MPS) QPTs with spontaneous symmetry breaking. For a concrete model, we take

  7. Observing a scale anomaly and a universal quantum phase transition in graphene.

    Science.gov (United States)

    Ovdat, O; Mao, Jinhai; Jiang, Yuhang; Andrei, E Y; Akkermans, E

    2017-09-11

    One of the most interesting predictions resulting from quantum physics, is the violation of classical symmetries, collectively referred to as anomalies. A remarkable class of anomalies occurs when the continuous scale symmetry of a scale-free quantum system is broken into a discrete scale symmetry for a critical value of a control parameter. This is an example of a (zero temperature) quantum phase transition. Such an anomaly takes place for the quantum inverse square potential known to describe 'Efimov physics'. Broken continuous scale symmetry into discrete scale symmetry also appears for a charged and massless Dirac fermion in an attractive 1/r Coulomb potential. The purpose of this article is to demonstrate the universality of this quantum phase transition and to present convincing experimental evidence of its existence for a charged and massless fermion in an attractive Coulomb potential as realized in graphene.When the continuous scale symmetry of a quantum system is broken, anomalies occur which may lead to quantum phase transitions. Here, the authors provide evidence for such a quantum phase transition in the attractive Coulomb potential of vacancies in graphene, and further envision its universality for diverse physical systems.

  8. Dimensionless ratios: Characteristics of quantum liquids and their phase transitions

    Science.gov (United States)

    Yu, Yi-Cong; Chen, Yang-Yang; Lin, Hai-Qing; Römer, Rudolf A.; Guan, Xi-Wen

    2016-11-01

    Dimensionless ratios of physical properties can characterize low-temperature phases in a wide variety of materials. As such, the Wilson ratio (WR), the Kadowaki-Woods ratio, and the Wiedemann-Franz law capture essential features of Fermi liquids in metals, heavy fermions, etc. Here we prove that the phases of many-body interacting multicomponent quantum liquids in one dimension (1D) can be described by WRs based on the compressibility, susceptibility, and specific heat associated with each component. These WRs arise due to additivity rules within subsystems reminiscent of the rules for multiresistor networks in series and parallel—a novel and useful characteristic of multicomponent Tomonaga-Luttinger liquids (TLL) independent of microscopic details of the systems. Using experimentally realized multispecies cold atomic gases as examples, we prove that the Wilson ratios uniquely identify phases of TLL, while providing universal scaling relations at the boundaries between phases. Their values within a phase are solely determined by the stiffnesses and sound velocities of subsystems and identify the internal degrees of freedom of said phase such as its spin degeneracy. This finding can be directly applied to a wide range of 1D many-body systems and reveals deep physical insights into recent experimental measurements of the universal thermodynamics in ultracold atoms and spins.

  9. Quantum critical phase and Lifshitz transition in an extended periodic Anderson model.

    Science.gov (United States)

    Laad, M S; Koley, S; Taraphder, A

    2012-06-13

    We study the quantum phase transition in f-electron systems as a quantum Lifshitz transition driven by selective-Mott localization in a realistic extended Anderson lattice model. Using dynamical mean-field theory (DMFT), we find that a quantum critical phase with anomalous ω/T scaling separates a heavy Landau-Fermi liquid from ordered phase(s). This non-Fermi liquid state arises from a lattice orthogonality catastrophe originating from orbital-selective Mott localization. Fermi surface reconstruction occurs via the interplay between and penetration of the Green function zeros to the poles, leading to violation of Luttinger's theorem in the strange metal. We show how this naturally leads to scale-invariant responses in transport. Thus, our work represents a specific DMFT realization of the hidden-FL and FL* theories, and holds promise for the study of 'strange' metal phases in quantum matter.

  10. Topological String in Quantum-Chromodynamical Chiral Phase Transitions

    Institute of Scientific and Technical Information of China (English)

    LI Yun-De

    2005-01-01

    @@ It is pointed out that if in heavy ion collision processes, the quark-gluon plasma SU(2) chiral phase transition really takes place and the phase transition is a second order. Then the topological string, i.e., the π string, will be formed. The main effect of this phenomenon is that there will be a number of pions produced by decay of the π string in the final state. The pions from the decay of the π string lead to the same effect of decreasing the Hanbury-Brown-Twiss peak in two-pion spectra which is just as that of the long-lived hadronic resonances.At relativistic heavy-ion collision and large hadron collision energies, it is expected that the factors are about α~ 0.7 - 0.9 and α~ 0.6 - 0.85, respectively.

  11. Minimal Models for a Superconductor-Insulator Conformal Quantum Phase Transition

    CERN Document Server

    Diamantini, M Cristina

    2013-01-01

    Conformal field theories do not only classify 2D classical critical behavior but they also govern a certain class of 2D quantum critical behavior. In this latter case it is the ground state wave functional of the quantum theory that is conformally invariant, rather than the classical action. We show that the superconducting-insulating (SI) quantum phase transition in 2D Josephson junction arrays (JJAs) is a (doubled) $c=1$ Gaussian conformal quantum critical point. The quantum action describing this system is a doubled Maxwell-Chern-Simons model in the strong coupling limit. We also argue that the SI quantum transitions in frustrated JJAs realize the other possible universality classes of conformal quantum critical behavior, corresponding to the unitary minimal models at central charge $c=1-6/m(m+1)$.

  12. Amplification of Quantum Meson Modes in the Late Time of the Chiral Phase Transition

    CERN Document Server

    Watanabe, K

    2007-01-01

    We investigate the time evolution of the quantum meson modes in the late time of chiral phase transition. In particular, it is shown that there exists a possible solution to the equation of motion for the quantum meson modes, which reveals a parametric resonance and/or resonance through forced oscillation induced by the small oscillation of the chiral condensate. After that, we demonstrate the unstable regions for the quantum meson modes in both the cases of a uniform and spatially expanding system.

  13. Nonequilibrium and nonhomogeneous phenomena around a first-order quantum phase transition

    Science.gov (United States)

    Del Re, Lorenzo; Fabrizio, Michele; Tosatti, Erio

    2016-03-01

    We consider nonequilibrium phenomena in a very simple model that displays a zero-temperature first-order phase transition. The quantum Ising model with a four-spin exchange is adopted as a general representative of first-order quantum phase transitions that belong to the Ising universality class, such as for instance the order-disorder ferroelectric transitions, and possibly first-order T =0 Mott transitions. In particular, we address quantum quenches in the exactly solvable limit of infinite connectivity and show that, within the coexistence region around the transition, the system can remain trapped in a metastable phase, as long as it is spatially homogeneous so that nucleation can be ignored. Motivated by the physics of nucleation, we then study in the same model static but inhomogeneous phenomena that take place at surfaces and interfaces. The first-order nature implies that both phases remain locally stable across the transition, and with that the possibility of a metastable wetting layer showing up at the surface of the stable phase, even at T =0 . We use mean-field theory plus quantum fluctuations in the harmonic approximation to study quantum surface wetting.

  14. Thermodynamic signatures of an underlying quantum phase transition: A grand canonical approach

    Energy Technology Data Exchange (ETDEWEB)

    Jimenez, Kevin, E-mail: kfjimenezfals@gmail.com; Reslen, Jose, E-mail: reslenjo@yahoo.com

    2016-08-06

    Highlights: • The grand-canonical statistics of a quantum phase transition is studied. • Thermodynamic quantities display features related to the quantum phase transition. • A mean field approach allows to obtain the partition function analytically. - Abstract: The grand canonical formalism is employed to study the thermodynamic structure of a model displaying a quantum phase transition when studied with respect to the canonical formalism. A numerical survey shows that the grand partition function diverges following a power law when the interaction parameter approaches a limiting constant. The power-law exponent takes a distinctive value when such limiting constant coincides with the critical point of the subjacent quantum phase transition. An approximated expression for the grand partition function is derived analytically implementing a mean field scheme and a number of thermodynamic observables are obtained. The system observables show signatures that can be used to track the critical point of the underlying transition. This result provides a simple fact that can be exploited to verify the existence of a quantum phase transition avoiding the zero temperature regime.

  15. Pulse laser induced graphite-to-diamond phase transition: the role of quantum electronic stress

    Science.gov (United States)

    Wang, ZhengFei; Liu, Feng

    2017-02-01

    First-principles calculations show that the pulse laser induced graphite-to-diamond phase transition is related to the lattice stress generated by the excited carriers, termed as "quantum electronic stress (QES)". We found that the excited carriers in graphite generate a large anisotropic QES that increases linearly with the increasing carrier density. Using the QES as a guiding parameter, structural relaxation spontaneously transforms the graphite phase into the diamond phase, as the QES is reduced and minimized. Our results suggest that the concept of QES can be generally applied as a good measure to characterize the pulse laser induced phase transitions, in analogy to pressure induced phase transitions.

  16. Effect of a fermion on quantum phase transitions in bosonic systems

    Energy Technology Data Exchange (ETDEWEB)

    Iachello, F., E-mail: francesco.iachello@yale.edu [Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, Connecticut 06520-8120 (United States); Leviatan, A., E-mail: ami@phys.huji.ac.il [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Petrellis, D., E-mail: petrellis@inp.demokritos.gr [Institute of Nuclear Physics, N.C.S.R. ' Demokritos' , GR-15310 Aghia Paraskevi, Attiki (Greece)

    2011-11-17

    The effect of a fermion with angular momentum j on quantum phase transitions of a (s,d) bosonic system is investigated. It is shown that the presence of a fermion strongly modifies the critical value at which the transition occurs, and its nature, even for small and moderate values of the coupling constant. The analogy with a bosonic system in an external field is mentioned. Experimental evidence for precursors of quantum phase transitions in bosonic systems plus a fermion (odd-even nuclei) is presented.

  17. Effect of a fermion on quantum phase transitions in bosonic systems

    CERN Document Server

    Iachello, F; Petrellis, D

    2011-01-01

    The effect of a fermion with angular momentum j on quantum phase transitions of a (s,d) bosonic system is investigated. It is shown that the presence of a fermion strongly modifies the critical value at which the transition occurs, and its nature, even for small and moderate values of the coupling constant. The analogy with a bosonic system in an external field is mentioned. Experimental evidence for precursors of quantum phase transitions in bosonic systems plus a fermion (odd-even nuclei) is presented.

  18. Quantum adiabatic algorithm and scaling of gaps at first-order quantum phase transitions.

    Science.gov (United States)

    Laumann, C R; Moessner, R; Scardicchio, A; Sondhi, S L

    2012-07-20

    Motivated by the quantum adiabatic algorithm (QAA), we consider the scaling of the Hamiltonian gap at quantum first-order transitions, generally expected to be exponentially small in the size of the system. However, we show that a quantum antiferromagnetic Ising chain in a staggered field can exhibit a first-order transition with only an algebraically small gap. In addition, we construct a simple classical translationally invariant one-dimensional Hamiltonian containing nearest-neighbor interactions only, which exhibits an exponential gap at a thermodynamic quantum first-order transition of essentially topological origin. This establishes that (i) the QAA can be successful even across first-order transitions but also that (ii) it can fail on exceedingly simple problems readily solved by inspection, or by classical annealing.

  19. Quantum Phase Transitions in the Sub-Ohmic Spin-Boson Model: Failure of the Quantum-Classical Mapping

    Science.gov (United States)

    Vojta, Matthias; Tong, Ning-Hua; Bulla, Ralf

    2005-02-01

    The effective theories for many quantum phase transitions can be mapped onto those of classical transitions. Here we show that the naive mapping fails for the sub-Ohmic spin-boson model which describes a two-level system coupled to a bosonic bath with power-law spectral density, J(ω)∝ωs. Using an ɛ expansion we prove that this model has a quantum transition controlled by an interacting fixed point at small s, and support this by numerical calculations. In contrast, the corresponding classical long-range Ising model is known to display mean-field transition behavior for 0quantum-classical mapping is argued to arise from the long-ranged interaction in imaginary time in the quantum model.

  20. Quantum phase transition in many-flavor supersymmetric QED$_{3}$

    CERN Document Server

    Russo, Jorge G

    2016-01-01

    We study $\\mathcal{N}=4$ supersymmetric QED in three dimensions, on a three-sphere, with 2N massive hypermultiplets and a Fayet-Iliopoulos parameter. We identify the exact partition function of the theory with a conical (Mehler) function. This implies a number of analytical formulas, including a recurrence relation and a second-order differential equation, associated with an integrable system. In the large N limit, the theory undergoes a second-order phase transition on a critical line in the parameter space. We discuss the critical behavior and compute the two-point correlation function of a gauge invariant mass operator, which is shown to diverge as one approaches criticality from the subcritical phase. Finally, we comment on the asymptotic 1/N expansion and on mirror symmetry.

  1. Regularity and chaos at critical points of first-order quantum phase transitions

    CERN Document Server

    Macek, Michal

    2011-01-01

    We study the interplay between regular and chaotic dynamics at the critical point of a first order quantum shape-phase transition in an interacting boson model of nuclei. A classical analysis reveals a distinct behavior of the coexisting phases in a broad energy range. The dynamics is completely regular in the deformed phase while it becomes strongly chaotic in the spherical phase. A quantum analysis of the spectra separates the regular states from the irregular ones, assigns them to particular phases and discloses persisting regular rotational bands in the deformed region.

  2. Partial Dynamical Symmetry at Critical-Points of Quantum Phase Transitions

    CERN Document Server

    Leviatan, A

    2007-01-01

    We show that partial dynamical symmetries (PDS) can occur at critical-points of quantum phase transitions, in which case, underlying competing symmetries are conserved exactly by a subset of states, and mix strongly in other states. Several types of PDS are demonstrated with the example of critical-point Hamiltonians for first- and second-order transitions in the framework of the interacting boson model, whose dynamical symmetries correspond to different shape-phases in nuclei.

  3. Multipartite non-locality and entanglement signatures of a field-induced quantum phase transition

    Science.gov (United States)

    Batle, Josep; Alkhambashi, Majid; Farouk, Ahmed; Naseri, Mosayeb; Ghoranneviss, Mahmood

    2017-02-01

    Quantum correlation measures are limited in practice to a few number of parties, since no general theory is still capable of reaching the thermodynamic limit. In the present work we study entanglement and non-locality for a cluster of spins belonging to a compound that displays a magnetocaloric effect. A quantum phase transition (QPT) is induced by an external magnetic field B, in such a way that the corresponding quantum fluctuations are reproduced at a much smaller scale than the experimental outcomes, and then described by means of the aforementioned quantum measures.

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

    Science.gov (United States)

    Ohtsuki, Tomi; Ohtsuki, Tomoki

    2017-04-01

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

  5. Direct Observation of Dynamical Quantum Phase Transitions in an Interacting Many-Body System

    Science.gov (United States)

    Jurcevic, P.; Shen, H.; Hauke, P.; Maier, C.; Brydges, T.; Hempel, C.; Lanyon, B. P.; Heyl, M.; Blatt, R.; Roos, C. F.

    2017-08-01

    The theory of phase transitions represents a central concept for the characterization of equilibrium matter. In this work we study experimentally an extension of this theory to the nonequilibrium dynamical regime termed dynamical quantum phase transitions (DQPTs). We investigate and measure DQPTs in a string of ions simulating interacting transverse-field Ising models. During the nonequilibrium dynamics induced by a quantum quench we show for strings of up to 10 ions the direct detection of DQPTs by revealing nonanalytic behavior in time. Moreover, we provide a link between DQPTs and the dynamics of other quantities such as the magnetization, and we establish a connection between DQPTs and entanglement production.

  6. On the Ising character of the quantum-phase transition in LiHoF4

    Directory of Open Access Journals (Sweden)

    R. Skomski

    2016-05-01

    Full Text Available It is investigated how a transverse magnetic field affects the quantum-mechanical character of LiHoF4, a system generally considered as a textbook example for an Ising-like quantum-phase transition. In small magnetic fields, the low-temperature behavior of the ions is Ising-like, involving the nearly degenerate low-lying Jz = ±  8 doublet. However, as the transverse field increases, there is a substantial admixture of states having |Jz| < 8. Near the quantum-phase-transition field, the system is distinctively non-Ising like, and all Jz eigenstates yield ground-state contributions of comparable magnitude. A classical analog to this mechanism is the micromagnetic single point in magnets with uniaxial anisotropy. Since Ho3+ has J = 8, the ion’s behavior is reminiscent of the classical limit (J = ∞, but quantum corrections remain clearly visible.

  7. From Quantum To Classical Dynamics: A Landau Continuous Phase Transition With Spontaneous Superposition Breaking

    CERN Document Server

    Pankovic, V; Predojevic, M; Krmar, M; Pankovic, Vladan; Hubsch, Tristan; Predojevic, Milan; Krmar, Miodrag

    2004-01-01

    Developing an earlier proposal (Ne'eman, Damnjanovic, etc), we show herein that there is a Landau continuous phase transition from the exact quantum dynamics to the effectively classical one, occurring via spontaneous superposition breaking (effective hiding), as a special case of the corresponding general formalism (Bernstein). Critical values of the order parameters for this transition are determined by Heisenberg's indeterminacy relations, change continuously, and are in excellent agreement with the recent and remarkable experiments with Bose condensation. It is also shown that such a phase transition can sucessfully model self-collapse (self-decoherence), as an effective classical phenomenon, on the measurement device. This then induces a relative collapse (relative decoherence) as an effective quantum phenomenon on the measured quantum object by measurement. We demonstrate this (including the case of Bose-Einstein condensation) in the well-known cases of the Stern-Gerlach spin measurement, Bell's inequal...

  8. 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.

  9. Evolution of order and chaos across a first-order quantum phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Leviatan, A., E-mail: ami@phys.huji.ac.il [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); Macek, M., E-mail: mmacek@phys.huji.ac.il [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)

    2012-07-24

    We study the evolution of the dynamics across a generic first-order quantum phase transition in an interacting boson model of nuclei. The dynamics inside the phase coexistence region exhibits a very simple pattern. A classical analysis reveals a robustly regular dynamics confined to the deformed region and well separated from a chaotic dynamics ascribed to the spherical region. A quantum analysis discloses regular bands of states in the deformed region, which persist to energies well above the phase-separating barrier, in the face of a complicated environment. The impact of kinetic collective rotational terms on this intricate interplay of order and chaos is investigated.

  10. Evolution of order and chaos across a first-order quantum phase transition

    CERN Document Server

    Leviatan, A

    2012-01-01

    We study the evolution of the dynamics across a generic first order quantum phase transition in an interacting boson model of nuclei. The dynamics inside the phase coexistence region exhibits a very simple pattern. A classical analysis reveals a robustly regular dynamics confined to the deformed region and well separated from a chaotic dynamics ascribed to the spherical region. A quantum analysis discloses regular bands of states in the deformed region, which persist to energies well above the phase-separating barrier, in the face of a complicated environment. The impact of kinetic collective rotational terms on this intricate interplay of order and chaos is investigated.

  11. Diffusion Quantum Monte Carlo Study of Martensitic Phase Transition: The Case of Phosphorene

    CERN Document Server

    Reeves, Kyle G; Kanai, Yosuke

    2016-01-01

    Recent technical advances in dealing with finite-size errors make quantum Monte Carlo methods quite appealing for treating extended systems in electronic structure calculations, especially when commonly-used density functional theory (DFT) methods might not be satisfactory. We present a theoretical study of martensitic phase transition of a two-dimensional phosphorene by employing diffusion Monte Carlo (DMC) approach to investigate the energetics of this phase transition. The DMC calculation supports DFT prediction of having a rather diffusive barrier that is characterized by having two transition states, in addition to confirming that the so-called black and blue phases of phosphorene are essentially degenerate. At the same time, the calculation shows the importance of treating correlation energy accurately for describing the energy changes in the martensitic phase transition, as is already widely appreciated for chemical bond formation/dissociation. Building on the atomistic characterization of the phase tr...

  12. On a First-Order Quantum Phase Transition in a Finite System

    CERN Document Server

    Leviatan, A

    2006-01-01

    We examine the dynamics at the critical-point of a general first-order quantum phase transition in a finite system. Suitable Hamiltonians are constructed whose spectra exhibit coexistence of states corresponding to two degenerate minima in the energy surface separated by an arbitrary barrier. Explicit expressions are derived for wave functions and obesrvables at the critical-point.

  13. Coulomb analogy for non-Hermitian degeneracies near quantum phase transitions.

    Science.gov (United States)

    Cejnar, Pavel; Heinze, Stefan; Macek, Michal

    2007-09-07

    Degeneracies near the real axis in a complex-extended parameter space of a Hermitian Hamiltonian are studied. We present a method to measure distributions of such degeneracies on the Riemann sheet of a selected level and apply it in classification of quantum phase transitions. The degeneracies are shown to behave similarly as complex zeros of a partition function.

  14. Wigner's dynamical transition state theory in phase space : classical and quantum

    NARCIS (Netherlands)

    Waalkens, Holger; Schubert, Roman; Wiggins, Stephen

    2008-01-01

    We develop Wigner's approach to a dynamical transition state theory in phase space in both the classical and quantum mechanical settings. The key to our development is the construction of a normal form for describing the dynamics in the neighbourhood of a specific type of saddle point that governs t

  15. Quantum phase transitions in an effective Hamiltonian: fast and slow systems

    Energy Technology Data Exchange (ETDEWEB)

    Sainz, I [School of Information and Communication Technology, Royal Institute of Technology (KTH), Electrum 229, SE-164 40 Kista (Sweden); Klimov, A B [Departamento de Fisica, Universidad de Guadalajara, Revolucion 1500, 44420 Guadalajara, Jalisco (Mexico); Roa, L [Center for Quantum Optics and Quantum Information, Departamento de Fisica, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)], E-mail: klimov@cencar.udg.mx

    2008-09-05

    An effective Hamiltonian describing interaction between generic fast and slow systems is obtained in the strong interaction limit. The result is applied for studying the effect of quantum phase transition as a bifurcation of the ground state of the slow subsystem. Examples such as atom-field and atom-atom interactions are analyzed in detail.

  16. Quantum phase transition and quench dynamics in the anisotropic Rabi model

    Science.gov (United States)

    Shen, Li-Tuo; Yang, Zhen-Biao; Wu, Huai-Zhi; Zheng, Shi-Biao

    2017-01-01

    We investigate the quantum phase transition (QPT) and quench dynamics in the anisotropic Rabi model when the ratio of the qubit transition frequency to the oscillator frequency approaches infinity. Based on the Schrieffer-Wolff transformation, we find an anti-Hermitian operator that maps the original Hamiltonian into a one-dimensional oscillator Hamiltonian within the spin-down subspace. We analytically derive the eigenenergy and eigenstate of the normal and superradiant phases and demonstrate that the system undergoes a second-order quantum phase transition at a critical border. The critical border is a straight line in a two-dimensional parameter space which essentially extends the dimensionality of QPT in the Rabi model. By combining the Kibble-Zurek mechanism and the adiabatic dynamics method, we find that the residual energy vanishes as the quench time tends to zero, which is a sharp contrast to the universal scaling where the residual energy diverges in the same limit.

  17. Quantum phase transition induced by Dzyaloshinskii-Moriya interactions in the kagome antiferromagnet

    OpenAIRE

    Cepas, Olivier; Fong, C. M.; Leung, P. W.; Lhuillier, C.

    2008-01-01

    We argue that the S=1/2 kagome antiferromagnet undergoes a quantum phase transition when the Dzyaloshinskii-Moriya coupling is increased. For $DD_c$ the system develops antiferromagnetic long-range order. The quantum critical point is found to be $D_c \\simeq 0.1J$ using exact diagonalizations and finite-size scaling. This suggests that the kagome compound ZnCu$_3(OH)$_6$Cl$_3$ may be in a quantum critical region controlled by this fixed point.

  18. 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.

  19. The Renormalization Group, Entropy, Thermodynamic Phase Transitions and Order in Quantum Field Theory

    CERN Document Server

    Pérez-Mercader, J

    1993-01-01

    We define an entropy for a quantum field theory by combining quantum fluctuations, scaling and the maximum entropy concept. This entropy has different behavior in asymptotically free and non--asymptotically free theories. We find that the transition between the two regimes (from the asymptotically free to the non--asymptotically free) takes place via a continuous phase transition. For asymptotically free theories there exist regimes where the ``temperatures" are negative. In asymptotically free theories there exist maser--like states mostly in the infrared; furthermore, as one goes into the ultraviolet and more matter states contribute to quantum processes, the quantum field system can shed entropy and cause the formation of thermodynamically stable {\\it entropy--ordered} states. It is shown how the known heavier quarks can be thus described.

  20. A quantum phase transition between a topological and a trivial semi-metal in holography

    CERN Document Server

    Landsteiner, Karl; Sun, Ya-Wen

    2015-01-01

    We present a holographic model of a topological Weyl semi-metal state. Key ingredient is a time-reversal breaking parameter and a mass deformation. Upon varying the ratio of mass to time reversal breaking parameter the model undergoes a quantum phase transition from a topologically non-trivial state to a trivial one. The order parameter for this phase transition is the anomalous Hall effect (AHE). The results can be interpreted in terms of the holographic RG flow leading to restoration of time reversal at the end point of the RG flow in the trivial phase.

  1. Scaling of magnetic fluctuations near a quantum phase transition

    DEFF Research Database (Denmark)

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

    1998-01-01

    We use inelastic neutron scattering to measure the magnetic fluctuations in a single crystal of the heavy fermion alloy CeCu5.9Au0.1 close to the antiferromagnetic quantum critical point. The energy (E), wave vector (Q), and temperature (T) dependent spectra obey E/T scaling at Q near (1,0,0). Th...

  2. 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.

  3. Quantum phase transition in a multiconnected superconducting Jaynes-Cummings lattice

    Science.gov (United States)

    Seo, Kangjun; Tian, Lin

    2015-05-01

    The connectivity and tunability of superconducting qubits and resonators provide us with an appealing platform to study the many-body physics of microwave excitations. Here we present a multiconnected Jaynes-Cummings lattice model which is symmetric with respect to the nonlocal qubit-resonator couplings. Our calculation shows that this model exhibits a Mott insulator-superfluid-Mott insulator phase transition at commensurate fillings, featured by symmetric quantum critical points. Phase diagrams in the grand canonical ensemble are also derived, which confirm the incompressibility of the Mott insulator phase. Different from a general-purposed quantum computer, it only requires two operations to demonstrate this phase transition: the preparation and the detection of commensurate many-body ground state. We discuss the realization of these operations in a superconducting circuit.

  4. Thermal and quantum phase transitions in atom-field systems: a microcanonical analysis

    Science.gov (United States)

    Bastarrachea-Magnani, M. A.; Lerma-Hernández, S.; Hirsch, J. G.

    2016-09-01

    The thermodynamical properties of a generalized Dicke model are calculated and related with the critical properties of its energy spectrum, namely the quantum phase transitions (QPT) and excited state quantum phase transitions (ESQPT). The thermal properties are calculated both in the canonical and the microcanonical ensembles. The latter deduction allows for an explicit description of the relation between thermal and energy spectrum properties. While in an isolated system the subspaces with different pseudospin are disconnected, and the whole energy spectrum is accessible, in the statistical ensemble the situation is radically different. The multiplicity of the lowest energy states for each pseudospin completely dominates the thermal behavior, making the set of degenerate states with the smallest pseudospin at a given energy the only ones playing a role in the thermal properties. As a result, the states in the region with positive thermal energy cannot be thermally populated because their negligible probability, making that energy region thermally unreachable at finite temperatures. The quantum phase transitions of the lowest energy states, from a normal to a superradiant phase, produce the thermal transition. The other critical phenomena, the ESQPTs occurring at excited energies, have no manifestation in the thermodynamics, although their effects could be seen in finite size corrections. A new superradiant phase is found, which only exists in the generalized model, and can be relevant in finite size systems.

  5. Quantum phase transition and Fermi liquid behavior in Pd1 -xNix nanoalloys

    Science.gov (United States)

    Swain, P.; Srivastava, Suneel K.; Srivastava, Sanjeev K.

    2015-01-01

    The Pd1 -xNix alloy system is an established ideal transition-metal system possessing a composition-induced paramagnetic-to-ferromagnetic quantum phase transition (QPT) at the critical concentration xc˜0.026 in bulk. A low-temperature non-Fermi liquid (NFL) behavior around xc usually indicates the presence of quantum criticality (QC) in this system. In this work, we explore the existence of such a QPT in nanoparticles of this alloy system. We synthesized single-phase, polydispersed and 40-50 nm mean diameter crystalline nanoparticles of Pd1 -xNix alloys, with x near xc and beyond, by a chemical reflux method. In addition to the determination of the size, composition, phase, and crystallinity of the alloys by microscopic and spectroscopic techniques, the existence of a possible QPT was explored by resistivity and dc magnetization measurements. A dip in the value of the exponent n near xc, and a concomitant peak in the constant A of the A Tn dependence of the low-temperature (T ) resistivity indicate the presence of a quantum-like phase transition in the system. The minimum value of n , however, remains within the Fermi liquid regime (n >2 ). The dc magnetization results suggest an anticipatory presence of a superparamagnetic-to-ferromagnetic QPT in the mean-sized nanoparticles. The observation of a possible quantum critical NFL behavior (n <2 ) through resistivity is argued to be inhibited by the electron-magnon scatterings present in the smaller nanoparticles.

  6. Signatures of a pressure-induced topological quantum phase transition in BiTeI.

    Science.gov (United States)

    Xi, Xiaoxiang; Ma, Chunli; Liu, Zhenxian; Chen, Zhiqiang; Ku, Wei; Berger, H; Martin, C; Tanner, D B; Carr, G L

    2013-10-11

    We report the observation of two signatures of a pressure-induced topological quantum phase transition in the polar semiconductor BiTeI using x-ray powder diffraction and infrared spectroscopy. The x-ray data confirm that BiTeI remains in its ambient-pressure structure up to 8 GPa. The lattice parameter ratio c/a shows a minimum between 2.0-2.9 GPa, indicating an enhanced c-axis bonding through p(z) band crossing as expected during the transition. Over the same pressure range, the infrared spectra reveal a maximum in the optical spectral weight of the charge carriers, reflecting the closing and reopening of the semiconducting band gap. Both of these features are characteristics of a topological quantum phase transition and are consistent with a recent theoretical proposal.

  7. 0 -π phase transition in hybrid superconductor-InSb nanowire quantum dot devices

    Science.gov (United States)

    Li, Sen; Kang, N.; Caroff, P.; Xu, H. Q.

    2017-01-01

    Hybrid superconductor-semiconducting nanowire devices provide an ideal platform to investigating interesting intragap bound states, such as the Andreev bound states (ABSs), Yu-Shiba-Rusinov (YSR) states, and the Majorana bound states. The competition between Kondo correlations and superconductivity in Josephson quantum dot (QD) devices results in two different ground states and the occurrence of a 0 -π quantum phase transition. Here we report on transport measurements on hybrid superconductor-InSb nanowire QD devices with different device geometries. We demonstrate a realization of continuous gate-tunable ABSs with both 0-type levels and π -type levels. This allow us to manipulate the transition between the 0 and π junction and explore charge transport and spectrum in the vicinity of the quantum phase transition regime. Furthermore, we find a coexistence of 0-type ABS and π -type ABS in the same charge state. By measuring temperature and magnetic field evolution of the ABSs, the different natures of the two sets of ABSs are verified, being consistent with the scenario of phase transition between the singlet and doublet ground state. Our study provides insight into Andreev transport properties of hybrid superconductor-QD devices and sheds light on the crossover behavior of the subgap spectrum in the vicinity of the 0 -π transition.

  8. Superconductor-insulator quantum phase transition in disordered FeSe thin films.

    Science.gov (United States)

    Schneider, R; Zaitsev, A G; Fuchs, D; V Löhneysen, H

    2012-06-22

    The evolution of two-dimensional electronic transport with increasing disorder in epitaxial FeSe thin films is studied. Disorder is generated by reducing the film thickness. The extreme sensitivity of the films to disorder results in a superconductor-insulator transition. The finite-size scaling analysis in the critical regime based on the Bose-glass model strongly supports the idea of a continuous quantum phase transition. The obtained value for the critical-exponent product of approximately 7/3 suggests that the transition is governed by quantum percolation. Finite-size scaling with the same critical-exponent product is also substantiated when the superconductor-insulator transition is tuned with an applied magnetic field.

  9. Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI.

    Science.gov (United States)

    Park, Joonbum; Jin, Kyung-Hwan; Jo, Y J; Choi, E S; Kang, W; Kampert, E; Rhyee, J-S; Jhi, Seung-Hoon; Kim, Jun Sung

    2015-11-02

    We report the pressure-induced topological quantum phase transition of BiTeI single crystals using Shubnikov-de Haas oscillations of bulk Fermi surfaces. The sizes of the inner and the outer FSs of the Rashba-split bands exhibit opposite pressure dependence up to P = 3.35 GPa, indicating pressure-tunable Rashba effect. Above a critical pressure P ~ 2 GPa, the Shubnikov-de Haas frequency for the inner Fermi surface increases unusually with pressure, and the Shubnikov-de Haas oscillations for the outer Fermi surface shows an abrupt phase shift. In comparison with band structure calculations, we find that these unusual behaviors originate from the Fermi surface shape change due to pressure-induced band inversion. These results clearly demonstrate that the topological quantum phase transition is intimately tied to the shape of bulk Fermi surfaces enclosing the time-reversal invariant momenta with band inversion.

  10. Pressure- and temperature-driven phase transitions in HgTe quantum wells

    Science.gov (United States)

    Krishtopenko, S. S.; Yahniuk, I.; But, D. B.; Gavrilenko, V. I.; Knap, W.; Teppe, F.

    2016-12-01

    We present theoretical investigations of pressure- and temperature-driven phase transitions in HgTe quantum wells grown on a CdTe buffer. Using the eight-band k .p Hamiltonian we calculate evolution of energy-band structure at different quantum well widths with hydrostatic pressure up to 20 kbars and temperature ranging up to 300 K. In particular, we show that, in addition to temperature, tuning of hydrostatic pressure allows us to drive transitions between semimetal, band insulator, and topological insulator phases. Our realistic band-structure calculations reveal that the band inversion under hydrostatic pressure and temperature may be accompanied by nonlocal overlapping between conduction and valence bands. The pressure and temperature phase diagrams are presented.

  11. 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.

  12. 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

  13. Nonequilibrium effective field theory for absorbing state phase transitions in driven open quantum spin systems

    Science.gov (United States)

    Buchhold, Michael; Everest, Benjamin; Marcuzzi, Matteo; Lesanovsky, Igor; Diehl, Sebastian

    2017-01-01

    Phase transitions to absorbing states are among the simplest examples of critical phenomena out of equilibrium. The characteristic feature of these models is the presence of a fluctuationless configuration which the dynamics cannot leave, which has proved a rather stringent requirement in experiments. Recently, a proposal to seek such transitions in highly tunable systems of cold-atomic gases offers to probe this physics and, at the same time, to investigate the robustness of these transitions to quantum coherent effects. Here, we specifically focus on the interplay between classical and quantum fluctuations in a simple driven open quantum model which, in the classical limit, reproduces a contact process, which is known to undergo a continuous transition in the "directed percolation" universality class. We derive an effective long-wavelength field theory for the present class of open spin systems and show that, due to quantum fluctuations, the nature of the transition changes from second to first order, passing through a bicritical point which appears to belong instead to the "tricritical directed percolation" class.

  14. Quantum phase transition in ultra small doubly connected superconducting cylinders

    Science.gov (United States)

    Sternfeld, I.; Koret, R.; Shtrikman, H.; Tsukernik, A.; Karpovski, M.; Palevski, A.

    2008-02-01

    The kinetic energy of Cooper pairs, in doubly connected superconducting cylinders, is a function of the applied flux and the ratio between the diameter of the cylinder and the zero temperature coherence length d/ ξ(0). If d >ξ(0) the known Little-Parks oscillations are observed. On the other hand if d ξ(0), we observed the LP oscillations. In the Al cylinders we did not observe a transition to the superconducting state due to the proximity effect, resulted from an Au layer coating the Al. However, we did observe Altshuler-Aronov-Spivak (h/2e) oscillations in these cylinders.

  15. Magnetic Quantum Phase Transitions of a Kondo Lattice Model with Ising Anisotropy

    Science.gov (United States)

    Zhu, Jian-Xin; Kirchner, Stefan; Si, Qimiao; Grempel, Daniel R.; Bulla, Ralf

    2006-03-01

    We study the Kondo Lattice model with Ising anisotropy, within an extended dynamical mean field theory (EDMFT) in the presence or absence of antiferromagnetic ordering. The EDMFT equations are studied using both the Quantum Monte Carlo (QMC) and Numerical Renormalization Group (NRG) methods. We discuss the overall magnetic phase diagram by studying the evolution, as a function of the ratio of the RKKY interaction and bare Kondo scale, of the local spin susceptibility, magnetic order parameter, and the effective Curie constant of a nominally paramagnetic solution with a finite moment. We show that, within the numerical accuracy, the quantum magnetic transition is second order. The local quantum critical aspect of the transition is also discussed.

  16. Adiabatic quenches and characterization of amplitude excitations in a continuous quantum phase transition

    Science.gov (United States)

    Hoang, Thai M.; Bharath, Hebbe M.; Boguslawski, Matthew J.; Anquez, Martin; Robbins, Bryce A.; Chapman, Michael S.

    2016-01-01

    Spontaneous symmetry breaking occurs in a physical system whenever the ground state does not share the symmetry of the underlying theory, e.g., the Hamiltonian. This mechanism gives rise to massless Nambu–Goldstone modes and massive Anderson–Higgs modes. These modes provide a fundamental understanding of matter in the Universe and appear as collective phase or amplitude excitations of an order parameter in a many-body system. The amplitude excitation plays a crucial role in determining the critical exponents governing universal nonequilibrium dynamics in the Kibble–Zurek mechanism (KZM). Here, we characterize the amplitude excitations in a spin-1 condensate and measure the energy gap for different phases of the quantum phase transition. At the quantum critical point of the transition, finite-size effects lead to a nonzero gap. Our measurements are consistent with this prediction, and furthermore, we demonstrate an adiabatic quench through the phase transition, which is forbidden at the mean field level. This work paves the way toward generating entanglement through an adiabatic phase transition. PMID:27503886

  17. Adiabatic quenches and characterization of amplitude excitations in a continuous quantum phase transition

    Science.gov (United States)

    Hoang, Thai M.; Bharath, Hebbe M.; Boguslawski, Matthew J.; Anquez, Martin; Robbins, Bryce A.; Chapman, Michael S.

    2016-08-01

    Spontaneous symmetry breaking occurs in a physical system whenever the ground state does not share the symmetry of the underlying theory, e.g., the Hamiltonian. This mechanism gives rise to massless Nambu-Goldstone modes and massive Anderson-Higgs modes. These modes provide a fundamental understanding of matter in the Universe and appear as collective phase or amplitude excitations of an order parameter in a many-body system. The amplitude excitation plays a crucial role in determining the critical exponents governing universal nonequilibrium dynamics in the Kibble-Zurek mechanism (KZM). Here, we characterize the amplitude excitations in a spin-1 condensate and measure the energy gap for different phases of the quantum phase transition. At the quantum critical point of the transition, finite-size effects lead to a nonzero gap. Our measurements are consistent with this prediction, and furthermore, we demonstrate an adiabatic quench through the phase transition, which is forbidden at the mean field level. This work paves the way toward generating entanglement through an adiabatic phase transition.

  18. Topological phase transition and quantum spin Hall edge states of antimony few layers

    Science.gov (United States)

    Kim, Sung Hwan; Jin, Kyung-Hwan; Park, Joonbum; Kim, Jun Sung; Jhi, Seung-Hoon; Yeom, Han Woong

    2016-09-01

    While two-dimensional (2D) topological insulators (TI’s) initiated the field of topological materials, only very few materials were discovered to date and the direct access to their quantum spin Hall edge states has been challenging due to material issues. Here, we introduce a new 2D TI material, Sb few layer films. Electronic structures of ultrathin Sb islands grown on Bi2Te2Se are investigated by scanning tunneling microscopy. The maps of local density of states clearly identify robust edge electronic states over the thickness of three bilayers in clear contrast to thinner islands. This indicates that topological edge states emerge through a 2D topological phase transition predicted between three and four bilayer films in recent theory. The non-trivial phase transition and edge states are confirmed for epitaxial films by extensive density-functional-theory calculations. This work provides an important material platform to exploit microscopic aspects of the quantum spin Hall phase and its quantum phase transition.

  19. Energy level structure and quantum phase transitions of spin systems with nonaxially symmetric Hamiltonians

    Energy Technology Data Exchange (ETDEWEB)

    Lopez-Moreno, Enrique; Grether, M; Velazquez, Victor, E-mail: elm@hp.fciencias.unam.mx [Facultad de Ciencias, Departamento de Fisica, Universidad Nacional Autonoma de Mexico, Cd. Universitaria, Circuito Exterior, 04510 Mexico DF (Mexico)

    2011-11-25

    A general spin system with a nonaxially symmetric Hamiltonian containing J{sub x}, J{sub z}-linear and J{sub z}-quadratic terms, widely used in many-body fermionic and bosonic systems and in molecular magnetism, is considered for the variations of general parameters describing intensity interaction changes of each of its terms. For this model Hamiltonian, a semiclassical energy surface (ES) is obtained by means of the coherent-state formalism. An analysis of this ES function, based on catastrophe theory, determines the separatrix in the control parameter space of the system Hamiltonian: the loci of singularities representing semiclassical phase transitions. Here we show that distinct regions of qualitatively different spectrum structures, as well as a singular behavior of quantum states, are ruled by this separatrix: here we show that the separatrix not only describes ground-state singularities, which have been associated with quantum phase transitions, but also reveals the structure of the excited spectrum, distinguishing different quantum phases within the parameter space. Finally, we consider magnetic susceptibility and heat capacity of the system at finite temperature, in order to study thermal properties and thermodynamical phase transitions in the perspective of the separatrix of this Hamiltonian system. (paper)

  20. Order, Chaos and Quasi Symmetries in a First-Order Quantum Phase Transition

    CERN Document Server

    Leviatan, A

    2014-01-01

    We study the competing order and chaos in a first-order quantum phase transition with a high barrier. The boson model Hamiltonian employed, interpolates between its U(5) (spherical) and SU(3) (deformed) limits. A classical analysis reveals regular (chaotic) dynamics at low (higher) energy in the spherical region, coexisting with a robustly regular dynamics in the deformed region. A quantum analysis discloses, amidst a complicated environment, persisting regular multiplets of states associated with partial U(5) and quasi SU(3) dynamical symmetries.

  1. Quantum phase transition in ultra small doubly connected superconducting cylinders

    Energy Technology Data Exchange (ETDEWEB)

    Sternfeld, I. [School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)], E-mail: itayst@post.tau.ac.il; Koret, R. [School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel); Shtrikman, H. [Department of Condensed Matter, Weizmann Institute of Science, Rehovot 76100 (Israel); Tsukernik, A. [Center for Nanoscience and Nanotechnology, Tel Aviv University, Tel Aviv 69978 (Israel); Karpovski, M.; Palevski, A. [School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)

    2008-02-15

    The kinetic energy of Cooper pairs, in doubly connected superconducting cylinders, is a function of the applied flux and the ratio between the diameter of the cylinder and the zero temperature coherence length d/{xi}(0). If d >{xi}(0) the known Little-Parks oscillations are observed. On the other hand if d <{xi}(0), the superconducting state is energetically not favored around odd multiples of half flux quanta even at T{approx}0, resulting in the so called destructive regime [Y. Liu, et al., Science 294 (2001) 2332]. We developed a novel technique to fabricate superconducting doubly connected nanocylinders with both diameter and thickness less than 100 nm, and performed magnetoresistance measurements on such Nb and Al cylinders. In the Nb cylinders, where d >{xi}(0), we observed the LP oscillations. In the Al cylinders we did not observe a transition to the superconducting state due to the proximity effect, resulted from an Au layer coating the Al. However, we did observe Altshuler-Aronov-Spivak (h/2e) oscillations in these cylinders.

  2. Universal space-time scaling symmetry in the dynamics of bosons across a quantum phase transition

    CERN Document Server

    Clark, Logan W; Chin, Cheng

    2016-01-01

    The dynamics of many-body systems spanning condensed matter, cosmology, and beyond is hypothesized to be universal when the systems cross continuous phase transitions. The universal dynamics is expected to satisfy a scaling symmetry of space and time with the crossing rate, inspired by the Kibble-Zurek mechanism. We test this symmetry based on Bose condensates in a shaken optical lattice. Shaking the lattice drives condensates across an effectively ferromagnetic quantum phase transition. After crossing the critical point, the condensates manifest delayed growth of spin fluctuations and develop anti-ferromagnetic spatial correlations resulting from sub-Poisson generation of topological defects. The characteristic times and lengths scale as power-laws of the crossing rate, yielding the temporal exponent 0.50(2) and the spatial exponent 0.26(2), consistent with theory. Furthermore, the fluctuations and correlations are invariant in scaled space-time coordinates, in support of the scaling symmetry of quantum crit...

  3. Dissipation-driven quantum phase transition in superconductor-graphene systems.

    Science.gov (United States)

    Lutchyn, Roman M; Galitski, Victor; Refael, Gil; Das Sarma, S

    2008-09-05

    We show that a system of Josephson junctions coupled via low-resistance tunneling contacts to graphene substrate(s) may effectively operate as a current switching device. The effect is based on the dissipation-driven superconductor-to-insulator quantum phase transition, which happens due to the interplay of the Josephson effect and Coulomb blockade. Coupling to a graphene substrate with gapless excitations further enhances charge fluctuations favoring superconductivity. The effect is shown to scale exponentially with the Fermi energy in graphene, which can be controlled by the gate voltage. We develop a theory that quantitatively describes the quantum phase transition in a two-dimensional Josephson junction array, but it is expected to provide a reliable qualitative description for one-dimensional systems as well.

  4. Valley polarized quantum Hall effect and topological insulator phase transitions in silicene

    KAUST Repository

    Tahir, M.

    2013-01-25

    The electronic properties of silicene are distinct from both the conventional two dimensional electron gas and the famous graphene due to strong spin orbit interaction and the buckled structure. Silicene has the potential to overcome limitations encountered for graphene, in particular the zero band gap and weak spin orbit interaction. We demonstrate a valley polarized quantum Hall effect and topological insulator phase transitions. We use the Kubo formalism to discuss the Hall conductivity and address the longitudinal conductivity for elastic impurity scattering in the first Born approximation. We show that the combination of an electric field with intrinsic spin orbit interaction leads to quantum phase transitions at the charge neutrality point, providing a tool to experimentally tune the topological state. Silicene constitutes a model system for exploring the spin and valley physics not accessible in graphene due to the small spin orbit interaction.

  5. 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.

  6. Precise measurements on a quantum phase transition in antiferromagnetic spinor Bose-Einstein condensates

    Science.gov (United States)

    Vinit, A.; Raman, C.

    2017-01-01

    We have experimentally investigated the quench dynamics of antiferromagnetic spinor Bose-Einstein condensates in the vicinity of a zero temperature quantum phase transition at zero quadratic Zeeman shift q . The rate of instability shows good agreement with predictions based upon solutions to the Bogoliubov-de Gennes equations. A key feature of this work was removal of magnetic field inhomogeneities, resulting in a steep change in behavior near the transition point. The quadratic Zeeman shift at the transition point was resolved to 250 mHz uncertainty, equivalent to an energy resolution of kB× (12 pK). A small (2-3 σ ) shift of the transition point was observed, from q =0 to q =+650 mHz, whose physical mechanism is currently unknown. In this work, we demonstrate a sub-Hz precision measurement of a phase transition in quantum gases. It paves the way toward observing shifts of the transition point due to finite particle number N that scale as 1 /N , and also to potential Heisenberg limited spectroscopy with antiferromagnetic spinor gases [L.-N. Wu and L. You, Phys. Rev. A 93, 033608 (2016), 10.1103/PhysRevA.93.033608].

  7. Heat capacity for systems with excited-state quantum phase transitions

    Science.gov (United States)

    Cejnar, Pavel; Stránský, Pavel

    2017-03-01

    Heat capacities of model systems with finite numbers of effective degrees of freedom are evaluated using canonical and microcanonical thermodynamics. Discrepancies between both approaches, which are observed even in the infinite-size limit, are particularly large in systems that exhibit an excited-state quantum phase transition. The corresponding irregularity of the spectrum generates a singularity in the microcanonical heat capacity and affects smoothly the canonical heat capacity.

  8. Edge states and quantum phase transition in graphene under in-plane effective exchange fields

    Science.gov (United States)

    Liu, Zheng-Fang; Wu, Qing-Ping; Chen, Ai-Xi; Xiao, Xian-Bo; Liu, Nian-Hua; Miao, Guo-Xing

    2017-02-01

    We investigated the edge states and quantum phase transition in graphene under an in-plane effective exchange field. The result shows that the combined effects of the in-plane effective exchange field and a staggered sublattice potential can induce zero-energy flat bands of edge states. Such flat-band edge states can evolve into helical-like ones in the presence of intrinsic spin-orbit coupling, with a unique spin texture. We also find that the bulk energy gap induced by the spin-orbit coupling and staggered sublattice potential can be closed and reopened with the in-plane effective exchange field, and the reopened bulk gap can be even larger than that induced by only the spin-orbit coupling and staggered sublattice potential, which is different from the case of an out-of-plane effective exchange field. The calculated spin-dependent Chern numbers suggest that the bulk gap closing and reopening is accompanied by a quantum phase transition from a trivial insulator phase across a metal phase into a spin-dependent quantum Hall phase.

  9. Quantum critical scaling for field-induced quantum phase transition in a periodic Anderson-like model polymer chain

    Science.gov (United States)

    Ding, L. J.; Zhong, Y.

    2017-07-01

    The quantum phase transition and thermodynamics of a periodic Anderson-like polymer chain in a magnetic field are investigated by Green's function theory. The T-h phase diagram is explored, wherein a crossover temperature T∗ denoting the gapless phase crossover into quantum critical regimes, smoothly connects near the critical fields to the universal linear line T∗ ∼ (h - hc,s), and ends at hc,s, providing a new route to capture quantum critical point (QCP). The quantum critical scaling around QCPs is demonstrated by analyzing magnetization, specific heat and Grüneisen parameter Γh, which provide direct access to distill the power-law critical exponents (β, δ and α) obeying the critical scaling relation α + β(1 + δ) = 2, analogous to the quantum spin system. Furthermore, scaling hypothesis equations are proposed to check the scaling analysis, for which all the data collapse onto a single curve or two independent branches for the plot against an appropriate scaling variable, indicating the self-consistency and reliability of the obtained critical exponents.

  10. Dynamical scalability and control of totally connected spin networks across quantum phase transitions

    Science.gov (United States)

    Acevedo, Óscar L.; Quiroga, Luis; Rodríguez, Ferney J.; Johnson, Neil F.

    2014-03-01

    Dynamical quantum phase crossings of spin networks have recently received increased attention thanks to their relation to adiabatic quantum computing, and their feasible realizations using ultra-cold atomic and molecular systems with a highly tunable degree of connectivity. Dynamical scaling of spatially distributed systems like Ising models have been widely studied, and successfully related to well-known theories like the Kibble-Zurek mechanism. The case of totally connected networks such as the Dicke Model and Lipkin-Meshkov-Glick Model, however, is known to exhibit a breakdown of these frameworks. Our analysis overcomes the lack of spatial correlation structure by developing a general approach which (i) is valid regardless the connectivity of the system, (ii) goes beyond critical exponents, and (iii) provides a time-resolved picture of dynamical scaling. By treating these models as a method for macroscopic quantum control of their subsystems, we have found microscopic signatures of the dynamical scaling as well as instances of dynamical enhancement of distinctive quantum properties such as entanglement and coherence. Our results yield novel prescriptions for the fields of quantum simulations and quantum control, and deepen our fundamental understanding of phase transitions.

  11. Fermi points and topological quantum phase transitions in a multi-band superconductor.

    Science.gov (United States)

    Puel, T O; Sacramento, P D; Continentino, M A

    2015-10-28

    The importance of models with an exact solution for the study of materials with non-trivial topological properties has been extensively demonstrated. The Kitaev model plays a guiding role in the search for Majorana modes in condensed matter systems. Also, the sp-chain with an anti-symmetric mixing among the s and p bands is a paradigmatic example of a topological insulator with well understood properties. Interestingly, these models share the same universality class for their topological quantum phase transitions. In this work we study a two-band model of spinless fermions with attractive inter-band interactions. We obtain its zero temperature phase diagram, which presents a rich variety of phases including a Weyl superconductor and a topological insulator. The transition from the topological to the trivial superconducting phase has critical exponents different from those of Kitaev's model.

  12. Novel quantum behavior generated by traveling across a quantum phase transition

    Science.gov (United States)

    Acevedo, O. L.; Rodriguez, F. J.; Quiroga, L.; Johnson, N. F.

    2012-02-01

    We report novel dynamical behavior in a multi-qubit--light system described by the Dicke model, which is being driven across its thermodynamic quantum-phase boundary. Analyzing the system's quantum fidelity, we find that the near-adiabatic regime exhibits the richest phenomena, with a strong asymmetry in the internal collective dynamics depending on which phase is the starting point. Depending on the quenching regime a highly non-trivial behavior emerges in both the qubit and radiation subsystems. For the former, we find that for some paths in parameter space the final fidelity of the near-adiabatic process does not depend on the direction of the trajectory, but depends only on the speed at which the path is traveled. This behavior is contrasted with Landau-Zener tunneling and the Kibble-Zurek mechanism. Furthermore, for some qubit subsystems, we identify purification and screening effects which could be used for quantum control. By contrast, the evolution of the Wigner function shows the radiation subsystem exhibits the emergence of complexity and non-classicality. These findings could be experimentally tested in several condensed matter scenarios -- for example, diamond-NV centers and superconductor qubits in confined radiation environments.

  13. Numerical evidence for a phase transition in 4d spin foam quantum gravity

    CERN Document Server

    Bahr, Benjamin

    2016-01-01

    Building on recent advances in defining Wilsonian RG flows, and in particular the notion of scales, for background-independent theories, we present a first investigation of the renormalization of the 4d spin foam path integral for quantum gravity, both analytically and numerically. Focussing on a specific truncation of the model using a hypercubic lattice, we compute the RG flow and find strong indications for a phase transition, as well as an interesting interplay between the different observed phases and the (broken) diffeomorphism symmetry of the model. Most notably, it appears that the critical point between the phases, which is a fixed point of the RG flow, is precisely where broken diffeomorphism symmetry is restored, which suggests that it might allow for the definition a continuum limit of the quantum gravity theory.

  14. Supersymmetrical bounding of asymmetric states and quantum phase transitions by anti-crossing of symmetric states

    Science.gov (United States)

    Afzal, Muhammad Imran; Lee, Yong Tak

    2016-12-01

    Von Neumann and Wigner theorized the bounding and anti-crossing of eigenstates. Experiments have demonstrated that owing to anti-crossing and similar radiation rates, the graphene-like resonance of inhomogeneously strained photonic eigenstates can generate a pseudomagnetic field, bandgaps and Landau levels, whereas exponential or dissimilar rates induce non-Hermicity. Here, we experimentally demonstrate higher-order supersymmetry and quantum phase transitions by resonance between similar one-dimensional lattices. The lattices consisted of inhomogeneous strain-like phases of triangular solitons. The resonance created two-dimensional, inhomogeneously deformed photonic graphene. All parent eigenstates were annihilated. Eigenstates of mildly strained solitons were annihilated at similar rates through one tail and generated Hermitian bounded eigenstates. The strongly strained solitons with positive phase defects were annihilated at exponential rates through one tail, which bounded eigenstates through non-Hermitianally generated exceptional points. Supersymmetry was evident, with preservation of the shapes and relative phase differences of the parent solitons. Localizations of energies generated from annihilations of mildly and strongly strained soliton eigenstates were responsible for geometrical (Berry) and topological phase transitions, respectively. Both contributed to generating a quantum Zeno phase, whereas only strong twists generated topological (Anderson) localization. Anti-bunching-like condensation was also observed.

  15. Quantum phase transition of light in a 1-D photon-hopping-controllable resonator array

    CERN Document Server

    Wu, Chun-Wang; Deng, Zhi-Jiao; Dai, Hong-Yi; Chen, Ping-Xing; Li, Cheng-Zu

    2011-01-01

    We give a concrete experimental scheme for engineering the insulator-superfluid transition of light in a one-dimensional (1-D) array of coupled superconducting stripline resonators. In our proposed architecture, the on-site interaction and the photon hopping rate can be tuned independently by adjusting the transition frequencies of the charge qubits inside the resonators and at the resonator junctions, respectively, which permits us to systematically study the quantum phase transition of light in a complete parameter space. By combining the techniques of photon-number-dependent qubit transition and fast read-out of the qubit state using a separate low-Q resonator mode, the statistical property of the excitations in each resonator can be obtained with a high efficiency. An analysis of the various decoherence sources and disorders shows that our scheme can serve as a guide to coming experiments involving a small number of coupled resonators.

  16. Fermi surface reconstruction and multiple quantum phase transitions in the antiferromagnet CeRhIn5.

    Science.gov (United States)

    Jiao, Lin; Chen, Ye; Kohama, Yoshimitsu; Graf, David; Bauer, E D; Singleton, John; Zhu, Jian-Xin; Weng, Zongfa; Pang, Guiming; Shang, Tian; Zhang, Jinglei; Lee, Han-Oh; Park, Tuson; Jaime, Marcelo; Thompson, J D; Steglich, Frank; Si, Qimiao; Yuan, H Q

    2015-01-20

    Conventional, thermally driven continuous phase transitions are described by universal critical behavior that is independent of the specific microscopic details of a material. However, many current studies focus on materials that exhibit quantum-driven continuous phase transitions (quantum critical points, or QCPs) at absolute zero temperature. The classification of such QCPs and the question of whether they show universal behavior remain open issues. Here we report measurements of heat capacity and de Haas-van Alphen (dHvA) oscillations at low temperatures across a field-induced antiferromagnetic QCP (Bc0 ≈ 50 T) in the heavy-fermion metal CeRhIn5. A sharp, magnetic-field-induced change in Fermi surface is detected both in the dHvA effect and Hall resistivity at B0* ≈ 30 T, well inside the antiferromagnetic phase. Comparisons with band-structure calculations and properties of isostructural CeCoIn5 suggest that the Fermi-surface change at B0* is associated with a localized-to-itinerant transition of the Ce-4f electrons in CeRhIn5. Taken in conjunction with pressure experiments, our results demonstrate that at least two distinct classes of QCP are observable in CeRhIn5, a significant step toward the derivation of a universal phase diagram for QCPs.

  17. Coexistence of order and chaos at critical points of first-order quantum phase transitions in nuclei

    CERN Document Server

    Macek, M

    2011-01-01

    We study the interplay between ordered and chaotic dynamics at the critical point of a generic first-order quantum phase transition in the interacting boson model of nuclei. Classical and quantum analyses reveal a distinct behavior of the coexisting phases. While the dynamics in the deformed phase is robustly regular, the spherical phase shows strongly chaotic behavior in the same energy intervals. The effect of collective rotations on the dynamics is investigated.

  18. Multipartite entanglement in an XXZ spin chain with Dzyaloshinskii-Moriya interaction and quantum phase transition

    Science.gov (United States)

    Cheng, Jun-Qing; Wu, Wei; Xu, Jing-Bo

    2017-09-01

    We investigate the multipartite entanglement and trace distance of the one-dimensional anisotropic spin-1/2 XXZ spin chain with the Dzyaloshinskii-Moriya interaction and find that the Dzyaloshinskii-Moriya interaction can influence the entanglement distribution and increase the proportion of multipartite entanglement in the entanglement structure. Furthermore, we explore the quantum phase transition of the XXZ spin chain with Dzyaloshinskii-Moriya interaction by making use of the multipartite entanglement and trace distance along with the quantum renormalization group method. It is found that the first derivatives of renormalized multipartite entanglement and trace distance for the ground state have dramatic changes near the critical point, and the renormalized multipartite entanglement and trace distance obey the universal finite-size scaling laws in the vicinity of the quantum critical point.

  19. 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.

  20. Characterization of a quantum phase transition in Dirac systems by means of the wave-packet dynamics

    Directory of Open Access Journals (Sweden)

    E. Romera

    2012-12-01

    Full Text Available We study the signatures of phase transitions in the time evolution of wave-packets by analyzing two simple model systems: a graphene quantum dot model in a magnetic field and a Dirac oscillator in a magnetic field. We have characterized the phase transitions using the autocorrelation function. Our work also reveals that the description in terms of Shannon entropy of the autocorrelation function is a clear phase transition indicator.

  1. Third Law of Thermodynamics and The Shape of the Phase Diagram for Systems With a First-Order Quantum Phase Transition.

    Science.gov (United States)

    Kirkpatrick, T R; Belitz, D

    2015-07-10

    The third law of thermodynamics constrains the phase diagram of systems with a first-order quantum phase transition. For a zero conjugate field, the coexistence curve has an infinite slope at T=0. If a tricritical point exists at T>0, then the associated tricritical wings are perpendicular to the T=0 plane, but not to the zero-field plane. These results are based on the third law and basic thermodynamics only, and are completely general. As an explicit example we consider the ferromagnetic quantum phase transition in clean metals, where a first-order quantum phase transition is commonly observed.

  2. 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.

  3. Numerical renormalization group for impurity quantum phase transitions: structure of critical fixed points

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Hyun-Jung [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut fuer Physik, Universitaet Augsburg, D-86135 Augsburg (Germany); Bulla, Ralf [Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut fuer Physik, Universitaet Augsburg, D-86135 Augsburg (Germany); Vojta, Matthias [Institut fuer Theorie der Kondensierten Materie, Universitaet Karlsruhe, D-76128 Karlsruhe (Germany)

    2005-11-02

    The numerical renormalization group method is used to investigate zero-temperature phase transitions in quantum impurity systems, in particular in the particle-hole symmetric soft-gap Anderson model. The model displays two stable phases whose fixed points can be built up of non-interacting single-particle states. In contrast, the quantum phase transitions turn out to be described by interacting fixed points, and their excitations cannot be described in terms of free particles. We show that the structure of the many-body spectrum of these critical fixed points can be understood using renormalized perturbation theory close to certain values of the bath exponents which play the role of critical dimensions. Contact is made with perturbative renormalization group calculations for the soft-gap Anderson and Kondo models. A complete description of the quantum critical many-particle spectra is achieved using suitable marginal operators; technically this can be understood as epsilon-expansion for full many-body spectra.

  4. Numerical renormalization group for impurity quantum phase transitions: structure of critical fixed points

    Science.gov (United States)

    Lee, Hyun-Jung; Bulla, Ralf; Vojta, Matthias

    2005-11-01

    The numerical renormalization group method is used to investigate zero-temperature phase transitions in quantum impurity systems, in particular in the particle-hole symmetric soft-gap Anderson model. The model displays two stable phases whose fixed points can be built up of non-interacting single-particle states. In contrast, the quantum phase transitions turn out to be described by interacting fixed points, and their excitations cannot be described in terms of free particles. We show that the structure of the many-body spectrum of these critical fixed points can be understood using renormalized perturbation theory close to certain values of the bath exponents which play the role of critical dimensions. Contact is made with perturbative renormalization group calculations for the soft-gap Anderson and Kondo models. A complete description of the quantum critical many-particle spectra is achieved using suitable marginal operators; technically this can be understood as epsilon-expansion for full many-body spectra.

  5. Quantum phase transitions and thermodynamics of the power-law Kondo model

    Science.gov (United States)

    Mitchell, Andrew K.; Vojta, Matthias; Bulla, Ralf; Fritz, Lars

    2013-11-01

    We revisit the physics of a Kondo impurity coupled to a fermionic host with a diverging power-law density of states near the Fermi level, ρ(ω)˜|ω|r, with exponent -1phases and also near the various quantum phase transitions. Antiferromagnetic Kondo coupling leads to strong screening with a negative zero-temperature impurity entropy, while ferromagnetic Kondo coupling can induce a stable fractional spin moment. We formulate the quantum field theories for all critical fixed points of the problem, which are fermionic in nature and allow for a perturbative renormalization-group treatment.

  6. Dynamical Quantum Phase Transitions: Role of Topological Nodes in Wave Function Overlaps

    Science.gov (United States)

    Huang, Zhoushen; Balatsky, Alexander V.

    2016-08-01

    A sudden quantum quench of a Bloch band from one topological phase toward another has been shown to exhibit an intimate connection with the notion of a dynamical quantum phase transition (DQPT), where the returning probability of the quenched state to the initial state—i.e., the Loschmidt echo—vanishes at critical times {t*}. Analytical results to date are limited to two-band models, leaving the exact relation between topology and DQPT unclear. In this Letter, we show that, for a general multiband system, a robust DQPT relies on the existence of nodes (i.e., zeros) in the wave function overlap between the initial band and the postquench energy eigenstates. These nodes are topologically protected if the two participating wave functions have distinctive topological indices. We demonstrate these ideas in detail for both one and two spatial dimensions using a three-band generalized Hofstadter model. We also discuss possible experimental observations.

  7. Mott insulating states and quantum phase transitions of correlated SU(2 N ) Dirac fermions

    Science.gov (United States)

    Zhou, Zhichao; Wang, Da; Meng, Zi Yang; Wang, Yu; Wu, Congjun

    2016-06-01

    The interplay between charge and spin degrees of freedom in strongly correlated fermionic systems, in particular of Dirac fermions, is a long-standing problem in condensed matter physics. We investigate the competing orders in the half-filled SU (2 N ) Hubbard model on a honeycomb lattice, which can be accurately realized in optical lattices with ultracold large-spin alkaline-earth fermions. Employing large-scale projector determinant quantum Monte Carlo simulations, we have explored quantum phase transitions from the gapless Dirac semimetals to the gapped Mott insulating phases in the SU(4) and SU(6) cases. Both of these Mott insulating states are found to be columnar valence bond solid (cVBS) and to be absent of the antiferromagnetic Néel ordering and the loop current ordering. Inside the cVBS phases, the dimer ordering is enhanced by increasing fermion components and behaves nonmonotonically as the interaction strength increases. Although the transitions generally should be of first order due to a cubic invariance possessed by the cVBS order, the coupling to gapless Dirac fermions can soften the transitions to second order through a nonanalytic term in the free energy. Our simulations provide important guidance for the experimental explorations of novel states of matter with ultracold alkaline-earth fermions.

  8. Phase transitions in strongly interacting quantum field theories. QED{sub 3} vs. QCD

    Energy Technology Data Exchange (ETDEWEB)

    Bonnet, J.A.

    2013-07-15

    In this thesis, we investigate strongly coupled quantum field theories on the examples of (2+1) dimensional Quantumelectrodynamics (QED{sub 3}) and (3+1) dimensional Quantum Chromodynamics (QCD) in the framework of Dyson-Schwinger equations. We firstly focus on the chiral phase transition in QED{sub 3} as a low-energy effective theory for high-temperature superconductors. These materials are inherently anisotropic, as shown by experiments. We therefore focus on the influence of an anisotropic spacetime onto the critical number of fermion flavors for chiral symmetry breaking at zero and finite temperature. The findings are summarized in phase diagrams for the critical number of fermion flavors as a function of the independent anisotropic velocities and temperature. These were the first calculations considering anisotropic QED{sub 3} at finite temperatures. Furthermore, the presented investigations elaborate on the critical scaling behavior close to the merging region of the thermal phase transition line and the quantum phase transition point. The most important results include the finding that anisotropy provides an external parameter that determines the scaling scenario. Secondly, the QCD part of this thesis consists of a feasibility study of the implementation of external magnetic fields into the Dyson-Schwinger formalism. This study serves as a basis for further investigations of e.g. the dynamical mass generation at finite temperatures and densities. This will allow to contribute to the discussions on the phenomenon of (inverse) magnetic catalysis from a functional methods' point of view. Furthermore, we present the first successful extraction of a dressed Wilson loop from Dyson-Schwinger equations. It represents an observable for confinement that was recently introduced in the framework of lattice gauge theory. In addition, its connection with the conventional Wilson loop allows for a direct extraction of the string tension.

  9. A Study of Topological Quantum Phase Transition and Majorana Localization Length for the Interacting Helical Liquid System

    Science.gov (United States)

    Dey, Dayasindhu; Saha, Sudip Kumar; Singha Deo, P.; Kumar, Manoranjan; Sarkar, Sujit

    2017-07-01

    We study the topological quantum phase transition and also the nature of this transition using the density matrix renormalization group method. We observe the existence of topological quantum phase transition for repulsive interaction, however this phase is more stable for the attractive interaction. The length scale dependent study shows many new and important results and we show explicitly that the major contribution to the excitation comes from the edge of the system when the system is in the topological state. We also show the dependence of Majorana localization length for various values of chemical potential.

  10. 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.

  11. Fermions and the AdS/CFT correspondence: quantum phase transitions and the emergent Fermi-liquid

    CERN Document Server

    Cubrovic, Mihailo; Schalm, Koenraad

    2009-01-01

    A central mystery in quantum condensed matter physics is the zero temperature quantum phase transition between strongly renormalized Fermi-liquids as found in heavy fermion intermetallics and possibly high Tc superconductors. Field theoretical statistical techniques are useless because of the fermion sign problem, but we will present here results showing that the mathematics of string theory is capable of describing fermionic quantum critical states. Using the Anti-de-Sitter/Conformal Field Theory (AdS/CFT) correspondence to relate fermionic quantum critical fields to a gravitational problem, we compute the spectral functions of fermions in the field theory. Deforming away from the relativistic quantum critical point by increasing the fermion density we show that a state emerges with all the features of the Fermi-liquid. Tuning the scaling dimensions of the critical fermion fields we find that the quasiparticle disappears at a quantum phase transition of a purely statistical nature, not involving any symmetry...

  12. Quantum Oscillation Signatures of Pressure-induced Topological Phase Transition in BiTeI

    OpenAIRE

    Joonbum Park; Kyung-Hwan Jin; Jo, Y. J.; Choi, E. S.; Kang, W.; Kampert, E.; J.-S. Rhyee; Seung-Hoon Jhi; Jun Sung Kim

    2015-01-01

    We report the pressure-induced topological quantum phase transition of BiTeI single crystals using Shubnikov-de Haas oscillations of bulk Fermi surfaces. The sizes of the inner and the outer FSs of the Rashba-split bands exhibit opposite pressure dependence up to P = 3.35 GPa, indicating pressure-tunable Rashba effect. Above a critical pressure P ~ 2 GPa, the Shubnikov-de Haas frequency for the inner Fermi surface increases unusually with pressure, and the Shubnikov-de Haas oscillations for t...

  13. The Open-System Dicke-Model Quantum Phase Transition with a Sub-Ohmic Bath

    CERN Document Server

    Nagy, D

    2015-01-01

    We show that the critical exponent of a quantum phase transition in a damped-driven open system is determined by the spectral density function of the reservoir. We consider the open-system variant of the Dicke model, where the driven boson mode and also the large N-spin couple to independent reservoirs at zero temperature. The critical exponent, which is $1$ if there is no spin-bath coupling, decreases below 1 when the spin couples to a sub-Ohmic reservoir.

  14. Quantum Phase Transition and Thermal Entanglement in the Isotropic XXX Model

    Institute of Scientific and Technical Information of China (English)

    马富武; 孔祥木

    2012-01-01

    We investigate the quantum phase transition (OPT) and the pairwise thermal entanglement in the three- qubit Heisenberg XXX chain with Dzyaloshinskii Moriya (DM) interaction under a magnetic field. The ground states of the system exist crossing points, which shows that the system exhibits a Q, PT. At a given temperature, the entanglement undergoes two sudden changes (platform-like behavior) as the DM interaction or external magnetic field increases. This special property can be used as the entanglement switch, which is also influenced by the temperature. We can modulate the DM interaction or external magnetic field to control the entanglement switch.

  15. Quantum Phase Transition and Thermal Entanglement in the Isotropic XXX Model

    Science.gov (United States)

    Ma, Fu-Wu; Kong, Xiang-Mu

    2012-06-01

    We investigate the quantum phase transition (QPT) and the pairwise thermal entanglement in the three-qubit Heisenberg XXX chain with Dzyaloshinskii—Moriya (DM) interaction under a magnetic field. The ground states of the system exist crossing points, which shows that the system exhibits a QPT. At a given temperature, the entanglement undergoes two sudden changes (platform-like behavior) as the DM interaction or external magnetic field increases. This special property can be used as the entanglement switch, which is also influenced by the temperature. We can modulate the DM interaction or external magnetic field to control the entanglement switch.

  16. The two-body random spin ensemble and a new type of quantum phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Pizorn, Iztok; Prosen, Tomaz [Department of Physics, FMF, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana (Slovenia); Mossmann, Stefan; Seligman, Thomas H [Instituto de Ciencias FIsicas, Universidad Nacional Autonoma de Mexico, CP 62132 Cuernavaca, Morelos (Mexico)], E-mail: tomaz.prosen@fmf.uni-lj.si

    2008-02-15

    We study in this paper the properties of a two-body random matrix ensemble for distinguishable spins. We require the ensemble to be invariant under the group of local transformations and analyze a parametrization in terms of the group parameters and the remaining parameters associated with the 'entangling' part of the interaction. We then specialize to a spin chain with nearest-neighbour interactions and numerically find a new type of quantum-phase transition related to the strength of a random external field, i.e. the time-reversal-breaking one-body interaction term.

  17. The two-body random spin ensemble and a new type of quantum phase transition

    Science.gov (United States)

    Pižorn, Iztok; Prosen, Tomaž; Mossmann, Stefan; Seligman, Thomas H.

    2008-02-01

    We study in this paper the properties of a two-body random matrix ensemble for distinguishable spins. We require the ensemble to be invariant under the group of local transformations and analyze a parametrization in terms of the group parameters and the remaining parameters associated with the 'entangling' part of the interaction. We then specialize to a spin chain with nearest-neighbour interactions and numerically find a new type of quantum-phase transition related to the strength of a random external field, i.e. the time-reversal-breaking one-body interaction term.

  18. Renormalizability and quantum stability of the phase transition in rigid string coupled to Kalb-Ramond fields, 2

    CERN Document Server

    Awada, M

    1995-01-01

    Recently we have shown that a phase transition occurs in the leading approximation of the large N limit in rigid strings coupled to long range Kalb-Ramond interactions. The disordered phase is essentially the Nambu-Goto-Polyakov string theory while the ordered phase is a new theory. In this part II letter we study the first subleading quantum corrections we started in I. We derive the renormalized mass gap equation and obtain the renormalized critical line of the interacting theory. Our main and final result is that the phase transition does indeed survive quantum fluctuations.

  19. Interaction-induced quantum anomalous Hall phase in bilayers of 3d transition-metal oxide

    Science.gov (United States)

    Wang, Yilin; Fang, Zhong; Dai, Xi

    2014-03-01

    In the present paper, we have studied the electronic structure of 3d transition-metal oxide LaCoO3 thin film grown on the [111] surface of SrTiO3. By using first-principles calculation under local density approximation implemented with Gutzwiller variational method (LDA+G), we have studied the bilayer systems of LaCoO3 thin films grown along the [111] direction on SrTiO3. The LDA results show that two nearly flat bands locate at the top and bottom of eg bands of Co atoms, and the Fermi level crosses the lower one, which is almost half-filled. After including both the spin-orbit coupling and the rotational invariant Coulomb interaction in the LDA+G method, we found that the Coulomb interaction will enhance the effective spin-orbit coupling, and a ferromagnetic insulator phase with a gap as large as 0.15 eV will be stabilized. Further calculations indicate that such a ferromagnetic insulator phase will have non zero Chern number one leading to quantum anomalous Hall effect. Increasing Hund's rule coupling in this system will generate a low spin to high spin transition and destroy the quantum anomalous Hall phase.

  20. Phase transitions

    CERN Document Server

    Solé, Ricard V

    2011-01-01

    Phase transitions--changes between different states of organization in a complex system--have long helped to explain physics concepts, such as why water freezes into a solid or boils to become a gas. How might phase transitions shed light on important problems in biological and ecological complex systems? Exploring the origins and implications of sudden changes in nature and society, Phase Transitions examines different dynamical behaviors in a broad range of complex systems. Using a compelling set of examples, from gene networks and ant colonies to human language and the degradation o

  1. The topological quantum phase transitions in Lieb lattice driven by the Rashba SOC and exchange field

    Science.gov (United States)

    Wang, Rui; Qiao, Qian; Wang, Bin; Ding, Xiu-Huan; Zhang, Yi-Fu

    2016-09-01

    The quantum spin Hall (QSH) effect and the quantum anomalous Hall (QAH) effect in Lieb lattice are investigated in the presence of both Rashba spin-orbit coupling (SOC) and uniform exchange field. The Lieb lattice has a simple cubic symmetry, which is characterized by the single Dirac-cone per Brillouin zone and the middle flat band in the band structure. The intrinsic SOC is essentially needed to open the full energy gap in the bulk. The QSH effect could survive even in the presence of the exchange field. In terms of the first Chern number and the spin Chern number, we study the topological nature and the topological phase transition from the time-reversal symmetry broken QSH effect to the QAH effect. For Lieb lattice ribbons, the energy spectrum and the wave-function distributions are obtained numerically, where the helical edge states and the chiral edge states reveal the non-trivial topological QSH and QAH properties, respectively.

  2. A chemically driven quantum phase transition in a two-molecule Kondo system

    Science.gov (United States)

    Esat, Taner; Lechtenberg, Benedikt; Deilmann, Thorsten; Wagner, Christian; Krüger, Peter; Temirov, Ruslan; Rohlfing, Michael; Anders, Frithjof B.; Tautz, F. Stefan

    2016-09-01

    The magnetic properties of nanostructures that consist of a small number of atoms or molecules are typically determined by magnetic exchange interactions. Here, we show that non-magnetic, chemical interactions can have a similarly decisive effect if spin-moment-carrying orbitals extend in space and therefore allow the direct coupling of magnetic properties to wavefunction overlap and the formation of bonding and antibonding orbitals. We demonstrate this for a dimer of metal-molecule complexes on the Au(111) surface. A changing wavefunction overlap between the two monomers drives the surface-adsorbed dimer through a quantum phase transition from an underscreened triplet to a singlet ground state, with one configuration being located extremely close to a quantum critical point.

  3. Phase Transition in the Density of States of Quantum Spin Glasses

    Energy Technology Data Exchange (ETDEWEB)

    Erdős, László, E-mail: lerdos@ist.ac.at [IST Austria (Austria); Schröder, Dominik, E-mail: schroeder.dominik@gmail.com [Ludwig-Maximilians-Universität München (Germany)

    2014-12-15

    We prove that the empirical density of states of quantum spin glasses on arbitrary graphs converges to a normal distribution as long as the maximal degree is negligible compared with the total number of edges. This extends the recent results of Keating et al. (2014) that were proved for graphs with bounded chromatic number and with symmetric coupling distribution. Furthermore, we generalise the result to arbitrary hypergraphs. We test the optimality of our condition on the maximal degree for p-uniform hypergraphs that correspond to p-spin glass Hamiltonians acting on n distinguishable spin- 1/2 particles. At the critical threshold p = n{sup 1/2} we find a sharp classical-quantum phase transition between the normal distribution and the Wigner semicircle law. The former is characteristic to classical systems with commuting variables, while the latter is a signature of noncommutative random matrix theory.

  4. Universal order parameters and quantum phase transitions: a finite-size approach.

    Science.gov (United States)

    Shi, Qian-Qian; Zhou, Huan-Qiang; Batchelor, Murray T

    2015-01-08

    We propose a method to construct universal order parameters for quantum phase transitions in many-body lattice systems. The method exploits the H-orthogonality of a few near-degenerate lowest states of the Hamiltonian describing a given finite-size system, which makes it possible to perform finite-size scaling and take full advantage of currently available numerical algorithms. An explicit connection is established between the fidelity per site between two H-orthogonal states and the energy gap between the ground state and low-lying excited states in the finite-size system. The physical information encoded in this gap arising from finite-size fluctuations clarifies the origin of the universal order parameter. We demonstrate the procedure for the one-dimensional quantum formulation of the q-state Potts model, for q = 2, 3, 4 and 5, as prototypical examples, using finite-size data obtained from the density matrix renormalization group algorithm.

  5. Phase Transitions for Quantum Markov Chains Associated with Ising Type Models on a Cayley Tree

    Science.gov (United States)

    Mukhamedov, Farrukh; Barhoumi, Abdessatar; Souissi, Abdessatar

    2016-05-01

    The main aim of the present paper is to prove the existence of a phase transition in quantum Markov chain (QMC) scheme for the Ising type models on a Cayley tree. Note that this kind of models do not have one-dimensional analogous, i.e. the considered model persists only on trees. In this paper, we provide a more general construction of forward QMC. In that construction, a QMC is defined as a weak limit of finite volume states with boundary conditions, i.e. QMC depends on the boundary conditions. Our main result states the existence of a phase transition for the Ising model with competing interactions on a Cayley tree of order two. By the phase transition we mean the existence of two distinct QMC which are not quasi-equivalent and their supports do not overlap. We also study some algebraic property of the disordered phase of the model, which is a new phenomena even in a classical setting.

  6. Flux-driven quantum phase transitions in two-leg Kitaev ladder topological superconductor systems

    Science.gov (United States)

    Wang, H. Q.; Shao, L. B.; Pan, Y. M.; Shen, R.; Sheng, L.; Xing, D. Y.

    2016-12-01

    We investigate a two-leg ladder topological superconductor system consisting of two parallel Kitaev chains with interchain coupling. It is found that either uniform or staggered fluxes threading through the ladder holes may change the ladder system from the BDI class in the Altland-Zirnbauer (AZ) classification to the D class. After explicitly calculating the topological Z and/or Z2 indices and from the evolution of Majorana zero energy states (MZES), we obtain the flux-dependent phase diagrams, and find that quantum phase transitions between topologically distinct phases characterized by different number of MZES may happen by simply tuning the flux, which could be realized experimentally in ultracold systems.

  7. Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions.

    Science.gov (United States)

    Weng, Z F; Smidman, M; Jiao, L; Lu, Xin; Yuan, H Q

    2016-09-01

    Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.

  8. Multiple quantum phase transitions and superconductivity in Ce-based heavy fermions

    Science.gov (United States)

    Weng, Z. F.; Smidman, M.; Jiao, L.; Lu, Xin; Yuan, H. Q.

    2016-09-01

    Heavy fermions have served as prototype examples of strongly-correlated electron systems. The occurrence of unconventional superconductivity in close proximity to the electronic instabilities associated with various degrees of freedom points to an intricate relationship between superconductivity and other electronic states, which is unique but also shares some common features with high temperature superconductivity. The magnetic order in heavy fermion compounds can be continuously suppressed by tuning external parameters to a quantum critical point, and the role of quantum criticality in determining the properties of heavy fermion systems is an important unresolved issue. Here we review the recent progress of studies on Ce based heavy fermion superconductors, with an emphasis on the superconductivity emerging on the edge of magnetic and charge instabilities as well as the quantum phase transitions which occur by tuning different parameters, such as pressure, magnetic field and doping. We discuss systems where multiple quantum critical points occur and whether they can be classified in a unified manner, in particular in terms of the evolution of the Fermi surface topology.

  9. Quantum correlation with sandwiched relative entropies: Advantageous as order parameter in quantum phase transitions.

    Science.gov (United States)

    Misra, Avijit; Biswas, Anindya; Pati, Arun K; Sen De, Aditi; Sen, Ujjwal

    2015-05-01

    Quantum discord is a measure of quantum correlations beyond the entanglement-separability paradigm. It is conceptualized by using the von Neumann entropy as a measure of disorder. We introduce a class of quantum correlation measures as differences between total and classical correlations, in a shared quantum state, in terms of the sandwiched relative Rényi and Tsallis entropies. We compare our results with those obtained by using the traditional relative entropies. We find that the measures satisfy all the plausible axioms for quantum correlations. We evaluate the measures for shared pure as well as paradigmatic classes of mixed states. We show that the measures can faithfully detect the quantum critical point in the transverse quantum Ising model and find that they can be used to remove an unquieting feature of nearest-neighbor quantum discord in this respect. Furthermore, the measures provide better finite-size scaling exponents of the quantum critical point than the ones for other known order parameters, including entanglement and information-theoretic measures of quantum correlations.

  10. Probing the Dynamics of a Superradiant Quantum Phase Transition with a Single Trapped Ion.

    Science.gov (United States)

    Puebla, Ricardo; Hwang, Myung-Joong; Casanova, Jorge; Plenio, Martin B

    2017-02-17

    We demonstrate that the quantum phase transition (QPT) of the Rabi model and critical dynamics near the QPT can be probed in the setup of a single trapped ion. We first demonstrate that there exists equilibrium and nonequilibrium scaling functions of the Rabi model by finding a proper rescaling of the system parameters and observables, and show that those scaling functions are representative of the universality class to which the Rabi model belongs. We then propose a scheme that can faithfully realize the Rabi model in the limit of a large ratio of the effective atomic transition frequency to the oscillator frequency using a single trapped ion and, therefore, the QPT. It is demonstrated that the predicted universal functions can indeed be observed based on our scheme. Finally, the effects of realistic noise sources on probing the universal functions in experiments are examined.

  11. Probing the Dynamics of a Superradiant Quantum Phase Transition with a Single Trapped Ion

    Science.gov (United States)

    Puebla, Ricardo; Hwang, Myung-Joong; Casanova, Jorge; Plenio, Martin B.

    2017-02-01

    We demonstrate that the quantum phase transition (QPT) of the Rabi model and critical dynamics near the QPT can be probed in the setup of a single trapped ion. We first demonstrate that there exists equilibrium and nonequilibrium scaling functions of the Rabi model by finding a proper rescaling of the system parameters and observables, and show that those scaling functions are representative of the universality class to which the Rabi model belongs. We then propose a scheme that can faithfully realize the Rabi model in the limit of a large ratio of the effective atomic transition frequency to the oscillator frequency using a single trapped ion and, therefore, the QPT. It is demonstrated that the predicted universal functions can indeed be observed based on our scheme. Finally, the effects of realistic noise sources on probing the universal functions in experiments are examined.

  12. Entanglement Entropy Signature of Quantum Phase Transitions in a Multiple Spin Interactions Model

    Institute of Scientific and Technical Information of China (English)

    HUANG Hai-Lin

    2011-01-01

    Through the Jordan-Wigner transformation, the entanglement entropy and ground state phase diagrams of exactly solvable spin model with alternating and multiple spin exchange interactions are investigated by means of Green's function theory.In the absence of four-spin interactions, the ground state presents plentiful quantum phases due to the multiple spin interactions and magnetic fields.It is shown that the two-site entanglement entropy is a good indicator of quantum phase transition (QPT).In addition, the alternating interactions can destroy the magnetization plateau and wash out the spin-gap of low-lying excitations.However, in the presence of four-spin interactions, apart from the second order QPTs, the system manifests the first order QPT at the tricritical point and an additional new phase called "spin waves", which is due to the collapse of the continuous tower-like low-lying excitations modulated by the four-spin interactions for large three-spin couplings.

  13. Superuniversality of topological quantum phase transition and global phase diagram of dirty topological systems in three dimensions

    Science.gov (United States)

    Goswami, Pallab; Chakravarty, Sudip

    2017-02-01

    The quantum phase transition between two clean, noninteracting topologically distinct gapped states in three dimensions is governed by a massless Dirac fermion fixed point, irrespective of the underlying symmetry class, and this constitutes a remarkably simple example of superuniversality. For a sufficiently weak disorder strength, we show that the massless Dirac fixed point is at the heart of the robustness of superuniversality. We establish this by considering both perturbative and nonperturbative effects of disorder. The superuniversality breaks down at a critical strength of disorder, beyond which the topologically distinct localized phases become separated by a delocalized diffusive phase. In the global phase diagram, the disorder controlled fixed point where superuniversality is lost, serves as a multicritical point, where the delocalized diffusive and two topologically distinct localized phases meet and the nature of the localization-delocalization transition depends on the underlying symmetry class. Based on these features, we construct the global phase diagrams of noninteracting, dirty topological systems in three dimensions. We also establish a similar structure of the phase diagram and the superuniversality for weak disorder in higher spatial dimensions. By noting that 1 /r2 power-law correlated disorder acts as a marginal perturbation for massless Dirac fermions in any spatial dimension d , we have established a general renormalization group framework for addressing disorder driven critical phenomena for fixed spatial dimension d >2 .

  14. The superconductor-metal quantum phase transition in ultra-narrow wires

    Science.gov (United States)

    Del Maestro, Adrian Giuseppe

    We present a complete description of a zero temperature phase transition between superconducting and diffusive metallic states in very thin wires due to a Cooper pair breaking mechanism originating from a number of possible sources. These include impurities localized to the surface of the wire, a magnetic field orientated parallel to the wire or, disorder in an unconventional superconductor. The order parameter describing pairing is strongly overdamped by its coupling to an effectively infinite bath of unpaired electrons imagined to reside in the transverse conduction channels of the wire. The dissipative critical theory thus contains current reducing fluctuations in the guise of both quantum and thermally activated phase slips. A full cross-over phase diagram is computed via an expansion in the inverse number of complex components of the superconducting order parameter (equal to one in the physical case). The fluctuation corrections to the electrical and thermal conductivities are determined, and we find that the zero frequency electrical transport has a non-monotonic temperature dependence when moving from the quantum critical to low temperature metallic phase, which may be consistent with recent experimental results on ultra-narrow MoGe wires. Near criticality, the ratio of the thermal to electrical conductivity displays a linear temperature dependence and thus the Wiedemann-Franz law is obeyed. We compute the constant of proportionality in a systematic expansion and find a universal and experimentally verifiable fluctuation correction to the Lorenz number. In the presence of quenched disorder, a novel algorithm is developed to solve the self-consistency condition arising when the number of complex order parameter components is taken to be large. In this limit, we find striking evidence for the flow to infinite randomness, and observe dynamically activated scaling consistent with predictions from the strong disorder renormalization group. Moreover, the infinite

  15. A ferroelectric quantum phase transition inside the superconducting dome of Sr1-xCaxTiO3-δ

    Science.gov (United States)

    Rischau, Carl Willem; Lin, Xiao; Grams, Christoph P.; Finck, Dennis; Harms, Steffen; Engelmayer, Johannes; Lorenz, Thomas; Gallais, Yann; Fauqué, Benoît; Hemberger, Joachim; Behnia, Kamran

    2017-07-01

    SrTiO3, a quantum paraelectric, becomes a metal with a superconducting instability after removal of an extremely small number of oxygen atoms. It turns into a ferroelectric upon substitution of a tiny fraction of strontium atoms with calcium. The two orders may be accidental neighbours or intimately connected, as in the picture of quantum critical ferroelectricity. Here, we show that in Sr1-xCaxTiO3-δ (0.002 content, a quantum phase transition destroys the ferroelectric order. We detect an upturn in the normal-state scattering and a significant modification of the superconducting dome in the vicinity of this quantum phase transition. The enhancement of the superconducting transition temperature with calcium substitution documents the role played by ferroelectric vicinity in the precocious emergence of superconductivity in this system, restricting possible theoretical scenarios for pairing.

  16. Solvable model for a dynamical quantum phase transition from fast to slow scrambling

    CERN Document Server

    Banerjee, Sumilan

    2016-01-01

    We propose an extension of the Sachdev-Ye-Kitaev (SYK) model that exhibits a quantum phase transition from the previously identified non-Fermi liquid fixed point to a Fermi liquid like state, while still allowing an exact solution in a suitable large $N$ limit. The extended model involves coupling the interacting $N$-site SYK model to a new set of $pN$ peripheral sites with only quadratic hopping terms between them. The conformal fixed point of the SYK model remains a stable low energy phase below a critical ratio of peripheral sites $pp_c$ the quadratic sites effectively screen the SYK dynamics, leading to a quadratic fixed point in the low temperature and frequency limit. The interactions have a perturbative effect in this regime leading to scrambling with Lyapunov exponent $\\lambda_L\\propto T^2$.

  17. Liquid Crystal Phase Transition driven three-dimensional Quantum Dot Organization

    Science.gov (United States)

    Rodarte, Andrea L.; Pandolfi, R. J.; Ghosh, S.; Hirst, L. S.

    2013-03-01

    We use a nematic liquid crystal (LC) to create organized assemblies of CdSe/ZnS core/shell quantum dots (QDs). At the isotropic-nematic LC phase transition, ordered domains of nematic LC expel the majority of dispersed QDs into the isotropic domains. The final LC phase produces a series of three dimensional columnar QD assemblies that are situated at defect points in the LC volume. Within each assembly the QD emission is spectrally-red-shifted due to resonant energy transfer. We use this spectral shift as a measure of the inter-dot separation and find that the QDs are packed uniformly in these assemblies over distances of microns between the glass plates of a standard LC cell. In addition, because the QD clusters form at defects, we can deterministically control the location of the assemblies by seeding the LC cell with defect nucleation points. Funding provided by NSF, UC MERI and UC MEXUS.

  18. Influence of quantum phase transition on spin conductivity in the anisotropic three-dimensional ferromagnetic model

    Science.gov (United States)

    Lima, L. S.

    2017-01-01

    We use the SU(3) Schwinger boson formalism to study the spin transport in the three-dimensional S=1 Heisenberg ferromagnet in the cubic lattice with an easy plane crystal field, considering first-, second- and third-neighbor interactions. We have got one single peak for the spin conductivity for this system at ω =ωk and a variation of the height of the peak with the parameters Dc and η, and hence an influence of the quantum phase transition, between the disordered paramagnetic phase and the ordered ones, on the spin conductivity of this system. We have considered the exchange interaction J1 as ferromagnetic and the interactions J2 and J3 as antiferromagnetic.

  19. Supersymmetrically bounding of asymmetric states and quantum phase transitions by anti-crossing of symmetric states

    CERN Document Server

    Afzal, Muhammad Imran; Lee, Yong Tak

    2016-01-01

    Von Neumann and Wigner theorized bounding of asymmetric eigenstates and anti-crossing of symmetric eigenstates. Experiments have shown that owing to anti-crossing and similar radiation rates, graphene-like resonance of inhomogeneously strained photonic eigenstates can generate pseudomagnetic field, bandgaps and Landau levels, while dissimilar rates induce non-Hermicity. Here, we showed experimentally higher-order supersymmetry and quantum phase transitions by resonance between similar one dimensional lattices. The lattices consisted of inhomgeneously strain-like phases of triangular solitons. The resonance created two dimensional inhomogeneously deformed photonic graphene. All parent eigenstates are annihilated. Where eigenstates of mildly strained solitons are annihilated with similar (power law) rates through one tail only and generated Hermitianally bounded eigenstates. The strongly strained solitons, positive defects are annihilated exponentially through both tails with dissimilar rates. Which bounded eig...

  20. Pressure-induced quantum phase transition in the itinerant ferromagnet UCoGa

    Science.gov (United States)

    Míšek, M.; Prokleška, J.; Opletal, P.; Proschek, P.; Kaštil, J.; Kamarád, J.; Sechovský, V.

    2017-05-01

    In this paper, we report the results of a high pressure study of the itinerant 5f-electron ferromagnet UCoGa. The work is focused on probing the expected ferromagnet-to-paramagnet quantum phase transition induced by high pressure and on the general features of the P-T(-H) phase diagram. Diamond anvil cells were employed to measure the magnetization and electrical resistivity under pressures up to ˜ 10 GPa. At ambient pressure, UCoGa exhibits collinear ferromagnetic ordering of uranium magnetic moments μU ˜ 0.74 μB (at 2 K) aligned along the c-axis of the hexagonal crystal structure below Curie temperature TC = 48K. With the application of pressure, gradual decrease of both, TC and the saturated magnetic moment, has been observed up to pressures ˜ 6 GPa. This is followed by a sharp drop of magnetic moment and a sudden disappearance of the magnetic order at the pressure of 6.5 GPa, suggesting a first-order phase transition, as expected for a clean system. The low temperature power law dependence of the electrical resistivity shows distinct anomalies around the ˜ 6 GPa, consistent with the pressure evolution of the magnetic moment and the ordering temperature. The tricritical point of the UCoGa phase diagram is located at approximately ˜ 30K and ˜ 6GPa.

  1. Unexpected mass acquisition of Dirac fermions at the quantum phase transition of a topological insulator

    Science.gov (United States)

    Sato, T.; Segawa, Kouji; Kosaka, K.; Souma, S.; Nakayama, K.; Eto, K.; Minami, T.; Ando, Yoichi; Takahashi, T.

    2011-11-01

    The three-dimensional (3D) topological insulator is a novel quantum state of matter where an insulating bulk hosts a linearly dispersing surface state, which can be viewed as a sea of massless Dirac fermions protected by the time-reversal symmetry (TRS). Breaking the TRS by a magnetic order leads to the opening of a gap in the surface state, and consequently the Dirac fermions become massive. It has been proposed theoretically that such a mass acquisition is necessary to realize novel topological phenomena, but achieving a sufficiently large mass is an experimental challenge. Here we report an unexpected discovery that the surface Dirac fermions in a solid-solution system TlBi(S1-xSex)2 acquire a mass without explicitly breaking the TRS. We found that this system goes through a quantum phase transition from the topological to the non-topological phase, and, by tracing the evolution of the electronic states using the angle-resolved photoemission, we observed that the massless Dirac state in TlBiSe2 switches to a massive state before it disappears in the non-topological phase. This result suggests the existence of a condensed-matter version of the `Higgs mechanism' where particles acquire a mass through spontaneous symmetry breaking.

  2. Regular and chaotic classical dynamics in the U(5)-SU(3) quantum phase transition of the IBM

    CERN Document Server

    Macek, M

    2012-01-01

    We study the classical dynamics in a generic first-order quantum phase transition between the U(5) and SU(3) limits of the interacting boson model. The dynamics is chaotic, of H\\'enon-Heiles type, in the spherical phase and is regular, yet sensitive to local degeneracies, in the deformed phase. Both types of dynamics persist in the coexistence region resulting in a divided phase space.

  3. Quantum discord and quantum phase transition in the XXZ spin chain with three-site interaction

    Science.gov (United States)

    Yang, Jing; Cong, Mei-Yan; Huang, Yan-Xia

    2016-12-01

    Pairwise quantum discord (QD) and entanglement of the three-qubit XXZ Heisenberg spin chain with two types of three-site interactions and an external magnetic field are investigated. Our study found that both entanglement and quantum discord could detect the quantum critical phenomena of this model. We were able to obtain a nonzero value of quantum discord even at high temperature with the increase of XZX+YZY or XZY-YZX three-site interaction, however, the cooperative effect of XZX+YZY and XZY-YZX interactions is more ideal. Furthermore, in contrast to XZY-YZX and XZX+YZY interactions, the cooperative effect of XZX+YZY and XZY-YZX three-site interactions is more efficient to enhance the maximum value of quantum discord. Likewise, the cooperative effect of XZX+YZY and XZY-YZX interactions is the most optimal to increase the range of magnetic field or anisotropy parameter where quantum discord maintains the maximum value.

  4. Gauge/gravity duality. From quantum phase transitions towards out-of-equilibrium physics

    Energy Technology Data Exchange (ETDEWEB)

    Ngo Thanh, Hai

    2011-05-02

    In this dissertation we use gauge/gravity duality to investigate various phenomena of strongly coupled field theories. Of special interest are quantum phase transitions, quantum critical points, transport phenomena of charges and the thermalization process of strongly coupled medium. The systems studied in this thesis might be used as models for describing condensed matter physics in a superfluid phase near the quantum critical point and the physics of quark-gluon plasma (QGP), a deconfinement phase of QCD, which has been recently created at the Relativistic Heavy Ion Collider (RHIC). Moreover, we follow the line of considering different gravity setups whose dual field descriptions show interesting phenomena of systems in thermal equilibrium, slightly out-of-equilibrium and far-from-equilibrium. We first focus on systems in equilibrium and construct holographic superfluids at finite baryon and isospin charge densities. For that we use two different approaches, the bottom-up with an U(2) Einstein-Yang-Mills theory with back-reaction and the top-down approach with a D3/D7 brane setup with two coincident D7-brane probes. In both cases we observe phase transitions from a normal to a superfluid phase at finite and also at zero temperature. In our setup, the gravity duals of superfluids are Anti-de Sitter black holes which develop vector-hair. Studying the order of phase transitions at zero temperature, in the D3/D7 brane setup we always find a second order phase transition, while in the Einstein-Yang-Mills theory, depending on the strength of the back-reaction, we obtain a continuous or first order transition. We then move to systems which are slightly out-of-equilibrium. Using the D3/D7 brane setup with N{sub c} coincident D3-branes and N{sub f} coincident D7-brane probes, we compute transport coefficients associated with massive N=2 supersymmetric hypermultiplet fields propagating through an N=4 SU(N{sub c}) super Yang-Mills plasma in the limit of N{sub f}<

  5. Phase transitions in two tunnel-coupled HgTe quantum wells: Bilayer graphene analogy and beyond

    Science.gov (United States)

    Krishtopenko, S. S.; Knap, W.; Teppe, F.

    2016-08-01

    HgTe quantum wells possess remarkable physical properties as for instance the quantum spin Hall state and the “single-valley” analog of graphene, depending on their layer thicknesses and barrier composition. However, double HgTe quantum wells yet contain more fascinating and still unrevealed features. Here we report on the study of the quantum phase transitions in tunnel-coupled HgTe layers separated by CdTe barrier. We demonstrate that this system has a 3/2 pseudo spin degree of freedom, which features a number of particular properties associated with the spin-dependent coupling between HgTe layers. We discover a specific metal phase arising in a wide range of HgTe and CdTe layer thicknesses, in which a gapless bulk and a pair of helical edge states coexist. This phase holds some properties of bilayer graphene such as an unconventional quantum Hall effect and an electrically-tunable band gap. In this “bilayer graphene” phase, electric field opens the band gap and drives the system into the quantum spin Hall state. Furthermore, we discover a new type of quantum phase transition arising from a mutual inversion between second electron- and hole-like subbands. This work paves the way towards novel materials based on multi-layered topological insulators.

  6. First order quantum phase transitions of the XX spin-1/2 chain in a uniform transverse field

    Energy Technology Data Exchange (ETDEWEB)

    Pan Feng [Department of Physics, Liaoning Normal University, Dalian 116029 (China) and Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)]. E-mail: daipan@dlut.edu.cn; Ma Nan [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Guan Xin [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Draayer, J.P. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)

    2007-08-06

    Quantum phase transitional behavior of a finite periodic XX spin-12 chain with nearest neighbor interaction in a uniform transverse field is studied based on the simple exact solutions. It is found that there are [N/2] level-crossing points in the ground state, where N is the periodic number of the system and [x] stands for the integer part of x, when the interaction strength and magnitude of the magnetic field satisfy certain conditions. The quantum phase transitional behavior in the thermodynamic is also studied.

  7. Revealing novel quantum phases in quantum antiferromagnets on random lattices

    Directory of Open Access Journals (Sweden)

    R. Yu

    2009-01-01

    Full Text Available Quantum magnets represent an ideal playground for the controlled realization of novel quantum phases and of quantum phase transitions. The Hamiltonian of the system can be indeed manipulated by applying a magnetic field or pressure on the sample. When doping the system with non-magnetic impurities, novel inhomogeneous phases emerge from the interplay between geometric randomness and quantum fluctuations. In this paper we review our recent work on quantum phase transitions and novel quantum phases realized in disordered quantum magnets. The system inhomogeneity is found to strongly affect phase transitions by changing their universality class, giving the transition a novel, quantum percolative nature. Such transitions connect conventionally ordered phases to unconventional, quantum disordered ones - quantum Griffiths phases, magnetic Bose glass phases - exhibiting gapless spectra associated with low-energy localized excitations.

  8. First-order quantum phase transitions: test ground for emergent chaoticity, regularity and persisting symmetries

    CERN Document Server

    Macek, M

    2014-01-01

    We present a comprehensive analysis of the emerging order and chaos and enduring symmetries, accompanying a generic (high-barrier) first-order quantum phase transition (QPT). The interacting boson model Hamiltonian employed, describes a QPT between spherical and deformed shapes, associated with its U(5) and SU(3) dynamical symmetry limits. A~classical analysis of the intrinsic dynamics reveals a rich but simply-divided phase space structure with a H\\'enon-Heiles type of chaotic dynamics ascribed to the spherical minimum and a robustly regular dynamics ascribed to the deformed minimum. The simple pattern of mixed but well-separated dynamics persists in the coexistence region and traces the crossing of the two minima in the Landau potential. A quantum analysis discloses a number of regular low-energy U(5)-like multiplets in the spherical region, and regular SU(3)-like rotational bands extending to high energies and angular momenta, in the deformed region. These two kinds of regular subsets of states retain thei...

  9. First-order quantum phase transitions: Test ground for emergent chaoticity, regularity and persisting symmetries

    Energy Technology Data Exchange (ETDEWEB)

    Macek, M., E-mail: mmacek@Racah.phys.huji.ac.il; Leviatan, A., E-mail: ami@phys.huji.ac.il

    2014-12-15

    We present a comprehensive analysis of the emerging order and chaos and enduring symmetries, accompanying a generic (high-barrier) first-order quantum phase transition (QPT). The interacting boson model Hamiltonian employed, describes a QPT between spherical and deformed shapes, associated with its U(5) and SU(3) dynamical symmetry limits. A classical analysis of the intrinsic dynamics reveals a rich but simply-divided phase space structure with a Hénon–Heiles type of chaotic dynamics ascribed to the spherical minimum and a robustly regular dynamics ascribed to the deformed minimum. The simple pattern of mixed but well-separated dynamics persists in the coexistence region and traces the crossing of the two minima in the Landau potential. A quantum analysis discloses a number of regular low-energy U(5)-like multiplets in the spherical region, and regular SU(3)-like rotational bands extending to high energies and angular momenta, in the deformed region. These two kinds of regular subsets of states retain their identity amidst a complicated environment of other states and both occur in the coexistence region. A symmetry analysis of their wave functions shows that they are associated with partial U(5) dynamical symmetry (PDS) and SU(3) quasi-dynamical symmetry (QDS), respectively. The pattern of mixed but well-separated dynamics and the PDS or QDS characterization of the remaining regularity, appear to be robust throughout the QPT. Effects of kinetic collective rotational terms, which may disrupt this simple pattern, are considered.

  10. Dynamical scaling in infinitely correlated many-body systems through a quantum phase transition

    Science.gov (United States)

    Acevedo, Oscar Leonardo; Quiroga, Luis; Rodriguez, Ferney Javier; Johnson, Neil

    2013-03-01

    We assess dynamical scaling of many two-level systems (TLSs) infinitely correlated, either through a mediating radiation mode as in the Dicke Model, or through a direct interaction between TLSs as in the Lipkin-Meshkov-Glick model. Those models are characterized by the presence of a Quantum Phase Transition (QPT) in the thermodynamic limit, and they belong to the same universality class. The assessment is done by means of exact computational simulations of finite-size systems under linear rampings of the interaction parameter crossing the quantum critical point. Our results exhibit significant differences with respect to previous works on dynamical scaling across QPTs in the near-adiabatic regime, which have focused on spin-chain models where correlation lengths can be defined. We have confirmed that in infinitely correlated models an effective system size can play the role of the correlation length in traditional scaling arguments. However, due to the infinite correlation among TLSs, the standard Kibble-Zurek mechanism is not realized as the system cannot fully enter an adiabatic evolution during the ordered phase. Also, in the two-level approximation, a suitable deviation from the standard Landau-Zener protocol must be performed in order to obtain scaling collapse.

  11. Temperature-driven topological quantum phase transitions in a phase-change material Ge2Sb2Te5

    Science.gov (United States)

    Eremeev, S. V.; Rusinov, I. P.; Echenique, P. M.; Chulkov, E. V.

    2016-12-01

    The Ge2Sb2Te5 is a phase-change material widely used in optical memory devices and is a leading candidate for next generation non-volatile random access memory devices which are key elements of various electronics and portable systems. Despite the compound is under intense investigation its electronic structure is currently not fully understood. The present work sheds new light on the electronic structure of the Ge2Sb2Te5 crystalline phases. We demonstrate by predicting from first-principles calculations that stable crystal structures of Ge2Sb2Te5 possess different topological quantum phases: a topological insulator phase is realized in low-temperature structure and Weyl semimetal phase is a characteristic of the high-temperature structure. Since the structural phase transitions are caused by the temperature the switching between different topologically non-trivial phases can be driven by variation of the temperature. The obtained results reveal the rich physics of the Ge2Sb2Te5 compound and open previously unexplored possibility for spintronics applications of this material, substantially expanding its application potential.

  12. Quantum phase transitions between bosonic symmetry-protected topological states without sign problem: Nonlinear sigma model with a topological term

    Science.gov (United States)

    You, Yi-Zhuang; Bi, Zhen; Mao, Dan; Xu, Cenke

    2016-03-01

    We propose a series of simple two-dimensional (2D) lattice interacting fermion models that we demonstrate at low energy describe bosonic symmetry-protected topological (SPT) states and quantum phase transitions between them. This is because due to interaction, the fermions are gapped both at the boundary of the SPT states and at the bulk quantum phase transition, thus these models at low energy can be described completely by bosonic degrees of freedom. We show that the bulk of these models is described by a Sp (N ) principal chiral model with a topological Θ term, whose boundary is described by a Sp (N ) principal chiral model with a Wess-Zumino-Witten term at level 1. The quantum phase transition between SPT states in the bulk is tuned by a particular interaction term, which corresponds to tuning Θ in the field theory, and the phase transition occurs at Θ =π . The simplest version of these models with N =1 is equivalent to the familiar O(4) nonlinear sigma model (NLSM) with a topological term, whose boundary is a (1 +1 )D conformal field theory with central charge c =1 . After breaking the O(4) symmetry to its subgroups, this model can be viewed as bosonic SPT states with U(1), or Z2 symmetries, etc. All of these fermion models, including the bulk quantum phase transitions, can be simulated with the determinant quantum Monte Carlo method without the sign problem. Recent numerical results strongly suggest that the quantum disordered phase of the O(4) NLSM with precisely Θ =π is a stable (2 +1 )D conformal field theory with gapless bosonic modes.

  13. 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.

  14. Quantum phase transitions in the collective degrees of freedom: nuclei and other many-body systems

    Science.gov (United States)

    Cejnar, Pavel; Stránský, Pavel

    2016-08-01

    Quantum phase transitions (QPTs) represent a quickly developing subject of theoretical and experimental research. Nuclear physics contributed to the formation of the QPT concept in the 1970s and remains an area where new viewpoints and original approaches to criticality in many-body systems can be created. In this review, we present a comprehensible introduction to the subject, with an emphasis on the role of nuclear physics, and point out some specific features of QPTs in the systems that exhibit an effective separation of some collective degrees of freedom. The focus on collectivity, which stems from the nuclear context, is an essential ingredient of our treatise. It leads to some consequences that find application in nuclei as well as in a wide spectrum of non-nuclear systems.

  15. Interplay of order and chaos across a first-order quantum shape-phase transition in nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Leviatan, A.; Macek, M. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)

    2012-10-20

    We study the nature of the dynamics in a first-order quantum phase transition between spherical and prolate-deformed nuclear shapes. Classical and quantum analyses reveal a change in the system from a chaotic Henon-Heiles behavior on the spherical side into a pronounced regular dynamics on the deformed side. Both order and chaos persist in the coexistence region and their interplay reflects the Landau potential landscape and the impact of collective rotations.

  16. Interplay of order and chaos across a first-order quantum shape-phase transition in nuclei

    CERN Document Server

    Leviatan, A

    2012-01-01

    We study the nature of the dynamics in a first-order quantum phase transition between spherical and prolate-deformed nuclear shapes. Classical and quantum analyses reveal a change in the system from a chaotic H\\'enon-Heiles behavior on the spherical side into a pronounced regular dynamics on the deformed side. Both order and chaos persist in the coexistence region and their interplay reflects the Landau potential landscape and the impact of collective rotations.

  17. Quantum field theory and phase transitions: universality and renormalization group; Theorie quantique des champs et transitions de phase: universalite et groupe de renormalisation

    Energy Technology Data Exchange (ETDEWEB)

    Zinn-Justin, J

    2003-08-01

    In the quantum field theory the problem of infinite values has been solved empirically through a method called renormalization, this method is satisfying only in the framework of renormalization group. It is in the domain of statistical physics and continuous phase transitions that these issues are the easiest to discuss. Within the framework of a course in theoretical physics the author introduces the notions of continuous limits and universality in stochastic systems operating with a high number of freedom degrees. It is shown that quasi-Gaussian and mean field approximation are unable to describe phase transitions in a satisfying manner. A new concept is required: it is the notion of renormalization group whose fixed points allow us to understand universality beyond mean field. The renormalization group implies the idea that long distance correlations near the transition temperature might be described by a statistical field theory that is a quantum field in imaginary time. Various forms of renormalization group equations are presented and solved in particular boundary limits, namely for fields with high numbers of components near the dimensions 4 and 2. The particular case of exact renormalization group is also introduced. (A.C.)

  18. Quantum quench in matrix models: Dynamical phase transitions, Selective equilibration and the Generalized Gibbs Ensemble

    CERN Document Server

    Mandal, Gautam

    2013-01-01

    Quantum quench dynamics is considered in a one dimensional unitary matrix model with a single trace potential. This model is integrable and has been studied in the context of non-critical string theory. We find dynamical phase transitions, and study the role of the quantum critical point. In course of the time evolutions, we find evidence of selective equilibration for a certain class of observables. The equilibrium is governed by the Generalized Gibbs Ensemble (GGE) and differs from the standard Gibbs ensemble. We compute the production of entropy which is O(N) for large N matrices. An important feature of the equilibration is the appearance of an energy cascade, reminiscent of the Richardson cascade in turbulence, where we find flow of energy from initial long wavelength modes to progressively shorter wavelength excitations. We discuss possible implication of the equilibration and of GGE in string theories and higher spin theories. In another related study, we compute time evolutions in a double trace unita...

  19. Renormalizability and quantum stability of the phase transition in rigid string coupled to Kalb-Ramond fields, 1

    CERN Document Server

    Awada, M

    1995-01-01

    Recently we have shown that a phase transition occurs in the leading approximation of the large N limit in rigid strings coupled to long range Kalb-Ramond interactions. The disordered phase is essentially the Nambu-Goto-Polyakov string theory while The ordered phase is a new theory. In this part I letter we study the first subleading quantum corrections of the free rigid string and derive the renormalization group equation. We show that the theory is asymptotically free, thus the extrinsic curvature of the string drops out at large distance scales in the disordered phase. In part II we generalize the results of this letter to the interacting theory of rigid strings with the long range Kalb-Ramond interactions. We derive the renormalized mass gap equation and obtain the renormalized critical line. Our main and final result is that the phase transition does indeed survive quantum fluctuations.

  20. Solvable model for a dynamical quantum phase transition from fast to slow scrambling

    Science.gov (United States)

    Banerjee, Sumilan; Altman, Ehud

    2017-04-01

    We propose an extension of the Sachdev-Ye-Kitaev (SYK) model that exhibits a quantum phase transition from the previously identified non-Fermi-liquid fixed point to a Fermi-liquid-like state, while still allowing an exact solution in a suitable large-N limit. The extended model involves coupling the interacting N -site SYK model to a new set of p N peripheral sites with only quadratic hopping terms between them. The conformal fixed point of the SYK model remains a stable low-energy phase below a critical ratio of peripheral sites p NFL) phase is characterized by a universal Lyapunov exponent λL→2 π T in the low-temperature limit; however, the temperature scale marking the crossover to the conformal regime vanishes continuously at the critical point pc. The residual entropy at T →0 , nonzero in the NFL, also vanishes continuously at the critical point. For p >pc the quadratic sites effectively screen the SYK dynamics, leading to a quadratic fixed point in the low-temperature and low-frequency limit. The interactions have a perturbative effect in this regime leading to scrambling with Lyapunov exponent λL∝T2 .

  1. The Dicke model phase transition in the quantum motion of a Bose-Einstein condensate in an optical cavity

    CERN Document Server

    Nagy, D; Szirmai, G; Domokos, P

    2009-01-01

    We show that the motion of a laser-driven Bose-Einstein condensate in a high-finesse optical cavity realizes the spin-boson Dicke-model. The quantum phase transition of the Dicke-model from the normal to the superradiant phase corresponds to the self-organization of atoms from the homogeneous into a periodically patterned distribution above a critical driving strength. The fragility of the ground state due to photon measurement induced back action is calculated.

  2. Magnetic-field- and pressure-induced quantum phase transition in CsFeCl3 proved via magnetization measurements

    Science.gov (United States)

    Kurita, Nobuyuki; Tanaka, Hidekazu

    2016-09-01

    We have performed magnetization measurements of the gapped quantum magnet CsFeCl3 at temperatures (T ) down to 0.5 K at ambient pressure and down to 1.8 K at hydrostatic pressures (P ) of up to 1.5 GPa. The lower-field (H ) phase boundary of the field-induced ordered phase at ambient pressure is found to follow the power-law behavior expressed by the formula HN(T ) -Hc∝TNϕ . The application of pressure extends the phase boundary to both a lower field and higher temperature. Above the critical pressure Pc˜0.9 GPa, the transition field HN associated with the excitation gap becomes zero, and a signature of the magnetic phase transition is found in the T dependence of magnetization in a very low applied field. This suggests that CsFeCl3 exhibits a pressure-induced magnetic phase transition at Pc.

  3. 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.

  4. Hidden quantum phase transition in Mn1 -xFexGe evidenced by small-angle neutron scattering

    Science.gov (United States)

    Altynbaev, E.; Siegfried, S.-A.; Moskvin, E.; Menzel, D.; Dewhurst, C.; Heinemann, A.; Feoktystov, A.; Fomicheva, L.; Tsvyashchenko, A.; Grigoriev, S.

    2016-11-01

    The magnetic system of the Mn1 -xFexGe solid solution is ordered in a spiral spin structure in the whole concentration range of x ∈[0 ÷1 ] . The close inspection of the small-angle neutron-scattering data reveals the quantum phase transition from the long-range ordered to short-range ordered helical structure upon increase of Fe concentration at x ∈[0.25 ÷0.4 ] . The short-range order (SRO) of the helical structure is identified as a Lorentzian contribution, while long-range order is associated with the Gaussian contribution into the scattering profile function. The scenario of the quantum phase transition with x as a driving parameter is similar to the thermal phase transition in pure MnGe. The quantum nature of the SRO is proved by the temperature-independent correlation length of the helical structure at low- and intermediate-temperature ranges with remarkable decrease above certain temperature TQ. We suggest the x -dependent modification of the effective Ruderman-Kittel-Kasuya-Yosida exchange interaction within the Heisenberg model of magnetism to explain the quantum critical regime in Mn1 -xFexGe .

  5. Quantum phase transitions between a class of symmetry protected topological states

    Energy Technology Data Exchange (ETDEWEB)

    Tsui, Lokman; Jiang, Hong-Chen; Lu, Yuan-Ming; Lee, Dung-Hai

    2015-07-01

    The subject of this paper is the phase transition between symmetry protected topological states (SPTs). We consider spatial dimension d and symmetry group G so that the cohomology group, Hd+1(G,U(1)), contains at least one Z2n or Z factor. We show that the phase transition between the trivial SPT and the root states that generate the Z2n or Z groups can be induced on the boundary of a (d+1)-dimensional View the MathML source-symmetric SPT by a View the MathML source symmetry breaking field. Moreover we show these boundary phase transitions can be “transplanted” to d dimensions and realized in lattice models as a function of a tuning parameter. The price one pays is for the critical value of the tuning parameter there is an extra non-local (duality-like) symmetry. In the case where the phase transition is continuous, our theory predicts the presence of unusual (sometimes fractionalized) excitations corresponding to delocalized boundary excitations of the non-trivial SPT on one side of the transition. This theory also predicts other phase transition scenarios including first order transition and transition via an intermediate symmetry breaking phase.

  6. Degenerate Fermi and non-Fermi liquids near a quantum critical phase transition

    Science.gov (United States)

    Kambe, S.; Sakai, H.; Tokunaga, Y.; Lapertot, G.; Matsuda, T. D.; Knebel, G.; Flouquet, J.; Walstedt, R. E.

    2014-11-01

    Recently there is renewed interest in quantum critical phase transitions (QCPT) at T = 0 K in metallic strongly correlated electron systems. From early experimental results, the QCPT in the Kondo-lattice compound YbRh2Si2 is not a case of the ordinary spin density wave (SDW) instability observed in Ce-based Kondo lattices, but a candidate for a novel locally critical case. Here, we observe that coexisting, static Fermi liquid (FL) and non-Fermi liquid (NFL) states are a key feature of the QCPT in YbRh2Si2. By means of nuclear magnetic resonance (NMR) spin-lattice relaxation time (T1) measurements on a single-crystalline sample, we find that the FL and NFL states are invariant, whereas their ratio in a crossover is field dependent near the QCPT. Such a pair of states has remained hidden in Ce compounds, owing presumably to the short lifetimes of the two states. We derive a scaling law for the occupation ratio of the two states, which could be widely applicable to Kondo-lattice systems.

  7. AC-field-induced quantum phase transitions in density of states

    Science.gov (United States)

    Yang, Kai-Hua; Liu, Kai-Di; Wang, Huai-Yu; Qin, Chang-Dong

    2016-02-01

    We investigate the joint effects of the intralead electron interaction and an external alternating gate voltage on the time-averaged local density of states (DOSs) of a quantum dot coupled to two Luttinger-liquid leads in the Kondo regime. A rich dependence of the DOSs on the driving amplitude and intralead interaction is demonstrated. We show that the feature is quite different for different interaction strengths in the presence of the ac field. It is shown that the photon-assisted transport processes cause an additional splitting of the Kondo peak or dip, which exhibits photon-assisted single-channel (1CK) or two-channel Kondo (2CK) physics behavior. The phase transition between photon-assisted 1CK and 2CK physics occurs when the interaction strength is moderately strong. The inelastic channels associated with photon-assisted electron tunneling can dominate electron transport for weak interaction when the ac amplitude is greater than the frequency by one order of magnitude. In the limit of strong interaction the DOSs scale as a power-law behavior which is strongly affected by the ac field.

  8. Entanglement and quantum phase transition in alternating XY spin chain with next-nearest neighbouring interactions

    Institute of Scientific and Technical Information of China (English)

    Shan Chuan-Jia; Cheng Wei-Wen; Liu Tang-Kun; Huang Yan-Xia; Li nong

    2008-01-01

    By using the method of density-matrix renormalization-group to solve the different spin-spin correlation functions,the nearest-neighbouring entanglement (NNE) and the next-nearest-neighbouring entanglement (NNNE) of one-dimensional alternating Heisenberg XY spin chain are investigated in the presence of alternating the-nearestneighbouring interaction of exchange couplings,external magnetic fields and the next-nearest neighbouring interaction.For a dimerised ferromagnetic spin chain,the NNNE appears only above a critical dimerized interaction,meanwhile,the dimerized interaction a effects a quantum phase transition point and improves the NNNE to a large extent.We also study the effect of ferromagnetic or antiferromagnetic next-nearest neighbouring (NNN) interaction on the dynamics of NNE and NNNE.The ferromagnetic NNN interaction increases and shrinks the NNE below and above a critical frustrated interaction respectively,while the antiferromagnetic NNN interaction always reduces the NNE.The antiferromagnetic NNN interaction results in a large value of NNNE compared with the case where the NNN interaction is ferromagnetic.

  9. Molecular dissociation in presence of catalysts: Interpreting bond breaking as a quantum dynamical phase transition

    CERN Document Server

    Ruderman, A; Santos, E; Pastawski, H M

    2015-01-01

    In this work we show that the molecular chemical bond formation and dissociation in presence of the d-band of a metal catalyst can be described as a Quantum Dynamical Phase Transition (QDPT). This agree with DFT calculations that predict sudden jumps in some observables as the molecule breaks. According to our model this phenomenon emerges because the catalyst provides for a non- Hermitian Hamiltonian. We show that when the molecule approaches the surface, as occurs in the Heyrovsky reaction of H 2, the bonding H 2 orbital has a smooth crossover into a bonding molecular orbital built with the closest H orbital and the surface metal d-states. The same occurs for the antibonding state. Meanwhile, two resonances appear within the continuous spectrum of the d- band which are associated with bonding and antibonding orbitals between the furthest H atom and the d-states at the second metallic layer. These move towards the band center where they collapse into a pure metallic resonance and an almost isolated H orbital...

  10. Molecular dissociation in the presence of catalysts: interpreting bond breaking as a quantum dynamical phase transition

    Science.gov (United States)

    Ruderman, A.; Dente, A. D.; Santos, E.; Pastawski, H. M.

    2015-08-01

    In this work we show that molecular chemical bond formation and dissociation in the presence of the d-band of a metal catalyst can be described as a quantum dynamical phase transition (QDPT). This agrees with DFT calculations that predict sudden jumps in some observables as the molecule breaks. According to our model this phenomenon emerges because the catalyst provides for a non-Hermitian Hamiltonian. We show that when the molecule approaches the surface, as occurs in the Heyrovsky reaction of H2, the bonding H2 orbital has a smooth crossover into a bonding molecular orbital built with the closest H orbital and the surface metal d-states. The same occurs for the antibonding state. Meanwhile, two resonances appear within the continuous spectrum of the d-band, which are associated with bonding and antibonding orbitals between the furthest H atom and the d-states at the second metallic layer. These move toward the band center, where they collapse into a pure metallic resonance and an almost isolated H orbital. This phenomenon constitutes a striking example of the non-trivial physics enabled when one deals with non-Hermitian Hamiltonian beyond the usual wide band approximation.

  11. Interaction-induced quantum phase revivals and evidence for the transition to the quantum chaotic regime in 1D atomic Bloch oscillations.

    Science.gov (United States)

    Meinert, F; Mark, M J; Kirilov, E; Lauber, K; Weinmann, P; Gröbner, M; Nägerl, H-C

    2014-05-16

    We study atomic Bloch oscillations in an ensemble of one-dimensional tilted superfluids in the Bose-Hubbard regime. For large values of the tilt, we observe interaction-induced coherent decay and matter-wave quantum phase revivals of the Bloch oscillating ensemble. We analyze the revival period dependence on interactions by means of a Feshbach resonance. When reducing the value of the tilt, we observe the disappearance of the quasiperiodic phase revival signature towards an irreversible decay of Bloch oscillations, indicating the transition from regular to quantum chaotic dynamics.

  12. Quantum phase transitions in the bosonic single-impurity Anderson model

    Science.gov (United States)

    Lee, H.-J.; Bulla, R.

    2007-04-01

    We consider a quantum impurity model in which a bosonic impurity level is coupled to a non-interacting bosonic bath, with the bosons at the impurity site subject to a local Coulomb repulsion U. Numerical renormalization group calculations for this bosonic single-impurity Anderson model reveal a zero-temperature phase diagram where Mott phases with reduced charge fluctuations are separated from a Bose-Einstein condensed phase by lines of quantum critical points. We discuss possible realizations of this model, such as atomic quantum dots in optical lattices. Furthermore, the bosonic single-impurity Anderson model appears as an effective impurity model in a dynamical mean-field theory of the Bose-Hubbard model.

  13. Temperature induced stress phase transition in CdTe quantum dots observed by dielectric constant and thermal diffusivity measurements

    Science.gov (United States)

    Moreira, S. G. C.; da Silva, E. C.; Mansanares, A. M.; Barbosa, L. C.; Cesar, C. L.

    2007-07-01

    The authors measured the dielectric constant by capacitance method and the thermal diffusivity by thermal lens technique in the temperature range from 20to300K for CdTe quantum dot doped borosilicate glass samples. Results show a huge difference between the thermal behavior of the pure glass matrix, without quantum dots, and of the doped glass, especially around 90 and 250K. The authors attributed this difference to the phase transition experienced by the CdTe nanocrystals due to the high pressure exerted by the glass matrix over the CdTe quantum dots. The temperature induced stress is caused by the thermal expansion coefficient mismatch between the quantum dot and the glass matrix.

  14. Kane-Mele Hubbard model on a zigzag ribbon: Stability of the topological edge states and quantum phase transitions

    Science.gov (United States)

    Chung, Chung-Hou; Lee, Der-Hau; Chao, Sung-Po

    2014-07-01

    We study the quantum phases and phase transitions of the Kane-Mele Hubbard (KMH) model on a zigzag ribbon of honeycomb lattice at a finite size via the weak-coupling renormalization group (RG) approach. In the noninteracting limit, the Kane-Mele (KM) model is known to support topological edge states where electrons show helical property with orientations of the spin and momentum being locked. The effective interedge hopping terms are generated due to finite-size effect. In the presence of an on-site Coulomb (Hubbard) interaction and the interedge hoppings, special focus is put on the stability of the topological edge states (TI phase) in the KMH model against (i) the charge and spin gaped (II) phase, (ii) the charge gaped but spin gapless (IC) phase, and (iii) the spin gaped but charge gapless (CI) phase depending on the number (even/odd) of the zigzag ribbons, doping level (electron filling factor) and the ratio of the Coulomb interaction to the interedge tunneling. We discuss different phase diagrams for even and odd numbers of zigzag ribbons. We find the TI-CI, II-IC, and II-CI quantum phase transitions are of the Kosterlitz-Thouless (KT) type. By computing various correlation functions, we further analyze the nature and leading instabilities of these phases. The relevance of our results for graphene is discussed.

  15. A variational description of the quantum phase transition in the sub-Ohmic spin-boson model

    CERN Document Server

    Chin, A W; Huelga, S F; Plenio, M B

    2011-01-01

    The sub-ohmic spin-boson model is known to possess a novel quantum phase transition at zero temperature between a localised and delocalised phase. We present here an analytical theory based on a variational ansatz for the ground state, which describes a continuous localization transition with mean-field exponents for $0transition. Analysing the ansatz itself, we give an intuitive microscopic description of the transition in terms of the changing correlations between the system and bath, and show that it is always accompanied by a divergence of the low-frequency boson occupations. The possible relevance of this divergence for some numerical approaches to this problem is discussed and illustrated by looking at the ground state obtained using density matrix renormalisation group methods.

  16. Magnetic-flux-driven topological quantum phase transition and manipulation of perfect edge states in graphene tube

    Science.gov (United States)

    Lin, S.; Zhang, G.; Li, C.; Song, Z.

    2016-08-01

    We study the tight-binding model for a graphene tube with perimeter N threaded by a magnetic field. We show exactly that this model has different nontrivial topological phases as the flux changes. The winding number, as an indicator of topological quantum phase transition (QPT) fixes at N/3 if N/3 equals to its integer part [N/3], otherwise it jumps between [N/3] and [N/3] + 1 periodically as the flux varies a flux quantum. For an open tube with zigzag boundary condition, exact edge states are obtained. There exist two perfect midgap edge states, in which the particle is completely located at the boundary, even for a tube with finite length. The threading flux can be employed to control the quantum states: transferring the perfect edge state from one end to the other, or generating maximal entanglement between them.

  17. Excited-state quantum phase transitions in many-body systems with infinite-range interaction: Localization, dynamics, and bifurcation

    Science.gov (United States)

    Santos, Lea F.; Távora, Marco; Pérez-Bernal, Francisco

    2016-07-01

    Excited-state quantum phase transitions (ESQPTs) are generalizations of quantum phase transitions to excited levels. They are associated with local divergences in the density of states. Here, we investigate how the presence of an ESQPT can be detected from the analysis of the structure of the Hamiltonian matrix, the level of localization of the eigenstates, the onset of bifurcation, and the speed of the system evolution. Our findings are illustrated for a Hamiltonian with infinite-range Ising interaction in a transverse field. This is a version of the Lipkin-Meshkov-Glick (LMG) model and the limiting case of the one-dimensional spin-1/2 system with tunable interactions realized with ion traps. From our studies for the dynamics, we uncover similarities between the LMG and the noninteracting XX models.

  18. Dicke phase transition with multiple superradiant states in quantum chaotic resonators

    KAUST Repository

    Liu, C.

    2014-06-12

    We experimentally investigate the Dicke phase transition in chaotic optical resonators realized with two-dimensional photonics crystals. This setup circumvents the constraints of the system originally investigated by Dicke and allows a detailed study of the various properties of the superradiant transition. Our experimental results, analytical prediction, and numerical modeling based on random-matrix theory demonstrate that the probability density P? of the resonance widths provides a new criterion to test the occurrence of the Dicke transition.

  19. 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.

  20. Phases and Phase Transitions

    Science.gov (United States)

    Gitterman, Moshe

    2014-09-01

    In discussing phase transitions, the first thing that we have to do is to define a phase. This is a concept from thermodynamics and statistical mechanics, where a phase is defined as a homogeneous system. As a simple example, let us consider instant coffee. This consists of coffee powder dissolved in water, and after stirring it we have a homogeneous mixture, i.e., a single phase. If we add to a cup of coffee a spoonful of sugar and stir it well, we still have a single phase -- sweet coffee. However, if we add ten spoonfuls of sugar, then the contents of the cup will no longer be homogeneous, but rather a mixture of two homogeneous systems or phases, sweet liquid coffee on top and coffee-flavored wet sugar at the bottom...

  1. Proposed realization of the Dicke-model quantum phase transition in an optical cavity QED system

    CERN Document Server

    Dimer, F; Estienne, B; Parkins, A S

    2006-01-01

    The Dicke model consisting of an ensemble of two-state atoms interacting with a single quantized mode of the electromagnetic field exhibits a zero-temperature phase transition at a critical value of the dipole coupling strength. We propose a scheme based on multilevel atoms and cavity-mediated Raman transitions to realise an effective Dicke system operating in the phase transition regime. Output light from the cavity carries signatures of the critical behavior which is analyzed for the thermodynamic limit where the number of atoms is very large.

  2. Simple empirical order parameter for a first-order quantum phase transition in atomic nuclei.

    Science.gov (United States)

    Bonatsos, Dennis; McCutchan, E A; Casten, R F; Casperson, R J

    2008-04-11

    A simple, empirical, easy-to-measure effective order parameter of a first-order phase transition in atomic nuclei is presented, namely, the ratio of the energies of the first excited 6+ and 0+ states, distinguishing between first- and second-order transitions, and taking on a special value in the critical region, as data in Nd-Dy show. In the large NB limit of the interacting boson approximation model, a repeating degeneracy between alternate yrast and successive 0+ states is found in the critical region around the line of a first-order phase transition, pointing to a possible underlying symmetry.

  3. Infinite randomness fixed point of the superconductor-metal quantum phase transition.

    Science.gov (United States)

    Del Maestro, Adrian; Rosenow, Bernd; Müller, Markus; Sachdev, Subir

    2008-07-18

    We examine the influence of quenched disorder on the superconductor-metal transition, as described by a theory of overdamped Cooper pairs which repel each other. The self-consistent pairing eigenmodes of a quasi-one-dimensional wire are determined numerically. Our results support the recent proposal by Hoyos et al. [Phys. Rev. Lett. 99, 230601 (2007)10.1103/PhysRevLett.99.230601] that the transition is characterized by the same strong-disorder fixed point describing the onset of ferromagnetism in the random quantum Ising chain in a transverse field.

  4. Convex-set description of quantum phase transitions in the transverse Ising model using reduced-density-matrix theory.

    Science.gov (United States)

    Schwerdtfeger, Christine A; Mazziotti, David A

    2009-06-14

    Quantum phase transitions in N-particle systems can be identified and characterized by the movement of the two-particle reduced density matrix (2-RDM) along the boundary of its N-representable convex set as a function of the Hamiltonian parameter controlling the phase transition [G. Gidofalvi and D. A. Mazziotti, Phys. Rev. A 74, 012501 (2006)]. For the one-dimensional transverse Ising model quantum phase transitions as well as their finite-lattice analogs are computed and characterized by the 2-RDM movement with respect to the transverse magnetic field strength g. The definition of a 2-RDM "speed" quantifies the movement of the 2-RDM per unit of g, which reaches its maximum at the critical point of the phase transition. For the infinite lattice the convex set of 2-RDMs and the 2-RDM speed are computed from the exact solution of the 2-RDM in the thermodynamic limit of infinite N [P. Pfeuty, Ann. Phys. 57, 79 (1970)]. For the finite lattices we compute the 2-RDM convex set and its speed by the variational 2-RDM method [D. A. Mazziotti, Phys. Rev. Lett. 93, 213001 (2004)] in which approximate ground-state 2-RDMs are calculated without N-particle wave functions by using constraints, known as N-representability conditions, to restrict the 2-RDMs to represent quantum system of N fermions. Advantages of the method include: (i) rigorous lower bounds on the ground-state energies, (ii) polynomial scaling of the calculation with N, and (iii) independence of the N-representability conditions from a reference wave function, which enables the modeling of multiple quantum phases. Comparing the 2-RDM convex sets for the finite- and infinite-site lattices reveals that the variational 2-RDM method accurately captures the shape of the convex set and the signature of the phase transition in the 2-RDM movement. From the 2-RDM all one- and two-particle expectation values (or order parameters) of the quantum Ising model can also be computed including the pair correlation function, which

  5. Classical and quantum Reissner-Nordström black hole thermodynamics and first order phase transition

    Science.gov (United States)

    Ghaffarnejad, Hossein

    2016-01-01

    First we consider classical Reissner-Nordström black hole (CRNBH) metric which is obtained by solving Einstein-Maxwell metric equation for a point electric charge e inside of a spherical static body with mass M. It has 2 interior and exterior horizons. Using Bekenstein-Hawking entropy theorem we calculate interior and exterior entropy, temperature, Gibbs free energy and heat capacity at constant electric charge. We calculate first derivative of the Gibbs free energy with respect to temperature which become a singular function having a singularity at critical point Mc=2|e|/√{3} with corresponding temperature Tc=1/24π√{3|e|}. Hence we claim first order phase transition is happened there. Temperature same as Gibbs free energy takes absolutely positive (negative) values on the exterior (interior) horizon. The Gibbs free energy takes two different positive values synchronously for 0< T< Tc but not for negative values which means the system is made from two subsystem. For negative temperatures entropy reaches to zero value at Tto-∞ and so takes Bose-Einstein condensation single state. Entropy increases monotonically in case 0< T< Tc. Regarding results of the work presented at Wang and Huang (Phys. Rev. D 63:124014, 2001) we calculate again the mentioned thermodynamical variables for remnant stable final state of evaporating quantum Reissner-Nordström black hole (QRNBH) and obtained results same as one in case of the CRNBH. Finally, we solve mass loss equation of QRNBH against advance Eddington-Finkelstein time coordinate and derive luminosity function. We obtain switching off of QRNBH evaporation before than the mass completely vanishes. It reaches to a could Lukewarm type of RN black hole which its final remnant mass is m_{final}=|e| in geometrical units. Its temperature and luminosity vanish but not in Schwarzschild case of evaporation. Our calculations can be take some acceptable statements about information loss paradox (ILP).

  6. Topological quantum phase transition and superconductivity induced by pressure in the bismuth tellurohalide BiTeI

    OpenAIRE

    Qi, Yanpeng; Shi, Wujun; Naumov, Pavel G.; Kumar, Nitesh; Sankar, Raman; Schnelle, Walter; Shekhar, Chandra; Chou, F. C.; Felser, Claudia; Yan, Binghai; Medvedev, Sergey A.

    2016-01-01

    A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor BiTeI with giant Rashba spin splitting. In this work, the evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr while the resist...

  7. Invariant correlational entropy as a signature of quantum phase transitions in nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Volya, Alexander; Zelevinsky, Vladimir

    2003-11-06

    We study phase transformations in finite nuclei as a function of interaction parameters. The signature of a transition is given by invariant correlational entropy that reflects the sensitivity of an individual many-body state to changes of external parameters; peaks in this quantity indicate the critical regions. This approach is able to reveal the pairing phase transition, identify the isovector and isoscalar pairing regions and determine the role of other interactions. We show the examples of the phase diagram in the parameter space.

  8. Learning phase transitions by confusion

    CERN Document Server

    van Nieuwenburg, Evert P L; Huber, Sebastian D

    2016-01-01

    Classifying phases of matter is a central problem in physics. For quantum mechanical systems, this task can be daunting owing to the exponentially large Hilbert space. Thanks to the available computing power and access to ever larger data sets, classification problems are now routinely solved using machine learning techniques. Here, we propose to use a neural network based approach to find phase transitions depending on the performance of the neural network after training it with deliberately incorrectly labelled data. We demonstrate the success of this method on the topological phase transition in the Kitaev chain, the thermal phase transition in the classical Ising model, and the many-body-localization transition in a disordered quantum spin chain. Our method does not depend on order parameters, knowledge of the topological content of the phases, or any other specifics of the transition at hand. It therefore paves the way to a generic tool to identify unexplored phase transitions.

  9. 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.

  10. Characterization of the quantum phase transition in a two-mode Dicke model for different cooperation numbers

    Science.gov (United States)

    Quezada, L. F.; Nahmad-Achar, E.

    2017-01-01

    We show how the use of variational states to approximate the ground state of a system can be employed to study a multimode Dicke model. One of the main contributions of this work is the introduction of a not very commonly used quantity, the cooperation number, and the study of its influence on the behavior of the system, paying particular attention to the quantum phase transitions and the accuracy of the used approximations. We also show how these phase transitions affect the dependence of the expectation values of some of the observables relevant to the system and the entropy of entanglement with respect to the energy difference between atomic states and the coupling strength between matter and radiation, thus characterizing the transitions in different ways.

  11. Signature of a continuous quantum phase transition in non-equilibrium energy absorption: Footprints of criticality on higher excited states.

    Science.gov (United States)

    Bhattacharyya, Sirshendu; Dasgupta, Subinay; Das, Arnab

    2015-11-16

    Understanding phase transitions in quantum matters constitutes a significant part of present day condensed matter physics. Quantum phase transitions concern ground state properties of many-body systems, and hence their signatures are expected to be pronounced in low-energy states. Here we report signature of a quantum critical point manifested in strongly out-of-equilibrium states with finite energy density with respect to the ground state and extensive (subsystem) entanglement entropy, generated by an external pulse. These non-equilibrium states are evidently completely disordered (e.g., paramagnetic in case of a magnetic ordering transition). The pulse is applied by switching a coupling of the Hamiltonian from an initial value (λI) to a final value (λF) for sufficiently long time and back again. The signature appears as non-analyticities (kinks) in the energy absorbed by the system from the pulse as a function of λF at critical-points (i.e., at values of λF corresponding to static critical-points of the system). As one excites higher and higher eigenstates of the final Hamiltonian H(λF) by increasing the pulse height (|λF - λI|), the non-analyticity grows stronger monotonically with it. This implies adding contributions from higher eigenstates help magnifying the non-analyticity, indicating strong imprint of the critical-point on them. Our findings are grounded on exact analytical results derived for Ising and XY chains in transverse field.

  12. Quantum Phase Transitions in Alternating-Bond Mixed Diamond Chains with Spins 1 and 1/2

    Science.gov (United States)

    Hida, Kazuo; Takano, Ken'ichi; Suzuki, Hidenori

    2010-04-01

    We investigate the mixed diamond chain composed of spins 1 and 1/2 when the exchange interaction is alternatingly distorted. Depending on the strengths of frustration and distortion, this system has various ground states. Each ground state consists of an array of spin clusters separated by singlet dimers by virtue of an infinite number of local conservation laws. We determine the ground-state phase diagram by numerically analyzing each spin cluster. In particular, for strong distortions, we find an infinite series of quantum phase transitions using the cluster expansion method and conformal field theory. This leads to an infinite series of steps in the behavior of Curie constant and residual entropy.

  13. No-go theorem for superradiant quantum phase transitions in cavity QED and counter-example in circuit QED.

    Science.gov (United States)

    Nataf, Pierre; Ciuti, Cristiano

    2010-09-07

    In cavity quantum electrodynamics (QED), the interaction between an atomic transition and the cavity field is measured by the vacuum Rabi frequency Ω(0). The analogous term 'circuit QED' has been introduced for Josephson junctions, because superconducting circuits behave as artificial atoms coupled to the bosonic field of a resonator. In the regime with Ω(0) comparable with the two-level transition frequency, 'superradiant' quantum phase transitions for the cavity vacuum have been predicted, for example, within the Dicke model. In this study, we prove that if the time-independent light-matter Hamiltonian is considered, a superradiant quantum critical point is forbidden for electric dipole atomic transitions because of the oscillator strength sum rule. In circuit QED, the analogous of the electric dipole coupling is the capacitive coupling, and such no-go property can be circumvented by Cooper pair boxes capacitively coupled to a resonator, because of their peculiar Hilbert space topology and a violation of the corresponding sum rule.

  14. Experimental signatures of an absorbing-state phase transition in an open driven many-body quantum system

    CERN Document Server

    Gutierrez, Ricardo; Archimi, Matteo; Castellucci, Francesco; Arimondo, Ennio; Ciampini, Donatella; Marcuzzi, Matteo; Lesanovsky, Igor; Morsch, Oliver

    2016-01-01

    Understanding and probing phase transitions in non-equilibrium systems is an ongoing challenge in physics. A particular instance are phase transitions that occur between a non-fluctuating absorbing phase, e.g., an extinct population, and one in which the relevant order parameter, such as the population density, assumes a finite value. Here we report the observation of signatures of such a non-equilibrium phase transition in an open driven quantum system. In our experiment rubidium atoms in a quasi one-dimensional cold disordered gas are laser-excited to Rydberg states under so-called facilitation conditions. This conditional excitation process competes with spontaneous decay and leads to a crossover between a stationary state with no excitations and one with a finite number of excitations. We relate the underlying physics to that of an absorbing state phase transition in the presence of a field which slightly offsets the system from criticality. We observe a characteristic power-law scaling of the Rydberg exc...

  15. Topological Quantum Phase Transition and Superconductivity Induced by Pressure in the Bismuth Tellurohalide BiTeI.

    Science.gov (United States)

    Qi, Yanpeng; Shi, Wujun; Naumov, Pavel G; Kumar, Nitesh; Sankar, Raman; Schnelle, Walter; Shekhar, Chandra; Chou, Fang-Cheng; Felser, Claudia; Yan, Binghai; Medvedev, Sergey A

    2017-03-06

    A pressure-induced topological quantum phase transition has been theoretically predicted for the semiconductor bismuth tellurohalide BiTeI with giant Rashba spin splitting. In this work, evolution of the electrical transport properties in BiTeI and BiTeBr is investigated under high pressure. The pressure-dependent resistivity in a wide temperature range passes through a minimum at around 3 GPa, indicating the predicted topological quantum phase transition in BiTeI. Superconductivity is observed in both BiTeI and BiTeBr, while resistivity at higher temperatures still exhibits semiconducting behavior. Theoretical calculations suggest that superconductivity may develop from the multivalley semiconductor phase. The superconducting transition temperature, Tc , increases with applied pressure and reaches a maximum value of 5.2 K at 23.5 GPa for BiTeI (4.8 K at 31.7 GPa for BiTeBr), followed by a slow decrease. The results demonstrate that BiTeX (X = I, Br) compounds with nontrivial topology of electronic states display new ground states upon compression.

  16. Strong correlation effects on topological quantum phase transitions in three dimensions

    Science.gov (United States)

    Amaricci, A.; Budich, J. C.; Capone, M.; Trauzettel, B.; Sangiovanni, G.

    2016-06-01

    We investigate the role of short-ranged electron-electron interactions in a paradigmatic model of three-dimensional topological insulators, using dynamical mean-field theory and focusing on nonmagnetically ordered solutions. The noninteracting band structure is controlled by a mass term M , whose value discriminates between three different insulating phases, a trivial band insulator and two distinct topologically nontrivial phases. We characterize the evolution of the transitions between the different phases as a function of the local Coulomb repulsion U and find a remarkable dependence of the U -M phase diagram on the value of the local Hund's exchange coupling J . However, regardless of the value of J , following the evolution of the topological transition line between a trivial band insulator and a topological insulator, we find a critical value of U separating a continuous transition from a first-order one. When the Hund's coupling is significant, a Mott insulator is stabilized at large U . In proximity of the Mott transition we observe the emergence of an anomalous "Mott-like" strong topological insulator state.

  17. Fluctuations of Imbalanced Fermionic Superfluids in Two Dimensions Induce Continuous Quantum Phase Transitions and Non-Fermi-Liquid Behavior

    Directory of Open Access Journals (Sweden)

    Philipp Strack

    2014-04-01

    Full Text Available We study the nature of superfluid pairing in imbalanced Fermi mixtures in two spatial dimensions. We present evidence that the combined effect of Fermi surface mismatch and order parameter fluctuations of the superfluid condensate can lead to continuous quantum phase transitions from a normal Fermi mixture to an intermediate Sarma-Liu-Wilczek superfluid with two gapless Fermi surfaces—even when mean-field theory (incorrectly predicts a first-order transition to a phase-separated “Bardeen-Cooper-Schrieffer plus excess fermions” ground state. We propose a mechanism for non-Fermi-liquid behavior from repeated scattering processes between the two Fermi surfaces and fluctuating Cooper pairs. Prospects for experimental observation with ultracold atoms are discussed.

  18. 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.

  19. Multimode mean-field model for the quantum phase transition of a Bose-Einstein condensate in an optical resonator

    Science.gov (United States)

    Kónya, G.; Szirmai, G.; Domokos, P.

    2011-11-01

    We develop a mean-field model describing the Hamiltonian interaction of ultracold atoms and the optical field in a cavity. The Bose-Einstein condensate is properly defined by means of a grand-canonical approach. The model is efficient because only the relevant excitation modes are taken into account. However, the model goes beyond the two-mode subspace necessary to describe the self-organization quantum phase transition observed recently. We calculate all the second-order correlations of the coupled atom field and radiation field hybrid bosonic system, including the entanglement between the two types of fields.

  20. Multimode mean-field model for the quantum phase transition of a Bose-Einstein condensate in an optical resonator

    CERN Document Server

    Konya, G; Domokos, P

    2011-01-01

    We develop a mean-field model describing the Hamiltonian interaction of ultracold atoms and the optical field in a cavity. The Bose-Einstein condensate is properly defined by means of a grand-canonical approach. The model is efficient because only the relevant excitation modes are taken into account. However, the model goes beyond the two-mode subspace necessary to describe the self-organization quantum phase transition observed recently. We calculate all the second-order correlations of the coupled atom field and radiation field hybrid bosonic system, including the entanglement between the two types of fields.

  1. Entanglement signatures of phase transition in higher-derivative quantum field theories II: Applications to lower dimensional systems

    CERN Document Server

    Kumar, S Santhosh

    2016-01-01

    We explicitly show that sixth order spatial derivative, Lorentz symmetry violating term in two dimensional space leads to quantum phase transition. We show that around the critical point, the number of zero modes increases dramatically that catalyze the change in the ground state property of the many-body wave function. We extend the analysis to three dimensional cylindrical geometry and show that the entanglement heat-capacity has similar profile to the heat capacity measurements of high temperature superconductors. We explicitly show that the long-range interaction in the two dimensional surface explain key features of high temperature superconductors.

  2. 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.

  3. Gravitationally induced quantum transitions

    Science.gov (United States)

    Landry, A.; Paranjape, M. B.

    2016-06-01

    In this paper, we calculate the probability for resonantly inducing transitions in quantum states due to time-dependent gravitational perturbations. Contrary to common wisdom, the probability of inducing transitions is not infinitesimally small. We consider a system of ultracold neutrons, which are organized according to the energy levels of the Schrödinger equation in the presence of the Earth's gravitational field. Transitions between energy levels are induced by an oscillating driving force of frequency ω . The driving force is created by oscillating a macroscopic mass in the neighborhood of the system of neutrons. The neutron lifetime is approximately 880 sec while the probability of transitions increases as t2. Hence, the optimal strategy is to drive the system for two lifetimes. The transition amplitude then is of the order of 1.06 ×10-5, and hence with a million ultracold neutrons, one should be able to observe transitions.

  4. Gravitationally induced quantum transitions

    CERN Document Server

    Landry, A

    2016-01-01

    In this letter, we calculate the probability for resonantly induced transitions in quantum states due to time dependent gravitational perturbations. Contrary to common wisdom, the probability of inducing transitions is not infinitesimally small. We consider a system of ultra cold neutrons (UCN), which are organized according to the energy levels of the Schr\\"odinger equation in the presence of the earth's gravitational field. Transitions between energy levels are induced by an oscillating driving force of frequency $\\omega$. The driving force is created by oscillating a macroscopic mass in the neighbourhood of the system of neutrons. The neutrons decay in 880 seconds while the probability of transitions increase as $t^2$. Hence the optimal strategy is to drive the system for 2 lifetimes. The transition amplitude then is of the order of $1.06\\times 10^{-5}$ hence with a million ultra cold neutrons, one should be able to observe transitions.

  5. Superfluid--Solid Quantum Phase Transitions and Landau-Ginzburg-Wilson Paradigm

    Science.gov (United States)

    Kuklov, A. B.; Prokof'ev, N. V.

    2005-03-01

    We study superfluid (SF)--solid zero-temperature transitions in 2d lattice boson/spin models by Worm-Algorithm Monte Carlo simulations. The SF -- Valence Bond Solid (VBS) transition was recently argued to be generically of II order in violation of the Ginzburg-Landau- Wilson (GLW) paradigm [1]. We simulate the J-current model on lattices up to 64x64x64, and observe that SF- columnar VBS and SF-checkerboard solid transitions are typically weak I-order ones and in small systems they may be confused with the continuous or high-symmetry points [2]. Thus, in the simulated model, the SF-VBS transition proceeds in agreement with the GLW paradigm. We explain this by dominance of standard particle and hole excitations, as opposed to fractionalized (spinon) excitations [1]. We developed a technique based on tunneling events (instantons) in the insulating phase which reveals charges of the revelant long-wave modes. While in 1d systems spinons are clearly seen in tunneling events, in two spatial dimensions tunneling is solely controlled by particles and holes in our system. This work is supported by NSF grant ITR-405460001 and PSC-CUNY- 665560035. [1] T. Senthil, A. Vishwanath, L. Balents, S. Sachdev, and M.P.A. Fisher, Science 303, 1490 (2004); [2] A.B. Kuklov, N.V. Prokof'ev, B.V. Svistunov, condmat/0406061; PRL, to be published.

  6. Dosimetric investigations of laser-induced phase transition of MX1-cell membranes by use of quantum dots

    Science.gov (United States)

    Beuthan, J.; Dressler, C.; Minet, O.; Müller, G.

    2006-05-01

    It is well known that laser scattered-light applicators when applied for laser-induced tumor therapy allow the precise thermal destruction of metastases. Using laser radiation in the NIR spectral range (usually, Nd:YAG laser systems λ = 1064 nm), a penetration depth of 5-10 cm (1/ e is the decrease in radiation intensity) is achieved in biological tissues. The major tissue-optical parameters, i.e., absorption coefficient μa, scattering coefficient μs, and the anisotropy factor g, show biological tissues to be strongly scattering media which have a so-called optical window in the NIR. As a consequence, the therapeutic laser radiation is scattered and absorbed at a deeper level, leading to a virtual enlargement of the laser applicator. The thermal sclerotization and the thermal cell damage originate within the absorbing volume of the laser radiation and spread outward by thermal diffusion. There are three dosimetrically relevant zones of thermal and biological damage: (1) a zone of thermal coagulation; (2) a threshold of partial necrosis (destruction of all metabolic processes in the cell is the maintenance of essential parts of the cytoskeleton and the plasma membrane); this is characterized by a specific temperature range, the so-called phase transition, which refers to the transition from the gel phase of the biomembrane to the fluid phase; the determination of this temperature zone is an integral part of the following experimental investigations on MX1 cells; (3) an external zone of thermal effects made up of partial and multiple damage with a statistical chance of survival. This paper describes the investigations on heat stress in cancer cells to verify the maximum phase transition of the outer MX1 cell membranes and the related results. For this purpose, a novel method of quantum dot fluorescence dosimetry was developed. The evaluation of the measured laser-induced fluorescences yields a first approximation of the determination of the phase transition on MX1

  7. Quantum Phase Transitions and New Scales in QCD-Like Theories

    Energy Technology Data Exchange (ETDEWEB)

    Unsal, Mithat

    2008-07-03

    It is commonly believed that in confining vector-like gauge theories the center and chiral symmetry realizations are parametrically entangled, and if phase transitions occur, they must take place around the strong scale {Lambda}{sup -1} of the gauge theory. We demonstrate that (non-thermal) vector-like theories formulated on R{sup 3} x S{sup 1} where S{sup 1} is a spatial circle exhibit new dynamical scales and new phenomena. There are chiral phase transitions taking place at {Lambda}{sup -1}/N{sub c} in the absence of any change in center symmetry. {Lambda}{sup -1}/N{sub c}, invisible in (planar) perturbation theory, is also the scale where abelian versus non-abelian confinement regimes meet. Large N{sub c} volume independence (a working Eguchi-Kawai reduction) provides new insights and independently confirms the existence of these scales. We show that certain phases and scales are outside the reach of holographic (supergravity) modeling of QCD.

  8. Exotic quantum phase transitions of 2+1d Dirac fermions, and connections to 2d and 3d topological insulators

    Science.gov (United States)

    Slagle, Kevin

    2015-03-01

    Using determinant quantum Monte Carlo simulations, we demonstrate that an extended Hubbard model on a bilayer honeycomb lattice has two novel quantum phase transitions, each with connections to symmetry protected topological states. 1) The first is a continuous phase transition between the weakly interacting gapless Dirac fermion phase and a strongly interacting fully gapped and symmetric trivial phase. Because there is no spontaneous symmetry breaking, this transition cannot be described by the standard Gross-Neveu model. We argue that this phase transition is related to the Z16 classification of the topological superconductor 3He-B phase with interactions. 2) The second is a quantum critical point between a quantum spin Hall insulator with spin Sz conservation and the previously mentioned strongly interacting gapped phase. At the critical point the single particle excitations remain gapped, while spin and charge gaps close. We argue that this transition is described by a bosonic O(4) nonlinear sigma model field theory with a topological Θ-term.

  9. Quantum chromodynamics phase transition in the early Universe and quark nuggets

    Indian Academy of Sciences (India)

    Abhijit Bhattacharyya; Shibaji Banerjee; Sanjay K Ghosh; Sibaji Raha; Bikash Sinha; Hiroshi Toki

    2003-05-01

    A first-order quark hadron phase transition in the early Universe may lead to the formation of quark nuggets. The baryon number distribution of these quark nuggets have been calculated and it has been found that there are sizeable number of quark nuggets in the stable sector. The nuggets can clump and form bigger objects in the mass range of 0.0003$M_{\\odot}$ to 0.12$M_{\\odot}$. It has been discussed that these bigger objects can be possible candidates for cold dark matter.

  10. 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.

  11. Universal transport signatures in two-electron molecular quantum dots: gate-tunable Hund's rule, underscreened Kondo effect and quantum phase transitions.

    Science.gov (United States)

    Florens, Serge; Freyn, Axel; Roch, Nicolas; Wernsdorfer, Wolfgang; Balestro, Franck; Roura-Bas, Pablo; Aligia, A A

    2011-06-22

    We review here some universal aspects of the physics of two-electron molecular transistors in the absence of strong spin-orbit effects. Several recent quantum dot experiments have shown that an electrostatic backgate could be used to control the energy dispersion of magnetic levels. We discuss how the generally asymmetric coupling of the metallic contacts to two different molecular orbitals can indeed lead to a gate-tunable Hund's rule in the presence of singlet and triplet states in the quantum dot. For gate voltages such that the singlet constitutes the (non-magnetic) ground state, one generally observes a suppression of low voltage transport, which can yet be restored in the form of enhanced cotunneling features at finite bias. More interestingly, when the gate voltage is controlled to obtain the triplet configuration, spin S = 1 Kondo anomalies appear at zero bias, with non-Fermi liquid features related to the underscreening of a spin larger than 1/2. Finally, the small bare singlet-triplet splitting in our device allows fine-tuning with the gate between these two magnetic configurations, leading to an unscreening quantum phase transition. This transition occurs between the non-magnetic singlet phase, where a two-stage Kondo effect occurs, and the triplet phase, where the partially compensated (underscreened) moment is akin to a magnetically 'ordered' state. These observations are put theoretically into a consistent global picture by using new numerical renormalization group simulations, tailored to capture sharp finite-voltage cotunneling features within the Coulomb diamonds, together with complementary out-of-equilibrium diagrammatic calculations on the two-orbital Anderson model. This work should shed further light on the complicated puzzle still raised by multi-orbital extensions of the classic Kondo problem.

  12. Excited-state quantum phase transitions in systems with two degrees of freedom: II. Finite-size effects

    Energy Technology Data Exchange (ETDEWEB)

    Stránský, Pavel [Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague (Czech Republic); Macek, Michal [Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague (Czech Republic); Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, CT 06520-8120 (United States); Leviatan, Amiram [Racah Institute of Physics, The Hebrew University, 91904 Jerusalem (Israel); Cejnar, Pavel, E-mail: pavel.cejnar@mff.cuni.cz [Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague (Czech Republic)

    2015-05-15

    This article extends our previous analysis Stránský et al. (2014) of Excited-State Quantum Phase Transitions (ESQPTs) in systems of dimension two. We focus on the oscillatory component of the quantum state density in connection with ESQPT structures accompanying a first-order ground-state transition. It is shown that a separable (integrable) system can develop rather strong finite-size precursors of ESQPT expressed as singularities in the oscillatory component of the state density. The singularities originate in effectively 1-dimensional dynamics and in some cases appear in multiple replicas with increasing excitation energy. Using a specific model example, we demonstrate that these precursors are rather resistant to proliferation of chaotic dynamics. - Highlights: • Oscillatory components of state density and spectral flow studied near ESQPTs. • Enhanced finite-size precursors of ESQPT caused by fully/partly separable dynamics. • These precursors appear due to criticality of a subsystem with lower dimension. • Separability-induced finite-size effects disappear in case of fully chaotic dynamics.

  13. Quantum anomalous Hall phase and half-metallic phase in ferromagnetic (111) bilayers of 4 d and 5 d transition metal perovskites

    Science.gov (United States)

    Chandra, Hirak Kumar; Guo, Guang-Yu

    2017-04-01

    Extraordinary electronic phases can form in artificial oxide heterostructures, which will provide a fertile ground for new physics and also give rise to novel device functions. Based on a systematic first-principles density functional theory study of the magnetic and electronic properties of the (111) superlattices (ABO3) 2/(AB'O3)10 of 4 d and 5 d transition metal perovskite (B = Ru, Rh, Ag, Re, Os, Ir, Au; AB'O3=LaAlO3 , SrTiO3) , we demonstrate that due to quantum confinement, bilayers (LaBO3)2 (B = Ru, Re, Os) and (SrBO3)2 (B = Rh, Os, Ir) are ferromagnetic with ordering temperatures up to room temperature. In particular, bilayer (LaOsO3)2 is an exotic spin-polarized quantum anomalous Hall insulator, while the other ferromagnetic bilayers are metallic with large Hall conductances comparable to the conductance quantum. Furthermore, bilayers (LaRuO3)2 and (SrRhO3)2 are half metallic, while the bilayer (SrIrO3)2 exhibits a peculiar colossal magnetic anisotropy. Our findings thus show that 4 d and 5 d metal perovskite (111) bilayers are a class of quasi-two-dimensional materials for exploring exotic quantum phases and also for advanced applications such as low-power nanoelectronics and oxide spintronics.

  14. ZnS quantum dot induced phase transitional changes and enhanced ferroelectric mesophase in QDs/FLC composites

    Science.gov (United States)

    Vimal, T.; Pandey, S.; Singh, D. P.; Gupta, S. K.; Agrahari, K.; Kumbhakar, P.; Kole, A. K.; Manohar, R.

    2017-01-01

    In the present study, we report the dielectric and electro - optical (E - O) study of ZnS quantum dots (QDs) dispersed ferroelectric liquid crystal (FLC) material. Change in the SmC*- SmA phase transition temperature has been investigated by the thermal study. Width of SmC* phase is found to be slightly increased due to the dispersion of ZnS QDs, which has also been observed in the dielectric and E - O study of composites. Fitting of spontaneous polarization curves on the temperature scale has been done theoretically to obtain the change in SmC*- SmA phase transition temperature. A significant modification in the FLC material parameters (like spontaneous polarization, optical response time, tilt angle and rotational viscosity) has been observed after the dispersion of QDs. These modifications are the consequences of the strong dipolar interaction between the FLC molecule and QDs. Significant fastening of the optical response time for low conc. of QDs dispersed FLC composite shows its utilization in advanced display devices.

  15. Magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 driven by the Stark effect.

    Science.gov (United States)

    Zhang, Zuocheng; Feng, Xiao; Wang, Jing; Lian, Biao; Zhang, Jinsong; Chang, Cuizu; Guo, Minghua; Ou, Yunbo; Feng, Yang; Zhang, Shou-Cheng; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Yayu

    2017-08-07

    The recent experimental observation of the quantum anomalous Hall effect has cast significant attention on magnetic topological insulators. In these magnetic counterparts of conventional topological insulators such as Bi2Te3, a long-range ferromagnetic state can be established by chemical doping with transition-metal elements. However, a much richer electronic phase diagram can emerge and, in the specific case of Cr-doped Bi2(SexTe1-x)3, a magnetic quantum phase transition tuned by the actual chemical composition has been reported. From an application-oriented perspective, the relevance of these results hinges on the possibility to manipulate magnetism and electronic band topology by external perturbations such as an electric field generated by gate electrodes-similar to what has been achieved in conventional diluted magnetic semiconductors. Here, we investigate the magneto-transport properties of Cr-doped Bi2(SexTe1-x)3 with different compositions under the effect of a gate voltage. The electric field has a negligible effect on magnetic order for all investigated compositions, with the remarkable exception of the sample close to the topological quantum critical point, where the gate voltage reversibly drives a ferromagnetic-to-paramagnetic phase transition. Theoretical calculations show that a perpendicular electric field causes a shift in the electronic energy levels due to the Stark effect, which induces a topological quantum phase transition and, in turn, a magnetic phase transition.

  16. 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.

  17. Semiclassical and Quantum Black Holes and their Evaporation, de Sitter and Anti-de Sitter Regimes, Gravitational and String Phase Transitions

    CERN Document Server

    Medrano, Marina Ramon

    2007-01-01

    An effective string theory in physically relevant cosmological and black hole space times is reviewed. Explicit computations of the quantum string entropy, partition function and quantum string emission by black holes (Schwarzschild, rotating, charged, asymptotically flat, de Sitter dS and AdS space times) in the framework of effective string theory in curved backgrounds provide an amount of new quantum gravity results as: (i) gravitational phase transitions appear with a distinctive universal feature: a square root branch point singularity in any space time dimensions. This is of the type of the de Vega - Sanchez transition for the thermal self-gravitating gas of point particles. (ii) There are no phase transitions in AdS alone. (iii) For $dS$ background, upper bounds of the Hubble constant H are found, dictated by the quantum string phase transition.(iv) The Hawking temperature and the Hagedorn temperature are the same concept but in different (semiclassical and quantum) gravity regimes respectively. (v) Th...

  18. Phase-selective quantum eraser

    Science.gov (United States)

    Heuer, A.; Pieplow, G.; Menzel, R.

    2015-07-01

    A quantum-eraser experiment is reported with photon pairs generated by two synchronously pumped parametric down-converters coupled via induced coherence. The complementarity between which-source information and two-photon interference fringe visibility is demonstrated explicitly. Changing the phase in a Mach-Zehnder interferometer allows a continuous transition from wavelike to particlelike behavior of photons.

  19. Zero energy modes in a superconductor with ferromagnetic adatom chains and quantum phase transitions

    Science.gov (United States)

    Čadež, Tilen; Sacramento, Pedro D.

    2016-12-01

    We study Majorana zero energy modes (MZEM) that occur in an s-wave superconducting surface, at the ends of a ferromagnetic (FM) chain of adatoms, in the presence of Rashba spin-orbit interaction (SOI) considering both non self-consistent and self-consistent superconducting order. We find that in the self-consistent solution, the average superconducting gap function over the adatom sites has a discontinuous drop with increasing exchange interaction at the same critical value where the topological phase transition occurs. We also study the MZEM for both treatments of superconducting order and find that the decay length is a linear function of the exchange coupling strength, chemical potential and superconducting order. For wider FM chains the MZEM occur at smaller exchange couplings and the slope of the decay length as a function of exchange coupling grows with chain width. Thus we suggest experimental detection of different delocalization of MZEM in chains of varying widths. We discuss similarities and differences between the MZEM for the two treatments of the superconducting order.

  20. Ising Spin Network States for Loop Quantum Gravity: a Toy Model for Phase Transitions

    CERN Document Server

    Feller, Alexandre

    2015-01-01

    Non-perturbative approaches to quantum gravity call for a deep understanding of the emergence of geometry and locality from the quantum state of the gravitational field. Without background geometry, the notion of distance should entirely emerge from the correlations between the gravity fluctuations. In the context of loop quantum gravity, quantum states of geometry are defined as spin networks. These are graphs decorated with spin and intertwiners, which represent quantized excitations of areas and volumes of the space geometry. Here, we develop the condensed matter point of view on extracting the physical and geometrical information out of spin network states: we introduce new Ising spin network states, both in 2d on a square lattice and in 3d on a hexagonal lattice, whose correlations map onto the usual Ising model in statistical physics. We construct these states from the basic holonomy operators of loop gravity and derive a set of local Hamiltonian constraints which entirely characterize our states. We di...

  1. Learning phase transitions by confusion

    Science.gov (United States)

    van Nieuwenburg, Evert P. L.; Liu, Ye-Hua; Huber, Sebastian D.

    2017-02-01

    Classifying phases of matter is key to our understanding of many problems in physics. For quantum-mechanical systems in particular, the task can be daunting due to the exponentially large Hilbert space. With modern computing power and access to ever-larger data sets, classification problems are now routinely solved using machine-learning techniques. Here, we propose a neural-network approach to finding phase transitions, based on the performance of a neural network after it is trained with data that are deliberately labelled incorrectly. We demonstrate the success of this method on the topological phase transition in the Kitaev chain, the thermal phase transition in the classical Ising model, and the many-body-localization transition in a disordered quantum spin chain. Our method does not depend on order parameters, knowledge of the topological content of the phases, or any other specifics of the transition at hand. It therefore paves the way to the development of a generic tool for identifying unexplored phase transitions.

  2. Critical quasiparticle theory applied to heavy fermion metals near an antiferromagnetic quantum phase transition.

    Science.gov (United States)

    Abrahams, Elihu; Wölfle, Peter

    2012-02-28

    We use the recently developed critical quasiparticle theory to derive the scaling behavior associated with a quantum critical point in a correlated metal. This is applied to the magnetic-field induced quantum critical point observed in YbRh(2)Si(2), for which we also derive the critical behavior of the specific heat, resistivity, thermopower, magnetization and susceptibility, the Grüneisen coefficient, and the thermal expansion coefficient. The theory accounts very well for the available experimental results.

  3. Full-counting statistics and phase transition in an open quantum system of non-interacting electrons

    Science.gov (United States)

    Medvedyeva, Mariya; Kehrein, Stefan

    2014-03-01

    We develop a method for calculating the full-counting statistics for a non-interacting fermionic system coupled to memory-less reservoirs. The evolution of the system is described by the Lindblad equation. We introduce the counting field in the Lindblad equation which yields the generating function and allows us to obtain all cumulants of the charge transport. In a uniform system the cumulants of order k are independent of the system size for systems longer than k+1 sites. The counting statistics from the Lindblad approach does not take into account the interference in the reservoirs which gives a decreased value of noise in comparison to the Green function approach which describes phase coherent leads. The two methods yield the same value for the current, which is due to current conservation. The Fano factors are different (and linearly related) and allow us to distinguish between memory-less and phase coherent reservoirs. We also consider the influence of dissipation along the chain allowing for both tunneling into and out of the chain along its length. Infinitesimally small dissipation along the chain induces a quantum phase transition which manifests itself as a discontinuity in transport properties and entropy.

  4. Quantum phase magnification

    Science.gov (United States)

    Hosten, O.; Krishnakumar, R.; Engelsen, N. J.; Kasevich, M. A.

    2016-06-01

    Quantum metrology exploits entangled states of particles to improve sensing precision beyond the limit achievable with uncorrelated particles. All previous methods required detection noise levels below this standard quantum limit to realize the benefits of the intrinsic sensitivity provided by these states. We experimentally demonstrate a widely applicable method for entanglement-enhanced measurements without low-noise detection. The method involves an intermediate quantum phase magnification step that eases implementation complexity. We used it to perform squeezed-state metrology 8 decibels below the standard quantum limit with a detection system that has a noise floor 10 decibels above the standard quantum limit.

  5. Exact-exchange spin-density functional theory of Wigner localization and phase transitions in quantum rings

    Energy Technology Data Exchange (ETDEWEB)

    Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg, E-mail: thorsten.arnold@physik.uni-erlangen.de, E-mail: marc.siegmund@physik.uni-erlangen.de [Lehrstuhl fuer Theoretische Festkoerperphysik, Universitaet Erlangen-Nuernberg, Staudtstrasse 7 B2, D-91058 Erlangen (Germany)

    2011-08-24

    We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r{sub S} is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r{sub S}. We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r{sub S}{sup c} at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r{sub S} the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid.

  6. Exact-exchange spin-density functional theory of Wigner localization and phase transitions in quantum rings.

    Science.gov (United States)

    Arnold, Thorsten; Siegmund, Marc; Pankratov, Oleg

    2011-08-24

    We apply exact-exchange spin-density functional theory in the Krieger-Li-Iafrate approximation to interacting electrons in quantum rings of different widths. The rings are threaded by a magnetic flux that induces a persistent current. A weak space and spin symmetry breaking potential is introduced to allow for localized solutions. As the electron-electron interaction strength described by the dimensionless parameter r(S) is increased, we observe-at a fixed spin magnetic moment-the subsequent transition of both spin sub-systems from the Fermi liquid to the Wigner crystal state. A dramatic signature of Wigner crystallization is that the persistent current drops sharply with increasing r(S). We observe simultaneously the emergence of pronounced oscillations in the spin-resolved densities and in the electron localization functions indicating a spatial electron localization showing ferrimagnetic order after both spin sub-systems have undergone the Wigner crystallization. The critical r(S)(c) at the transition point is substantially smaller than in a fully spin-polarized system and decreases further with decreasing ring width. Relaxing the constraint of a fixed spin magnetic moment, we find that on increasing r(S) the stable phase changes from an unpolarized Fermi liquid to an antiferromagnetic Wigner crystal and finally to a fully polarized Fermi liquid.

  7. Quantum measurement as a driven phase transition: An exactly solvable model

    NARCIS (Netherlands)

    Allahverdyan, A.; Balian, R.

    2001-01-01

    A model of quantum measurement is proposed, which aims to describe statistical mechanical aspects of this phenomenon, starting from a purely Hamiltonian formulation. The macroscopic measurement apparatus is modeled as an ideal Bose gas, the order parameter of which, that is, the amplitude of the con

  8. Topological phase transition and evolution of edge states in In-rich InGaN/GaN quantum wells under hydrostatic pressure.

    Science.gov (United States)

    Łepkowski, S P; Bardyszewski, W

    2017-02-08

    Combining the k · p method with the third-order elasticity theory, we perform a theoretical study of the pressure-induced topological phase transition and the pressure evolution of topologically protected edge states in InN/GaN and In-rich InGaN/GaN quantum wells. We show that for a certain range of the quantum well parameters, thanks to a negative band gap pressure coefficient, it is possible to continuously drive the system from the normal insulator state through the topological insulator into the semimetal phase. The critical pressure for the topological phase transition depends not only on the quantum well thickness but also on the width of the Hall bar, which determines the coupling between the edge states localized at the opposite edges. We also find that in narrow Hall bar structures, near the topological phase transition, a significant Rashba-type spin splitting of the lower and upper branches of the edge state dispersion curve appears. This effect originates from the lack of the mirror symmetry of the quantum well potential caused by the built-in electric field, and can be suppressed by increasing the Hall bar width. When the pressure increases, the energy dispersion of the edge states becomes more parabolic-like and the spin splitting decreases. A further increase of pressure leads to the transition to a semimetal phase, which occurs due to the closure of the indirect 2D bulk band gap. The difference between the critical pressure at which the system becomes semimetallic, and the pressure for the topological phase transition, correlates with the variation of the pressure coefficient of the band gap in the normal insulator state.

  9. Topological phase transition and evolution of edge states in In-rich InGaN/GaN quantum wells under hydrostatic pressure

    Science.gov (United States)

    Łepkowski, S. P.; Bardyszewski, W.

    2017-02-01

    Combining the k · p method with the third-order elasticity theory, we perform a theoretical study of the pressure-induced topological phase transition and the pressure evolution of topologically protected edge states in InN/GaN and In-rich InGaN/GaN quantum wells. We show that for a certain range of the quantum well parameters, thanks to a negative band gap pressure coefficient, it is possible to continuously drive the system from the normal insulator state through the topological insulator into the semimetal phase. The critical pressure for the topological phase transition depends not only on the quantum well thickness but also on the width of the Hall bar, which determines the coupling between the edge states localized at the opposite edges. We also find that in narrow Hall bar structures, near the topological phase transition, a significant Rashba-type spin splitting of the lower and upper branches of the edge state dispersion curve appears. This effect originates from the lack of the mirror symmetry of the quantum well potential caused by the built-in electric field, and can be suppressed by increasing the Hall bar width. When the pressure increases, the energy dispersion of the edge states becomes more parabolic-like and the spin splitting decreases. A further increase of pressure leads to the transition to a semimetal phase, which occurs due to the closure of the indirect 2D bulk band gap. The difference between the critical pressure at which the system becomes semimetallic, and the pressure for the topological phase transition, correlates with the variation of the pressure coefficient of the band gap in the normal insulator state.

  10. 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.

  11. Boltzmann-Gibbs states in topological quantum walks and associated many-body systems: fidelity and Uhlmann parallel transport analysis of phase transitions

    Science.gov (United States)

    Mera, Bruno; Vlachou, Chrysoula; Paunković, Nikola; Vieira, Vítor R.

    2017-09-01

    We perform the fidelity analysis for Boltzmann-Gibbs-like states in order to investigate whether the topological order of 1D fermionic systems at zero temperature is maintained at finite temperatures. We use quantum walk protocols that are known to simulate topological phases and the respective quantum phase transitions for chiral symmetric Hamiltonians. Using the standard approaches of the fidelity analysis and the study of edge states, we conclude that no thermal-like phase transitions occur as temperature increases, i.e. the topological behaviour is washed out gradually. We also show that the behaviour of the Uhlmann geometric factor associated to the considered fidelity exhibits the same behaviour as the latter, thus confirming the results obtained using the previously established approaches.

  12. Quantum shape phase transitions from spherical to deformed for Bose-Fermi systems: the effect of the odd particle around the critical point

    Directory of Open Access Journals (Sweden)

    Böyükata M.

    2014-03-01

    Full Text Available Quantum phase transitions in odd-nuclei are investigated within the framework of the interacting boson-fermion model with a description based on the concept of intrinsic states. We consider the case of a single j=9/2 odd-particle coupled to an even-even boson core that performs a transition from spherical to deformed prolate and to deformed gamma-unstable shapes varying a control parameter in the boson Hamiltonian. The effect of the coupling of the odd particle to this core is discussed along the shape transition and, in particular, at the critical point.

  13. Quantum Transition-State Theory

    CERN Document Server

    Hele, Timothy J H

    2014-01-01

    This dissertation unifies one of the central methods of classical rate calculation, `Transition-State Theory' (TST), with quantum mechanics, thereby deriving a rigorous `Quantum Transition-State Theory' (QTST). The resulting QTST is identical to ring polymer molecular dynamics transition-state theory (RPMD-TST), which was previously considered a heuristic method, and whose results we thereby validate. The key step in deriving a QTST is alignment of the flux and side dividing surfaces in path-integral space to obtain a quantum flux-side time-correlation function with a non-zero $t\\to 0_+$ limit. We then prove that this produces the exact quantum rate in the absence of recrossing by the exact quantum dynamics, fulfilling the requirements of a QTST. Furthermore, strong evidence is presented that this is the only QTST with positive-definite Boltzmann statistics and therefore the pre-eminent method for computation of thermal quantum rates in direct reactions.

  14. Quantum phase transition and von Neumann entropy of quasiperiodic Hubbard chains

    Institute of Scientific and Technical Information of China (English)

    Zhu Xuan; Tong Pei-Qing

    2008-01-01

    The half-filled Hubbard chains with the Fibonacci and Harper modulating site potentials are studied in a selfconsistent mean-field approximation.A new order parameter is introduced to describe a charge density order.We also calculate the yon Neumann entropy of the ground state.The results show that the yon Neumann entropy can identify a CDW/SDW (charge density wave/spin density wave) transition for quasiperiodic models.

  15. Entanglement as an Observer-Dependent Concept: An Application to Quantum Phase Transitions

    CERN Document Server

    Ortiz, G; Barnum, H; Knill, E; Viola, L; Ortiz, Gerardo; Somma, Rolando; Barnum, Howard; Knill, Emanuel; Viola, Lorenza

    2004-01-01

    This paper addresses the following main question: Do we have a theoretical understanding of entanglement applicable to a full variety of physical settings? It is clear that not only the assumption of distinguishability, but also the few-subsystem scenario, are too narrow to embrace all possible physical settings. In particular, the need to go beyond the traditional subsystem-based framework becomes manifest when one tries to apply the conventional concept of entanglement to the physics of matter, since the constituents of a quantum many-body system are indistinguishable particles. We shall discuss here a notion of generalized entanglement, which can be applied to any operator language (fermions, bosons, spins, etc.) used to describe a physical system and which includes the conventional entanglement settings introduced to date in a unified fashion. This is realized by noticing that entanglement is an observer-dependent concept, whose properties are determined by the expectations of a distinguished set of obser...

  16. A Quantum Version of Wigner's Transition State Theory

    NARCIS (Netherlands)

    Schubert, R.; Waalkens, H.; Wiggins, S.

    2009-01-01

    A quantum version of a recent realization of Wigner's transition state theory in phase space is presented. The theory developed builds on a quantum normal form which locally decouples the quantum dynamics near the transition state to any desired order in (h) over bar. This leads to an explicit algor

  17. A Quantum Version of Wigner’s Transition State Theory

    NARCIS (Netherlands)

    Schubert, R.; Waalkens, H.; Wiggins, S.

    2009-01-01

    A quantum version of a recent realization of Wigner’s transition state theory in phase space is presented. The theory developed builds on a quantum normal form which locally decouples the quantum dynamics near the transition state to any desired order in ħ. This leads to an explicit algorithm to com

  18. Quantum Enhanced Phase Retrieval

    CERN Document Server

    Liberman, Liat; Poem, Eilon; Silberberg, Yaron

    2015-01-01

    The retrieval of phases from intensity measurements is a key process in many fields in science, from optical microscopy to x-ray crystallography. Here we study phase retrieval of a one-dimensional multi-phase object that is illuminated by quantum states of light. We generalize the iterative Gerchberg-Saxton algorithm to photon correlation measurements on the output plane, rather than the standard intensity measurements. We report a numerical comparison of classical and quantum phase retrieval of a small one-dimensional object of discrete phases from its far-field diffraction. While the classical algorithm was ambiguous and often converged to wrong solutions, quantum light produced a unique reconstruction with smaller errors and faster convergence. We attribute these improvements to a larger Hilbert space that constrains the algorithm.

  19. Controlled quantum evolutions and transitions

    Energy Technology Data Exchange (ETDEWEB)

    Petroni, Nicola Cufaro [INFN Sezione di Bari, INFM Unitadi Bari and Dipartimento Interateneo di Fisica dell' Universitae del Politecnico di Bari, Bari (Italy); De Martino, Salvatore; De Siena, Silvio; Illuminati, Fabrizio [INFM Unitadi Salerno, INFN Sezione di Napoli - Gruppo collegato di Salerno and Dipartimento di Fisica dell' Universitadi Salerno, Baronissi, Salerno (Italy)

    1999-10-29

    We study the nonstationary solutions of Fokker-Planck equations associated to either stationary or non stationary quantum states. In particular, we discuss the stationary states of quantum systems with singular velocity fields. We introduce a technique that allows arbitrary evolutions ruled by these equations to account for controlled quantum transitions. As a first significant application we present a detailed treatment of the transition probabilities and of the controlling time-dependent potentials associated to the transitions between the stationary, the coherent, and the squeezed states of the harmonic oscillator. (author)

  20. Controlled quantum evolutions and transitions

    CERN Document Server

    Petroni, N C; De Siena, S; Illuminati, F

    1999-01-01

    We study the nonstationary solutions of Fokker-Planck equations associated to either stationary or nonstationary quantum states. In particular we discuss the stationary states of quantum systems with singular velocity fields. We introduce a technique that allows to realize arbitrary evolutions ruled by these equations, to account for controlled quantum transitions. The method is illustrated by presenting the detailed treatment of the transition probabilities and of the controlling time-dependent potentials associated to the transitions between the stationary, the coherent, and the squeezed states of the harmonic oscillator. Possible extensions to anharmonic systems and mixed states are briefly discussed and assessed.

  1. BOOK REVIEW: Quantum Analogues: From Phase Transitions to Black Holes and Cosmology

    Science.gov (United States)

    Liberati, Stefano

    2008-09-01

    'And I cherish more than anything else the analogies, my most trustworthy masters. They know all the secrets of nature, and they ought to be least neglected in geometry.' These words of the great astronomer Johannes Kepler embody the philosophy behind the research recounted in this interesting book—a book composed of nine selected lectures (and a nice introduction by Bill Unruh) from the international workshop on 'Quantum Simulations via Analogues', which was held in the Max Planck Institute for the Physics of Complex Systems in Dresden during the summer of 2005. Analogue models of (and for) gravity have a long and distinguished history dating back to the earliest years of general relativity. However the last decade has seen a remarkable and steady development of analogue gravity models based on condensed matter systems, leading to some hundreds of published articles, numerous workshops, and several books. While the main driver for this booming field has definitely been the puzzling physics associated with quantum effects in black holes, more recently much attention has also been devoted to other interesting issues—such as cosmological particle production or the cosmological constant problem. Moreover, together with these new themes there has been a persistent interest in the possibility of simulating cosmic topological defects in the laboratory (although it should be said that momentum for this line of research has been somewhat weakened by the progressive decrease of interest in cosmological topological defects as an alternative to inflationary scenarios). All these aspects are faithfully accounted for in this book, which does a good job at presenting a vivid snapshot of many (if not quite all) of the most interesting lines of research in the field. All the articles have a self-consistent structure—which allows one to read them in arbitrary order and appreciate the full richness of each topic. However, when considered together I would say that they also

  2. Field-driven quantum phase transitions in S =1/2 spin chains

    Science.gov (United States)

    Iaizzi, Adam; Damle, Kedar; Sandvik, Anders W.

    2017-05-01

    We study the magnetization process of a one-dimensional extended Heisenberg model, the J -Q model, as a function of an external magnetic field h . In this model, J represents the traditional antiferromagnetic Heisenberg exchange and Q is the strength of a competing four-spin interaction. Without external field, this system hosts a twofold-degenerate dimerized (valence-bond solid) state above a critical value qc≈0.85 where q ≡Q /J . The dimer order is destroyed and replaced by a partially polarized translationally invariant state at a critical field value. We find magnetization jumps (metamagnetism) between the partially polarized and fully polarized state for q >qmin , where we have calculated qmin=2/9 exactly. For q >qmin , two magnons (flipped spins on a fully polarized background) attract and form a bound state. Quantum Monte Carlo studies confirm that the bound state corresponds to the first step of an instability leading to a finite magnetization jump for q >qmin . Our results show that neither geometric frustration nor spin anisotropy are necessary conditions for metamagnetism. Working in the two-magnon subspace, we also find evidence pointing to the existence of metamagnetism in the unfrustrated J1-J2 chain (J1>0 ,J20 . While the expected "zero-scale-factor" universality is clearly seen for q =0 and q ≪qmin , for q closer to qmin we find that extremely low temperatures are required to observe the asymptotic behavior, due to the influence of the tricritical point at qmin. In the low-energy theory, one can expect the quartic nonlinearity to vanish at qmin and a marginal sixth-order term should govern the scaling, which leads to a crossover at a temperature T*(q ) between logarithmic tricritical scaling and zero-scale-factor universality, with T*(q ) →0 when q →qmin .

  3. Cosmological phase transitions from lattice field theory

    Energy Technology Data Exchange (ETDEWEB)

    Jansen, Karl [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany). John von Neumann-Inst. fuer Computing NIC

    2011-11-22

    In this proceedings contribution we discuss the fate of the electroweak and the quantum chromodynamics phase transitions relevant for the early stage of the universe at non-zero temperature. These phase transitions are related to the Higgs mechanism and the breaking of chiral symmetry, respectively. We will review that non-perturbative lattice field theory simulations show that these phase transitions actually do not occur in nature and that physical observables show a completely smooth behaviour as a function of the temperature.

  4. 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.

  5. Martensitic phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Petry, W.; Neuhaus, J. [Techn. Universitaet Muenchen, Physik Department E13, Munich (Germany)

    1996-11-01

    Many elements transform from a high temperature bcc phase to a more dense packed temperature phase. The great majority of these transitions are of 1st order, displacive and reconstructive. The lattice potentials which govern these martensitic transitions can be probed by inelastic neutron scattering, thereby answering fundamental questions like : Will the transition be announced by dynamical or static fluctuations? What are the trajectories for the displacements needed for the transformation? Does the vibrational entropy stabilize the high temperature phase? Are the unusual transport properties in these materials related to their ability to transform? (author) 17 figs., 1 tab., 46 refs.

  6. Quantum phase transitions and phase diagram for a one-dimensional p-wave superconductor with an incommensurate potential.

    Science.gov (United States)

    Cai, X

    2014-04-16

    The effect of the incommensurate potential is studied for the one-dimensional p-wave superconductor. It is determined by analyzing various properties, such as the superconducting gap, the long-range order of the correlation function, the inverse participation ratio and the Z2 topological invariant, etc. In particular, two important aspects of the effect are investigated: (1) as disorder, the incommensurate potential destroys the superconductivity and drives the system into the Anderson localized phase; (2) as a quasi-periodic potential, the incommensurate potential causes band splitting and turns the system with certain chemical potential into the band insulator phase. A full phase diagram is also presented in the chemical potential-incommensurate potential strength plane.

  7. Phase transitions modern applications

    CERN Document Server

    Gitterman, Moshe

    2014-01-01

    This book provides a comprehensive review of the theory of phase transitions and its modern applications, based on the five pillars of the modern theory of phase transitions i.e. the Ising model, mean field, scaling, renormalization group and universality. This expanded second edition includes, along with a description of vortices and high temperature superconductivity, a discussion of phase transitions in chemical reaction and moving systems. The book covers a close connection between phase transitions and small world phenomena as well as scale-free systems such as the stock market and the Internet. Readership: Scientists working in different fields of physics, chemistry, biology and economics as well as teaching material for undergraduate and graduate courses.

  8. The SAT phase transition

    Institute of Scientific and Technical Information of China (English)

    许可; 李未

    1999-01-01

    Phase transition is an important feature of SAT problem. For random k-SAT model, it is proved that as r(ratio of clauses to variables) increases, the structure of solutions will undergo a sudden change like satisfiability phase transition when r reaches a threshold point (r=rcr). This phenomenon shows that the satisfying truth assignments suddenly shift from being relatively different from each other to being very similar to each other.##属性不符

  9. Quantum phase transitions and collective enhancement of level density in odd–A and odd–odd nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Karampagia, S., E-mail: karampag@nscl.msu.edu [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321 (United States); Renzaglia, A. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-1321 (United States); Zelevinsky, V. [National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824-1321 (United States); Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-1321 (United States)

    2017-06-15

    The nuclear shell model assumes an effective mean-field plus interaction Hamiltonian in a specific configuration space. We want to understand how various interaction matrix elements affect the observables, the collectivity in nuclei and the nuclear level density for odd–A and odd–odd nuclei. Using the sd and pf shells, we vary specific groups of matrix elements and study the evolution of energy levels, transition rates and the level density. In all cases studied, a transition between a “normal” and a collective phase is induced, accompanied by an enhancement of the level density in the collective phase. In distinction to neighboring even–even nuclei, the enhancement of the level density is observed already at the transition point. The collective phase is reached when the single-particle transfer matrix elements are dominant in the shell model Hamiltonian, providing a sign of their fundamental role.

  10. Exceptional Points and Dynamical Phase Transitions

    Directory of Open Access Journals (Sweden)

    I. Rotter

    2010-01-01

    Full Text Available In the framework of non-Hermitian quantum physics, the relation between exceptional points,dynamical phase transitions and the counter intuitive behavior of quantum systems at high level density is considered. The theoretical results obtained for open quantum systems and proven experimentally some years ago on a microwave cavity, may explain environmentally induce deffects (including dynamical phase transitions, which have been observed in various experimental studies. They also agree(qualitatively with the experimental results reported recently in PT symmetric optical lattices.

  11. Interplay of topology and interactions in quantum Hall topological insulators: U(1) symmetry, tunable Luttinger liquid, and interaction-induced phase transitions

    Science.gov (United States)

    Kharitonov, Maxim; Juergens, Stefan; Trauzettel, Björn

    2016-07-01

    We consider a class of quantum Hall topological insulators: topologically nontrivial states with zero Chern number at finite magnetic field, in which the counterpropagating edge states are protected by a symmetry (spatial or spin) other than time-reversal. HgTe-type heterostructures and graphene are among the relevant systems. We study the effect of electron interactions on the topological properties of the system. We particularly focus on the vicinity of the topological phase transition, marked by the crossing of two Landau levels, where the system is a strongly interacting quantum Hall ferromagnet. We analyze the edge properties using the formalism of the nonlinear σ -model. We establish the symmetry requirement for the topological protection in this interacting system: effective continuous U(1) symmetry with respect to uniaxial isospin rotations must be preserved. If U(1) symmetry is preserved, the topologically nontrivial phase persists; its edge is a helical Luttinger liquid with highly tunable effective interactions. We obtain explicit analytical expressions for the parameters of the Luttinger liquid in the quantum-Hall-ferromagnet regime. However, U(1) symmetry may be broken, either spontaneously or by U(1)-asymmetric interactions. In either case, interaction-induced transitions occur to the respective topologically trivial phases with gapped edge charge excitations.

  12. Electronic phase transitions

    CERN Document Server

    Kopaev, YuV

    1992-01-01

    Electronic Phase Transitions deals with topics, which are presently at the forefront of scientific research in modern solid-state theory. Anderson localization, which has fundamental implications in many areas of solid-state physics as well as spin glasses, with its influence on quite different research activities such as neural networks, are two examples that are reviewed in this book. The ab initio statistical mechanics of structural phase transitions is another prime example, where the interplay and connection of two unrelated disciplines of solid-state theory - first principle ele

  13. Photoinduced phase transitions

    CERN Document Server

    Nasu, K

    2004-01-01

    A new class of insulating solids was recently discovered. Whenirradiated by a few visible photons, these solids give rise to amacroscopic excited domain that has new structural and electronicorders quite different from the starting ground state. This occurrenceis called "photoinduced phase transition", and this multi-authoredbook reviews recent theoretical and experimental studies of this newphenomenon.

  14. Quantum statistical model of nuclear multifragmentation in the canonical ensemble method 24.60.-k; 24.60.Ky; 25.70.Pq; 25.70.-z; Nuclear multifragmentation; First-order phase transition; Quantum statistics; Canonical ensemble

    CERN Document Server

    Parvan, A S; Ploszajczak, M

    2000-01-01

    A quantum statistical model of nuclear multifragmentation is proposed. The recurrence equation method used within the canonical ensemble makes the model solvable and transparent to physical assumptions and allows to get results without involving the Monte Carlo technique. The model exhibits the first-order phase transition. Quantum statistics effects are clearly seen on the microscopic level of occupation numbers but are almost washed out for global thermodynamic variables and the averaged observables studied. In the latter case, the recurrence relations for multiplicity distributions of both intermediate-mass and all fragments are derived and the specific changes in the shape of multiplicity distributions in the narrow region of the transition temperature is stressed. The temperature domain favorable to search for the HBT effect is noted.

  15. Phase transitions in dissipative Josephson chains

    Energy Technology Data Exchange (ETDEWEB)

    Bobbert, P.A.; Fazio, R.; Schoen, G. (Department of Applied Physics, Delft University of Technology, 2628 CJ Delft, The Netherlands (NL)); Zimanyi, G.T. (Department of Physics, University of California, Davis, Davis, California 95616 (USA))

    1990-03-01

    We study the zero-temperature phase transitions of a chain of Josephson junctions, taking into account the quantum fluctuations due to the charging energy and the effects of an Ohmic dissipation. We map the problem onto a generalized Coulomb gas model, which then is transformed into a sine-Gordon field theory. Apart from the expected dipole unbinding transition, which describes a transition between globally superconducting and resistive behavior, we find a quadrupole unbinding transition at a critical strength of the dissipation. This transition separates two superconducting states characterized by different local properties.

  16. Emergence and Phase Transitions

    Science.gov (United States)

    Sikkema, Arnold

    2006-05-01

    Phase transitions are well defined in physics through concepts such as spontaneous symmetry breaking, order parameter, entropy, and critical exponents. But emergence --- also exhibiting whole-part relations (such as top-down influence), unpredictability, and insensitivity to microscopic detail --- is a loosely-defined concept being used in many disciplines, particularly in psychology, biology, philosophy, as well as in physics[1,2]. I will review the concepts of emergence as used in the various fields and consider the extent to which the methods of phase transitions can clarify the usefulness of the concept of emergence both within the discipline of physics and beyond.1. Robert B. Laughlin, A Different Universe: Reinventing Physics from the Bottom Down (New York: Basic Books, 2005). 2. George F.R. Ellis, ``Physics and the Real World'', Physics Today, vol. 58, no. 7 (July 2005) pp. 49-54.

  17. Phase transitions in geometrothermodynamics

    CERN Document Server

    Quevedo, H; Taj, S; Vazquez, A

    2010-01-01

    Using the formalism of geometrothermodynamics, we investigate the geometric properties of the equilibrium manifold for diverse thermodynamic systems. Starting from Legendre invariant metrics of the phase manifold, we derive thermodynamic metrics for the equilibrium manifold whose curvature becomes singular at those points where phase transitions of first and second order occur. We conclude that the thermodynamic curvature of the equilibrium manifold, as defined in geometrothermodynamics, can be used as a measure of thermodynamic interaction in diverse systems with two and three thermodynamic degrees of freedom.

  18. Quantum-classical transitions in complex networks

    Science.gov (United States)

    Javarone, Marco Alberto; Armano, Giuliano

    2013-04-01

    The inherent properties of specific physical systems can be used as metaphors for investigation of the behavior of complex networks. This insight has already been put into practice in previous work, e.g., studying the network evolution in terms of phase transitions of quantum gases or representing distances among nodes as if they were particle energies. This paper shows that the emergence of different structures in complex networks, such as the scale-free and the winner-takes-all networks, can be represented in terms of a quantum-classical transition for quantum gases. In particular, we propose a model of fermionic networks that allows us to investigate the network evolution and its dependence on the system temperature. Simulations, performed in accordance with the cited model, clearly highlight the separation between classical random and winner-takes-all networks, in full correspondence with the separation between classical and quantum regions for quantum gases. We deem this model useful for the analysis of synthetic and real complex networks.

  19. QCD Phase Transitions, Volume 15

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, T.; Shuryak, E.

    1999-03-20

    The title of the workshop, ''The QCD Phase Transitions'', in fact happened to be too narrow for its real contents. It would be more accurate to say that it was devoted to different phases of QCD and QCD-related gauge theories, with strong emphasis on discussion of the underlying non-perturbative mechanisms which manifest themselves as all those phases. Before we go to specifics, let us emphasize one important aspect of the present status of non-perturbative Quantum Field Theory in general. It remains true that its studies do not get attention proportional to the intellectual challenge they deserve, and that the theorists working on it remain very fragmented. The efforts to create Theory of Everything including Quantum Gravity have attracted the lion share of attention and young talent. Nevertheless, in the last few years there was also a tremendous progress and even some shift of attention toward emphasis on the unity of non-perturbative phenomena. For example, we have seen some efforts to connect the lessons from recent progress in Supersymmetric theories with that in QCD, as derived from phenomenology and lattice. Another example is Maldacena conjecture and related development, which connect three things together, string theory, super-gravity and the (N=4) supersymmetric gauge theory. Although the progress mentioned is remarkable by itself, if we would listen to each other more we may have chance to strengthen the field and reach better understanding of the spectacular non-perturbative physics.

  20. Photon Cascade from a Single Crystal Phase Nanowire Quantum Dot

    DEFF Research Database (Denmark)

    Bouwes Bavinck, Maaike; Jöns, Klaus D; Zieliński, Michal

    2016-01-01

    unprecedented potential to be controlled with atomic layer accuracy without random alloying. We show for the first time that crystal phase quantum dots are a source of pure single-photons and cascaded photon-pairs from type II transitions with excellent optical properties in terms of intensity and line width...... quantum optical properties for single photon application and quantum optics.......We report the first comprehensive experimental and theoretical study of the optical properties of single crystal phase quantum dots in InP nanowires. Crystal phase quantum dots are defined by a transition in the crystallographic lattice between zinc blende and wurtzite segments and therefore offer...

  1. Influence of counter-rotating interaction on quantum phase transition in Dicke-Hubbard lattice: an extended coherent-state approach

    Science.gov (United States)

    Lu, Yongchuan; Wang, Chen

    2016-10-01

    We investigate the ground-state behavior of the Dicke-Hubbard model including counter-rotating terms. By generalizing an extended coherent-state approach within mean-field theory, we self-consistently obtain the ground-state energy and delocalized order parameter. Localization-delocalization quantum phase transition of photons is clearly observed by breaking the parity symmetry. Particularly, Mott lobes are fully suppressed, and the delocalized order parameter shows monotonic enhancement by increasing qubit-cavity coupling strength, in sharp contrast to the Dicke-Hubbard model under rotating-wave approximation. Moreover, the corresponding phase boundaries are stabilized by decreasing photon hopping strength, compared to the Rabi-Hubbard model.

  2. Electroweak phase transitions

    CERN Document Server

    Fodor, Z

    2000-01-01

    Recent developments on the four dimensional (4d) lattice studies of the finite temperature electroweak phase transition (EWPT) are summarized. The phase diagram is given in the continuum limit. The finite temperature SU(2)-Higgs phase transition is of first order for Higgs-boson masses m/sub H/<66.5+or-1.4 GeV. Above this endpoint only a rapid cross-over can be seen. The full 4d result agrees completely with that of the dimensional reduction approximation. The Higgs-boson endpoint mass in the standard model (SM) would be 72.1+or-1. 4 GeV. Taking into account the LEP Higgs-boson mass lower bound excludes any EWPT in the SM. A one-loop calculation of the static potential in the SU(2)-Higgs model enables a precise comparison between lattice simulations and perturbative results. The most popular extension of the SM, the minimal supersymmetric SM (MSSM) is also studied on 4d lattices. (17 refs).

  3. 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.

  4. Decoherence of many-spin systems in NMR: From molecular characterization to an environmentally induced quantum dynamical phase transition

    CERN Document Server

    Alvarez, Gonzalo A

    2007-01-01

    The control of open quantum systems has a fundamental relevance for fields ranging from quantum information processing to nanotechnology. Typically, the system whose coherent dynamics one wants to manipulate, interacts with an environment that smoothly degrades its quantum dynamics. Thus, a precise understanding of the inner mechanisms of this process, called "decoherence", is critical to develop strategies to control the quantum dynamics. In this thesis we solved the generalized Liouville-von Neumann quantum master equation to obtain the dynamics of many-spin systems interacting with a spin bath. We also solve the spin dynamics within the Keldysh formalism. Both methods lead to identical solutions and together gave us the possibility to obtain numerous physical predictions that contrast well with Nuclear Magnetic Resonance experiments. We applied these tools for molecular characterizations, development of new numerical methodologies and the control of quantum dynamics in experimental implementations. But, mo...

  5. Electromechanical transition in quantum dots

    Science.gov (United States)

    Micchi, G.; Avriller, R.; Pistolesi, F.

    2016-09-01

    The strong coupling between electronic transport in a single-level quantum dot and a capacitively coupled nanomechanical oscillator may lead to a transition towards a mechanically bistable and blocked-current state. Its observation is at reach in carbon-nanotube state-of-art experiments. In a recent publication [Phys. Rev. Lett. 115, 206802 (2015), 10.1103/PhysRevLett.115.206802] we have shown that this transition is characterized by pronounced signatures on the oscillator mechanical properties: the susceptibility, the displacement fluctuation spectrum, and the ring-down time. These properties are extracted from transport measurements, however the relation between the mechanical quantities and the electronic signal is not always straightforward. Moreover the dependence of the same quantities on temperature, bias or gate voltage, and external dissipation has not been studied. The purpose of this paper is to fill this gap and provide a detailed description of the transition. Specifically we find (i) the relation between the current-noise and the displacement spectrum; (ii) the peculiar behavior of the gate-voltage dependence of these spectra at the transition; (iii) the robustness of the transition towards the effect of external fluctuations and dissipation.

  6. Transition probability spaces in loop quantum gravity

    CERN Document Server

    Guo, Xiao-Kan

    2016-01-01

    We study the (generalized) transition probability spaces, in the sense of Mielnik and Cantoni, for spacetime quantum states in loop quantum gravity. First, we show that loop quantum gravity admits the structures of transition probability spaces. This is achieved by first checking such structures in covariant quantum mechanics, and then passing to spin foam models via the general boundary formulation. The transition probability space thus defined gives a simple way to reconstruct the Hilbert space of the canonical theory and the relevant quantum logical structure. Second, we show that the transition probability space and in particular the spin foam model are 2-categories. Then we discuss how to realize property transitions and causality in this categorical context in connection with presheaves on quantaloids and respectively causal categories. We conclude that transition probability spaces provide us with an alternative framework to understand various foundational questions of loop quantum gravity.

  7. Exact diagonalization for spin-1/2 chains and the first order quantum phase transitions of the XXX chain in a uniform transverse field

    Energy Technology Data Exchange (ETDEWEB)

    Pan Feng [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Guan Xin [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Ma Nan [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Han Wenjuan [Department of Physics, Liaoning Normal University, Dalian 116029 (China); Draayer, J P [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)

    2007-09-26

    A simple Mathematica code based on the differential realization of hard-core boson operators for finding exact solutions of the periodic-N spin-1/2 systems with or beyond nearest neighbor interactions is proposed; it can easily be used to study general spin-1/2 interaction systems. As an example, the code is applied to study XXX spin-1/2 chains with nearest neighbor interaction in a uniform transverse field. It shows that there are [N/2] level-crossing points in the ground state, where N is the periodic number of the system and [x] stands for the integer part of x, when the interaction strength and magnitude of the magnetic field satisfy certain conditions. The quantum phase transitional behavior in the ground state of the system in the thermodynamic limit is also studied.

  8. Robust Adaptive Quantum Phase Estimation

    CERN Document Server

    Roy, Shibdas; Huntington, Elanor H

    2014-01-01

    Quantum parameter estimation is central to many fields such as quantum computation, communications and metrology. Optimal estimation theory has been instrumental in achieving the best accuracy in quantum parameter estimation, which is possible when we have very precise knowledge of and control over the model. However, uncertainties in key parameters underlying the system are unavoidable and may impact the quality of the estimate. We show here how quantum optical phase estimation of a squeezed state of light exhibits improvement when using a robust fixed-interval smoother designed with uncertainties explicitly introduced in parameters underlying the phase noise.

  9. Dynamical moments reveal a topological quantum transition in a photonic quantum walk

    CERN Document Server

    Cardano, Filippo; Massa, Francesco; Piccirillo, Bruno; de Lisio, Corrado; De Filippis, Giulio; Cataudella, Vittorio; Santamato, Enrico; Marrucci, Lorenzo

    2015-01-01

    Many phenomena in solid-state physics can be understood in terms of their topological properties. Recently, controlled protocols of quantum walks are proving to be effective simulators of such phenomena. Here we report the realization of a photonic quantum walk showing both the trivial and the non-trivial topologies associated with chiral symmetry in one-dimensional periodic systems, as in the Su-Schrieffer-Heeger model of polyacetylene. We find that the probability distribution moments of the walker position after many steps behave differently in the two topological phases and can be used as direct indicators of the quantum transition: while varying a control parameter, these moments exhibit a slope discontinuity at the transition point, and remain constant in the non-trivial phase. Extending this approach to higher dimensions, different topological classes, and other typologies of quantum phases may offer new general instruments for investigating quantum transitions in such complex systems.

  10. Mixed phases during the phase transitions

    CERN Document Server

    Tatsumi, Toshitaka; Maruyama, Toshiki

    2011-01-01

    Quest for a new form of matter inside compact stars compels us to examine the thermodynamical properties of the phase transitions. We closely consider the first-order phase transitions and the phase equilibrium on the basis of the Gibbs conditions, taking the liquid-gas phase transition in asymmetric nuclear matter as an example. Characteristic features of the mixed phase are figured out by solving the coupled equations for mean-fields and densities of constituent particles self-consistently within the Thomas-Fermi approximation. The mixed phase is inhomogeneous matter composed of two phases in equilibrium; it takes a crystalline structure with a unit of various geometrical shapes, inside of which one phase with a characteristic shape, called "pasta", is embedded in another phase by some volume fraction. This framework enables us to properly take into account the Coulomb interaction and the interface energy, and thereby sometimes we see the mechanical instability of the geometric structures of the mixed phase...

  11. Quantum processes on phase space

    CERN Document Server

    Anastopoulos, C

    2003-01-01

    Quantum theory predicts probabilities as well as relative phases between different alternatives of the system. A unified description of both probabilities and phases comes through a generalisation of the notion of a density matrix for histories; this object is the decoherence functional of the consistent histories approach. If we take phases as well as probabilities as primitive elements of our theory, we abandon Kolmogorov probability and can describe quantum theory in terms of fundamental commutative observables, without being obstructed by Bell's and related theorems. Generalising the theory of stochastic processes, we develop the description of relative phases and probabilities for paths on the classical phase space. This description provides a theory of quantum processes. We identify a number of basic postulates and study its corresponding properties. We strongly emphasise the notion of conditioning and are able to write ``quantum differential equations'' as analogous to stochastic differential equations...

  12. Quantum Shuttle in Phase Space

    DEFF Research Database (Denmark)

    Novotny, Tomas; Donarini, Andrea; Jauho, Antti-Pekka

    2003-01-01

    Abstract: We present a quantum theory of the shuttle instability in electronic transport through a nanostructure with a mechanical degree of freedom. A phase space formulation in terms of the Wigner function allows us to identify a crossover from the tunneling to the shuttling regime, thus...... extending the previously found classical results to the quantum domain. Further, a new dynamical regime is discovered, where the shuttling is driven exclusively by the quantum noise....

  13. Quantum Phase Liquids-Fermionic Superfluid without Phase Coherence

    OpenAIRE

    Wu, Ya-Jie; Zhou, Jiang; Kou, Su-Peng

    2014-01-01

    We investigate the two dimensional generalized attractive Hubbard model in a bipartite lattice, and and a "quantum phase liquid" phase, in which the fermions are paired but don't have phase coherence at zero temperature, in analogy to quantum spin liquid phase. Then, two types of topological quantum phase liquids with a small external magnetic field-Z2 quantum phase liquids and chiral quantum phase liquids-are discussed.

  14. 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.

  15. A conditional quantum phase gate between two 3-state atoms

    CERN Document Server

    Yi, X X; You, L

    2002-01-01

    We propose a scheme for conditional quantum logic between two 3-state atoms that share a quantum data-bus such as a single mode optical field in cavity QED systems, or a collective vibrational state of trapped ions. Making use of quantum interference, our scheme achieves successful conditional phase evolution without any real transitions of atomic internal states or populating the quantum data-bus. In addition, it only requires common addressing of the two atoms by external laser fields.

  16. Conditional quantum phase gate between two 3-state atoms.

    Science.gov (United States)

    Yi, X X; Su, X H; You, L

    2003-03-07

    We propose a scheme for conditional quantum logic between two 3-state atoms that share a quantum data bus such as a single mode optical field in cavity QED systems, or a collective vibrational state of trapped ions. Making use of quantum interference, our scheme achieves successful conditional phase evolution without any real transitions of atomic internal states or populating the quantum data bus. In addition, it requires only common addressing of the two atoms by external laser fields.

  17. Sinai Diffusion at Quasi-1D Topological Phase Transitions

    Science.gov (United States)

    Bagrets, Dmitry; Altland, Alexander; Kamenev, Alex

    2016-11-01

    We consider critical quantum transport in disordered topological quantum wires at the transition between phases with different topological indices. Focusing on the example of thermal transport in class D ("Majorana") quantum wires, we identify a transport universality class distinguished for anomalous retardation in the propagation of excitations—a quantum generalization of Sinai diffusion. We discuss the expected manifestations of this transport mechanism for heat propagation in topological superconductors near criticality and provide a microscopic theory explaining the phenomenon.

  18. Phase transitions in quantum crystals : on growth of magnetically ordered 3He and a search for supersolid 4He

    NARCIS (Netherlands)

    Bueno, Juan

    2007-01-01

    Due to its rich magnetic phase diagram and its superfluidity, 3He is a very interesting system if magnetic effects on the crystal growth mechanisms want to be studied. Solid 3He orders magnetically into the U2D2 phase (an antiferromagnetic phase with two planes of spins pointing up and two planes o

  19. Phase Transitions of Simple Systems

    CERN Document Server

    Berry, Stephen

    2008-01-01

    This monograph develops a unified microscopic basis for phases and phase changes of bulk matter and small systems in terms of classical physics. The origins of such phase changes are derived from simple but physically relevant models of how transitions between rigid crystalline, glassy and fluid states occur, how phase equilibria arise, and how bulk properties evolve from those of small systems.

  20. Equations of state and phase transitions in (Mg,Fe)SiO3 perovskite and post-perovskites, position of the phase boundary and its double crossing, by Quantum Monte Carlo

    Science.gov (United States)

    Cohen, R. E.; Lin, Y.

    2015-12-01

    We have performed quantum Monte Carlo (QMC) simulations and density functional theory calculations to study the equations of state and phase transitions in (Mg,Fe)SiO3 perovskite (Pv, bridgmanite) and post-perovskite (PPv) .[1] The ground-state energies were derived using quantum QMC simulations and the temperature-dependent Helmholtz free energies were calculated within the quasiharmonic approximation and density functional perturbation theory. Quantum Monte Carlo (QMC) within Diffusion Monte Carlo (DMC) is a stochastic numerical solution of Schrödinger's equation within the fixed many-particle nodes obtained, in our case, from a determinant of DFT orbitals. Agreement with experiments is improved over DFT alone. Furthermore, we obtain statistical error bounds on the results, rather than the unconstrained errors of DFT. The Pv-PPv phase boundary calculated from our QMC equations of state is also consistent with experiments, and better than previous DFT computations. In order to understand the H-phase reported in (Mg,Fe)SiO3 [2], we have performed evolutionary structure searching for FeSiO3.[3] We find a new structure type which may be consistent with the experimental observations, but is a lower pressure, less dense, phase. We have built a thermodynamic model for (Mg,Fe)SiO3 perovskite as a function of P and T, and will discuss implications for the location of the phase boundary in D'' and its double crossing [4]. This work is supported by NSF and the ERC Advanced Grant ToMCaT. [1] Y. Lin, R. E. Cohen, S. Stackhouse, K. P. Driver, B. Militzer, L. Shulenburger, and J. Kim, Phys. Rev. B 90 (2014). [2] L. Zhang et al., Science 344, 877 (2014). [3] R. E. Cohen and Y. Lin, Phys. Rev. B 90 (2014). [4] J.W. Hernlund, C. Thomas and P.J. Tackley, Nature 434, 882 (2005).

  1. Electroweak phase transition in technicolor

    CERN Document Server

    Jarvinen, Matti

    2010-01-01

    Several phenomenologically viable walking technicolor models have been proposed recently. I demonstrate that these models can have first order electroweak phase transitions, which are sufficiently strong for electroweak baryogenesis. Strong dynamics can also lead to several separate transitions at the electroweak scale, with the possibility of a temporary restoration and an extra breaking of the electroweak symmetry. First order phase transitions will produce gravitational waves, which may be detectable at future experiments.

  2. Magnetic resonance of phase transitions

    CERN Document Server

    Owens, Frank J; Farach, Horacio A

    1979-01-01

    Magnetic Resonance of Phase Transitions shows how the effects of phase transitions are manifested in the magnetic resonance data. The book discusses the basic concepts of structural phase and magnetic resonance; various types of magnetic resonances and their underlying principles; and the radiofrequency methods of nuclear magnetic resonance. The text also describes quadrupole methods; the microwave technique of electron spin resonance; and the Mössbauer effect. Phase transitions in various systems such as fluids, liquid crystals, and crystals, including paramagnets and ferroelectrics, are also

  3. Multiobjective Optimization and Phase Transitions

    CERN Document Server

    Seoane, Luís F

    2015-01-01

    Many complex systems obey to optimality conditions that are usually not simple. Conflicting traits often interact making a Multi Objective Optimization (MOO) approach necessary. Recent MOO research on complex systems report about the Pareto front (optimal designs implementing the best trade-off) in a qualitative manner. Meanwhile, research on traditional Simple Objective Optimization (SOO) often finds phase transitions and critical points. We summarize a robust framework that accounts for phase transitions located through SOO techniques and indicates what MOO features resolutely lead to phase transitions. These appear determined by the shape of the Pareto front, which at the same time is deeply related to the thermodynamic Gibbs surface. Indeed, thermodynamics can be written as an MOO from where its phase transitions can be parsimoniously derived; suggesting that the similarities between transitions in MOO-SOO and Statistical Mechanics go beyond mere coincidence.

  4. Non-equilibrium phase transitions

    CERN Document Server

    Henkel, Malte; Lübeck, Sven

    2009-01-01

    This book describes two main classes of non-equilibrium phase-transitions: (a) static and dynamics of transitions into an absorbing state, and (b) dynamical scaling in far-from-equilibrium relaxation behaviour and ageing. The first volume begins with an introductory chapter which recalls the main concepts of phase-transitions, set for the convenience of the reader in an equilibrium context. The extension to non-equilibrium systems is made by using directed percolation as the main paradigm of absorbing phase transitions and in view of the richness of the known results an entire chapter is devoted to it, including a discussion of recent experimental results. Scaling theories and a large set of both numerical and analytical methods for the study of non-equilibrium phase transitions are thoroughly discussed. The techniques used for directed percolation are then extended to other universality classes and many important results on model parameters are provided for easy reference.

  5. Geometrical Phases in Quantum Mechanics

    Science.gov (United States)

    Christian, Joy Julius

    In quantum mechanics, the path-dependent geometrical phase associated with a physical system, over and above the familiar dynamical phase, was initially discovered in the context of adiabatically changing environments. Subsequently, Aharonov and Anandan liberated this phase from the original formulation of Berry, which used Hamiltonians, dependent on curves in a classical parameter space, to represent the cyclic variations of the environments. Their purely quantum mechanical treatment, independent of Hamiltonians, instead used the non-trivial topological structure of the projective space of one-dimensional subspaces of an appropriate Hilbert space. The geometrical phase, in their treatment, results from a parallel transport of the time-dependent pure quantum states along a curve in this space, which is endowed with an abelian connection. Unlike Berry, they were able to achieve this without resort to an adiabatic approximation or to a time-independent eigenvalue equation. Prima facie, these two approaches are conceptually quite different. After a review of both approaches, an exposition bridging this apparent conceptual gap is given; by rigorously analyzing a model composite system, it is shown that, in an appropriate correspondence limit, the Berry phase can be recovered as a special case from the Aharonov-Anandan phase. Moreover, the model composite system is used to show that Berry's correction to the traditional Born-Oppenheimer energy spectra indeed brings the spectra closer to the exact results. Then, an experimental arrangement to measure geometrical phases associated with cyclic and non-cyclic variations of quantum states of an entangled composite system is proposed, utilizing the fundamental ideas of the recently opened field of two-particle interferometry. This arrangement not only resolves the controversy regarding the true nature of the phases associated with photon states, but also unequivocally predicts experimentally accessible geometrical phases in a

  6. Statistical moments of quantum-walk dynamics reveal topological quantum transitions

    Science.gov (United States)

    Cardano, Filippo; Maffei, Maria; Massa, Francesco; Piccirillo, Bruno; de Lisio, Corrado; de Filippis, Giulio; Cataudella, Vittorio; Santamato, Enrico; Marrucci, Lorenzo

    2016-04-01

    Many phenomena in solid-state physics can be understood in terms of their topological properties. Recently, controlled protocols of quantum walk (QW) are proving to be effective simulators of such phenomena. Here we report the realization of a photonic QW showing both the trivial and the non-trivial topologies associated with chiral symmetry in one-dimensional (1D) periodic systems. We find that the probability distribution moments of the walker position after many steps can be used as direct indicators of the topological quantum transition: while varying a control parameter that defines the system phase, these moments exhibit a slope discontinuity at the transition point. Numerical simulations strongly support the conjecture that these features are general of 1D topological systems. Extending this approach to higher dimensions, different topological classes, and other typologies of quantum phases may offer general instruments for investigating and experimentally detecting quantum transitions in such complex systems.

  7. Statistical moments of quantum-walk dynamics reveal topological quantum transitions.

    Science.gov (United States)

    Cardano, Filippo; Maffei, Maria; Massa, Francesco; Piccirillo, Bruno; de Lisio, Corrado; De Filippis, Giulio; Cataudella, Vittorio; Santamato, Enrico; Marrucci, Lorenzo

    2016-04-22

    Many phenomena in solid-state physics can be understood in terms of their topological properties. Recently, controlled protocols of quantum walk (QW) are proving to be effective simulators of such phenomena. Here we report the realization of a photonic QW showing both the trivial and the non-trivial topologies associated with chiral symmetry in one-dimensional (1D) periodic systems. We find that the probability distribution moments of the walker position after many steps can be used as direct indicators of the topological quantum transition: while varying a control parameter that defines the system phase, these moments exhibit a slope discontinuity at the transition point. Numerical simulations strongly support the conjecture that these features are general of 1D topological systems. Extending this approach to higher dimensions, different topological classes, and other typologies of quantum phases may offer general instruments for investigating and experimentally detecting quantum transitions in such complex systems.

  8. Thermoelectric power as evidence for a Quantum Phase Transition in electron-doped cuprates Pr2-xCexCuO4-y .

    Science.gov (United States)

    Li, Pengcheng; Greene, R. L.; Behnia, K.

    2006-03-01

    We report magnetic field driven normal state thermoelectric power (S) measurement in electron-doped cuprate system Pr2-xCexCuO4-y as a function of doping (x from 0.11 to 0.19) down to 2K. Consistent with the normal state Hall effect^a, S in the underdoped region (0.11-0.15) is negative. S changes sign at certain temperatures in overdoped samples (0.16-0.18), which supports the picture of a spin density wave rearrangement of the Fermi surface^b. More significantly, both S and S/T at 2K (at 9T) increase dramatically from x=0.11 to 0.16, and then saturate in the overdoped region. This kink around x=0.16 is similar to the previous Hall effect result^a in Pr2-xCexCuO4-y. Our results are further evidence for antiferromagnetism to paramagnetism quantum phase transition in electron-doped cuprates. a. Y. Dagan et al, Physical Review Letters, 92 (16) 167001, 2004 b. A. Zimmers et al, Europhysics Letters 70 (2) 225, 2005

  9. On the Chiral Phase Transition in the Linear Sigma Model

    CERN Document Server

    Phat, T H; Hoa, L V; Phat, Tran Huu; Anh, Nguyen Tuan; Hoa, Le Viet

    2004-01-01

    The Cornwall-Jackiw-Tomboulis (CJT) effective action for composite operators at finite temperature is used to investigate the chiral phase transition within the framework of the linear sigma model as the low-energy effective model of quantum chromodynamics (QCD). A new renormalization prescription for the CJT effective action in the Hartree-Fock (HF) approximation is proposed. A numerical study, which incorporates both thermal and quantum effect, shows that in this approximation the phase transition is of first order. However, taking into account the higher-loop diagrams contribution the order of phase transition is unchanged.

  10. Emergent Non-Fermi-Liquid at the Quantum Critical Point of a Topological Phase Transition in Two Dimensions.

    Science.gov (United States)

    Isobe, Hiroki; Yang, Bohm-Jung; Chubukov, Andrey; Schmalian, Jörg; Nagaosa, Naoto

    2016-02-19

    We study the effects of Coulomb interaction between 2D Weyl fermions with anisotropic dispersion which displays relativistic dynamics along one direction and nonrelativistic dynamics along the other. Such a dispersion can be realized in phosphorene under electric field or strain, in TiO_{2}/VO_{2} superlattices, and, more generally, at the quantum critical point between a nodal semimetal and an insulator in systems with a chiral symmetry. Using the one-loop renormalization group approach in combination with the large-N expansion, we find that the system displays interaction-driven non-Fermi liquid behavior in a wide range of intermediate frequencies and marginal Fermi liquid behavior at the smallest frequencies. In the non-Fermi liquid regime, the quasiparticle residue Z at energy E scales as Z∝E^{a} with a>0, and the parameters of the fermionic dispersion acquire anomalous dimensions. In the marginal Fermi-liquid regime, Z∝(|logE|)^{-b} with universal b=3/2.

  11. Quantum Griffiths Phase Inside the Ferromagnetic Phase of Ni1 -xVx

    Science.gov (United States)

    Wang, Ruizhe; Gebretsadik, Adane; Ubaid-Kassis, Sara; Schroeder, Almut; Vojta, Thomas; Baker, Peter J.; Pratt, Francis L.; Blundell, Stephen J.; Lancaster, Tom; Franke, Isabel; Möller, Johannes S.; Page, Katharine

    2017-06-01

    We study by means of bulk and local probes the d -metal alloy Ni1 -xVx close to the quantum critical concentration, xc≈11.6 %, where the ferromagnetic transition temperature vanishes. The magnetization-field curve in the ferromagnetic phase takes an anomalous power-law form with a nonuniversal exponent that is strongly x dependent and mirrors the behavior in the paramagnetic phase. Muon spin rotation experiments demonstrate inhomogeneous magnetic order and indicate the presence of dynamic fluctuating magnetic clusters. These results provide strong evidence for a quantum Griffiths phase on the ferromagnetic side of the quantum phase transition.

  12. Recent theoretical advances on superradiant phase transitions

    Science.gov (United States)

    Baksic, Alexandre; Nataf, Pierre; Ciuti, Cristiano

    2013-03-01

    The Dicke model describing a single-mode boson field coupled to two-level systems is an important paradigm in quantum optics. In particular, the physics of ``superradiant phase transitions'' in the ultrastrong coupling regime is the subject of a vigorous research activity in both cavity and circuit QED. Recently, we explored the rich physics of two interesting generalizations of the Dicke model: (i) A model describing the coupling of a boson mode to two independent chains A and B of two-level systems, where chain A is coupled to one quadrature of the boson field and chain B to the orthogonal quadrature. This original model leads to a quantum phase transition with a double symmetry breaking and a fourfold ground state degeneracy. (ii) A generalized Dicke model with three-level systems including the diamagnetic term. In contrast to the case of two-level atoms for which no-go theorems exist, in the case of three-level system we prove that the Thomas-Reich-Kuhn sum rule does not always prevent a superradiant phase transition.

  13. Quantum critical transport at a continuous metal-insulator transition

    Science.gov (United States)

    Haldar, P.; Laad, M. S.; Hassan, S. R.

    2016-08-01

    In contrast to the first-order correlation-driven Mott metal-insulator transition, continuous disorder-driven transitions are intrinsically quantum critical. Here, we investigate transport quantum criticality in the Falicov-Kimball model, a representative of the latter class in the strong disorder category. Employing cluster-dynamical mean-field theory, we find clear and anomalous quantum critical scaling behavior manifesting as perfect mirror symmetry of scaling curves on both sides of the MIT. Surprisingly, we find that the beta function β (g ) scales as log(g ) deep into the bad-metallic phase as well, providing a sound unified basis for these findings. We argue that such strong localization quantum criticality may manifest in real three-dimensional systems where disorder effects are more important than electron-electron interactions.

  14. Quantum mechanics in phase space

    DEFF Research Database (Denmark)

    Hansen, Frank

    1984-01-01

    A reformulation of quantum mechanics for a finite system is given using twisted multiplication of functions on phase space and Tomita's theory of generalized Hilbert algebras. Quantization of a classical observable h is achieved when the twisted exponential Exp0(-h) is defined as a tempered....... Generalized Weyl-Wigner maps related to the notion of Hamiltonian weight are studied and used in the formulation of a twisted spectral theory for functions on phase space. Some inequalities for Wigner functions on phase space are proven. A brief discussion of the classical limit obtained through dilations...

  15. Higgs Couplings and Electroweak Phase Transition

    CERN Document Server

    Katz, Andrey

    2014-01-01

    We argue that extensions of the Standard Model (SM) with a strongly first-order electroweak phase transition generically predict significant deviations of the Higgs couplings to gluons, photons, and Z bosons from their SM values. Precise experimental measurements of the Higgs couplings at the LHC and at the proposed next-generation facilities will allow for a robust test of the phase transition dynamics. To illustrate this point, in this paper we focus on the scenario in which loops of a new scalar field are responsible for the first-order phase transition, and study a selection of benchmark models with various SM gauge quantum numbers of the new scalar. We find that the current LHC measurement of the Higgs coupling to gluons already excludes the possibility of a first-order phase transition induced by a scalar in a sextet, or larger, representation of the SU(3)_c. Future LHC experiments (including HL-LHC) will be able to definitively probe the case when the new scalar is a color triplet. If the new scalar is...

  16. Quantum Transitions Between Classical Histories: Bouncing Cosmologies

    CERN Document Server

    Hartle, James

    2015-01-01

    In a quantum theory of gravity spacetime behaves classically when quantum probabilities are high for histories of geometry and field that are correlated in time by the Einstein equation. Probabilities follow from the quantum state. This quantum perspective on classicality has important implications: (a) Classical histories are generally available only in limited patches of the configuration space on which the state lives. (b) In a given patch states generally predict relative probabilities for an ensemble of possible classical histories. (c) In between patches classical predictability breaks down and is replaced by quantum evolution connecting classical histories in different patches. (d) Classical predictability can break down on scales well below the Planck scale, and with no breakdown in the classical equations of motion. We support and illustrate (a)-(d) by calculating the quantum transition across the de Sitter like throat connecting asymptotically classical, inflating histories in the no-boundary quantu...

  17. The QCD phase transitions: From mechanism to observables

    Energy Technology Data Exchange (ETDEWEB)

    Shuryak, E.V.

    1997-09-22

    This paper contains viewgraphs on quantum chromodynamic phase transformations during heavy ion collisions. Some topics briefly described are: finite T transitions of I molecule pairs; finite density transitions of diquarks polymers; and the softtest point of the equation of state as a source of discontinuous behavior as a function of collision energy or centrality.

  18. Incommensurate phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Currat, R. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

    1996-11-01

    We review the characteristic aspects of modulated crystals from the point of view of inelastic neutron scattering. We discuss the phenomenological Landau theory of the normal-to-incommensurate displacive instability and its predictions concerning the fluctuation spectrum of the modulated phase. General results on the form of the normal-mode eigenvectors and on the inelastic scattering channels through which they couple to the probe are established using the superspace approach. We illustrate these results on a simple discrete model symmetry and we review available inelastic neutron scattering data on several displacively modulated compounds. (author) 21 figs., 73 refs.

  19. Phase transition of holographic entanglement entropy in massive gravity

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Xiao-Xiong, E-mail: xxzeng@itp.ac.cn [School of Material Science and Engineering, Chongqing Jiaotong University, Chongqing 400074 (China); Key Laboratory of Frontiers in Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Zhang, Hongbao, E-mail: hzhang@vub.ac.be [Department of Physics, Beijing Normal University, Beijing 100875 (China); Theoretische Natuurkunde, Vrije Universiteit Brussel, and The International Solvay Institutes, Pleinlaan 2, B-1050 Brussels (Belgium); Li, Li-Fang, E-mail: lilf@itp.ac.cn [State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190 (China)

    2016-05-10

    The phase structure of holographic entanglement entropy is studied in massive gravity for the quantum systems with finite and infinite volumes, which in the bulk is dual to calculating the minimal surface area for a black hole and black brane respectively. In the entanglement entropy–temperature plane, we find for both the black hole and black brane there is a Van der Waals-like phase transition as the case in thermal entropy–temperature plane. That is, there is a first order phase transition for the small charge and a second order phase transition at the critical charge. For the first order phase transition, the equal area law is checked and for the second order phase transition, the critical exponent of the heat capacity is obtained. All the results show that the phase structure of holographic entanglement entropy is the same as that of thermal entropy regardless of the volume of the spacetime on the boundary.

  20. Phase transitions in operational risk.

    Science.gov (United States)

    Anand, Kartik; Kühn, Reimer

    2007-01-01

    In this paper we explore the functional correlation approach to operational risk. We consider networks with heterogeneous a priori conditional and unconditional failure probability. In the limit of sparse connectivity, self-consistent expressions for the dynamical evolution of order parameters are obtained. Under equilibrium conditions, expressions for the stationary states are also obtained. Consequences of the analytical theory developed are analyzed using phase diagrams. We find coexistence of operational and nonoperational phases, much as in liquid-gas systems. Such systems are susceptible to discontinuous phase transitions from the operational to nonoperational phase via catastrophic breakdown. We find this feature to be robust against variation of the microscopic modeling assumptions.

  1. Quantum gates with topological phases

    CERN Document Server

    Ionicioiu, R

    2003-01-01

    We investigate two models for performing topological quantum gates with the Aharonov-Bohm (AB) and Aharonov-Casher (AC) effects. Topological one- and two-qubit Abelian phases can be enacted with the AB effect using charge qubits, whereas the AC effect can be used to perform all single-qubit gates (Abelian and non-Abelian) for spin qubits. Possible experimental setups suitable for a solid state implementation are briefly discussed.

  2. Melonic phase transition in group field theory

    CERN Document Server

    Baratin, Aristide; Oriti, Daniele; Ryan, James P; Smerlak, Matteo

    2013-01-01

    Group field theories have recently been shown to admit a 1/N expansion dominated by so-called `melonic graphs', dual to triangulated spheres. In this note, we deepen the analysis of this melonic sector. We obtain a combinatorial formula for the melonic amplitudes in terms of a graph polynomial related to a higher dimensional generalization of the Kirchhoff tree-matrix theorem. Simple bounds on these amplitudes show the existence of a phase transition driven by melonic interaction processes. We restrict our study to the Boulatov-Ooguri models, which describe topological BF theories and are the basis for the construction of four dimensional models of quantum gravity.

  3. Quantum Phase Extraction in Isospectral Electronic Nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Moon, Christopher

    2010-04-28

    Quantum phase is not a direct observable and is usually determined by interferometric methods. We present a method to map complete electron wave functions, including internal quantum phase information, from measured single-state probability densities. We harness the mathematical discovery of drum-like manifolds bearing different shapes but identical resonances, and construct quantum isospectral nanostructures possessing matching electronic structure but divergent physical structure. Quantum measurement (scanning tunneling microscopy) of these 'quantum drums' [degenerate two-dimensional electron states on the Cu(111) surface confined by individually positioned CO molecules] reveals that isospectrality provides an extra topological degree of freedom enabling robust quantum state transplantation and phase extraction.

  4. Symmetry structure and phase transitions

    Indian Academy of Sciences (India)

    Ashok Goyal; Meenu Dahiya; Deepak Chandra

    2003-05-01

    We study chiral symmetry structure at finite density and temperature in the presence of external magnetic field and gravity, a situation relevant in the early Universe and in the core of compact stars. We then investigate the dynamical evolution of phase transition in the expanding early Universe and possible formation of quark nuggets and their survival.

  5. Phase transitions in finite systems

    Energy Technology Data Exchange (ETDEWEB)

    Chomaz, Ph. [Grand Accelerateur National d' Ions Lourds (GANIL), DSM-CEA / IN2P3-CNRS, 14 - Caen (France); Gulminelli, F. [Caen Univ., 14 (France). Lab. de Physique Corpusculaire

    2002-07-01

    In this series of lectures we will first review the general theory of phase transition in the framework of information theory and briefly address some of the well known mean field solutions of three dimensional problems. The theory of phase transitions in finite systems will then be discussed, with a special emphasis to the conceptual problems linked to a thermodynamical description for small, short-lived, open systems as metal clusters and data samples coming from nuclear collisions. The concept of negative heat capacity developed in the early seventies in the context of self-gravitating systems will be reinterpreted in the general framework of convexity anomalies of thermo-statistical potentials. The connection with the distribution of the order parameter will lead us to a definition of first order phase transitions in finite systems based on topology anomalies of the event distribution in the space of observations. Finally a careful study of the thermodynamical limit will provide a bridge with the standard theory of phase transitions and show that in a wide class of physical situations the different statistical ensembles are irreducibly inequivalent. (authors)

  6. Quantum charge pumps with topological phases in a Creutz ladder

    Science.gov (United States)

    Sun, Ning; Lim, Lih-King

    2017-07-01

    The quantum charge pumping phenomenon connects band topology through the dynamics of a one-dimensional quantum system. In terms of a microscopic model, the Su-Schrieffer-Heeger/Rice-Mele quantum pump continues to serve as a fruitful starting point for many considerations of topological physics. Here we present a generalized Creutz scheme as a distinct two-band quantum pump model. By noting that it undergoes two kinds of topological band transitions accompanying with a Zak-phase difference of π and 2 π , respectively, various charge pumping schemes are studied by applying an elaborate Peierls phase substitution. Translating into real space, the transportation of quantized charges is a result of cooperative quantum interference effect. In particular, an all-flux quantum pump emerges which operates with time-varying fluxes only and transports two charge units. This makes cold atoms with artificial gauge fields a unique system where this kind of phenomena can be realized.

  7. Controllable multiple-quantum transitions in a T-shaped small quantum dot-ring system

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Xiongwen, E-mail: hnsxw617@163.com [Department of Physics, Huaihua University, Huaihua 418008 (China); Chen, Baoju; Song, Kehui [Department of Physics, Huaihua University, Huaihua 418008 (China); Zhou, Guanghui [Department of Physics and Key Laboratory for Low-Dimensional Quantum Structures and Manipulation (Ministry of Education), Hunan Normal University, Changsha 410081 (China)

    2016-05-01

    Based on the tight-binding model and the slave boson mean field approximation, we investigate the electron transport properties in a small quantum dot (QD)-ring system. Namely, a strongly correlated QD not only attaches directly to two normal metallic electrodes, but also forms a magnetic control Aharonov–Bohm quantum ring with a few noninteracting QDs. We show that the parity effect, the Kondo effect, and the multiple Fano effects coexist in our system. Moreover, the parities, defined by the odd- and even-numbered energy levels in this system, can be switched by adjusting magnetic flux phase ϕ located at the center of the quantum ring, which induces multiple controllable Fano-interference energy pathways. Therefore, the constructive and destructive multi-Fano interference transition, the Kondo and Fano resonance transition at the Fermi level, the Fano resonance and ani-resonance transition are realized in the even parity system. They can also be observed in the odd parity system when one adjusts the phase ϕ and the gate voltage V{sub g} applied to the noninteracting QDs. The multi-quantum transitions determine some interesting transport properties such as the current switch and its multi-flatsteps, the differential conductance switch at zero bias voltage and its oscillation or quantization at the low bias voltage. These results may be useful for the observation of multiple quantum effect interplays experimentally and the design of controllable QD-based device.

  8. Controllable multiple-quantum transitions in a T-shaped small quantum dot-ring system

    Science.gov (United States)

    Chen, Xiongwen; Chen, Baoju; Song, Kehui; Zhou, Guanghui

    2016-05-01

    Based on the tight-binding model and the slave boson mean field approximation, we investigate the electron transport properties in a small quantum dot (QD)-ring system. Namely, a strongly correlated QD not only attaches directly to two normal metallic electrodes, but also forms a magnetic control Aharonov-Bohm quantum ring with a few noninteracting QDs. We show that the parity effect, the Kondo effect, and the multiple Fano effects coexist in our system. Moreover, the parities, defined by the odd- and even-numbered energy levels in this system, can be switched by adjusting magnetic flux phase ϕ located at the center of the quantum ring, which induces multiple controllable Fano-interference energy pathways. Therefore, the constructive and destructive multi-Fano interference transition, the Kondo and Fano resonance transition at the Fermi level, the Fano resonance and ani-resonance transition are realized in the even parity system. They can also be observed in the odd parity system when one adjusts the phase ϕ and the gate voltage Vg applied to the noninteracting QDs. The multi-quantum transitions determine some interesting transport properties such as the current switch and its multi-flatsteps, the differential conductance switch at zero bias voltage and its oscillation or quantization at the low bias voltage. These results may be useful for the observation of multiple quantum effect interplays experimentally and the design of controllable QD-based device.

  9. Topological phases: Wormholes in quantum matter

    NARCIS (Netherlands)

    Schoutens, K.

    2009-01-01

    Proliferation of so-called anyonic defects in a topological phase of quantum matter leads to a critical state that can be visualized as a 'quantum foam', with topology-changing fluctuations on all length scales.

  10. Entropy of phase measurement quantum phase via quadrature measurement

    CERN Document Server

    My, R; My, Robert; Uni, Palacky

    1995-01-01

    The content of phase information of an arbitrary phase--sensitive measurement is evaluated using the maximum likelihood estimation. The phase distribution is characterized by the relative entropy--a nonlinear functional of input quantum state. As an explicit example the multiple measurement of quadrature operator is interpreted as quantum phase detection achieving the ultimate resolution predicted by the Fisher information.

  11. Phase transitions and critical phenomena

    CERN Document Server

    Domb, Cyril

    2001-01-01

    The field of phase transitions and critical phenomena continues to be active in research, producing a steady stream of interesting and fruitful results. It has moved into a central place in condensed matter studies.Statistical physics, and more specifically, the theory of transitions between states of matter, more or less defines what we know about 'everyday' matter and its transformations.The major aim of this serial is to provide review articles that can serve as standard references for research workers in the field, and for graduate students and others wishing to obtain reliable in

  12. Resonant quantum transitions in trapped antihydrogen atoms

    CERN Document Server

    Amole, C; Baquero-Ruiz, M; Bertsche, W; Bowe, P D; Butler, E; Capra, A; Cesar, C L; Charlton, M; Deller, A; Donnan, P H; Eriksson, S; Fajans, J; Friesen, T; Fujiwara, M C; Gill, D R; Gutierrez, A; Hangst, J S; Hardy, W N; Hayden, M E; Humphries, A J; Isaac, C A; Jonsell, S; Kurchaninov, L; Little, A; Madsen, N; McKenna, J T K; Menary, S; Napoli, S C; Nolan, P; Olchanski, K; Olin, A; Pusa, P; Rasmussen, C Ø; Robicheaux, F; Sarid, E; Shields, C R; Silveira, D M; Stracka, S; So, C; Thompson, R I; van der Werf, D P; Wurtele, J S

    2012-01-01

    The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom’s stature lies in its simplicity and in the accuracy with which its spectrum can be measured1 and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and—by comparison with measurements on its antimatter counterpart, antihydrogen—the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state2, 3 of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave...

  13. Quantum criticality at the superconductor-insulator transition revealed by specific heat measurements.

    Science.gov (United States)

    Poran, S; Nguyen-Duc, T; Auerbach, A; Dupuis, N; Frydman, A; Bourgeois, Olivier

    2017-02-22

    The superconductor-insulator transition (SIT) is considered an excellent example of a quantum phase transition that is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low-energy fluctuations near quantum criticality may be experimentally detected by specific heat, cp, measurements. Here we use a unique highly sensitive experiment to measure cp of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature marking the onset of Cooper pairs formation. As the film thickness is tuned towards the SIT, is relatively unchanged, while the magnitude of the jump and low-temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition.

  14. Quantum criticality at the superconductor-insulator transition revealed by specific heat measurements

    Science.gov (United States)

    Poran, S.; Nguyen-Duc, T.; Auerbach, A.; Dupuis, N.; Frydman, A.; Bourgeois, Olivier

    2017-01-01

    The superconductor–insulator transition (SIT) is considered an excellent example of a quantum phase transition that is driven by quantum fluctuations at zero temperature. The quantum critical point is characterized by a diverging correlation length and a vanishing energy scale. Low-energy fluctuations near quantum criticality may be experimentally detected by specific heat, cp, measurements. Here we use a unique highly sensitive experiment to measure cp of two-dimensional granular Pb films through the SIT. The specific heat shows the usual jump at the mean field superconducting transition temperature marking the onset of Cooper pairs formation. As the film thickness is tuned towards the SIT, is relatively unchanged, while the magnitude of the jump and low-temperature specific heat increase significantly. This behaviour is taken as the thermodynamic fingerprint of quantum criticality in the vicinity of a quantum phase transition. PMID:28224994

  15. Quantum mechanics and the second law of thermodynamics: an insight gleaned from magnetic hysteresis in the first order phase transition of an isolated mesoscopic-size type I superconductor

    Science.gov (United States)

    Keefe, Peter D.

    2012-11-01

    J Bardeen proposed that the adiabatic phase transition of mesoscopic-size type I superconductors must be accompanied by magnetic hysteresis in the critical magnetic field of sufficient magnitude to satisfy the second law of thermodynamics, herein referred to as ‘Bardeen Hysteresis’. Bardeen Hysteresis remains speculative in that it has not been reported in the literature. This paper investigates Bardeen Hysteresis as a possible accompaniment to the adiabatic phase transition of isolated mesoscopic-size type I superconductors and its implications with respect to the second law of thermodynamics. A causal mechanism for Bardeen Hysteresis is discussed which contrasts with the long accepted causal mechanism of magnetic hysteresis, as first summarized by Pippard, herein referred to as ‘Pippard Hysteresis’. The paper offers guidance for an experimental verification and comments on how the existence of Bardeen Hysteresis has relation to a quantum mechanical basis for the second law of thermodynamics.

  16. Quantum phase diagram of Polar Molecules in 1D Double Wire Systems

    Science.gov (United States)

    Chang, Chi-Ming; Wang, Daw-Wei

    2007-03-01

    We study the quantum phase transitions of fermionic polar molecules loaded in a double wire potential. By tuning the magnitude and direction of external electric field we observed many interesting quantum phases in different parameter range, including an easy-plane spin density wave, a triplet superconducting phase, and a truly long range order of easy-axis ferromagnetic phase in strong interacting regime. We also discuss how these exotic quantum phases can be measured in the existing experimental techniques.

  17. The Semiclassical Regime of the Chaotic Quantum-Classical Transition

    CERN Document Server

    Greenbaum, B D; Shizume, K; Sundaram, B; Greenbaum, Benjamin D.; Habib, Salman; Shizume, Kosuke; Sundaram, Bala

    2004-01-01

    An analysis of the semiclassical regime of the quantum-classical transition is given for open, bounded, one dimensional chaotic dynamical systems. Previous numerical work has shown that in this regime, the results from a quantum master equation are very close to those obtained from a classical Fokker-Planck equation. We provide an explanation of these results by demonstrating that environmental noise plays the dual roles of suppressing the development of fine structure in classical phase space and damping nonlocal contributions to the semiclassical Wigner function. A numerical investigation of the chaotic Duffing oscillator supports these conclusions.

  18. Origin of time before inflation from a topological phase transition

    Science.gov (United States)

    Bellini, Mauricio

    2017-09-01

    We study the origin of the universe (or pre-inflation) by suggesting that the primordial space-time in the universe suffered a global topological phase transition, from a 4D Euclidean manifold to an asymptotic 4D hyperbolic one. We introduce a complex time, τ, such that its real part becomes dominant after started the topological phase transition. Before the big bang, τ is a space-like coordinate, so that can be considered as a reversal variable. After the phase transition is converted in a causal variable. The formalism solves in a natural manner the quantum to classical transition of the geometrical relativistic quantum fluctuations: σ, which has a geometric origin.

  19. Sliding Over a Phase Transition

    Science.gov (United States)

    Tosatti, Erio; Benassi, Andrea; Vanossi, Andrea; Santoro, Giuseppe E.

    2011-03-01

    The frictional response experienced by a stick-slip slider when a phase transition occurs in the underlying solid substrate is a potentially exciting, poorly explored problem. We show, based on 2-dimensional simulations modeling the sliding of a nanotip, that indeed friction may be heavily affected by a continuous structural transition. First, friction turns nonmonotonic as temperature crosses the transition, peaking at the critical temperature Tc where fluctuations are strongest. Second, below Tc friction depends upon order parameter directions, and is much larger for those where the frictional slip can cause a local flip. This may open a route towards control of atomic scale friction by switching the order parameter direction by an external field or strain, with possible application to e.g., displacive ferroelectrics such as BaTi O3 , as well as ferro- and antiferro-distortive materials. Supported by project ESF FANAS/AFRI sponsored by the Italian Research Council (CNR).

  20. Electroweak phase transition recent results

    CERN Document Server

    Csikor, Ferenc

    2000-01-01

    Recent results of four-dimensional (4d) lattice simulations on the finite temperature electroweak phase transition (EWPT) are discussed. The phase transition is of first order in the SU(2)-Higgs model below the end point Higgs mass 66.5$\\pm$1.4 GeV. For larger masses a rapid cross-over appears. This result completely agrees with the results of the dimensional reduction approach. Including the full Standard Model (SM) perturbatively the end point is at 72.1$\\pm$1.4 GeV. Combined with recent LEP Higgs mass lower bounds, this excludes any EWPT in the SM. A one-loop calculation of the static potential makes possible a precise comparison of the lattice and perturbative results. Recent 4d lattice studies of the Minimal Supersymmetric SM (MSSM) are also mentioned.

  1. Classifying the Quantum Phases of Matter

    Science.gov (United States)

    2015-01-01

    2013), arXiv:1305.2176. [10] J. Haah, Lattice quantum codes and exotic topological phases of matter , arXiv:1305.6973. [11[ M. Hastings and S...CLASSIFYING THE QUANTUM PHASES OF MATTER CALIFORNIA INSTITUTE OF TECHNOLOGY JANUARY 2015 FINAL TECHNICAL REPORT...REPORT 3. DATES COVERED (From - To) JAN 2012 – AUG 2014 4. TITLE AND SUBTITLE CLASSIFYING THE QUANTUM PHASES OF MATTER 5a. CONTRACT NUMBER FA8750-12-2

  2. Topological phase transitions in superradiance lattices

    CERN Document Server

    Wang, Da-Wei; Yuan, Luqi; Liu, Ren-Bao; Zhu, Shi-Yao

    2015-01-01

    The discovery of the quantum Hall effect (QHE) reveals a new class of matter phases, topological insulators (TI's), which have been extensively studied in solid-state materials and recently in photonic structures, time-periodic systems and optical lattices of cold atoms. All these topological systems are lattices in real space. Our recent study shows that Scully's timed Dicke states (TDS) can form a superradiance lattice (SL) in momentum space. Here we report the discovery of topological phase transitions in a two-dimensional SL in electromagnetically induced transparency (EIT). By periodically modulating the three EIT coupling fields, we can create a Haldane model with in-situ tunable topological properties. The Chern numbers of the energy bands and hence the topological properties of the SL manifest themselves in the contrast between diffraction signals emitted by superradiant TDS. The topological superradiance lattices (TSL) provide a controllable platform for simulating exotic phenomena in condensed matte...

  3. Chiral phase transitions in quantum chromodynamics at finite temperature: Hard-thermal-loop resummed Dyson–Schwinger equation in the real time formalism

    Indian Academy of Sciences (India)

    Hisao Nakkagawa; Hiroshi Yokota; Koji Yoshida; Yuko Fueki

    2003-05-01

    Chiral phase transition in thermal QCD is studied by using the Dyson–Schwinger (DS) equation in the real time hard thermal loop approximation. Our results on the critical temperature and the critical coupling are significantly different from those in the preceding analyses in the ladder DS equation, showing the importance of properly taking into account the essential thermal effects, namely the Landau damping and the unstable nature of thermal quasiparticles.

  4. Phase Diagram in Quantum Chromodynamics

    CERN Document Server

    Apostol, M

    2013-01-01

    It is suggested that the hadronization of the quark-gluon plasma is a first-order phase transition described by a critical curve in the temperature-(quark) density plane which terminates in a critical point. Such a critical curve is derived from the van der Waals equation and its parameters are estimated by using the theoretical approach given in M. Apostol, Roum. Reps. Phys. 59 249 (2007); Mod. Phys. Lett. B21 893 (2007). The main assumption is that quark-gluon plasma created by high-energy nucleus-nucleus collisions is a gas of ultrarelativistic quarks in equilibrium with gluons (vanishing chemical potential, indefinite number of quarks). This plasma expands, gets cool and dilute and hadronizes at a certain transition temperature and transition density. The transition density is very close to the saturation density of the nuclear matter and, it is suggested that both these points are very close to the critical point n~1fm^{-3} (quark density) and T~200MeV (temperature).

  5. Phase Information in Quantum Oracle Computing

    OpenAIRE

    Machta, J.

    1998-01-01

    Computational devices may be supplied with external sources of information (oracles). Quantum oracles may transmit phase information which is available to a quantum computer but not a classical computer. One consequence of this observation is that there is an oracle which is of no assistance to a classical computer but which allows a quantum computer to solve undecidable problems. Thus useful relativized separations between quantum and classical complexity classes must exclude the transmissio...

  6. Observation of topological transitions in interacting quantum circuits.

    Science.gov (United States)

    Roushan, P; Neill, C; Chen, Yu; Kolodrubetz, M; Quintana, C; Leung, N; Fang, M; Barends, R; Campbell, B; Chen, Z; Chiaro, B; Dunsworth, A; Jeffrey, E; Kelly, J; Megrant, A; Mutus, J; O'Malley, P J J; Sank, D; Vainsencher, A; Wenner, J; White, T; Polkovnikov, A; Cleland, A N; Martinis, J M

    2014-11-13

    Topology, with its abstract mathematical constructs, often manifests itself in physics and has a pivotal role in our understanding of natural phenomena. Notably, the discovery of topological phases in condensed-matter systems has changed the modern conception of phases of matter. The global nature of topological ordering, however, makes direct experimental probing an outstanding challenge. Present experimental tools are mainly indirect and, as a result, are inadequate for studying the topology of physical systems at a fundamental level. Here we employ the exquisite control afforded by state-of-the-art superconducting quantum circuits to investigate topological properties of various quantum systems. The essence of our approach is to infer geometric curvature by measuring the deflection of quantum trajectories in the curved space of the Hamiltonian. Topological properties are then revealed by integrating the curvature over closed surfaces, a quantum analogue of the Gauss-Bonnet theorem. We benchmark our technique by investigating basic topological concepts of the historically important Haldane model after mapping the momentum space of this condensed-matter model to the parameter space of a single-qubit Hamiltonian. In addition to constructing the topological phase diagram, we are able to visualize the microscopic spin texture of the associated states and their evolution across a topological phase transition. Going beyond non-interacting systems, we demonstrate the power of our method by studying topology in an interacting quantum system. This required a new qubit architecture that allows for simultaneous control over every term in a two-qubit Hamiltonian. By exploring the parameter space of this Hamiltonian, we discover the emergence of an interaction-induced topological phase. Our work establishes a powerful, generalizable experimental platform to study topological phenomena in quantum systems.

  7. Phase transitions at finite density

    CERN Document Server

    Friman, Bengt

    2012-01-01

    I discuss the analytic structure of thermodynamic quantities for complex values of thermodynamic variables within Landau theory. In particular, the singularities connected with phase transitions of second order, first order and cross over types are examined. A conformal mapping is introduced, which may be used to explore the thermodynamics of strongly interacting matter at finite values of the baryon chemical potential $\\mu$ starting from lattice QCD results at $\\mu^{2}\\leq 0$. This method allows us to improve the convergence of a Taylor expansion about $\\mu=0$ and to enhance the sensitivity to physical singularities in the complex $\\mu$ plane. The technique is illustrated by an application to a second-order transition in a chiral effective model.

  8. Second- and First-Order Phase Transitions in CDT

    CERN Document Server

    Ambjorn, J; Jurkiewicz, J; Loll, R

    2012-01-01

    Causal Dynamical Triangulations (CDT) is a proposal for a theory of quantum gravity, which implements a path-integral quantization of gravity as the continuum limit of a sum over piecewise flat spacetime geometries. We use Monte Carlo simulations to analyse the phase transition lines bordering the physically interesting de Sitter phase of the four-dimensional CDT model. Using a range of numerical criteria, we present strong evidence that the so-called A-C transition is first order, while the B-C transition is second order. The presence of a second-order transition may be related to an ultraviolet fixed point of quantum gravity and thus provide the key to probing physics at and possibly beyond the Planck scale.

  9. Interacting Weyl fermions: Phases, phase transitions, and global phase diagram

    Science.gov (United States)

    Roy, Bitan; Goswami, Pallab; Juričić, Vladimir

    2017-05-01

    We study the effects of short-range interactions on a generalized three-dimensional Weyl semimetal, where the band touching points act as the (anti)monopoles of Abelian Berry curvature of strength n . We show that any local interaction has a negative scaling dimension -2 /n . Consequently, all Weyl semimetals are stable against weak short-range interactions. For sufficiently strong interactions, we demonstrate that the Weyl semimetal either undergoes a first-order transition into a band insulator or a continuous transition into a symmetry breaking phase. A translational symmetry breaking axion insulator and a rotational symmetry breaking semimetal are two prominent candidates for the broken symmetry phase. At the one-loop order, the correlation length exponent for continuous transitions is ν =n /2 , indicating their non-Gaussian nature for any n >1 . We also discuss the scaling of the thermodynamic and transport quantities in general Weyl semimetals as well as inside broken symmetry phases.

  10. Phase Transition in Tensor Models

    CERN Document Server

    Delepouve, Thibault

    2015-01-01

    Generalizing matrix models, tensor models generate dynamical triangulations in any dimension and support a $1/N$ expansion. Using the intermediate field representation we explicitly rewrite a quartic tensor model as a field theory for a fluctuation field around a vacuum state corresponding to the resummation of the entire leading order in $1/N$ (a resummation of the melonic family). We then prove that the critical regime in which the continuum limit in the sense of dynamical triangulations is reached is precisely a phase transition in the field theory sense for the fluctuation field.

  11. Gibbs measures and phase transitions

    CERN Document Server

    Georgii, Hans-Otto

    2011-01-01

    From a review of the first edition: ""This book […] covers in depth a broad range of topics in the mathematical theory of phase transition in statistical mechanics. […] It is in fact one of the author's stated aims that this comprehensive monograph should serve both as an introductory text and as a reference for the expert."" (F. Papangelou, Zentralblatt MATH) The second edition has been extended by a new section on large deviations and some comments on the more recent developments in the area.

  12. Light scattering near phase transitions

    CERN Document Server

    Cummins, HZ

    1983-01-01

    Since the development of the laser in the early 1960's, light scattering has played an increasingly crucial role in the investigation of many types of phase transitions and the published work in this field is now widely dispersed in a large number of books and journals.A comprehensive overview of contemporary theoretical and experimental research in this field is presented here. The reviews are written by authors who have actively contributed to the developments that have taken place in both Eastern and Western countries.

  13. Phase transitions and critical phenomena

    CERN Document Server

    Domb, Cyril

    2000-01-01

    The field of phase transitions and critical phenomena continues to be active in research, producing a steady stream of interesting and fruitful results. No longer an area of specialist interest, it has acquired a central focus in condensed matter studies. The major aim of this serial is to provide review articles that can serve as standard references for research workers in the field, and for graduate students and others wishing to obtain reliable information on important recent developments.The two review articles in this volume complement each other in a remarkable way. Both deal with what m

  14. Semiclassics of the Chaotic Quantum-Classical Transition

    CERN Document Server

    Greenbaum, B D; Shizume, K; Sundaram, B; Greenbaum, Benjamin D.; Habib, Salman; Shizume, Kosuke; Sundaram, Bala

    2006-01-01

    We elucidate the basic physical mechanisms responsible for the quantum-classical transition in one-dimensional, bounded chaotic systems subject to unconditioned environmental interactions. We show that such a transition occurs due to the dual role of noise in regularizing the semiclassical Wigner function and averaging over fine structures in classical phase space. The results are interpreted in the novel context of applying recent advances in the theory of measurement and open systems to the semiclassical quantum regime. We use these methods to show how a local semiclassical picture is stabilized and can then be approximated by a classical distribution at arbitrary times. The general results are demonstrated explicitly via numerical simulations of the chaotic Duffing oscillator.

  15. Continuous quantum phase transitions in the one-dimensional spin-1/2 axial next-nearest-neighbour Ising model in two orthogonal magnetic fields

    Indian Academy of Sciences (India)

    Kunle Adegoke; Helmut Büttner

    2010-02-01

    We have investigated the one-dimensional spin-1/2 axial next-nearest-neighbour Ising (ANNNI) model in two orthogonal magnetic fields at zero temperature. There are four different possible ground state configurations for the ANNNI model in a longitudinal field, in the thermodynamic limit. The inclusion of a transverse field introduces quantum fluctuations which destroy the existing spin order along certain critical lines. The effects of the fluctuations in three of the four ordered regions were investigated using the finite-size scaling technique. The phase boundaries of the ANNNI model in two orthogonal magnetic fields were thus determined numerically. For certain limits of the Hamiltonian we compared the obtained results with the existing literature and our results were in good agreement with the results in the existing literature.

  16. Switchable Metal-Insulator Phase Transition Metamaterials.

    Science.gov (United States)

    Hajisalem, Ghazal; Nezami, Mohammadreza S; Gordon, Reuven

    2017-05-10

    We investigate the switching of a gap plasmon tunnel junction between conducting and insulating states. Hysteresis is observed in the second and the third harmonic generation power dependence, which arises by thermally induced disorder ("melting") of a two-carbon self-assembled monolayer between an ultraflat gold surface and metal nanoparticles. The hysteresis is observed for a variety of nanoparticle sizes, but not for larger tunnel junctions where there is no appreciable tunneling. By combining quantum corrected finite-difference time-domain simulations with nonlinear scattering theory, we calculate the changes in the harmonic generation between the tunneling and the insulating states, and good agreement is found with the experiments. This paves the way to a new class of metal-insulator phase transition switchable metamaterials, which may provide next-generation information processing technologies.

  17. Valleytronics and phase transition in silicene

    Science.gov (United States)

    Aftab, Tayyaba

    2017-03-01

    Magnetic and transport properties of silicene in the presence of perpendicular electromagnetic fields and a ferromagnetic material are studied. It is shown that for small exchange field, the magnetic moment associated with each valley is opposite for the other and it gives a shift in band energy, by a Zeeman-like coupling term. Thus opening a new horizon for valley-orbit coupling. Magnetic proximity effect is seen to adjust the spintronics of each valley. Valley polarization is calculated using the semi classical formulation of electron dynamics. It can be modified and measured due to its contribution in Hall conductivity. Quantum phase transitions are observed in silicene, providing a tool to control the topological state experimentally. The strong dependence of the physical properties on valley degree of freedom is an important step towards valleytronics.

  18. Phase space methods for degenerate quantum gases

    CERN Document Server

    Dalton, Bryan J; Barnett, Stephen M

    2015-01-01

    Recent experimental progress has enabled cold atomic gases to be studied at nano-kelvin temperatures, creating new states of matter where quantum degeneracy occurs - Bose-Einstein condensates and degenerate Fermi gases. Such quantum states are of macroscopic dimensions. This book presents the phase space theory approach for treating the physics of degenerate quantum gases, an approach already widely used in quantum optics. However, degenerate quantum gases involve massive bosonic and fermionic atoms, not massless photons. The book begins with a review of Fock states for systems of identical atoms, where large numbers of atoms occupy the various single particle states or modes. First, separate modes are considered, and here the quantum density operator is represented by a phase space distribution function of phase space variables which replace mode annihilation, creation operators, the dynamical equation for the density operator determines a Fokker-Planck equation for the distribution function, and measurable...

  19. The quantum phase operator a review

    CERN Document Server

    Barnett, Stephen M

    2013-01-01

    Describing the phase of an electromagnetic field mode or harmonic oscillator has been an obstacle since the early days of modern quantum theory. The quantum phase operator was even more problematic with the invention of the maser and laser in the 1950s and 1960s. This problem was not solved until the Pegg-Barnett formalism was developed in the 1980s. Edited by one of the scientists who created this key solution, The Quantum Phase Operator: A Review charts the development of phase and angle operators from their first appearance to modern theory. Bringing together vital works that have been publ

  20. Behavior of the Lyapunov Exponent and Phase Transition in Nuclei

    Institute of Scientific and Technical Information of China (English)

    WANG Nan; WU Xi-Zhen; LI Zhu-Xia; WANG Ning; ZHUO Yi-Zhong; SUN Xiu-Quan

    2000-01-01

    Based on the quantum molecular dynamics model, we investigate the dynamical behaviors of the excited nuclear system to simulate the latter stage of heavy ion reactions, which associate with a liquid-gas phase transition. We try to search a microscopic way to describe the phase transition in realnuclei. The Lyapunov exponent is employed and examined for our purpose. We find out that the Lyapunov exponent is one of good microscopic quantities to describe the phase transition in hot nuclei. Coulomb potential and the finite size effect may give a strong influence on the critical temperature. However, the collision term plays a minor role in the process of the liquid-gas phase transition in finite systems.

  1. Quark Deconfinement Phase Transition in Neutron Stars

    CERN Document Server

    Alaverdyan, G B

    2009-01-01

    The hadron-quark phase transition in the interior of compact stars is investigated, when the transition proceeds through a mixed phase. The hadronic phase is described in the framework of relativistic mean-field theory, when also the scalar-isovector delta-meson mean-field is taken into account. The changes of the parameters of phase transition caused by the presence of delta-meson field are explored. The results of calculation of structure of the mixed phase (Glendenning construction) are compared with the results of usual first-order phase transition (Maxwell construction).

  2. Interacting Weyl fermions: Phases, phase transitions and global phase diagram

    CERN Document Server

    Roy, Bitan; Juricic, Vladimir

    2016-01-01

    We study the effects of short-range interactions on a generalized three-dimensional Weyl semimetal, where the band touching points act as the (anti)monopoles of Abelian Berry curvature of strength $n$. We show that any local interaction has a \\emph{negative} scaling dimension $-2/n$. Consequently all Weyl semimetals are stable against weak short-range interactions. For sufficiently strong interactions, we demonstrate that the Weyl semimetal either undergoes a first order transition into a band insulator or a continuous transition into a symmetry breaking phase. A translational symmetry breaking axion insulator and a rotational symmetry breaking semimetal are two prominent candidates for the broken symmetry phase. At one loop level, the correlation length exponent for continuous transitions is $\

  3. Efimov-driven phase transitions of the unitary Bose gas.

    Science.gov (United States)

    Piatecki, Swann; Krauth, Werner

    2014-03-20

    Initially predicted in nuclear physics, Efimov trimers are bound configurations of three quantum particles that fall apart when any one of them is removed. They open a window into a rich quantum world that has become the focus of intense experimental and theoretical research, as the region of 'unitary' interactions, where Efimov trimers form, is now accessible in cold-atom experiments. Here we use a path-integral Monte Carlo algorithm backed up by theoretical arguments to show that unitary bosons undergo a first-order phase transition from a normal gas to a superfluid Efimov liquid, bound by the same effects as Efimov trimers. A triple point separates these two phases and another superfluid phase, the conventional Bose-Einstein condensate, whose coexistence line with the Efimov liquid ends in a critical point. We discuss the prospects of observing the proposed phase transitions in cold-atom systems.

  4. The flat phase of quantum polymerized membranes

    CERN Document Server

    Coquand, O

    2016-01-01

    We investigate the flat phase of quantum polymerized phantom membranes by means of a nonperturbative renormalization group approach. We first implement this formalism for general quantum polymerized membranes and derive the flow equations that encompass both quantum and thermal fluctuations. We then deduce and analyze the flow equations relevant to study the flat phase and discuss their salient features : quantum to classical crossover and, in each of these regimes, strong to weak coupling crossover. We finally illustrate these features in the context of free standing graphene physics.

  5. Quantum Phase Analysis of Field-Free Molecular Alignment

    CERN Document Server

    Yun, Sang Jae; Lee, Jongmin; Nam, Chang Hee

    2015-01-01

    We present quantum mechanical explanations for unresolved phenomena observed in field-free molecular alignment by a femtosecond laser pulse. Quantum phase analysis of molecular rotational states reveals the physical origin of the following phenomena: strong alignment peaks appear periodically, and the temporal shape of each alignment peak changes in an orderly fashion depending on molecular species; the strongest alignment is not achieved at the first peak; the transition between aligned and anti-aligned states is very fast compared to the time scale of rotational dynamics. These features are understood in a unified way analogous to that describing a carrier-envelope-phase-stabilized mode-locked laser.

  6. Signals of the QCD Phase Transition in the Heavens

    CERN Document Server

    Schaffner-Bielich, J

    2007-01-01

    The modern phase diagram of strongly interacting matter reveals a rich structure at high-densities due to phase transitions related to the chiral symmetry of quantum chromodynamics (QCD) and the phenomenon of color superconductivity. These exotic phases have significant impacts on high-density astrophysics as the properties of neutron stars and the evolution of astrophysical systems as proto-neutron stars, core-collapse supernovae and neutron star mergers. Most recent pulsar mass measurements and constraints on neutron star radii are critically discussed. Astrophysical signals for exotic matter and phase transitions in high-density matter proposed recently in the literature are outlined. A strong first order phase transition leads to the emergence of a third family of compact stars besides white dwarfs and neutron stars. The different microphysics of quark matter results in an enhanced r-mode stability window for rotating compact stars compared to normal neutron stars. Future telescope and satellite data will...

  7. The Structural Phase Transition in Solid DCN

    DEFF Research Database (Denmark)

    Dietrich, O. W.; Mackenzie, Gordon A.; Pawley, G. S.

    1976-01-01

    Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase transition from a tetragonal to an orthorhombic form at 160 K is a first order transition. A transverse acoustic phonon mode, which has the symmetry of the transition was observed at very low energ...... energies and showed “softening” as the transition was approached from above.......Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase transition from a tetragonal to an orthorhombic form at 160 K is a first order transition. A transverse acoustic phonon mode, which has the symmetry of the transition was observed at very low...

  8. Efficient Computation of Transition State Resonances and Reaction Rates from a Quantum Normal Form

    NARCIS (Netherlands)

    Schubert, Roman; Waalkens, Holger; Wiggins, Stephen

    2006-01-01

    A quantum version of a recent formulation of transition state theory in phase space is presented. The theory developed provides an algorithm to compute quantum reaction rates and the associated Gamov-Siegert resonances with very high accuracy. The algorithm is especially efficient for multi-degree-o

  9. A Holographic Model of Quantum Hall Transition

    CERN Document Server

    Mezzalira, Andrea

    2015-01-01

    We consider a phenomenological holographic model, inspired by the D3/D7 system with a 2+1 dimensional intersection, at finite chemical potential and magnetic field. At large 't Hooft coupling the system is unstable and needs regularization; the UV cutoff can be decoupled by considering a certain double scaling limit. At finite chemical potential the model exhibits a phase transition between states with filling fractions plus and minus one--half as the magnetic field is varied. By varying the parameters of the model, this phase transition can be made to happen at arbitrary values of the magnetic field.

  10. QGP phase transition and multiplicity fluctuations

    Institute of Scientific and Technical Information of China (English)

    杨纯斌; 王晓荣; 蔡勖

    1997-01-01

    The scaled factorial moments in QGP phase transitions are studied analytically by the extended Ginzburg-Landau model.The dependence of InFq on phase space interval is different for the first- and second-order QGP phase transitions.When lnFq are fitted to polynomials of X=δ1/3,the relative sign between the fitted coefficients of X and bq,l calculated theoretically can be used to judge the order of phase transitions.Two sets of experimental data are reanalysed and the phase transitions are the first order for one set of data but the second order for another.

  11. Quantum superconductor-insulator transition: implications of BKT critical behavior.

    Science.gov (United States)

    Schneider, T; Weyeneth, S

    2013-07-31

    We explore the implications of Berezinskii-Kosterlitz-Thouless (BKT) critical behavior on the two-dimensional (2D) quantum superconductor-insulator (QSI) transition driven by the tuning parameter x. Concentrating on the sheet resistance R(x,T) BKT behavior implies: an explicit quantum scaling function for R(x,T) along the superconducting branch ending at the nonuniversal critical value Rc = R(xc); a BKT-transition line T(c)(x) [proportionality] (x - x(c))(zν[overline]), where z is the dynamic exponent and ν[overline] the exponent of the zero-temperature correlation length; independent estimates of zν[overline], z and ν[overline] from the x dependence of the nonuniversal parameters entering the BKT expression for the sheet resistance. To illustrate the potential and the implications of this scenario we analyze the data of Bollinger et al (2011 Nature 472 458) taken on gate voltage tuned epitaxial films of La2-xSrxCuO4 that are one unit cell in thickness. The resulting estimates, z ~/= 3.1 and ν[overline] ~/= 0.52, indicate a clean 2D-QSI critical point where hyperscaling, the proportionality between d/λ(2)(0) and Tc, and the correspondence between the quantum phase transitions in D dimensions and the classical ones in (D + z) dimensions are violated.

  12. Insights into phase transitions and entanglement from density functional theory

    Science.gov (United States)

    Wei, Bo-Bo

    2016-11-01

    Density functional theory (DFT) has met great success in solid state physics, quantum chemistry and in computational material sciences. In this work we show that DFT could shed light on phase transitions and entanglement at finite temperatures. Specifically, we show that the equilibrium state of an interacting quantum many-body system which is in thermal equilibrium with a heat bath at a fixed temperature is a universal functional of the first derivatives of the free energy with respect to temperature and other control parameters respectively. This insight from DFT enables us to express the average value of any physical observable and any entanglement measure as a universal functional of the first derivatives of the free energy with respect to temperature and other control parameters. Since phase transitions are marked by the nonanalytic behavior of free energy with respect to control parameters, the physical quantities and entanglement measures may present nonanalytic behavior at critical point inherited from their dependence on the first derivative of free energy. We use two solvable models to demonstrate these ideas. These results give new insights for phase transitions and provide new profound connections between entanglement and phase transitions in interacting quantum many-body physics.

  13. Structural phase transitions and topological defects in ion Coulomb crystals

    Energy Technology Data Exchange (ETDEWEB)

    Partner, Heather L. [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany); Nigmatullin, Ramil [Institute of Quantum Physics, Albert-Einstein Allee-11, Ulm University, 89069 Ulm (Germany); Burgermeister, Tobias; Keller, Jonas; Pyka, Karsten [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany); Plenio, Martin B. [Center for Integrated Quantum Science and Technology, Albert-Einstein-Allee 11, Ulm University, 89069 Ulm (Germany); Institute for Theoretical Physics, Albert-Einstein-Allee 11, Ulm University, 89069 Ulm (Germany); Retzker, Alex [Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Givat Ram (Israel); Zurek, Wojciech H. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87544 (United States); Campo, Adolfo del [Department of Physics, University of Massachusetts Boston, Boston, MA 02125 (United States); Mehlstäubler, Tanja E., E-mail: tanja.mehlstaeubler@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

    2015-03-01

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed nonadiabatically. For a second order phase transition, the Kibble–Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

  14. Structural phase transitions and topological defects in ion Coulomb crystals

    Energy Technology Data Exchange (ETDEWEB)

    Partner, Heather L. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Nigmatullin, Ramil [Institute of Quantum Physics, Ulm Univ., Ulm (Germany); Burgermeister, Tobias [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Keller, Jonas [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Pyka, Karsten [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Plenio, Martin B. [Center for Integrated Quantum Science and Technology, Ulm Univ., Ulm, (Germany):Institute for Theoretical Physics, Ulm Univ.,Ulm, (Germany); Retzker, Alex [Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram (Israel); Zurek, Wojciech Hubert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); del Campo, Adolfo [Univ. of Massachusetts, Amherst, MA (United States). Dept. of Physics; Mehlstaubler, Tanja E. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany)

    2014-11-19

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed non-adiabatically. For a second order phase transition, the Kibble-Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

  15. Current fluctuations at a phase transition

    Science.gov (United States)

    Gerschenfeld, A.; Derrida, B.

    2011-10-01

    The ABC model is a simple diffusive one-dimensional non-equilibrium system which exhibits a phase transition. Here we show that the cumulants of the currents of particles through the system become singular near the phase transition. At the transition, they exhibit an anomalous dependence on the system size (an anomalous Fourier's law). An effective theory for the dynamics of the single mode which becomes unstable at the transition allows one to predict this anomalous scaling.

  16. Unconventional geometric quantum phase gates with a cavity QED system

    Science.gov (United States)

    Zheng, Shi-Biao

    2004-11-01

    We propose a scheme for realizing two-qubit quantum phase gates via an unconventional geometric phase shift with atoms in a cavity. In the scheme the atoms interact simultaneously with a highly detuned cavity mode and a classical field. The atoms undergo no transitions during the gate operation, while the cavity mode is displaced along a circle in the phase space, aquiring a geometric phase conditional upon the atomic state. Under certain conditions, the atoms are disentangled with the cavity mode and thus the gate is insensitive to both the atomic spontaneous emission and the cavity decay.

  17. Phase transition for gluon field: a qualitative analysis

    CERN Document Server

    Dzhunushaliev, Vladimir

    2012-01-01

    The phase transition for SU(3) gauge field (without quarks) is considered. It is shown that the phase transition is due to the fact that at high temperatures the partition function should be calculated as for a gas of gluons, whereas at low temperatures as the sum over energy levels of correlated quantum states of SU(3) gauge field. A correlated quantum state for strongly interacting fields is defined as a nonperturbative quantum state of strongly interacting fields. The energy spectrum of these quantum states are discrete one. A lower bound of the phase transition temperature by comparing of the average energy for the perturbative and nonperturbative regimes is estimated (for glueball being in thermal equilibrium with the thermostat). It is shown that this quantity is associated with a mass gap. In a scalar model of glueball its energy is calculated. It is shown that this energy is the mass gap. If we set the glueball mass $ \\approx 1.5 \\cdot 10^3$ Mev then it is found that the corresponding value of couplin...

  18. Chiral phase transition in QED$_3$ at finite temperature

    CERN Document Server

    Wei, Wei; Zong, Hong-Shi

    2016-01-01

    Chiral phase transition in (2+1)-dimensional quantum electrodynamics (QED$_3$) at finite temperature is investigated in the framework of truncated Dyson-Schwinger equations (DSEs). We go beyond the widely used instantaneous approximation and adopt a method that retains the full frequency dependence of the fermion self-energy. We also take further step to include the effects of wave-function renormalizations and introduce a minimal dressing of the bare vertex. Finally, with the more complete solutions of the truncated DSEs, we revisit the study of chiral phase transition in finite-temperature QED$_3$.

  19. Holographic Phase Transition Probed by Nonlocal Observables

    Directory of Open Access Journals (Sweden)

    Xiao-Xiong Zeng

    2016-01-01

    Full Text Available From the viewpoint of holography, the phase structure of a 5-dimensional Reissner-Nordström-AdS black hole is probed by the two-point correlation function, Wilson loop, and entanglement entropy. As the case of thermal entropy, we find for all the probes that the black hole undergoes a Hawking-Page phase transition, a first-order phase transition, and a second-order phase transition successively before it reaches a stable phase. In addition, for these probes, we find that the equal area law for the first-order phase transition is valid always and the critical exponent of the heat capacity for the second-order phase transition coincides with that of the mean field theory regardless of the size of the boundary region.

  20. When is the deconfinement phase transition universal?

    CERN Document Server

    Holland, K; Wiese, U J

    2003-01-01

    Pure Yang-Mills theory has a finite-temperature phase transition, separating the confined and deconfined bulk phases. Svetitsky and Yaffe conjectured that if this phase transition is of second order, it belongs to the universality class of transitions for particular scalar field theories in one lower dimension. We examine Yang-Mills theory with the symplectic gauge groups Sp(N). We find new evidence supporting the Svetitsky-Yaffe conjecture and make our own conjecture as to which gauge theories have a universal second order deconfinement phase transition.

  1. 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.

  2. Signatures of a quantum Griffiths phase in a d-metal alloy close to its ferromagnetic quantum critical point.

    Science.gov (United States)

    Schroeder, Almut; Ubaid-Kassis, Sara; Vojta, Thomas

    2011-03-09

    We report magnetization measurements close to the ferromagnetic quantum phase transition of the d-metal alloy Ni(1 - x)V(x) at a vanadium concentration of x(c)≈11.4%. In the diluted regime (x > x(c)), the temperature (T) and magnetic field (H) dependences of the magnetization are characterized by nonuniversal power laws and display H/T scaling in a wide temperature and field range. The exponents vary strongly with x and follow the predictions of a quantum Griffiths phase. We also discuss the deviations and limits of the quantum Griffiths phase as well as the phase boundaries due to bulk and cluster physics.

  3. Quantum to classical transitions in causal relations

    Science.gov (United States)

    Ried, Katja; MacLean, Jean-Philippe W.; Spekkens, Robert W.; Resch, Kevin J.

    2017-06-01

    The landscape of causal relations that can hold among a set of systems in quantum theory is richer than in classical physics. In particular, a pair of time-ordered systems can be related as cause and effect or as the effects of a common cause, and each of these causal mechanisms can be coherent or not. Furthermore, one can combine these mechanisms in different ways: by probabilistically realizing either one or the other or by having both act simultaneously (termed a physical mixture). In the latter case, it is possible for the two mechanisms to be combined quantum coherently. Previous work has shown how to experimentally realize one example of each class of possible causal relations. Here, we make a theoretical and experimental study of the transitions between these classes. In particular, for each of the two distinct types of coherence that can exist in mixtures of common-cause and cause-effect relations—coherence in the individual causal pathways and coherence in the way the causal relations are combined—we determine how it degrades under noise and we confirm these expectations in a quantum-optical experiment.

  4. Finite-size scaling at quantum transitions

    Science.gov (United States)

    Campostrini, Massimo; Pelissetto, Andrea; Vicari, Ettore

    2014-03-01

    We develop the finite-size scaling (FSS) theory at quantum transitions. We consider various boundary conditions, such as open and periodic boundary conditions, and characterize the corrections to the leading FSS behavior. Using renormalization-group (RG) theory, we generalize the classical scaling ansatz to describe FSS in the quantum case, classifying the different sources of scaling corrections. We identify nonanalytic corrections due to irrelevant (bulk and boundary) RG perturbations and analytic contributions due to regular backgrounds and analytic expansions of the nonlinear scaling fields. To check the general predictions, we consider the quantum XY chain in a transverse field. For this model exact or numerically accurate results can be obtained by exploiting its fermionic quadratic representation. We study the FSS of several observables, such as the free energy, the energy differences between low-energy levels, correlation functions of the order parameter, etc., confirming the general predictions in all cases. Moreover, we consider bipartite entanglement entropies, which are characterized by the presence of additional scaling corrections, as predicted by conformal field theory.

  5. Resonant quantum transitions in trapped antihydrogen atoms.

    Science.gov (United States)

    Amole, C; Ashkezari, M D; Baquero-Ruiz, M; Bertsche, W; Bowe, P D; Butler, E; Capra, A; Cesar, C L; Charlton, M; Deller, A; Donnan, P H; Eriksson, S; Fajans, J; Friesen, T; Fujiwara, M C; Gill, D R; Gutierrez, A; Hangst, J S; Hardy, W N; Hayden, M E; Humphries, A J; Isaac, C A; Jonsell, S; Kurchaninov, L; Little, A; Madsen, N; McKenna, J T K; Menary, S; Napoli, S C; Nolan, P; Olchanski, K; Olin, A; Pusa, P; Rasmussen, C Ø; Robicheaux, F; Sarid, E; Shields, C R; Silveira, D M; Stracka, S; So, C; Thompson, R I; van der Werf, D P; Wurtele, J S

    2012-03-07

    The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom's stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and--by comparison with measurements on its antimatter counterpart, antihydrogen--the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.

  6. Crystal Phase Quantum Well Emission with Digital Control.

    Science.gov (United States)

    Assali, S; Lähnemann, J; Vu, T T T; Jöns, K D; Gagliano, L; Verheijen, M A; Akopian, N; Bakkers, E P A M; Haverkort, J E M

    2017-09-18

    One of the major challenges in the growth of quantum well and quantum dot heterostructures is the realization of atomically sharp interfaces. Nanowires provide a new opportunity to engineer the band structure as they facilitate the controlled switching of the crystal structure between the zinc-blende (ZB) and wurtzite (WZ) phases. Such a crystal phase switching results in the formation of crystal phase quantum wells (CPQWs) and quantum dots (CPQDs). For GaP CPQWs, the inherent electric fields due to the discontinuity of the spontaneous polarization at the WZ/ZB junctions lead to the confinement of both types of charge carriers at the opposite interfaces of the WZ/ZB/WZ structure. This confinement leads to a novel type of transition across a ZB flat plate barrier. Here, we show digital tuning of the visible emission of WZ/ZB/WZ CPQWs in a GaP nanowire by changing the thickness of the ZB barrier. The energy spacing between the sharp emission lines is uniform and is defined by the addition of single ZB monolayers. The controlled growth of identical quantum wells with atomically flat interfaces at predefined positions featuring digitally tunable discrete emission energies may provide a new route to further advance entangled photons in solid state quantum systems.

  7. A superconductor to superfluid phase transition in liquid metallic hydrogen.

    Science.gov (United States)

    Babaev, Egor; Sudbø, Asle; Ashcroft, N W

    2004-10-07

    Although hydrogen is the simplest of atoms, it does not form the simplest of solids or liquids. Quantum effects in these phases are considerable (a consequence of the light proton mass) and they have a demonstrable and often puzzling influence on many physical properties, including spatial order. To date, the structure of dense hydrogen remains experimentally elusive. Recent studies of the melting curve of hydrogen indicate that at high (but experimentally accessible) pressures, compressed hydrogen will adopt a liquid state, even at low temperatures. In reaching this phase, hydrogen is also projected to pass through an insulator-to-metal transition. This raises the possibility of new state of matter: a near ground-state liquid metal, and its ordered states in the quantum domain. Ordered quantum fluids are traditionally categorized as superconductors or superfluids; these respective systems feature dissipationless electrical currents or mass flow. Here we report a topological analysis of the projected phase of liquid metallic hydrogen, finding that it may represent a new type of ordered quantum fluid. Specifically, we show that liquid metallic hydrogen cannot be categorized exclusively as a superconductor or superfluid. We predict that, in the presence of a magnetic field, liquid metallic hydrogen will exhibit several phase transitions to ordered states, ranging from superconductors to superfluids.

  8. Phase transitions of quadrupolar fluids

    Science.gov (United States)

    O'Shea, Seamus F.; Dubey, Girija S.; Rasaiah, Jayendran C.

    1997-07-01

    Gibbs ensemble simulations are reported for Lennard-Jones particles with embedded quadrupoles of strength Q*=Q/(ɛσ5)1/2=2.0 where ɛ and σ are the Lennard-Jones parameters. Calculations revealing the effect of the dispersive forces on the liquid-vapor coexistence were carried out by scaling the attractive r-6 term in the Lennard-Jones pair potential by a factor λ ranging from 0 to 1. Liquid-vapor coexistence is observed for all values of λ including λ=0 for Q*=2.0, unlike the corresponding dipolar fluid studied by van Leeuwen and Smit et al. [Phys. Rev. Lett. 71, 3991 (1993)] which showed no phase transition below λ=0.35 when the reduced dipole moment μ*=2.0. The simulation data are analyzed to estimate the critical properties of the quadrupolar fluid and their dependence on the strength λ of the dispersive force. The critical temperature and pressure show a clear quadratic dependence on λ, while the density is less confidently identified as being linear in λ. The compressibility is roughly linear in λ.

  9. Hexatic and Microemulsion Phases in the 2d Quantum Plasma

    Science.gov (United States)

    Clark, Bryan; Casula, Michele; Ceperley, David

    2009-03-01

    It has been long known that the two-dimensional one component plasma supports both a Wigner-crystal and liquid phase. Classically [1,2], it is known that a hexatic phase exists but it is not known how this hexatic phase extends into the quantum regime. Moreover, at low temperature, phenomenological arguments [3] from Jamei, et. al. suggest the existence of microemulsion phases including stripes and bubbles. We use diffusion and path integral Monte Carlo to map out this phase diagram. We are able to extend the hexatic phase into the quantum regime as well as quantify the nature of the defects and exponents in the long range quantum system. We also specify the the nature, extent and existence (or lack thereof) of the expected low-T microemulsion phases. [0pt] [1] Muto, S. & Aoki, H. Crystallization of a classical two-dimensional electron system: Positional and orientational orders. Phys. Rev. B 59, 14911(1999).[0pt] [2] He, W.J. et al. Phase transition in a classical two-dimensional electron system. Phys. Rev. B 68, 195104(2003).[0pt] [3] Jamei, R., Kivelson, S. & Spivak, B. Universal Aspects of Coulomb-Frustrated Phase Separation. Phys. Rev. Lett. 94, 056805-4(2005).

  10. On Arbitrary Phases in Quantum Amplitude Amplification

    CERN Document Server

    Hoyer, P

    2000-01-01

    We consider the use of arbitrary phases in quantum amplitude amplification which is a generalization of quantum searching. We prove that the phase condition in amplitude amplification is given by $\\tan(\\phi/2)=\\tan(\\phi/2)(1-2a)$, where $\\phi$ and $\\phi$ are the phases used and where $a$ is the success probability of the given algorithm. Thus the choice of phases depends nontrivially and nonlinearly on the success probability. Utilizing this condition, we give methods for constructing quantum algorithms that succeed with certainty and for implementing arbitrary rotations. We also conclude that phase errors of order up to $\\frac{1}{\\sqrt{a}}$ can be tolerated in amplitude amplification.

  11. Joint estimation of phase and phase diffusion for quantum metrology

    CERN Document Server

    Vidrighin, Mihai D; Genoni, Marco G; Jin, Xian-Min; Kolthammer, W Steven; Kim, M S; Datta, Animesh; Barbieri, Marco; Walmsley, Ian A

    2014-01-01

    Phase estimation, at the heart of many quantum metrology and communication schemes, can be strongly affected by noise, whose amplitude may not be known, or might be subject to drift. Here, we investigate the joint estimation of a phase shift and the amplitude of phase diffusion, at the quantum limit. For several relevant instances, this multiparameter estimation problem can be effectively reshaped as a two-dimensional Hilbert space model, encompassing the description of an interferometer phase probed with relevant quantum states -- split single-photons, coherent states or N00N states. For these cases, we obtain a trade-off bound on the statistical variances for the joint estimation of phase and phase diffusion, as well as optimum measurement schemes. We use this bound to quantify the effectiveness of an actual experimental setup for joint parameter estimation for polarimetry. We conclude by discussing the form of the trade-off relations for more general states and measurements.

  12. Formulation and picture of quantum phase

    Institute of Scientific and Technical Information of China (English)

    YAO ZhiXin; ZHONG JianWei; PAN BaiLiang

    2009-01-01

    Based on the concept of classical phase, we formulate a new explanation for the quantum phase from the quantum mechanical point of view. The quantum phase is the canonically conjugate variable of an angular momentum operator, which corresponds to the angular position φ in an actual physical space with a classical reference frame, but it takes a complex exponential form e~(iφ)-cosφ+i sinφin the abstract Hilbert space of a quantum reference frame. This formulation is simply the famous Euler formula in a complex number field. In particular, when φ= π/2, the correlative quantum phase is a unitary pure imaginary number e~(iπ/2)=cos(π/2)+i sin(π/2) = i. By using a photon state-vector function that is the general solution of photon Schrodinger equation and can completely describe a photon's behavior, we discuss the relationship between the angular momentum of a photon and the phase of the photon; we also analyze the intrinsic relationship between the macroscopic light wave phase and the microscopic photon phase.

  13. Formulation and picture of quantum phase

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Based on the concept of classical phase,we formulate a new explanation for the quantum phase from the quantum mechanical point of view. The quantum phase is the canonically conjugate variable of an angular momentum operator,which corresponds to the angular position θ in an actual physical space with a classical reference frame,but it takes a complex exponential form eiθ≡cosθ +i sinθ in the abstract Hilbert space of a quantum reference frame. This formulation is simply the famous Euler formula in a complex number field. In particular,when θ = π/2,the correlative quantum phase is a unitary pure imaginary number eiπ/2 ≡cos(π/2)+i sin(π/2) ≡ i. By using a photon state-vector function that is the general solution of photon Schrdinger equation and can completely describe a photon’s behavior,we discuss the relationship between the angular momentum of a photon and the phase of the photon; we also analyze the intrinsic relationship between the macroscopic light wave phase and the microscopic photon phase.

  14. Phase transitions in the web of science

    Science.gov (United States)

    Phillips, J. C.

    2015-06-01

    The Internet age is changing the structure of science, and affecting interdisciplinary interactions. Publication profiles connecting mathematics with molecular biology and condensed matter physics over the last 40 years exhibit common phase transitions indicative of the critical role played by specific interdisciplinary interactions. The strengths of the phase transitions quantify the importance of interdisciplinary interactions.

  15. The Structural Phase Transition in Solid DCN

    DEFF Research Database (Denmark)

    Dietrich, O. W.; Mackenzie, Gordon A.; Pawley, G. S.

    1975-01-01

    Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase change from a tetragonal to an orthorhombic form at 160K is a first-order transition. A transverse acoustic phonon mode, which has the symmetry of the phase change, was observed at very low energies...... and showed 'softening' as the transition temperature was approached from above....

  16. SUSY and the Electroweak Phase Transition

    CERN Document Server

    Farrar, Glennys R S; Farrar, Glennys R.; Losada, Marta

    1996-01-01

    We analyze the effective 3 dimensional theory previously constructed for the MSSM and multi-Higgs models to determine the regions of parameter space in which the electroweak phase transition is sufficiently strong for a $B+L$ asymmetry to survive in the low temperature phase. We find that the inclusion of all supersymmetric scalars and all 1-loop corrections has the effect of enhancing the strength of the phase transition. Without a light stop or extension of the MSSM the phase transition is sufficiently first order only if the lightest Higgs mass $M_{h}\\lsi 70$ GeV and $tan\\beta\\lsi 1.75$.

  17. Quantum critical transport at a continuous metal-insulator transition

    OpenAIRE

    Haldar, P.; Laad, M. S.; Hassan, S. R.

    2016-01-01

    In contrast to the first-order correlation-driven Mott metal-insulator transition (MIT), contin- uous disorder-driven transitions are intrinsically quantum critical. Here, we investigate transport quantum criticality in the Falicov-Kimball model, a representative of the latter class in the "strong disorder" category. Employing cluster-dynamical mean-field theory (CDMFT), we find clear and anomalous quantum critical scaling behavior manifesting as perfect mirror symmetry of scaling curves on b...

  18. Dynamic symmetries and quantum nonadiabatic transitions

    Science.gov (United States)

    Li, Fuxiang; Sinitsyn, Nikolai A.

    2016-12-01

    Kramers degeneracy theorem is one of the basic results in quantum mechanics. According to it, the time-reversal symmetry makes each energy level of a half-integer spin system at least doubly degenerate, meaning the absence of transitions or scatterings between degenerate states if the Hamiltonian does not depend on time explicitly. We generalize this result to the case of explicitly time-dependent spin Hamiltonians. We prove that for a spin system with the total spin being a half integer, if its Hamiltonian and the evolution time interval are symmetric under a specifically defined time reversal operation, the scattering amplitude between an arbitrary initial state and its time reversed counterpart is exactly zero. We also discuss applications of this result to the multistate Landau-Zener (LZ) theory.

  19. Fluctuations and topological transitions of quantum Hall stripes: Nematics as anisotropic hexatics

    Science.gov (United States)

    Ettouhami, A. M.; Doiron, C. B.; Côté, R.

    2007-10-01

    We study fluctuations and topological melting transitions of quantum Hall stripes near half filling of intermediate Landau levels. Taking the stripe state to be an anisotropic Wigner crystal (AWC) allows us to identify the quantum Hall nematic state conjectured in previous studies of the two-dimensional (2D) electron gas as an anisotropic hexatic. The transition temperature from the AWC to the quantum Hall nematic state is explicitly calculated, and a tentative phase diagram for the 2D electron gas near half filling is suggested.

  20. Quantum Phases of Matter in Optical Lattices

    Science.gov (United States)

    2015-06-30

    findings contained in this report are those of the author(s) and should not contrued as an official Department of the Army position , policy or...phases in beyond-standard optical lattices”, Oct 25, 2013 Nikhil Monga, John Shumway, Kaden Hazzard, Erich Mueller, Steven Desch, " Renormalization of...Ho, “Cold Atoms in Curved Space ”, Quantum Materials-Perspectives and Opportunities, The Rice Center for Quantum Materials, December 15, 2014

  1. Decorated defect condensate: A window to unconventional quantum phases in Weyl semimetals

    Science.gov (United States)

    You, Yizhi

    2016-11-01

    We investigate the unconventional quantum phases in Weyl semimetals. The emergent boson fields, coupling with the Weyl fermion bilinears, contain a Wess-Zumino-Witten term or topological Θ term inherited from the momentum space monopoles carried by Weyl points. Three types of unconventional quantum critical points will be studied in the following order. (1) The transition between two distinct symmetry breaking phases whose criticality is beyond Landau's paradigm. (2) The transition between a symmetry breaking state to a topological ordered state. (3) The transition between 3 d topological order phase to trivial disordered phase whose criticality could be traced back to a Z2 symmetry breaking transition in 4 d . The essence of these unconventional critical points lies in the fact that the topological defect of an order parameter carries either a nontrivial quantum number or a topological term so the condensation of the defects would either break some symmetry or give rise to a topological order phase with nontrivial braiding statistics.

  2. Chirality effects on 2D phase transitions

    DEFF Research Database (Denmark)

    Scalas, E.; Brezesinski, G.; Möhwald, H.

    1996-01-01

    -nearest neighbours (NNN) and an NNN-distorted lattice is observed. At 5 degrees C, the transition pressure is 15 mN m(-1), whereas at 20 degrees C it is 18 mN m(-1). Chirality destroys this transition: the pure enantiomer always exhibits an oblique lattice with tilted molecules, and the azimuths of tilt...... and distortion continuously vary from a direction close to NN to a direction close to NNN. The nature of the phase transition and the influence of chirality on it are discussed within the framework of Landau's theory of phase transitions....

  3. New insight into the Berezinskii-Kosterlitz-Thouless phase transition

    CERN Document Server

    Gerber, Urs; Rejón-Barrera, Fernando G

    2014-01-01

    We investigate the 2d XY model by using the constraint angle action, which belongs to the class of topological lattice actions. These actions violate important features usually demanded for a lattice action, such as the correct classical continuum limit and the applicability of perturbation theory. Nevertheless, they still lead to the same universal quantum continuum limit and show excellent scaling behavior. By using the constraint angle action we gain new insight into the Berezinskii-Kosterlitz-Thouless phase transition of the 2d XY model. This phase transition is of special interest since it is one of the few examples of a phase transition beyond second order. It is of infinite order and therefore an essential phase transition. In particular, we observe an excellent scaling behavior of the helicity modulus, which characterizes this phase transition. We also observe that the mechanism of (un)binding vortex--anti-vortex pairs follows the usual pattern, although free vortices do not require any energy in the ...

  4. The geometric phase in quantum physics

    Energy Technology Data Exchange (ETDEWEB)

    Bohm, A.

    1993-03-01

    After an explanatory introduction, a quantum system in a classical time-dependent environment is discussed; an example is a magnetic moment in a classical magnetic field. At first, the general abelian case is discussed in the adiabatic approximation. Then the geometric phase for nonadiabatic change of the environment (Anandan--Aharonov phase) is introduced, and after that general cyclic (nonadiabatic) evolution is discussed. The mathematics of fiber bundles is introduced, and some of its results are used to describe the relation between the adiabatic Berry phase and the geometric phase for general cyclic evolution of a pure state. The discussion is restricted to the abelian, U(1) phase.

  5. Fluctuation-induced continuous transition and quantum criticality in Dirac semimetals

    Science.gov (United States)

    Classen, Laura; Herbut, Igor F.; Scherer, Michael M.

    2017-09-01

    We establish a scenario where fluctuations of new degrees of freedom at a quantum phase transition change the nature of a transition beyond the standard Landau-Ginzburg paradigm. To this end, we study the quantum phase transition of gapless Dirac fermions coupled to a Z3 symmetric order parameter within a Gross-Neveu-Yukawa model in 2+1 dimensions, appropriate for the Kekulé transition in honeycomb lattice materials. For this model, the standard Landau-Ginzburg approach suggests a first-order transition due to the symmetry-allowed cubic terms in the action. At zero temperature, however, quantum fluctuations of the massless Dirac fermions have to be included. We show that they reduce the putative first-order character of the transition and can even render it continuous, depending on the number of Dirac fermions Nf. A nonperturbative functional renormalization group approach is employed to investigate the phase transition for a wide range of fermion numbers and we obtain the critical Nf, where the nature of the transition changes. Furthermore, it is shown that for large Nf the change from the first to second order of the transition as a function of dimension occurs exactly in the physical 2+1 dimensions. We compute the critical exponents and predict sizable corrections to scaling for Nf=2 .

  6. Cosmological perturbations from an inhomogeneous phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Matsuda, Tomohiro, E-mail: matsuda@sit.ac.j [Laboratory of Physics, Saitama Institute of Technology, Fusaiji, Okabe-machi, Saitama 369-0293 (Japan)

    2009-07-21

    A mechanism for generating metric perturbations in inflationary models is considered. Long-wavelength inhomogeneities of light scalar fields in a decoupled sector may give rise to superhorizon fluctuations of couplings and masses in the low-energy effective action. Cosmological phase transitions may then occur that are not simultaneous in space, but occur with time lags in different Hubble patches that arise from the long-wavelength inhomogeneities. Here an interesting model in which cosmological perturbations may be created at the electroweak phase transition is considered. The results show that phase transitions may be a generic source of non-Gaussianity.

  7. On the quantum phase problem

    Energy Technology Data Exchange (ETDEWEB)

    Vargas-MartInez, J M; Moya-Cessa, H [INAOE, Coordinacion de Optica, Apartado Postal 51 y 216, 72000 Puebla (Mexico)

    2004-03-01

    Based on the phase operator introduced by Turski we present a formalism for phase that passes Barnett-Pegg's acid test giving the correct phase variance for a number state. We show that this formalism is in fact the radially integrated Q-function formalism that is used to obtain phase properties. It is also shown that depending on the commutation relation used for phase and number, the phase fluctuations for a coherent state obtained from the integrated Q-function tend to the 1/2{rho}{sup 2} limit while for the Pegg-Barnett formalism they tend to 1/(4{rho}{sup 2}+3/{pi}{sup 2}) just like the fluctuations from the integrated Wigner function, where {rho} is the amplitude of the coherent state00.

  8. Quantum phases of a qutrit

    Energy Technology Data Exchange (ETDEWEB)

    Klimov, Andrei B [Departamento de FIsica, Universidad de Guadalajara, Revolucion 1500, 44420 Guadalajara, Jalisco (Mexico); Sanchez-Soto, Luis L [Departamento de Optica, Facultad de FIsica, Universidad Complutense, 28040 Madrid (Spain); Guise, Hubert de [Department of Physics, Lakehead University, Thunder Bay, Ontario P7B 5E1 (Canada); Bjoerk, Gunnar [Department of Microelectronics and Information Technology, Royal Institute of Technology (KTH), Electrum 229, SE-164 40 Kista (Sweden)

    2004-04-02

    We consider various approaches to treat the phases of a qutrit. Although it is possible to represent qutrits in a convenient geometrical manner by resorting to a generalization of the Poincare sphere, we argue that the appropriate way of dealing with this problem is through phase operators associated with the algebra su(3). The rather unusual properties of these phases are caused by the small dimension of the system and are explored in detail. We also examine the positive operator-valued measures that can describe the qutrit phase properties.

  9. UNIVERSALITY OF PHASE TRANSITION DYNAMICS: TOPOLOGICAL DEFECTS FROM SYMMETRY BREAKING

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-02-13

    In the course of a non-equilibrium continuous phase transition, the dynamics ceases to be adiabatic in the vicinity of the critical point as a result of the critical slowing down (the divergence of the relaxation time in the neighborhood of the critical point). This enforces a local choice of the broken symmetry and can lead to the formation of topological defects. The Kibble-Zurek mechanism (KZM) was developed to describe the associated nonequilibrium dynamics and to estimate the density of defects as a function of the quench rate through the transition. During recent years, several new experiments investigating formation of defects in phase transitions induced by a quench both in classical and quantum mechanical systems were carried out. At the same time, some established results were called into question. We review and analyze the Kibble-Zurek mechanism focusing in particular on this surge of activity, and suggest possible directions for further progress.

  10. Entropic Phase Maps in Discrete Quantum Gravity

    Directory of Open Access Journals (Sweden)

    Benjamin F. Dribus

    2017-06-01

    Full Text Available Path summation offers a flexible general approach to quantum theory, including quantum gravity. In the latter setting, summation is performed over a space of evolutionary pathways in a history configuration space. Discrete causal histories called acyclic directed sets offer certain advantages over similar models appearing in the literature, such as causal sets. Path summation defined in terms of these histories enables derivation of discrete Schrödinger-type equations describing quantum spacetime dynamics for any suitable choice of algebraic quantities associated with each evolutionary pathway. These quantities, called phases, collectively define a phase map from the space of evolutionary pathways to a target object, such as the unit circle S 1 ⊂ C , or an analogue such as S 3 or S 7 . This paper explores the problem of identifying suitable phase maps for discrete quantum gravity, focusing on a class of S 1 -valued maps defined in terms of “structural increments” of histories, called terminal states. Invariants such as state automorphism groups determine multiplicities of states, and induce families of natural entropy functions. A phase map defined in terms of such a function is called an entropic phase map. The associated dynamical law may be viewed as an abstract combination of Schrödinger’s equation and the second law of thermodynamics.

  11. Supersymmetric phase transition in Josephson-tunnel-junction arrays

    Energy Technology Data Exchange (ETDEWEB)

    Foda, O.

    1988-08-31

    The fully frustrated XY model in two dimensions exhibits a vortex-unbinding as well as an Ising transition. If the Ising transition overlaps with the critical line that ends on the vortex transition: T/sub I/less than or equal toT/sub V/, then the model is equivalent, at the overlap temperature, to a free massless field theory of 1 boson and 1 Majorana fermion, which is a superconformal field theory, of central charge c=3/2. The model is experimentally realized in terms of an array of Josephson-tunnel junctions in a transverse magnetic field. The experiment reveals a phase transition consistent with T/sub I/=T/sub V/. Thus, at the critical temperature, the array provides a physical realization of a supersymmetric quantum field theory.

  12. Robust quantum data locking from phase modulation

    Science.gov (United States)

    Lupo, Cosmo; Wilde, Mark M.; Lloyd, Seth

    2014-08-01

    Quantum data locking is a uniquely quantum phenomenon that allows a relatively short key of constant size to (un)lock an arbitrarily long message encoded in a quantum state, in such a way that an eavesdropper who measures the state but does not know the key has essentially no information about the message. The application of quantum data locking in cryptography would allow one to overcome the limitations of the one-time pad encryption, which requires the key to have the same length as the message. However, it is known that the strength of quantum data locking is also its Achilles heel, as the leakage of a few bits of the key or the message may in principle allow the eavesdropper to unlock a disproportionate amount of information. In this paper we show that there exist quantum data locking schemes that can be made robust against information leakage by increasing the length of the key by a proportionate amount. This implies that a constant size key can still lock an arbitrarily long message as long as a fraction of it remains secret to the eavesdropper. Moreover, we greatly simplify the structure of the protocol by proving that phase modulation suffices to generate strong locking schemes, paving the way to optical experimental realizations. Also, we show that successful data locking protocols can be constructed using random code words, which very well could be helpful in discovering random codes for data locking over noisy quantum channels.

  13. Phase transitions, scaling and renormalisation in nonequilibrium systems

    CERN Document Server

    Hanney, T E

    2002-01-01

    critical fixed point. Extensions to include disorder, to higher dimensions, and to other models are all possible using the method. Using the mapping between the Master equation and the Schroedinger equation in imaginary time, this scaling procedure is rephrased as a new blocking for quantum-spin systems. Existing methods of real space renormalisation for quantum-spin systems are applied to a variety of previously unconsidered exclusion models. In particular, it is shown how such techniques can be applied to models whose dynamics conserve particle number. Finally, by applying a Trotter decomposition to the quantum-spin Hamiltonian, it is shown how a nonequilibrium exclusion model can be written in terms of a classical Hamiltonian for Ising spin variables in one higher dimension. This mapping admits the possibility rescaling time and length scales separately, and with reference to a specific update mechanism. Nonequilibrium phase transitions and critical phenomena in simple lattice-based interacting particle mo...

  14. Quantum Fourier Transform and Phase Estimation in Qudit System

    Institute of Scientific and Technical Information of China (English)

    CAO Ye; PENG Shi-Guo; ZHENG Chao; LONG Gui-Lu

    2011-01-01

    The quantum Fourier transform and quantum phase estimation are the key components for many quantum algorithms, such as order-finding, factoring, and etc.In this article, the general procedure of quantum Fourier transform and phase estimation are investigated for high dimensional case.They can be seen as subroutines in a main program run in a qudit quantum computer, and the quantum circuits are given.

  15. Magnetic Fields from the Electroweak Phase Transition

    CERN Document Server

    Törnkvist, O

    1998-01-01

    I review some of the mechanisms through which primordial magnetic fields may be created in the electroweak phase transition. I show that no magnetic fields are produced initially from two-bubble collisions in a first-order transition. The initial field produced in a three-bubble collision is computed. The evolution of fields at later times is discussed.

  16. The transition to chaotic phase synchronization

    DEFF Research Database (Denmark)

    Mosekilde, E.; Laugesen, J. L.; Zhusubaliyev, Zh. T.

    2012-01-01

    The transition to chaotic phase synchronization for a periodically driven spiral-type chaotic oscillator is known to involve a dense set of saddle-node bifurcations. By following the synchronization transition through the cascade of period-doubling bifurcations in a forced Ro¨ssler system, this p...

  17. A Gaussian measure of quantum phase noise

    Science.gov (United States)

    Schleich, Wolfgang P.; Dowling, Jonathan P.

    1992-01-01

    We study the width of the semiclassical phase distribution of a quantum state in its dependence on the average number of photons (m) in this state. As a measure of phase noise, we choose the width, delta phi, of the best Gaussian approximation to the dominant peak of this probability curve. For a coherent state, this width decreases with the square root of (m), whereas for a truncated phase state it decreases linearly with increasing (m). For an optimal phase state, delta phi decreases exponentially but so does the area caught underneath the peak: all the probability is stored in the broad wings of the distribution.

  18. Non-monotonicity in the quantum-classical transition: Chaos induced by quantum effects

    CERN Document Server

    Kapulkin, A; Kapulkin, Arie; Pattanayak, Arjendu K.

    2007-01-01

    The transition from classical to quantum behavior for chaotic systems is understood to be accompanied by the suppression of chaotic effects as the relative size of $\\hbar$ is increased. We show evidence to the contrary in the behavior of the quantum trajectory dynamics of a dissipative quantum chaotic system, the double-well Duffing oscillator. The classical limit in the case considered has regular behavior, but as the effective $\\hbar$ is increased we see chaotic behavior. This chaos then disappears deeper into the quantum regime, which means that the quantum-classical transition in this case is non-monotonic in $\\hbar$.

  19. Transit time MESFET phase shifter

    OpenAIRE

    Walters, Peter C.; Roger D. Pollard; Richardson, John R.

    1992-01-01

    The phase shift of a signal through a common-source MESFET can be changed with little effect on the amplitude by altering the gate-drain spacing. The feasibility of employing this principle to realize a highly compact, monolithic phase shifter has been investigated. The behaviour of the devices with differing gate-drain spacing has been measured and modelled and a design for a monolithic implementation is presented.

  20. Molecular markers of phase transition in locusts

    Institute of Scientific and Technical Information of China (English)

    ARNOLD DE LOOF; ILSE CLAEYS; GERT SIMONET; PETER VERLEYEN; TIM VANDERSMISSEN; FILIP SAS; JURGEN HUYBRECHTS

    2006-01-01

    The changes accompanying the transition from the gregarious to the solitary phase state in locusts are so drastic that for a long time these phases were considered as distinct species. It was Boris Uvarov who introduced the concept of polyphenism. Decades of research revealed that phase transition implies changes in morphometry, the color of the cuticle, behavior and several aspects of physiology. In particular, in the recent decade, quite a number of molecular studies have been undertaken to uncover phase-related differences.They resulted in novel insights into the role of corazonin, neuroparsins, some protease inhibitors, phenylacetonitrile and so on. The advent of EST-databases of locusts (e.g. Kang et al., 2004) is a most encouraging novel development in physiological and behavioral locust research. Yet, the answer to the most intriguing question, namely whether or not there is a primordial molecular inducer of phase transition, is probably not within reach in the very near future.

  1. Polymorphic phase transition in Superhydrous Phase B

    Science.gov (United States)

    Koch-Müller, M.; Dera, P.; Fei, Y.; Hellwig, H.; Liu, Z.; Orman, J. Van; Wirth, R.

    2005-09-01

    We synthesized superhydrous phase B (shy-B) at 22 GPa and two different temperatures: 1200°C (LT) and 1400°C (HT) using a multi-anvil apparatus. The samples were investigated by transmission electron microscopy (TEM), single crystal X-ray diffraction, Raman and IR spectroscopy. The IR spectra were collected on polycrystalline thin-films and single crystals using synchrotron radiation, as well as a conventional IR source at ambient conditions and in situ at various pressures (up to 15 GPa) and temperatures (down to -180°C). Our studies show that shy-B exists in two polymorphic forms. As expected from crystal chemistry, the LT polymorph crystallizes in a lower symmetry space group ( Pnn2), whereas the HT polymorph assumes a higher symmetry space group ( Pnnm). TEM shows that both modifications consist of nearly perfect crystals with almost no lattice defects or inclusions of additional phases. IR spectra taken on polycrystalline thin films exhibit just one symmetric OH band and 29 lattice modes for the HT polymorph in contrast to two intense but asymmetric OH stretching bands and at least 48 lattice modes for the LT sample. The IR spectra differ not only in the number of bands, but also in the response of the bands to changes in pressure. The pressure derivatives for the IR bands are higher for the HT polymorph indicating that the high symmetry form is more compressible than the low symmetry form. Polarized, low-temperature single-crystal IR spectra indicate that in the LT-polymorph extensive ordering occurs not only at the Mg sites but also at the hydrogen sites.

  2. Polymorphic Phase Transition in Superhydrous Phase B

    Energy Technology Data Exchange (ETDEWEB)

    Koch-Muller,M.; Dera, P.; Fei, Y.; Hellwig, H.; Liu, Z.; Van Orman, J.; Wirth, R.

    2005-01-01

    We synthesized superhydrous phase B (shy-B) at 22 GPa and two different temperatures: 1200 C (LT) and 1400 C (HT) using a multi-anvil apparatus. The samples were investigated by transmission electron microscopy (TEM), single crystal X-ray diffraction, Raman and IR spectroscopy. The IR spectra were collected on polycrystalline thin-films and single crystals using synchrotron radiation, as well as a conventional IR source at ambient conditions and in situ at various pressures (up to 15 GPa) and temperatures (down to -180 C). Our studies show that shy-B exists in two polymorphic forms. As expected from crystal chemistry, the LT polymorph crystallizes in a lower symmetry space group (Pnn2), whereas the HT polymorph assumes a higher symmetry space group (Pnnm). TEM shows that both modifications consist of nearly perfect crystals with almost no lattice defects or inclusions of additional phases. IR spectra taken on polycrystalline thin films exhibit just one symmetric OH band and 29 lattice modes for the HT polymorph in contrast to two intense but asymmetric OH stretching bands and at least 48 lattice modes for the LT sample. The IR spectra differ not only in the number of bands, but also in the response of the bands to changes in pressure. The pressure derivatives for the IR bands are higher for the HT polymorph indicating that the high symmetry form is more compressible than the low symmetry form. Polarized, low-temperature single-crystal IR spectra indicate that in the LT-polymorph extensive ordering occurs not only at the Mg sites but also at the hydrogen sites.

  3. Contemporary research of dynamically induced phase transitions

    Science.gov (United States)

    Hull, L. M.

    2017-01-01

    Dynamically induced phase transitions in metals, within the present discussion, are those that take place within a time scale characteristic of the shock waves and any reflections or rarefactions involved in the loading structure along with associated plastic flow. Contemporary topics of interest include the influence of loading wave shape, the effect of shear produced by directionality of the loading relative to the sample dimensions and initial velocity field, and the loading duration (kinetic effects, hysteresis) on the appearance and longevity of a transformed phase. These topics often arise while considering the loading of parts of various shapes with high explosives, are typically two or three-dimensional, and are often selected because of the potential of the transformed phase to significantly modify the motion. In this paper, we look at current work on phase transitions in metals influenced by shear reported in the literature, and relate recent work conducted at Los Alamos on iron's epsilon phase transition that indicates a significant response to shear produced by reflected elastic waves. A brief discussion of criteria for the occurrence of stress induced phase transitions is provided. Closing remarks regard certain physical processes, such as fragmentation and jet formation, which may be strongly influenced by phase transitions.

  4. Quantum Griffiths singularity of superconductor-metal transition in Ga thin films.

    Science.gov (United States)

    Xing, Ying; Zhang, Hui-Min; Fu, Hai-Long; Liu, Haiwen; Sun, Yi; Peng, Jun-Ping; Wang, Fa; Lin, Xi; Ma, Xu-Cun; Xue, Qi-Kun; Wang, Jian; Xie, X C

    2015-10-30

    The Griffiths singularity in a phase transition, caused by disorder effects, was predicted more than 40 years ago. Its signature, the divergence of the dynamical critical exponent, is challenging to observe experimentally. We report the experimental observation of the quantum Griffiths singularity in a two-dimensional superconducting system. We measured the transport properties of atomically thin gallium films and found that the films undergo superconductor-metal transitions with increasing magnetic field. Approaching the zero-temperature quantum critical point, we observed divergence of the dynamical critical exponent, which is consistent with the Griffiths singularity behavior. We interpret the observed superconductor-metal quantum phase transition as the infinite-randomness critical point, where the properties of the system are controlled by rare large superconducting regions.

  5. Novel understanding for the transitions in the ultra-quantum limit of graphite

    Science.gov (United States)

    Zhu, Zengwei; McDonald, Ross; Shekhter, Arkady; Ramshaw, Brad; Modic, Kimberly; Balakirev, Fedor; Harrison, Neil

    2015-03-01

    A fascinating transition was documented in the ultra-quantum limit of graphite between 22T and 53T. Recently, another unexpected high-field transition was observed around 75T. The relative simple band structure, though the complicated phase transitions, suggesting more researches should be carried out to understand the mysterious transitions. We performed temperature- and angle-dependent in-plane and out-of-plane magnetoresistance measurements in the ultra-quantum limit on graphite. Our experiments reveal the transition between 22T and 53T is more complicating and interesting than the previous reports. We explain the cause of the transition properly with novel understanding. This research performed under the DOE BES ``Science at 100 tesla'' and supported at the NHMFL by NSF Cooperative Agreement No. DMR-1157490. Z. Z acknowledges the supports from LANL ``Director's funding'' and Chinese ``Youth 1000 Talents Plan.''

  6. Quantum entanglement transition in vertically coupledtwo single-electron quantum dots with charged impurity

    Institute of Scientific and Technical Information of China (English)

    MANZhong-xiao; ZHANGZhan-jun

    2004-01-01

    Effects of a charged impurity on the ground state of two vertically coupled identical single-electron quantum dots with and without applied magnetic field are investigated. In the absence of the magnetic field, the investigations of the charged impurity effect on the quantum entanglement (QE) in some low-lying states are carried out. It is found that, both the positive charged impurity (PCI) and the negative charged impurity (NCI)reduce the QE in the low-lying states under oonsideration except that the QE in the ground state is enhanced by the NCI. Additionally, in the domain of B from 0 Tesla to 15 Tesla, the ground state energy E, the ground state angular momentum L and the ground state QE entropy S are worked out. As far as the ground state are concerned, the PCI (NCI) blocks (induces) the angular momentum phase transition and the QE phase transition besides the known fact (i. e., the PCI/NCI decreases/increases the energy) in the magnetic field.

  7. Quantum entanglement transition in vertically coupled two single-electron quantum dots with charged impurity

    Institute of Scientific and Technical Information of China (English)

    MAN Zhong-xiao; ZHANG Zhan-jun

    2004-01-01

    Effects of a charged impurity on the ground state of two vertically coupled identical single-electron quantum dots with and without applied magnetic field are investigated. In the absence of the magnetic field, the investigations of the charged impurity effect on the quantum entanglement (QE) in some low-lying states are carried out. It is found that, both the positive charged impurity (PCI) and the negative charged impurity (NCI)reduce the QE in the low-lying states under consideration except that the QE in the ground state is enhanced by the NCI. Additionally, in the domain of B from 0 Tesla to 15 Tesla, the ground state energy E, the ground state angular momentum L and the ground state QE entropy S are worked out. As far as the ground state are concerned, the PCI (NCI) blocks (induces) the angular momentum phase transition and the QE phase transition besides the known fact (i. e., the PCI/NCI decreases/increases the energy) in the magnetic field.

  8. Photoluminescence response of colloidal quantum dots on VO2 film across metal to insulator transition.

    Science.gov (United States)

    Kuznetsov, Sergey N; Cheremisin, Alexander B; Stefanovich, Genrikh B

    2014-01-01

    We have proposed a method to probe metal to insulator transition in VO2 measuring photoluminescence response of colloidal quantum dots deposited on the VO2 film. In addition to linear luminescence intensity decrease with temperature that is well known for quantum dots, temperature ranges with enhanced photoluminescence changes have been found during phase transition in the oxide. Corresponding temperature derived from luminescence dependence on temperature closely correlates with that from resistance measurement during heating. The supporting reflectance data point out that photoluminescence response mimics a reflectance change in VO2 across metal to insulator transition. Time-resolved photoluminescence study did not reveal any significant change of luminescence lifetime of deposited quantum dots under metal to insulator transition. It is a strong argument in favor of the proposed explanation based on the reflectance data. 71.30. + h; 73.21.La; 78.47.jd.

  9. An absorbing phase transition from a structured active particle phase

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, Cristobal [Instituto Mediterraneo de Estudios Avanzados IMEDEA (CSIC-UIB), Campus de la Universidad de las Islas Baleares, E-07122 Palma de Mallorca (Spain); Ramos, Francisco [Departamento de Electromagnetismo y Fisica de la Materia and Instituto de Fisica Teorica y Computacional Carlos I, Facultad de Ciencias, Universidad de Granada, 18071 Granada (Spain); Hernandez-GarcIa, Emilio [Instituto Mediterraneo de Estudios Avanzados IMEDEA (CSIC-UIB), Campus de la Universidad de las Islas Baleares, E-07122 Palma de Mallorca (Spain)

    2007-02-14

    In this work we study the absorbing state phase transition of a recently introduced model for interacting particles with neighbourhood-dependent reproduction rates. The novelty of the transition is that as soon as the active phase is reached by increasing a control parameter a periodically arranged structure of particle clusters appears. A numerical study in one and two dimensions shows that the system falls into the directed percolation universality class.

  10. Quantum Theory of Hyperfine Structure Transitions in Diatomic Molecules.

    Science.gov (United States)

    Klempt, E.; And Others

    1979-01-01

    Described is an advanced undergraduate laboratory experiment in which radio-frequency transitions between molecular hyperfine structure states may be observed. Aspects of the quantum theory applied to the analysis of this physical system, are discussed. (Authors/BT)

  11. Magnetic phase transitions in layered intermetallic compounds

    Science.gov (United States)

    Mushnikov, N. V.; Gerasimov, E. G.; Rosenfeld, E. V.; Terent'ev, P. B.; Gaviko, V. S.

    2012-10-01

    Magnetic, magnetoelastic, and magnetotransport properties have been studied for the RMn2Si2 and RMn6Sn6 (R is a rare earth metal) intermetallic compounds with natural layered structure. The compounds exhibit wide variety of magnetic structures and magnetic phase transitions. Substitution of different R atoms allows us to modify the interatomic distances and interlayer exchange interactions thus providing the transition from antiferromagnetic to ferromagnetic state. Near the boundary of this transition the magnetic structures are very sensitive to the external field, temperature and pressure. The field-induced transitions are accompanied by considerable change in the sample size and resistivity. It has been shown that various magnetic structures and magnetic phase transitions observed in the layered compounds arise as a result of competition of the Mn-Mn and Mn-R exchange interactions.

  12. Numerical Study of Phase Transition in Thermoviscoelasticity

    Institute of Scientific and Technical Information of China (English)

    ShaoqingTANG

    1997-01-01

    We study the spatially periodic problem of thermoviscoelasticity with nonmonotone structure relations.By pseudo-spectral method.we demosnstrate numerically phase transitions for certain symmetric initial data.Without symmetry,the simulations show that a translation occurs for the phase boundary.

  13. Extended ensemble theory, spontaneous symmetry breaking, and phase transitions

    Science.gov (United States)

    Xiao, Ming-wen

    2006-09-01

    In this paper, as a personal review, we suppose a possible extension of Gibbs ensemble theory so that it can provide a reasonable description of phase transitions and spontaneous symmetry breaking. The extension is founded on three hypotheses, and can be regarded as a microscopic edition of the Landau phenomenological theory of phase transitions. Within its framework, the stable state of a system is determined by the evolution of order parameter with temperature according to such a principle that the entropy of the system will reach its minimum in this state. The evolution of order parameter can cause a change in representation of the system Hamiltonian; different phases will realize different representations, respectively; a phase transition amounts to a representation transformation. Physically, it turns out that phase transitions originate from the automatic interference among matter waves as the temperature is cooled down. Typical quantum many-body systems are studied with this extended ensemble theory. We regain the Bardeen Cooper Schrieffer solution for the weak-coupling superconductivity, and prove that it is stable. We find that negative-temperature and laser phases arise from the same mechanism as phase transitions, and that they are unstable. For the ideal Bose gas, we demonstrate that it will produce Bose Einstein condensation (BEC) in the thermodynamic limit, which confirms exactly Einstein's deep physical insight. In contrast, there is no BEC either within the phonon gas in a black body or within the ideal photon gas in a solid body. We prove that it is not admissible to quantize the Dirac field by using Bose Einstein statistics. We show that a structural phase transition belongs physically to the BEC happening in configuration space, and that a double-well anharmonic system will undergo a structural phase transition at a finite temperature. For the O(N)-symmetric vector model, we demonstrate that it will yield spontaneous symmetry breaking and produce

  14. A Continuous Transition Between Quantum and Classical Mechanics (I)

    OpenAIRE

    Ghose, Partha

    2001-01-01

    In spite of its popularity, it has not been possible to vindicate the conventional wisdom that classical mechanics is a limiting case of quantum mechanics. The purpose of the present paper is to offer an alternative formulation of classical mechanics which provides a continuous transition to quantum mechanics via environment-induced decoherence.

  15. Quantum-to-classical transition in cavity quantum electrodynamics.

    Science.gov (United States)

    Fink, J M; Steffen, L; Studer, P; Bishop, Lev S; Baur, M; Bianchetti, R; Bozyigit, D; Lang, C; Filipp, S; Leek, P J; Wallraff, A

    2010-10-15

    The quantum properties of electromagnetic, mechanical or other harmonic oscillators can be revealed by investigating their strong coherent coupling to a single quantum two level system in an approach known as cavity quantum electrodynamics (QED). At temperatures much lower than the characteristic energy level spacing the observation of vacuum Rabi oscillations or mode splittings with one or a few quanta asserts the quantum nature of the oscillator. Here, we study how the classical response of a cavity QED system emerges from the quantum one when its thermal occupation-or effective temperature-is raised gradually over 5 orders of magnitude. In this way we explore in detail the continuous quantum-to-classical crossover and demonstrate how to extract effective cavity field temperatures from both spectroscopic and time-resolved vacuum Rabi measurements.

  16. Phase Transition in the Simplest Plasma Model

    CERN Document Server

    Iosilevskiy, Igor

    2009-01-01

    We have investigated the phase transition of the gas-liquid type, with an upper critical point, in a variant of the One Component Plasma model (OCP) that has a uniform but compressible compensating background. We have calculated the parameters of the critical and triple points, spinodals, and two-phase coexistence curves (binodals). We have analyzed the connection of this simplest plasma phase transition with anomalies in the spatial charge profiles of equilibrium non-uniform plasma in the local-density approximations of Thomas-Fermi or Poisson-Boltzmann-type.

  17. Theory of phase transitions rigorous results

    CERN Document Server

    Sinai, Ya G

    1982-01-01

    Theory of Phase Transitions: Rigorous Results is inspired by lectures on mathematical problems of statistical physics presented in the Mathematical Institute of the Hungarian Academy of Sciences, Budapest. The aim of the book is to expound a series of rigorous results about the theory of phase transitions. The book consists of four chapters, wherein the first chapter discusses the Hamiltonian, its symmetry group, and the limit Gibbs distributions corresponding to a given Hamiltonian. The second chapter studies the phase diagrams of lattice models that are considered at low temperatures. The no

  18. End point of the electroweak phase transition

    CERN Document Server

    Csikor, Ferenc; Heitger, J; Aoki, Y; Ukawa, A

    1999-01-01

    We study the hot electroweak phase transition (EWPT) by 4-dimensional lattice simulations on lattices with symmetric and asymmetric lattice spacings and give the phase diagram. A continuum extrapolation is done. We find first order phase transition for Higgs-boson masses $m_H<66.5 \\pm 1.4$ GeV. Above this end point a rapid cross-over occurs. Our result agrees with that of the dimensional reduction approach. It also indicates that the fermionic sector of the Standard Model (SM) may be included perturbatively. We get for the SM end point $72.4 the SM.

  19. Quantum transitions and quantum entanglement from Dirac-like dynamics simulated by trapped ions

    Science.gov (United States)

    Bittencourt, Victor A. S. V.; Bernardini, Alex E.; Blasone, Massimo

    2016-05-01

    Quantum transition probabilities and quantum entanglement for two-qubit states of a four-level trapped ion quantum system are computed for time-evolving ionic states driven by Jaynes-Cummings Hamiltonians with interactions mapped onto a SU(2 )⊗SU(2 ) group structure. Using the correspondence of the method of simulating a 3 +1 dimensional Dirac-like Hamiltonian for bispinor particles into a single trapped ion, one preliminarily obtains the analytical tools for describing ionic state transition probabilities as a typical quantum oscillation feature. For Dirac-like structures driven by generalized Poincaré classes of coupling potentials, one also identifies the SU(2 )⊗SU(2 ) internal degrees of freedom corresponding to intrinsic parity and spin polarization as an adaptive platform for computing the quantum entanglement between the internal quantum subsystems which define two-qubit ionic states. The obtained quantum correlational content is then translated into the quantum entanglement of two-qubit ionic states with quantum numbers related to the total angular momentum and to its projection onto the direction of the trapping magnetic field. Experimentally, the controllable parameters simulated by ion traps can be mapped into a Dirac-like system in the presence of an electrostatic field which, in this case, is associated to ionic carrier interactions. Besides exhibiting a complete analytical profile for ionic quantum transitions and quantum entanglement, our results indicate that carrier interactions actively drive an overall suppression of the quantum entanglement.

  20. Phase Transition Induced Fission in Lipid Vesicles

    CERN Document Server

    Leirer, C; Myles, V M; Schneider, M F

    2010-01-01

    In this work we demonstrate how the first order phase transition in giant unilamellar vesicles (GUVs) can function as a trigger for membrane fission. When driven through their gel-fluid phase transition GUVs exhibit budding or pearl formation. These buds remain connected to the mother vesicle presumably by a small neck. Cooling these vesicles from the fluid phase (T>Tm) through the phase transition into the gel state (T