The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the...The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearestneighbor(NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.展开更多
Loschmidt’s paradox is extended by replacing its assumption of time reversibility with full CPT symmetry. Mobility is identified as a means for expressing collisions or dissipation, and the cross product of its gradi...Loschmidt’s paradox is extended by replacing its assumption of time reversibility with full CPT symmetry. Mobility is identified as a means for expressing collisions or dissipation, and the cross product of its gradient with the magnetic field, for expressing parity. Three phenomena incorporating such cross products are identified. The first is the cross product of the mobility gradient with the magnetic field. The second combines this cross product with the E cross B drift. The third is the reciprocal of the Nernst effect expressed as a cross product of the temperature gradient and the magnetic field. Simulations are conducted for testing Loschmidt’s extended paradox. Onsager’s exclusion of magnetic fields and rotation from reciprocals violates CPT symmetry and is unjustified. All three cross-product phenomena skew statistics in a fashion unanticipated by Boltzmann’s assumptions in his H-Theorem. CPT symmetric systems fall outside the assumptions of the theorem which is not rendered invalid but simply limited to its domain of applicability. Therefore, these systems do not violate the second law as Boltzmann defines it. They bypass it.展开更多
The effect of the three-site interaction （α） on the critical behaviors of the XY spin chain is studied in terms of the Loschmidt echo （LE）. The critical lines can be shifted by α, and the anisotropy parameter of...The effect of the three-site interaction （α） on the critical behaviors of the XY spin chain is studied in terms of the Loschmidt echo （LE）. The critical lines can be shifted by α, and the anisotropy parameter of the XY chain has no effect on the critical lines. The scaling behaviors of the LE reveal that the dynamical behaviors of the LE are reliable for characterizing quantum phase transition （QPT）.展开更多
By introducing the Dzyaloshinsky-Moriya （DM） interaction, the Loschmidt Echo （LE） of a quantum sys- tem consisting of a central spin and its surrounding environment characterized by an XY spin chain was investigat...By introducing the Dzyaloshinsky-Moriya （DM） interaction, the Loschmidt Echo （LE） of a quantum sys- tem consisting of a central spin and its surrounding environment characterized by an XY spin chain was investigated analytically and numerically. At the critical points of the magnetic field, the LE presents an obvious decay. The decay amplitude can be tuned by the DM interaction. In some specific intervals the DM interaction can remarkably delay the decay of the LE. On the other hand, the DM interaction can change the effects of the anisotropy parameter on the LE.展开更多
Quantum dynamics of many-body systems is a fascinating and significant subject for both theory and experiment.The question of how an isolated many-body system evolves to its steady state after a sudden perturbation or...Quantum dynamics of many-body systems is a fascinating and significant subject for both theory and experiment.The question of how an isolated many-body system evolves to its steady state after a sudden perturbation or quench still remains challenging.In this paper,using the Bethe ansatz wave function,we study the quantum dynamics of an inhomogeneous Gaudin magnet.We derive explicit analytical expressions for various local dynamic quantities with an arbitrary number of flipped bath spins,such as:the spin distribution function,the spin-spin correlation function,and the Loschmidt echo.We also numerically study the relaxation behavior of these dynamic properties,gaining considerable insight into coherence and entanglement between the central spin and the bath.In particular,we find that the spin-spin correlations relax to their steady value via a nearly logarithmic scaling,whereas the Loschmidt echo shows an exponential relaxation to its steady value.Our results advance the understanding of relaxation dynamics and quantum correlations of long-range interacting models of the Gaudin type.展开更多
One of the issues of Thermodynamics is the question of what exactly thermo-dynamic equilibrium means.It is often interpreted as thermalequilibrium.The question is if this is correct.This is especially relevant for the...One of the issues of Thermodynamics is the question of what exactly thermo-dynamic equilibrium means.It is often interpreted as thermalequilibrium.The question is if this is correct.This is especially relevant for the case of the atmosphere,where gravitational energy also plays a role,which might allow for temperature gradients in equilibrium.In order to answer this question,this work goes back to Boltzmann’s original ideas.As will be shown here,thermo-dynamic equilibrium also means thermal equilibrium in this case.Moreover,it will also be shown why a lapse rate(a linear drop of temperature with alti-tude)is observed in a mechanically stable atmosphere.The implications for climate research are discussed.展开更多
Dynamical quantum phase transitions(DQPTs),characterized by non-analytic behavior in rate function and abrupt changes in dynamic topological order parameters(DTOPs)over time,have garnered enormous attention in recent ...Dynamical quantum phase transitions(DQPTs),characterized by non-analytic behavior in rate function and abrupt changes in dynamic topological order parameters(DTOPs)over time,have garnered enormous attention in recent decades.However,in non-Hermitian systems,the special biorthogonality of the bases makes the definition of DQPTs complex.In this work,we delve into the comprehensive investigation of self-normal DQPTs(originally used in Hermitian systems)to compare them with their biorthogonal counterpart,within the context of non-Hermitian quantum walks(QWs).We present a detailed analysis of the behaviors of Loschmidt rate functions and DTOPs under these two distinct theoretical approaches.While both self-normal and biorthogonal methods can be used to detect DQPTs in quench dynamics between different topological phases,we theoretically present their differences in the definition of critical momenta and critical times by analyzing the Fisher zeros and fixed points.Finally,we present an experiment that observes both types of DQPTs using one-dimensional discrete-time QWs with single photons.展开更多
基金supported in part by the Key-Area Research and Development Program of Guang-Dong Province, China (Grant No. 2018B030326001)the National Key R&D Program of China (Grant No. 2017YFA0304300)+5 种基金supported by the Japan Society for the Promotion of Science (JSPS) (Postdoctoral Fellowship via Grant No. P19326, and KAKENHI via Grant No. JP19F19326)support from the Natural Science Foundation of Beijing, China (Grant No. Z190012)the National Natural Science Foundation of of China (Grant No. 11890704)support from the National Natural Science Foundation of China (Grant No. T2121001)Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000)Beijing Natural Science Foundation, China (Grant No. Z200009)。
文摘The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearestneighbor(NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.
文摘Loschmidt’s paradox is extended by replacing its assumption of time reversibility with full CPT symmetry. Mobility is identified as a means for expressing collisions or dissipation, and the cross product of its gradient with the magnetic field, for expressing parity. Three phenomena incorporating such cross products are identified. The first is the cross product of the mobility gradient with the magnetic field. The second combines this cross product with the E cross B drift. The third is the reciprocal of the Nernst effect expressed as a cross product of the temperature gradient and the magnetic field. Simulations are conducted for testing Loschmidt’s extended paradox. Onsager’s exclusion of magnetic fields and rotation from reciprocals violates CPT symmetry and is unjustified. All three cross-product phenomena skew statistics in a fashion unanticipated by Boltzmann’s assumptions in his H-Theorem. CPT symmetric systems fall outside the assumptions of the theorem which is not rendered invalid but simply limited to its domain of applicability. Therefore, these systems do not violate the second law as Boltzmann defines it. They bypass it.
基金Supported by Natural Science Foundation of Shanxi Province of China (2010JM1011)Science Foundation of Xi’an University of Posts and Telecommunications(1050409)
文摘The effect of the three-site interaction （α） on the critical behaviors of the XY spin chain is studied in terms of the Loschmidt echo （LE）. The critical lines can be shifted by α, and the anisotropy parameter of the XY chain has no effect on the critical lines. The scaling behaviors of the LE reveal that the dynamical behaviors of the LE are reliable for characterizing quantum phase transition （QPT）.
基金Supported by Scientific Research Project for Shaanxi Provincial Department of Education(12Jk0957)Science Foundation of Xi’an University of Posts and Telecommunications(1050409,1051206)
文摘By introducing the Dzyaloshinsky-Moriya （DM） interaction, the Loschmidt Echo （LE） of a quantum sys- tem consisting of a central spin and its surrounding environment characterized by an XY spin chain was investigated analytically and numerically. At the critical points of the magnetic field, the LE presents an obvious decay. The decay amplitude can be tuned by the DM interaction. In some specific intervals the DM interaction can remarkably delay the decay of the LE. On the other hand, the DM interaction can change the effects of the anisotropy parameter on the LE.
基金support from NSAF(Grant No.U1930402)supported by the key NSFC grant No.12134015 and No.11874393+2 种基金the National Key R&D Program of China No.2017YFA0304500,the National Key R&D Program of China No.2016YFA0301200support from NSFC(Grants No.11974040 and No.12150610464),NSFC 11734002financial support from National Science Association Funds U1930402
文摘Quantum dynamics of many-body systems is a fascinating and significant subject for both theory and experiment.The question of how an isolated many-body system evolves to its steady state after a sudden perturbation or quench still remains challenging.In this paper,using the Bethe ansatz wave function,we study the quantum dynamics of an inhomogeneous Gaudin magnet.We derive explicit analytical expressions for various local dynamic quantities with an arbitrary number of flipped bath spins,such as:the spin distribution function,the spin-spin correlation function,and the Loschmidt echo.We also numerically study the relaxation behavior of these dynamic properties,gaining considerable insight into coherence and entanglement between the central spin and the bath.In particular,we find that the spin-spin correlations relax to their steady value via a nearly logarithmic scaling,whereas the Loschmidt echo shows an exponential relaxation to its steady value.Our results advance the understanding of relaxation dynamics and quantum correlations of long-range interacting models of the Gaudin type.
文摘One of the issues of Thermodynamics is the question of what exactly thermo-dynamic equilibrium means.It is often interpreted as thermalequilibrium.The question is if this is correct.This is especially relevant for the case of the atmosphere,where gravitational energy also plays a role,which might allow for temperature gradients in equilibrium.In order to answer this question,this work goes back to Boltzmann’s original ideas.As will be shown here,thermo-dynamic equilibrium also means thermal equilibrium in this case.Moreover,it will also be shown why a lapse rate(a linear drop of temperature with alti-tude)is observed in a mechanically stable atmosphere.The implications for climate research are discussed.
基金supported by the National Key R&D Program of China(Grant No.2023YFA1406701)National Natural Science Foundation of China(Grants No.12025401,92265209,12474352,92476106,and 12088101)Kunkun Wang and Lei Xiao acknowledge support from Beijing National Laboratory for Condensed Matter Physics(No.2024BNLCMPKF010).
文摘Dynamical quantum phase transitions(DQPTs),characterized by non-analytic behavior in rate function and abrupt changes in dynamic topological order parameters(DTOPs)over time,have garnered enormous attention in recent decades.However,in non-Hermitian systems,the special biorthogonality of the bases makes the definition of DQPTs complex.In this work,we delve into the comprehensive investigation of self-normal DQPTs(originally used in Hermitian systems)to compare them with their biorthogonal counterpart,within the context of non-Hermitian quantum walks(QWs).We present a detailed analysis of the behaviors of Loschmidt rate functions and DTOPs under these two distinct theoretical approaches.While both self-normal and biorthogonal methods can be used to detect DQPTs in quench dynamics between different topological phases,we theoretically present their differences in the definition of critical momenta and critical times by analyzing the Fisher zeros and fixed points.Finally,we present an experiment that observes both types of DQPTs using one-dimensional discrete-time QWs with single photons.
