A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the ＂quantum speed-up capacity＂ which ...A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the ＂quantum speed-up capacity＂ which reveals the potential ability of a quantum system to be accelerated. We explore the evolutions of the speed-up capacity in different quantum channels for two-qubit states. We find that although the dynamics of the capacity is varying in different kinds of channels, it is positive in most situations which are considered in the context except one case in the amplitude-damping channel. We give the reasons for the different features of the dynamics. Anyway, the speed-up capacity can be improved by the memory effect. We find two ways which may be used to control the capacity in an experiment： selecting an appropriate coefficient of an initial state or changing the memory degree of environments.展开更多
Many quantum systems of interest are initially correlated with their environments and the reduced dynamics of open systems are an interesting while challenging topic. Affine maps, as an extension of completely positiv...Many quantum systems of interest are initially correlated with their environments and the reduced dynamics of open systems are an interesting while challenging topic. Affine maps, as an extension of completely positive maps, are a useful tool to describe the reduced dynamics of open systems with initial correlations. However, it is unciear what kind of initial state shares an affine map. In this study, we give a sumcient condition of initial states, in which the reduced dynamics can always be described by an affihe map. Our result shows that if the initial states of the combined system constitute a convex set, and if the correspondence between the initial states of the open system and those of the combined system, defined by taking the partial trace, is a bijection, then the reduced dynamics of the open system can be described by an affine map.展开更多
For the n-qubit stochastic open quantum systems,based on the Lyapunov stability theorem and LaSalle’s invariant set principle,a pure state switching control based on on-line estimated state feedback(short for OQST-SF...For the n-qubit stochastic open quantum systems,based on the Lyapunov stability theorem and LaSalle’s invariant set principle,a pure state switching control based on on-line estimated state feedback(short for OQST-SFC)is proposed to realize the state transition the pure state of the target state including eigenstate and superposition state.The proposed switching control consists of a constant control and a control law designed based on the Lyapunov method,in which the Lyapunov function is the state distance of the system.The constant control is used to drive the system state from an initial state to the convergence domain only containing the target state,and a Lyapunov-based control is used to make the state enter the convergence domain and then continue to converge to the target state.At the same time,the continuous weak measurement of quantum system and the quantum state tomography method based on the on-line alternating direction multiplier(QST-OADM)are used to obtain the system information and estimate the quantum state which is used as the input of the quantum system controller.Then,the pure state feedback switching control method based on the on-line estimated state feedback is realized in an n-qubit stochastic open quantum system.The complete derivation process of n-qubit QST-OADM algorithm is given;Through strict theoretical proof and analysis,the convergence conditions to ensure any initial state of the quantum system to converge the target pure state are given.The proposed control method is applied to a 2-qubit stochastic open quantum system for numerical simulation experiments.Four possible different position cases between the initial estimated state and that of the controlled system are studied and discussed,and the performances of the state transition under the corresponding cases are analyzed.展开更多
In this paper, the structure characteristics of open complex giant systems are concretely analysed in depth, thus the view and its significance to support the meta synthesis engineering with manifold knowledge models...In this paper, the structure characteristics of open complex giant systems are concretely analysed in depth, thus the view and its significance to support the meta synthesis engineering with manifold knowledge models are clarified. Furthermore, the knowledge based multifaceted modeling methodology for open complex giant systems is emphatically studied. The major points are as follows: (1) nonlinear mechanism and general information partition law; (2) from the symmetry and similarity to the acquisition of construction knowledge; (3) structures for hierarchical and nonhierarchical organizations; (4) the integration of manifold knowledge models; (5) the methodology of knowledge based multifaceted modeling.展开更多
We propose and discuss a novel concept of robust set stabilization by permissible controls; this concept is helpful when dealing with both a priori information of model parameters and different permissible controls in...We propose and discuss a novel concept of robust set stabilization by permissible controls; this concept is helpful when dealing with both a priori information of model parameters and different permissible controls including quantum measurements. Both controllability and stabilization can be regarded as the special case of the novel concept. An instance is presented for a kind of uncertain open quantum systems to further justify this gen- eralized concept. It is underlined that a new type of hybrid control based on periodically perturbed projective measurements can be the permissible control of uncertain open quantum systems when perturbed projective measurements are available. The sufficient conditions are given for the robust set stabilization of uncertain quantum open systems by the hybrid control, and the design of the hybrid control is reduced to selecting the period of measurements.展开更多
We investigate the quantum thermal transistor effect in nonequilibrium three-level systems by applying the polarontransformed Redfield equation combined with full counting statistics.The steady state heat currents are...We investigate the quantum thermal transistor effect in nonequilibrium three-level systems by applying the polarontransformed Redfield equation combined with full counting statistics.The steady state heat currents are obtained via this unified approach over a wide region of system–bath coupling,and can be analytically reduced to the Redfield and nonequilibrium noninteracting blip approximation results in the weak and strong coupling limits,respectively.A giant heat amplification phenomenon emerges in the strong system–bath coupling limit,where transitions mediated by the middle thermal bath are found to be crucial to unravel the underlying mechanism.Moreover,the heat amplification is also exhibited with moderate coupling strength,which can be properly explained within the polaron framework.展开更多
In open quantum systems,the Liouvillian gap characterizes the relaxation time toward the steady state.However,accurately computing this quantity is notoriously difficult due to the exponential growth of the Hilbert sp...In open quantum systems,the Liouvillian gap characterizes the relaxation time toward the steady state.However,accurately computing this quantity is notoriously difficult due to the exponential growth of the Hilbert space and the non-Hermitian nature of the Liouvillian superoperator.In this work,we propose a variational quantum algorithm for efficiently estimating the Liouvillian gap.By utilizing the Choi-Jamio lkowski isomorphism,we reformulate the problem as finding the first excitation energy of an effective non-Hermitian Hamiltonian.Our method employs variance minimization with an orthogonality constraint to locate the first excited state and adopts a two-stage optimization scheme to enhance convergence.Moreover,to address scenarios with degenerate steady states,we introduce an iterative energy-offset scanning technique.Numerical simulations on the dissipative XXZ model confirm the accuracy and robustness of our algorithm across a range of system sizes and dissipation strengths.These results demonstrate the promise of variational quantum algorithms for simulating open quantum many-body systems on near-term quantum hardware.展开更多
Non-Hermiticity can lead to the emergence of many intriguing phenomena that are absent in Hermitian systems,enabled by exceptional topological defects,among which Weyl exceptional rings(WER)are particularly interestin...Non-Hermiticity can lead to the emergence of many intriguing phenomena that are absent in Hermitian systems,enabled by exceptional topological defects,among which Weyl exceptional rings(WER)are particularly interesting.The topology of a WER can be characterized by the quantized Berry phase and a nonzero Chern number,both encoded in the eigenvectors of the non-Hermitian Hamiltonian.So far,WERs have been realized with classical wave systems,whose eigenvectors can be well described by classical physics.We here report the first quantum-mechanical implementation of WERs and investigate the related topology transitions.The experiment system consists of a superconducting qubit and a dissipative resonator,coupled to each other.The high flexibility of the system enables us to characterize its eigenvectors on different manifolds of parameter space,each of which corresponds to a quantum-mechanical entangled state.We extract both the quantized Berry phase and Chern number from these eigenvectors,and demonstrate the topological transition triggered by shrinking the size of the corresponding loop or manifold in parameter space.展开更多
Over the last decade,nuclear theory has made dramatic progress in few-body and ab initio many-body calculations.These great advances stem from chiral efective feld theory(xEFT),which provides an efcient expansion and ...Over the last decade,nuclear theory has made dramatic progress in few-body and ab initio many-body calculations.These great advances stem from chiral efective feld theory(xEFT),which provides an efcient expansion and consistent treatment of nuclear forces as inputs of modern many-body calculations,among which the in-medium similarity renormalization group(IMSRG)and its variants play a vital role.On the other hand,signifcant eforts have been made to provide a unifed description of the structure,decay,and reactions of the nuclei as open quantum systems.While a fully comprehensive and microscopic model has yet to be realized,substantial progress over recent decades has enhanced our understanding of open quantum systems around the dripline,which are often characterized by exotic structures and decay modes.To study these interesting phenomena,Gamow coupled-channel(GCC)method,in which the open quantum nature of few-body valence nucleons coupled to a deformed core,has been developed.This review focuses on the developments of the advanced IMSRG and GCC and their applications to nuclear structure and reactions.展开更多
Quantum Fisher information(QFI)associated with local metrology has been used to parameter estimation in open quantum systems.In this work,we calculated the QFI for a moving Unruh-DeWitt detector coupled with massless ...Quantum Fisher information(QFI)associated with local metrology has been used to parameter estimation in open quantum systems.In this work,we calculated the QFI for a moving Unruh-DeWitt detector coupled with massless scalar fields in n-dimensional spacetime,and analyzed the behavior of QFI with various parameters,such as the dimension of spacetime,evolution time,and Unruh temperature.We discovered that the QFI of state parameter decreases monotonically from 1 to 0 over time.Additionally,we noted that the QFI for small evolution times is several orders of magnitude higher than the QFI for long evolution times.We also found that the value of QFI decreases at first and then stabilizes as the Unruh temperature increases.It was observed that the QFI depends on initial state parameterθ,and Fθis the maximum forθ=0 orθ=π,Fφis the maximum forθ=π/2.We also obtain that the maximum value of QFI for state parameters varies for different spacetime dimensions with the same evolution time.展开更多
In order to realize interoperability to a large number of autonomous and heterogeneous information sources with high efficiency, an agent-based multi-broker architecture （AMA）-HustEven, is constructed. A group of br...In order to realize interoperability to a large number of autonomous and heterogeneous information sources with high efficiency, an agent-based multi-broker architecture （AMA）-HustEven, is constructed. A group of broker agents are designed to provide brokering services in a peer-to-peer （P2P） manner for the non- broker agents （user agents, resource agents, query agents）. Thus, the scalability and robustness of the system are enhanced. Ontology is also used by the broker agents for facilitating interoperability among all the agents in HustEven. Unlike any other AMAs, an interdomain ontology is built in this system to represent the relationships among the common concepts in the innerdomain ontologies. Therefore, a broker forwards the queries only to the other related brokers according to the interdomain ontology and the communication overhead among the brokers is reduced. Obviously, the application of the interdomain ontology enables a broker to fully take advantage of the multi-broker architecture. The experimental results show that the HustEven performs more efficiently than any other existing systems.展开更多
The no-evolution, concordance expanding universe cosmology and no-evolution, static universe tired light model are compared against observational data on eight cosmology tests. The no-evolution tired light model is fo...The no-evolution, concordance expanding universe cosmology and no-evolution, static universe tired light model are compared against observational data on eight cosmology tests. The no-evolution tired light model is found to make a superior fit on all tests. Any attempts to introduce evolutionary corrections to improve the concordance cosmology fit on one test often worsen its fit on other tests. Light curve data of high redshift gamma ray bursts and quasars fail to support claims for cosmological time dilation due to expansion. Also, the SCP supernova light curve test results are considered to be flawed by selection effect biases. The big bang theory also has difficulty accounting for redshift quantization, for the multi-megaparsec periodicity seen in the distribution of galaxy superclusters, and for the discovery of galaxies at redshifts as high as <em>z</em> ~11.9. In overview, it is concluded that a static universe cosmology must be sought to explain the origin of the universe. One possible choice is a cosmology that predicts nonconservative tired-light redshifting in intergalactic space, the continuous creation of neutrons in space, the rate of matter creation scaling with both celestial body mass and temperature, galaxies growing progressively in size, and changing their morphology in the manner suggested by Jeans and Hubble.展开更多
We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. ...We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. First, we derive closed-form expressions for the produced work and efficiency, which strongly depend on the squeezing parameter rh. Then, we prove that the effect of squeezing heats the working medium to a higher effective temperature, which leads to better overall performance. In particular, the efficiency increases with the degree of squeezing, surpassing the standard Carnot limit when the ratio of the temperatures of the hot and cold reservoirs is small. Furthermore, we derive the analytical expressions for the efficiency at maximum work and the maximum produced work in the high and low temperature regimes,and we find that at extreme temperatures the squeezing parameter rhdoes not affect the performance of the QSHE. Finally,the performance of the QSHE depends on the nature of the working medium.展开更多
Counter-rotating-wave terms(CRWTs)are traditionally viewed to be crucial in open small quantum systems with strong system–bath dissipation.Here by exemplifying in a nonequilibrium qubit–phonon hybrid model,we show t...Counter-rotating-wave terms(CRWTs)are traditionally viewed to be crucial in open small quantum systems with strong system–bath dissipation.Here by exemplifying in a nonequilibrium qubit–phonon hybrid model,we show that CRWTs can play the significant role in quantum heat transfer even with weak system–bath dissipation.By using extended coherent phonon states,we obtain the quantum master equation with heat exchange rates contributed by rotating-waveterms(RWTs)and CRWTs,respectively.We find that including only RWTs,the steady state heat current and current fluctuations will be significantly suppressed at large temperature bias,whereas they are strongly enhanced by considering CRWTs in addition.Furthermore,for the phonon statistics,the average phonon number and two-phonon correlation are nearly insensitive to strong qubit–phonon hybridization with only RWTs,whereas they will be dramatically cooled down via the cooperative transitions based on CRWTs in addition.Therefore,CRWTs in quantum heat transfer system should be treated carefully.展开更多
Quantum speed limit time and entanglement in a system composed of coupled quantum dots are investigated.The excess electron spin in each quantum dot constitutes the physical system(qubit).Also the spin interaction is ...Quantum speed limit time and entanglement in a system composed of coupled quantum dots are investigated.The excess electron spin in each quantum dot constitutes the physical system(qubit).Also the spin interaction is modeled through the Heisenberg model and the spins are imposed by an external magnetic field.Taking into account the spin relaxation as a non-Markovian process,the quantum speed limit and entanglement evolution are discussed.Our findings reveal that increasing the magnetic field leads to the faster quantum evolution.In addition,the temperature increment causes the longer quantum speed limit time as well as the entanglement degradation.展开更多
We study,in the framework of open quantum systems,the entanglement generation of two atoms in between two parallel mirrors in a thermal bath of quantum scalar fields.We find that the presence of mirrors plays an impor...We study,in the framework of open quantum systems,the entanglement generation of two atoms in between two parallel mirrors in a thermal bath of quantum scalar fields.We find that the presence of mirrors plays an important role in entanglement generation and protection.The entanglement dynamics is crucially dependent on the geometric configurations of the two-atom system with respect to the mirrors,and the ranges of temperature and interatomic separation within which entanglement can be generated are significantly changed compared with those in a free space.In particular,when the atomic transition wavelength is larger than twice the distance between the two mirrors,the atoms behave as if they were isolated from the environment and the entanglement can persist in the steady state if the atoms are initially entangled and no entanglement can be created if they are initially separable,no matter how the atoms are placed with respect to the mirrors and to each other.This is in sharp contrast to the fact that in a free space,steady-state entanglement is possible only when the two atoms are placed extremely close to each other,while in the presence of one mirror,it is possible when the two atoms placed extremely close to the mirror.展开更多
From the perspective of Markovian piecewise deterministic processes(PDPs),we investigate the derivation of a kinetic uncertainty relation(KUR),which was originally proposed in Markovian open quantum systems.First,stat...From the perspective of Markovian piecewise deterministic processes(PDPs),we investigate the derivation of a kinetic uncertainty relation(KUR),which was originally proposed in Markovian open quantum systems.First,stationary distributions of classical PDPs are explicitly constructed.Then,a tilting method is used to derive a rate functional of large deviations.Finally,based on an improved approximation scheme,we recover the KUR.These classical results are directly extended to the open quantum systems.We use a driven two-level quantum system to exemplify the quantum results.展开更多
Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated.The physical system studied is the excess electron spin in two adjacent quantum dot...Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated.The physical system studied is the excess electron spin in two adjacent quantum dots.The influences of magnetic field inhomogeneity as well as spin-orbit coupling are studied.Moreover,the spin interaction with surrounding magnetic environment is investigated as a non-Markovian process.The spin-orbit interaction provides two important features:the formation of entanglement when two qubits are initially in a separated state and the degradation and rebirth of the entanglement.展开更多
In principle, non-Hermitian quantum equations of motion can be formulated using as a starting point either the Heisenberg＇s or the Schroedinger＇s picture of quantum dynamics. Here it is shown in both cases how to ma...In principle, non-Hermitian quantum equations of motion can be formulated using as a starting point either the Heisenberg＇s or the Schroedinger＇s picture of quantum dynamics. Here it is shown in both cases how to map the algebra of commutators, defining the time evolution in terms of a non-Hermitian Hamiltonian, onto a non-Hamiltonian algebra with a Hermitian Hamiltonian. The logic behind such a derivation is reversible, so that any Hermitian Hamiltonian can be used in the formulation of non-Hermitian dynamics through a suitable algebra of generalized （non-Hamiltonian） commutators. These results provide a general structure （a template） for non-Hermitian equations of motion to be used in the computer simulation of open quantum systems dynamics.展开更多
The hierarchical equation of motion method has become one of the most popular numerical methods for describing the dissipative dynamics of open quantum systems linearly coupled to environment.However,its applications ...The hierarchical equation of motion method has become one of the most popular numerical methods for describing the dissipative dynamics of open quantum systems linearly coupled to environment.However,its applications to systems with strong electron correlation are largely restrained by the computational cost,which is mainly caused by the high truncation tier L required to accurately characterize the strong correlation effect.In this work,we develop an adiabatic terminator by decoupling the principal dissipation mode with the fastest dissipation rate from the slower ones.The adiabatic terminator leads to substantially enhanced convergence with respect to L as demonstrated by the numerical tests carried out on a single impurity Anderson model.Moreover,the adiabatic terminator alleviates the numerical instability problems in the long-time dissipative dynamics.展开更多
基金supported by the EU FP7 Marie–Curie Career Integration Fund(Grant No.631883)the Royal Society Research Fund(Grant No.RG150036)the Fundamental Research Fund for the Central Universities,China(Grant No.2018IB010)
文摘A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the ＂quantum speed-up capacity＂ which reveals the potential ability of a quantum system to be accelerated. We explore the evolutions of the speed-up capacity in different quantum channels for two-qubit states. We find that although the dynamics of the capacity is varying in different kinds of channels, it is positive in most situations which are considered in the context except one case in the amplitude-damping channel. We give the reasons for the different features of the dynamics. Anyway, the speed-up capacity can be improved by the memory effect. We find two ways which may be used to control the capacity in an experiment： selecting an appropriate coefficient of an initial state or changing the memory degree of environments.
基金Supported by the National Natural Science Foundation of China under Grant No 11175105
文摘Many quantum systems of interest are initially correlated with their environments and the reduced dynamics of open systems are an interesting while challenging topic. Affine maps, as an extension of completely positive maps, are a useful tool to describe the reduced dynamics of open systems with initial correlations. However, it is unciear what kind of initial state shares an affine map. In this study, we give a sumcient condition of initial states, in which the reduced dynamics can always be described by an affihe map. Our result shows that if the initial states of the combined system constitute a convex set, and if the correspondence between the initial states of the open system and those of the combined system, defined by taking the partial trace, is a bijection, then the reduced dynamics of the open system can be described by an affine map.
基金supported by the National Natural Science Foundation of China(62473354).
文摘For the n-qubit stochastic open quantum systems,based on the Lyapunov stability theorem and LaSalle’s invariant set principle,a pure state switching control based on on-line estimated state feedback(short for OQST-SFC)is proposed to realize the state transition the pure state of the target state including eigenstate and superposition state.The proposed switching control consists of a constant control and a control law designed based on the Lyapunov method,in which the Lyapunov function is the state distance of the system.The constant control is used to drive the system state from an initial state to the convergence domain only containing the target state,and a Lyapunov-based control is used to make the state enter the convergence domain and then continue to converge to the target state.At the same time,the continuous weak measurement of quantum system and the quantum state tomography method based on the on-line alternating direction multiplier(QST-OADM)are used to obtain the system information and estimate the quantum state which is used as the input of the quantum system controller.Then,the pure state feedback switching control method based on the on-line estimated state feedback is realized in an n-qubit stochastic open quantum system.The complete derivation process of n-qubit QST-OADM algorithm is given;Through strict theoretical proof and analysis,the convergence conditions to ensure any initial state of the quantum system to converge the target pure state are given.The proposed control method is applied to a 2-qubit stochastic open quantum system for numerical simulation experiments.Four possible different position cases between the initial estimated state and that of the controlled system are studied and discussed,and the performances of the state transition under the corresponding cases are analyzed.
文摘In this paper, the structure characteristics of open complex giant systems are concretely analysed in depth, thus the view and its significance to support the meta synthesis engineering with manifold knowledge models are clarified. Furthermore, the knowledge based multifaceted modeling methodology for open complex giant systems is emphatically studied. The major points are as follows: (1) nonlinear mechanism and general information partition law; (2) from the symmetry and similarity to the acquisition of construction knowledge; (3) structures for hierarchical and nonhierarchical organizations; (4) the integration of manifold knowledge models; (5) the methodology of knowledge based multifaceted modeling.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61673389,61273202 and 61134008
文摘We propose and discuss a novel concept of robust set stabilization by permissible controls; this concept is helpful when dealing with both a priori information of model parameters and different permissible controls including quantum measurements. Both controllability and stabilization can be regarded as the special case of the novel concept. An instance is presented for a kind of uncertain open quantum systems to further justify this gen- eralized concept. It is underlined that a new type of hybrid control based on periodically perturbed projective measurements can be the permissible control of uncertain open quantum systems when perturbed projective measurements are available. The sufficient conditions are given for the robust set stabilization of uncertain quantum open systems by the hybrid control, and the design of the hybrid control is reduced to selecting the period of measurements.
基金the National Natural Science Foundation of China(Grant Nos.11704093 and 11705008)Beijing Institute of Technology Research Fund Program for Young Scholars,China.
文摘We investigate the quantum thermal transistor effect in nonequilibrium three-level systems by applying the polarontransformed Redfield equation combined with full counting statistics.The steady state heat currents are obtained via this unified approach over a wide region of system–bath coupling,and can be analytically reduced to the Redfield and nonequilibrium noninteracting blip approximation results in the weak and strong coupling limits,respectively.A giant heat amplification phenomenon emerges in the strong system–bath coupling limit,where transitions mediated by the middle thermal bath are found to be crucial to unravel the underlying mechanism.Moreover,the heat amplification is also exhibited with moderate coupling strength,which can be properly explained within the polaron framework.
基金supported by the National Natural Science Foundation of China(Grant Nos.12375013 and 12275090)the Guangdong Basic and Applied Basic Research Fund(Grant No.2023A1515011460)Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2200001)。
文摘In open quantum systems,the Liouvillian gap characterizes the relaxation time toward the steady state.However,accurately computing this quantity is notoriously difficult due to the exponential growth of the Hilbert space and the non-Hermitian nature of the Liouvillian superoperator.In this work,we propose a variational quantum algorithm for efficiently estimating the Liouvillian gap.By utilizing the Choi-Jamio lkowski isomorphism,we reformulate the problem as finding the first excitation energy of an effective non-Hermitian Hamiltonian.Our method employs variance minimization with an orthogonality constraint to locate the first excited state and adopts a two-stage optimization scheme to enhance convergence.Moreover,to address scenarios with degenerate steady states,we introduce an iterative energy-offset scanning technique.Numerical simulations on the dissipative XXZ model confirm the accuracy and robustness of our algorithm across a range of system sizes and dissipation strengths.These results demonstrate the promise of variational quantum algorithms for simulating open quantum many-body systems on near-term quantum hardware.
基金supported by the National Natural Science Foundation of China(12274080,12474356,12475015,and U21A20436)Innovation Program for Quantum Science and Technology(2021ZD0300200 and 2021ZD0301705)。
文摘Non-Hermiticity can lead to the emergence of many intriguing phenomena that are absent in Hermitian systems,enabled by exceptional topological defects,among which Weyl exceptional rings(WER)are particularly interesting.The topology of a WER can be characterized by the quantized Berry phase and a nonzero Chern number,both encoded in the eigenvectors of the non-Hermitian Hamiltonian.So far,WERs have been realized with classical wave systems,whose eigenvectors can be well described by classical physics.We here report the first quantum-mechanical implementation of WERs and investigate the related topology transitions.The experiment system consists of a superconducting qubit and a dissipative resonator,coupled to each other.The high flexibility of the system enables us to characterize its eigenvectors on different manifolds of parameter space,each of which corresponds to a quantum-mechanical entangled state.We extract both the quantized Berry phase and Chern number from these eigenvectors,and demonstrate the topological transition triggered by shrinking the size of the corresponding loop or manifold in parameter space.
基金National Key R&D Program of China under Grant Nos.2023YFA1606400 and 2022YFA1602303National Natural Science Foundation of China under Grants Nos.12335007,12035001,11921006,12347106,12147101,and 12205340+1 种基金Gansu Natural Science Foundation under Grant No.22JR5RA123U.S.Department of Energy(DOE),Office of Science,under SciDAC-5(NUCLEI collaboration)。
文摘Over the last decade,nuclear theory has made dramatic progress in few-body and ab initio many-body calculations.These great advances stem from chiral efective feld theory(xEFT),which provides an efcient expansion and consistent treatment of nuclear forces as inputs of modern many-body calculations,among which the in-medium similarity renormalization group(IMSRG)and its variants play a vital role.On the other hand,signifcant eforts have been made to provide a unifed description of the structure,decay,and reactions of the nuclei as open quantum systems.While a fully comprehensive and microscopic model has yet to be realized,substantial progress over recent decades has enhanced our understanding of open quantum systems around the dripline,which are often characterized by exotic structures and decay modes.To study these interesting phenomena,Gamow coupled-channel(GCC)method,in which the open quantum nature of few-body valence nucleons coupled to a deformed core,has been developed.This review focuses on the developments of the advanced IMSRG and GCC and their applications to nuclear structure and reactions.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12105097 and 12035005)the Science Research Fund of the Education Department of Hunan Province,China(Grant No.23B0480).
文摘Quantum Fisher information(QFI)associated with local metrology has been used to parameter estimation in open quantum systems.In this work,we calculated the QFI for a moving Unruh-DeWitt detector coupled with massless scalar fields in n-dimensional spacetime,and analyzed the behavior of QFI with various parameters,such as the dimension of spacetime,evolution time,and Unruh temperature.We discovered that the QFI of state parameter decreases monotonically from 1 to 0 over time.Additionally,we noted that the QFI for small evolution times is several orders of magnitude higher than the QFI for long evolution times.We also found that the value of QFI decreases at first and then stabilizes as the Unruh temperature increases.It was observed that the QFI depends on initial state parameterθ,and Fθis the maximum forθ=0 orθ=π,Fφis the maximum forθ=π/2.We also obtain that the maximum value of QFI for state parameters varies for different spacetime dimensions with the same evolution time.
基金The National Natural Science Foundation of China(No60673128)
文摘In order to realize interoperability to a large number of autonomous and heterogeneous information sources with high efficiency, an agent-based multi-broker architecture （AMA）-HustEven, is constructed. A group of broker agents are designed to provide brokering services in a peer-to-peer （P2P） manner for the non- broker agents （user agents, resource agents, query agents）. Thus, the scalability and robustness of the system are enhanced. Ontology is also used by the broker agents for facilitating interoperability among all the agents in HustEven. Unlike any other AMAs, an interdomain ontology is built in this system to represent the relationships among the common concepts in the innerdomain ontologies. Therefore, a broker forwards the queries only to the other related brokers according to the interdomain ontology and the communication overhead among the brokers is reduced. Obviously, the application of the interdomain ontology enables a broker to fully take advantage of the multi-broker architecture. The experimental results show that the HustEven performs more efficiently than any other existing systems.
文摘The no-evolution, concordance expanding universe cosmology and no-evolution, static universe tired light model are compared against observational data on eight cosmology tests. The no-evolution tired light model is found to make a superior fit on all tests. Any attempts to introduce evolutionary corrections to improve the concordance cosmology fit on one test often worsen its fit on other tests. Light curve data of high redshift gamma ray bursts and quasars fail to support claims for cosmological time dilation due to expansion. Also, the SCP supernova light curve test results are considered to be flawed by selection effect biases. The big bang theory also has difficulty accounting for redshift quantization, for the multi-megaparsec periodicity seen in the distribution of galaxy superclusters, and for the discovery of galaxies at redshifts as high as <em>z</em> ~11.9. In overview, it is concluded that a static universe cosmology must be sought to explain the origin of the universe. One possible choice is a cosmology that predicts nonconservative tired-light redshifting in intergalactic space, the continuous creation of neutrons in space, the rate of matter creation scaling with both celestial body mass and temperature, galaxies growing progressively in size, and changing their morphology in the manner suggested by Jeans and Hubble.
文摘We analyze the performance of a quantum Stirling heat engine(QSHE), using a two-level system and a harmonic oscillator as the working medium, that is in contact with a squeezed thermal reservoir and a cold reservoir. First, we derive closed-form expressions for the produced work and efficiency, which strongly depend on the squeezing parameter rh. Then, we prove that the effect of squeezing heats the working medium to a higher effective temperature, which leads to better overall performance. In particular, the efficiency increases with the degree of squeezing, surpassing the standard Carnot limit when the ratio of the temperatures of the hot and cold reservoirs is small. Furthermore, we derive the analytical expressions for the efficiency at maximum work and the maximum produced work in the high and low temperature regimes,and we find that at extreme temperatures the squeezing parameter rhdoes not affect the performance of the QSHE. Finally,the performance of the QSHE depends on the nature of the working medium.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11704093,11775159,and 11935010)the Natural Science Foundation of Shanghai,China(Grant Nos.18ZR1442800 and 18JC1410900)the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology.
文摘Counter-rotating-wave terms(CRWTs)are traditionally viewed to be crucial in open small quantum systems with strong system–bath dissipation.Here by exemplifying in a nonequilibrium qubit–phonon hybrid model,we show that CRWTs can play the significant role in quantum heat transfer even with weak system–bath dissipation.By using extended coherent phonon states,we obtain the quantum master equation with heat exchange rates contributed by rotating-waveterms(RWTs)and CRWTs,respectively.We find that including only RWTs,the steady state heat current and current fluctuations will be significantly suppressed at large temperature bias,whereas they are strongly enhanced by considering CRWTs in addition.Furthermore,for the phonon statistics,the average phonon number and two-phonon correlation are nearly insensitive to strong qubit–phonon hybridization with only RWTs,whereas they will be dramatically cooled down via the cooperative transitions based on CRWTs in addition.Therefore,CRWTs in quantum heat transfer system should be treated carefully.
文摘Quantum speed limit time and entanglement in a system composed of coupled quantum dots are investigated.The excess electron spin in each quantum dot constitutes the physical system(qubit).Also the spin interaction is modeled through the Heisenberg model and the spins are imposed by an external magnetic field.Taking into account the spin relaxation as a non-Markovian process,the quantum speed limit and entanglement evolution are discussed.Our findings reveal that increasing the magnetic field leads to the faster quantum evolution.In addition,the temperature increment causes the longer quantum speed limit time as well as the entanglement degradation.
基金supported in part by the NSFC under Grants No.11805063,No.11690034,and No.12075084the Hunan Provincial Natural Science Foundation of China under Grant No.2020JJ3026。
文摘We study,in the framework of open quantum systems,the entanglement generation of two atoms in between two parallel mirrors in a thermal bath of quantum scalar fields.We find that the presence of mirrors plays an important role in entanglement generation and protection.The entanglement dynamics is crucially dependent on the geometric configurations of the two-atom system with respect to the mirrors,and the ranges of temperature and interatomic separation within which entanglement can be generated are significantly changed compared with those in a free space.In particular,when the atomic transition wavelength is larger than twice the distance between the two mirrors,the atoms behave as if they were isolated from the environment and the entanglement can persist in the steady state if the atoms are initially entangled and no entanglement can be created if they are initially separable,no matter how the atoms are placed with respect to the mirrors and to each other.This is in sharp contrast to the fact that in a free space,steady-state entanglement is possible only when the two atoms are placed extremely close to each other,while in the presence of one mirror,it is possible when the two atoms placed extremely close to the mirror.
基金supported by the National Natural Science Foundation of China under Grant No.12075016,No.11575016。
文摘From the perspective of Markovian piecewise deterministic processes(PDPs),we investigate the derivation of a kinetic uncertainty relation(KUR),which was originally proposed in Markovian open quantum systems.First,stationary distributions of classical PDPs are explicitly constructed.Then,a tilting method is used to derive a rate functional of large deviations.Finally,based on an improved approximation scheme,we recover the KUR.These classical results are directly extended to the open quantum systems.We use a driven two-level quantum system to exemplify the quantum results.
文摘Quantum speed limit and entanglement of a two-spin Heisenberg XYZ system in an inhomogeneous external magnetic field are investigated.The physical system studied is the excess electron spin in two adjacent quantum dots.The influences of magnetic field inhomogeneity as well as spin-orbit coupling are studied.Moreover,the spin interaction with surrounding magnetic environment is investigated as a non-Markovian process.The spin-orbit interaction provides two important features:the formation of entanglement when two qubits are initially in a separated state and the degradation and rebirth of the entanglement.
基金Supported by the National Research Foundation of South Africa
文摘In principle, non-Hermitian quantum equations of motion can be formulated using as a starting point either the Heisenberg＇s or the Schroedinger＇s picture of quantum dynamics. Here it is shown in both cases how to map the algebra of commutators, defining the time evolution in terms of a non-Hermitian Hamiltonian, onto a non-Hamiltonian algebra with a Hermitian Hamiltonian. The logic behind such a derivation is reversible, so that any Hermitian Hamiltonian can be used in the formulation of non-Hermitian dynamics through a suitable algebra of generalized （non-Hamiltonian） commutators. These results provide a general structure （a template） for non-Hermitian equations of motion to be used in the computer simulation of open quantum systems dynamics.
文摘The hierarchical equation of motion method has become one of the most popular numerical methods for describing the dissipative dynamics of open quantum systems linearly coupled to environment.However,its applications to systems with strong electron correlation are largely restrained by the computational cost,which is mainly caused by the high truncation tier L required to accurately characterize the strong correlation effect.In this work,we develop an adiabatic terminator by decoupling the principal dissipation mode with the fastest dissipation rate from the slower ones.The adiabatic terminator leads to substantially enhanced convergence with respect to L as demonstrated by the numerical tests carried out on a single impurity Anderson model.Moreover,the adiabatic terminator alleviates the numerical instability problems in the long-time dissipative dynamics.
