We investigate quantum phase transitions in XY spin models using Dzyaloshinsky-Moriya(DM) interactions. We identify the quantum critical points via quantum Fisher information and quantum coherence, finding that higher...We investigate quantum phase transitions in XY spin models using Dzyaloshinsky-Moriya(DM) interactions. We identify the quantum critical points via quantum Fisher information and quantum coherence, finding that higher DM couplings suppress quantum phase transitions. However, quantum coherence(characterized by the l_1-norm and relative entropy) decreases as the DM coupling increases. Herein, we present both analytical and numerical results.展开更多
We present a family of graphical representations for the O(N)spin model,where N≥1 represents the spin dimension,and N=1,2,3 corresponds to the Ising,XY and Heisenberg models,respectively.With an integer parameter 0≤...We present a family of graphical representations for the O(N)spin model,where N≥1 represents the spin dimension,and N=1,2,3 corresponds to the Ising,XY and Heisenberg models,respectively.With an integer parameter 0≤ℓ≤N/2,each configuration is the coupling of ℓ copies of subgraphs consisting of directed flows and N−2ℓ copies of subgraphs constructed by undirected loops,which we call the XY and Ising subgraphs,respectively.On each lattice site,the XY subgraphs satisfy the Kirchhoff flow-conservation law and the Ising subgraphs obey the Eulerian bond condition.Then,we formulate worm-type algorithms and simulate the O(N)model on the simple-cubic lattice for N from 2 to 6 at all possibleℓ.It is observed that the worm algorithm has much higher efficiency than the Metropolis method,and,for a given N,the efficiency is an increasing function ofℓ.Besides Monte Carlo simulations,we expect that these graphical representations would provide a convenient basis for the study of the O(N)spin model by other state-of-the-art methods like the tensor network renormalization.展开更多
In the present paper we propose a spin-1/2 chain which provides an exactly solvable example to studythe Ising criticality with the central charge c = 1/2. We performthe diagonalization of this model in the presence of...In the present paper we propose a spin-1/2 chain which provides an exactly solvable example to studythe Ising criticality with the central charge c = 1/2. We performthe diagonalization of this model in the presence ofmagnetic field. From the full energy spectrum, the central charge and the scaling dimensions are given at the criticalpoint. The results show evidently that the quantum Ising criticality exists in such a system.展开更多
We proposed a simple spin-1/2 model which provides an exactly solvable example to study the Ising criticality with central charge . By mapping it onto the real Majorana fermions, the Ising critical behavior is explore...We proposed a simple spin-1/2 model which provides an exactly solvable example to study the Ising criticality with central charge . By mapping it onto the real Majorana fermions, the Ising critical behavior is explored explicitly, although its bosonized form is not the double frequency sine-Gordon model.展开更多
In this paper we investigated the stability of konjac glucomnnan（KGM） chain hydrogen networks based on the quantum spin model. Dissipative particle dynamics method was applied in the structure simulation of KGM. The...In this paper we investigated the stability of konjac glucomnnan（KGM） chain hydrogen networks based on the quantum spin model. Dissipative particle dynamics method was applied in the structure simulation of KGM. The results reveled that acetyl residues of KGM were bonded with water molecules in aqueous solutions. Increasing the hydrogen bond formation decreases the energy in acetyl system. The expect-valuation of the thermal state with respect to the Hamiltonian is negative. Hence, the total energy of konjac glucomnnan chain with the acetyl groups decreases, which indicates the increasing stability of konjac glucomnnan chain. Our approach could provide a new insight into the investigation on the stability of konjac glucomnnan chain.展开更多
This paper presents a novel suspension support tailored for wind tunnel tests of spinning projectiles based on Wire-Driven Parallel Robot(WDPR),uniquely characterized by an SPM(Spinning Projectile Model)-centered mobi...This paper presents a novel suspension support tailored for wind tunnel tests of spinning projectiles based on Wire-Driven Parallel Robot(WDPR),uniquely characterized by an SPM(Spinning Projectile Model)-centered mobile platform.First,an SPM-centered mobile platform,featuring two redundant and another unconstrained Degree of Freedom(DOF),and its suspension support mechanism are designed together,collectively constructing a WDPR endowed with kinematic redundancy.Afterward,the kinematics of the mechanism,boundary equations for the redundant DOFs,and relevant kinematic performance indices are then proposed and formulated.The results from both prototype experiments and numerical assessments are presented.The capability of the support mechanism to replicate the complex coupled motions of the SPM is verified by the experimental results,while the proposed kinematics and boundary equations are also validated.Furthermore,it is revealed by numerical assessments that the redundant DOFs of the mobile platform exert a minimal impact on the kinematic performance of the suspension support.Finally,the optimal global attitude performance is obtained when these DOFs are set to zero if they are restricted to constants.However,local attitude performance can be further improved by the variable values.展开更多
We generalize the Heisenberg star consisting of a spin-1/2 central spin and a homogeneously coupled spin bath modeled by the XXX ring[Richter J and Voigt A 1994 J.Phys.A:Math.Gen.271139-1149]to the case of arbitrary c...We generalize the Heisenberg star consisting of a spin-1/2 central spin and a homogeneously coupled spin bath modeled by the XXX ring[Richter J and Voigt A 1994 J.Phys.A:Math.Gen.271139-1149]to the case of arbitrary central-spin size S<N/2,where N is the number of bath spins.We describe how to block-diagonalize the model based on the Bethe ansatz solution of the XXX ring,with the dimension of each block Hamiltonian≤2 S+1.We obtain all the eigenenergies and explicit expressions of the sub-ground states in each l-subspace with l being the total angular momentum of the bath.Both the eigenenergies and the sub-ground states have distinct structures depending whether S≤l or l<S.The absolute ground-state energy and the corresponding l as functions of the intrabath coupling are numerically calculated for N=16 and S=1,2,…,7 and their behaviors are quantitatively explained in the weak and strong intrabath coupling limits.We then study the dynamics of the antiferromagnetic order within an XXX bath prepared in the Néel state.Effects of the initial state of the central spin,the value of S,and the system-bath coupling strength on the staggered magnetization dynamics are investigated.By including a Zeeman term for the central spin and the anisotropy in the intrabath coupling,we also study the polarization dynamics of the central spin for a bath prepared in the spin coherent state.Under the resonant condition and at the isotropic point of the bath,the polarization dynamics for S>1/2 exhibit collapse-revival behaviors with fine structures.However,the collapserevival phenomena are found to be fragile with respect to the anisotropy of the intrabath coupling.展开更多
The U(1)symmetry of the X X Z central spin model with an arbitrary central magnetic field B is broken,since its total spin in the z-direction is not conserved.We obtain the exact solutions of the system by using the o...The U(1)symmetry of the X X Z central spin model with an arbitrary central magnetic field B is broken,since its total spin in the z-direction is not conserved.We obtain the exact solutions of the system by using the off-diagonal Bethe ansatz method.The thermodynamic limit is investigated based on the solutions.We find that the contribution of the inhomogeneous term in the associated T-Q relation to the ground state energy satisfies an N^(-1)scaling law,where N is the total number of spins.This result makes it possible to investigate the properties of the system in the thermodynamic limit.By assuming the structural form of the Bethe roots in the thermodynamic limit,we obtain the contribution of the direction of B to the ground state energy.It is shown that the contribution of the direction of the central magnetic field is a finite value in the thermodynamic limit.This is the phenomenon caused by the U(1)symmetry breaking of the system.展开更多
The quantum phase transition(QPT)and quantum criticality of an anisotropic spin-1/2 XY chain under the interplay of magnetic field and Dzyaloshinskii-Moriya(DM)interaction,which is interpreted as an electric field,are...The quantum phase transition(QPT)and quantum criticality of an anisotropic spin-1/2 XY chain under the interplay of magnetic field and Dzyaloshinskii-Moriya(DM)interaction,which is interpreted as an electric field,are investigated,wherein the anisotropic parameter plays a similar role as the superconducting pairing gap in the interacting Kitaev topological superconductor model that protects the topological order.It is shown that the thermal Drude weight is a good quantity to characterize the gapped(D_(th)=0)and gapless(D_(th)>0)ground states.The continuous QPT is marked by a quantum critical point(QCP)associated with entropy accumulation,which is manifested by a characteristic Güneisen ratio(GR)with or without selfduality symmetry.It is shown that at a self-dual QCP,the GR keeps a finite value as T→0,while at a general QCP without self-duality symmetry,it displays a power-law temperature dependent divergence:Γ(T,r_(c))∼±T^(−1),which provides a novel thermodynamic means for probing QPT.展开更多
Multi-mode cavities have now attracted much attention both experimentally and theoretically. In this paper, inspired by recent experiments of cavity-assisted Raman transitions, we realize a two-axis spin Hamiltonian H...Multi-mode cavities have now attracted much attention both experimentally and theoretically. In this paper, inspired by recent experiments of cavity-assisted Raman transitions, we realize a two-axis spin Hamiltonian H = q（J_x^2＋ χJ_y^2） ＋ ω_0J_z in two cavities. This realized Hamiltonian has a distinct property that all parameters can be tuned independently. For proper parameters, the well-studied one- and two-axis twisting Hamiltonians are recovered, and the scaling of N^（-1） of the maximal squeezing factor can occur naturally. On the other hand, in the two-axis twisting Hamiltonian, spin squeezing is usually reduced when increasing the atomic resonant frequency ω_0. Surprisingly, we find that by combining with the dimensionless parameter χ（-1）, this atomic resonant frequency ω_0 can enhance spin squeezing greatly. These results are beneficial for achieving the required spin squeezing in experiments.展开更多
The temperature effect on tunnelling splitting in the spin boson model with a super-ohmic bath is studied by the small polaron theory. The coherent-incoherent transition temperature is calculated and its dependence on...The temperature effect on tunnelling splitting in the spin boson model with a super-ohmic bath is studied by the small polaron theory. The coherent-incoherent transition temperature is calculated and its dependence on dissipation strength and bare tunnelling splitting is analysed. In additional to the traditional transition point described in textbooks, a new kind of transition is found in the low dissipation region, showing different temperature dependence in the transition. The relation to the corresponding transition in the polaron-phonon system is also discussed.展开更多
We investigate spin squeezing effects of trapped ions in an off-resonance optical potential system using the arbitrary range spin spin interaction and transverse field model. The collective spin noises at any time are...We investigate spin squeezing effects of trapped ions in an off-resonance optical potential system using the arbitrary range spin spin interaction and transverse field model. The collective spin noises at any time are analyzed exactly. The general expression of spin squeezing factor is presented for arbitrary-range spin interaction. For the nearest-neighbor and next-nearest neighbor spin interaction model, the analytic solutions are reduced from the general expressions. It is shown that the maximum spin squeezing is enhanced for the general arbitrary-range spin interaction compared with the nearest-neighbor interaction model as the long-range interaction with arbitrary sites enforces stronger correlation.展开更多
Information storage technology based on anisotropic ferromagnets with sufficiently high magneto-optical effects has received much attention in recent years.Magneto-optical recording combines the merits of magnetic and...Information storage technology based on anisotropic ferromagnets with sufficiently high magneto-optical effects has received much attention in recent years.Magneto-optical recording combines the merits of magnetic and optical techniques.We investigate the magneto-optical effects on a biquadratic ferromagnet and show that the dynamics of the system are governed by a perturbed nonlinear Schro¨dinger equation.The evolutions of amplitude and velocity of the soliton are found to be time independent,thereby admitting the lossless propagation of the electromagnetic soliton in the medium,which may have potential applications in soliton based optical communication systems.We also exploit the role of perturbation,which has a significant impact on the propagation of an electromagnetic soliton.展开更多
Fidelity measures the similarity between two states and is widely adapted by the condensed matter community as a probe of quantum phase transitions in many-body systems. Despite its success in witnessing quantum criti...Fidelity measures the similarity between two states and is widely adapted by the condensed matter community as a probe of quantum phase transitions in many-body systems. Despite its success in witnessing quantum critical points, information about the fine structure of a quantum phase one can get from this approach is still limited. Here, we proposed a scheme called fidelity spectrum, By studying the fidelity spectrum, one can obtain information about the characteristics of a phase. In particular, we investigated the spectra in the one-dimensional transverse-field Ising model and the two- dimensional Kitaev model on a honeycomb lattice. It was found that the sPectra have qualitative differences in the critical and non-critical regions of the two models. From the distributions of them, the dominating k modes in a particular phase could also be captured.展开更多
Magnetization dynamics in uniformly magnetized ferromagnetic media is studied by using Landau-Lifshitz-Gilbert equation. The nonlinear evolution equation is integrable with site-dependent and biquadratic exchange inte...Magnetization dynamics in uniformly magnetized ferromagnetic media is studied by using Landau-Lifshitz-Gilbert equation. The nonlinear evolution equation is integrable with site-dependent and biquadratic exchange interaction by means of Landau-Lifshitz （LL） equation which is well understood. In the present work, we construct the exact solitary solutions of the nonlinear evolution equation, particularly, we employ the modified extended tangent hyperbolic function method. We show the shape changing property of solitons for the given integrable system in the presence of damping as well as inhomogeneities.展开更多
The infinite time-evolving block decimation algorithm(i TEBD)provides an efficient way to determine the ground state and dynamics of the quantum lattice systems in the thermodynamic limit.In this paper we suggest an o...The infinite time-evolving block decimation algorithm(i TEBD)provides an efficient way to determine the ground state and dynamics of the quantum lattice systems in the thermodynamic limit.In this paper we suggest an optimized way to take the i TEBD calculation,which takes advantage of additional reduced decompositions to speed up the calculation.The numerical calculations show that for a comparable computation time our method provides more accurate results than the traditional i TEBD,especially for lattice systems with large on-site degrees of freedom.展开更多
With the prevalent conception of self-replication (SR, a hallmark of living systems) as a non-equilibrium process subject to thermodynamic laws, a complementary approach derives the low energy quantum states arising f...With the prevalent conception of self-replication (SR, a hallmark of living systems) as a non-equilibrium process subject to thermodynamic laws, a complementary approach derives the low energy quantum states arising from a Hamiltonian that appears to be specific for bio-systems by its containing some strongly binding terms. The bindings attract <em>properties</em> of the template (T) and the reactants to form a replicate (R). The criterion for SR that emerges from the theory is that second order (bi-linear) interaction terms between degrees of motion of T-R and the thermal bath dominate negatively over a linear self-energy term, and thereby provide a binding between the attributes of T and R. The formalism (reminiscent of the Kramers-Anderson mechanism for superexchange) is from first principles, but hinges on a drastic simplification by modelling the T, R and bath variables on interacting qubits and by congesting the attraction into a single (control) parameter. The development relies on further simplifying features, such as Random Phase Approximations and an Effective Hamiltonian formalism. The entropic balance to replication is considered and found to reside in the far surroundings.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
A comprehensive research of the antiferromagnetic （AFM） structures of perovskite-type EuZrO3 is carried out by use of the double-time Green＇s function. Two possible types of AFM configurations are considered, and t...A comprehensive research of the antiferromagnetic （AFM） structures of perovskite-type EuZrO3 is carried out by use of the double-time Green＇s function. Two possible types of AFM configurations are considered, and theoretical results are compared with experimental results to extract the values of parameters J1, J2, and D. The obtained exchanges are employed to calculate the magnetic susceptibility, which is then in turn compared with the experimental one. Therefore, we think that the magnetic structure of EuZrO3 may be an isotropic G-type structure or an anisotropic A-type structure.展开更多
A bilayer nano-stanene-like structure with Ruderman-Kittel-Kasuya-Yoshida(RKKY)coupling described by the Ising model is proposed. The magnetic and thermodynamic properties are studied using the effective-field theory ...A bilayer nano-stanene-like structure with Ruderman-Kittel-Kasuya-Yoshida(RKKY)coupling described by the Ising model is proposed. The magnetic and thermodynamic properties are studied using the effective-field theory with correlations. The exchange coupling,longitudinal magnetic field, number of non-magnetic layers, and anisotropies had major influences on the magnetization, specific heat, and internal energy. Different saturation magnetizations are observed on the magnetization curve. The variation in the system blocking temperature is studied. The results provide theoretical guidance for the magnetic investigation of nanomaterials with RKKY coupling.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11675113,and 11765016)the Natural Science Foundation of Beijing(Grant No.KZ201810028042)Jiangxi Education Department Fund(Grant Nos.GJJ161056,and KJLD14088)
文摘We investigate quantum phase transitions in XY spin models using Dzyaloshinsky-Moriya(DM) interactions. We identify the quantum critical points via quantum Fisher information and quantum coherence, finding that higher DM couplings suppress quantum phase transitions. However, quantum coherence(characterized by the l_1-norm and relative entropy) decreases as the DM coupling increases. Herein, we present both analytical and numerical results.
基金supported by the National Natural Science Foundation of China(under Grant No.12275263)the Innovation Program for Quantum Science and Technology(under Grant No.2021ZD0301900)the Natural Science Foundation of Fujian Province of China:2023J02032.
文摘We present a family of graphical representations for the O(N)spin model,where N≥1 represents the spin dimension,and N=1,2,3 corresponds to the Ising,XY and Heisenberg models,respectively.With an integer parameter 0≤ℓ≤N/2,each configuration is the coupling of ℓ copies of subgraphs consisting of directed flows and N−2ℓ copies of subgraphs constructed by undirected loops,which we call the XY and Ising subgraphs,respectively.On each lattice site,the XY subgraphs satisfy the Kirchhoff flow-conservation law and the Ising subgraphs obey the Eulerian bond condition.Then,we formulate worm-type algorithms and simulate the O(N)model on the simple-cubic lattice for N from 2 to 6 at all possibleℓ.It is observed that the worm algorithm has much higher efficiency than the Metropolis method,and,for a given N,the efficiency is an increasing function ofℓ.Besides Monte Carlo simulations,we expect that these graphical representations would provide a convenient basis for the study of the O(N)spin model by other state-of-the-art methods like the tensor network renormalization.
文摘In the present paper we propose a spin-1/2 chain which provides an exactly solvable example to studythe Ising criticality with the central charge c = 1/2. We performthe diagonalization of this model in the presence ofmagnetic field. From the full energy spectrum, the central charge and the scaling dimensions are given at the criticalpoint. The results show evidently that the quantum Ising criticality exists in such a system.
基金National Natural Science Foundation of China，the RFDP
文摘We proposed a simple spin-1/2 model which provides an exactly solvable example to study the Ising criticality with central charge . By mapping it onto the real Majorana fermions, the Ising critical behavior is explored explicitly, although its bosonized form is not the double frequency sine-Gordon model.
基金supported by the Natural Science Foundation of China(31271837 and 31471704)
文摘In this paper we investigated the stability of konjac glucomnnan（KGM） chain hydrogen networks based on the quantum spin model. Dissipative particle dynamics method was applied in the structure simulation of KGM. The results reveled that acetyl residues of KGM were bonded with water molecules in aqueous solutions. Increasing the hydrogen bond formation decreases the energy in acetyl system. The expect-valuation of the thermal state with respect to the Hamiltonian is negative. Hence, the total energy of konjac glucomnnan chain with the acetyl groups decreases, which indicates the increasing stability of konjac glucomnnan chain. Our approach could provide a new insight into the investigation on the stability of konjac glucomnnan chain.
基金supported by the National Natural Science Foundation of China(No.12072304).
文摘This paper presents a novel suspension support tailored for wind tunnel tests of spinning projectiles based on Wire-Driven Parallel Robot(WDPR),uniquely characterized by an SPM(Spinning Projectile Model)-centered mobile platform.First,an SPM-centered mobile platform,featuring two redundant and another unconstrained Degree of Freedom(DOF),and its suspension support mechanism are designed together,collectively constructing a WDPR endowed with kinematic redundancy.Afterward,the kinematics of the mechanism,boundary equations for the redundant DOFs,and relevant kinematic performance indices are then proposed and formulated.The results from both prototype experiments and numerical assessments are presented.The capability of the support mechanism to replicate the complex coupled motions of the SPM is verified by the experimental results,while the proposed kinematics and boundary equations are also validated.Furthermore,it is revealed by numerical assessments that the redundant DOFs of the mobile platform exert a minimal impact on the kinematic performance of the suspension support.Finally,the optimal global attitude performance is obtained when these DOFs are set to zero if they are restricted to constants.However,local attitude performance can be further improved by the variable values.
基金supported by the National Key R&D Program of China under Grant No.2021YFA1400803by the Natural Science Foundation of China(NSFC)under Grant No.11705007。
文摘We generalize the Heisenberg star consisting of a spin-1/2 central spin and a homogeneously coupled spin bath modeled by the XXX ring[Richter J and Voigt A 1994 J.Phys.A:Math.Gen.271139-1149]to the case of arbitrary central-spin size S<N/2,where N is the number of bath spins.We describe how to block-diagonalize the model based on the Bethe ansatz solution of the XXX ring,with the dimension of each block Hamiltonian≤2 S+1.We obtain all the eigenenergies and explicit expressions of the sub-ground states in each l-subspace with l being the total angular momentum of the bath.Both the eigenenergies and the sub-ground states have distinct structures depending whether S≤l or l<S.The absolute ground-state energy and the corresponding l as functions of the intrabath coupling are numerically calculated for N=16 and S=1,2,…,7 and their behaviors are quantitatively explained in the weak and strong intrabath coupling limits.We then study the dynamics of the antiferromagnetic order within an XXX bath prepared in the Néel state.Effects of the initial state of the central spin,the value of S,and the system-bath coupling strength on the staggered magnetization dynamics are investigated.By including a Zeeman term for the central spin and the anisotropy in the intrabath coupling,we also study the polarization dynamics of the central spin for a bath prepared in the spin coherent state.Under the resonant condition and at the isotropic point of the bath,the polarization dynamics for S>1/2 exhibit collapse-revival behaviors with fine structures.However,the collapserevival phenomena are found to be fragile with respect to the anisotropy of the intrabath coupling.
基金the National Natural Science Foundation of China(Grant Nos.11847245,11874393,and 12134015)the Doctoral Scientific Research Foundation of Yunnan Normal University(Grant No.00900205020503180)+2 种基金the National Natural Science Foundation of China(Grant Nos.12275214,11805152,12047502,and 11947301)the Natural Science Basic Research Program of Shaanxi Province(Grant Nos.2021JCW-19and 2019JQ-107)the Shaanxi Key Laboratory for Theoretical Physics Frontiers in China。
文摘The U(1)symmetry of the X X Z central spin model with an arbitrary central magnetic field B is broken,since its total spin in the z-direction is not conserved.We obtain the exact solutions of the system by using the off-diagonal Bethe ansatz method.The thermodynamic limit is investigated based on the solutions.We find that the contribution of the inhomogeneous term in the associated T-Q relation to the ground state energy satisfies an N^(-1)scaling law,where N is the total number of spins.This result makes it possible to investigate the properties of the system in the thermodynamic limit.By assuming the structural form of the Bethe roots in the thermodynamic limit,we obtain the contribution of the direction of B to the ground state energy.It is shown that the contribution of the direction of the central magnetic field is a finite value in the thermodynamic limit.This is the phenomenon caused by the U(1)symmetry breaking of the system.
文摘The quantum phase transition(QPT)and quantum criticality of an anisotropic spin-1/2 XY chain under the interplay of magnetic field and Dzyaloshinskii-Moriya(DM)interaction,which is interpreted as an electric field,are investigated,wherein the anisotropic parameter plays a similar role as the superconducting pairing gap in the interacting Kitaev topological superconductor model that protects the topological order.It is shown that the thermal Drude weight is a good quantity to characterize the gapped(D_(th)=0)and gapless(D_(th)>0)ground states.The continuous QPT is marked by a quantum critical point(QCP)associated with entropy accumulation,which is manifested by a characteristic Güneisen ratio(GR)with or without selfduality symmetry.It is shown that at a self-dual QCP,the GR keeps a finite value as T→0,while at a general QCP without self-duality symmetry,it displays a power-law temperature dependent divergence:Γ(T,r_(c))∼±T^(−1),which provides a novel thermodynamic means for probing QPT.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11422433,11447028,61227902,11434007,and 61275211)the Natural Science Foundation of Zhejiang Province,China(Grant No.LY13A040001)the Scientific Research Foundation of the Education Department of Zhejiang Province,China(Grant No.Y201122352)
文摘Multi-mode cavities have now attracted much attention both experimentally and theoretically. In this paper, inspired by recent experiments of cavity-assisted Raman transitions, we realize a two-axis spin Hamiltonian H = q（J_x^2＋ χJ_y^2） ＋ ω_0J_z in two cavities. This realized Hamiltonian has a distinct property that all parameters can be tuned independently. For proper parameters, the well-studied one- and two-axis twisting Hamiltonians are recovered, and the scaling of N^（-1） of the maximal squeezing factor can occur naturally. On the other hand, in the two-axis twisting Hamiltonian, spin squeezing is usually reduced when increasing the atomic resonant frequency ω_0. Surprisingly, we find that by combining with the dimensionless parameter χ（-1）, this atomic resonant frequency ω_0 can enhance spin squeezing greatly. These results are beneficial for achieving the required spin squeezing in experiments.
基金Project supported by the National Natural Science Foundation of China (Grant No 10575045)
文摘The temperature effect on tunnelling splitting in the spin boson model with a super-ohmic bath is studied by the small polaron theory. The coherent-incoherent transition temperature is calculated and its dependence on dissipation strength and bare tunnelling splitting is analysed. In additional to the traditional transition point described in textbooks, a new kind of transition is found in the low dissipation region, showing different temperature dependence in the transition. The relation to the corresponding transition in the polaron-phonon system is also discussed.
基金Supported by the National Natural Science Foundation of China under Grant No 51427801
文摘We investigate spin squeezing effects of trapped ions in an off-resonance optical potential system using the arbitrary range spin spin interaction and transverse field model. The collective spin noises at any time are analyzed exactly. The general expression of spin squeezing factor is presented for arbitrary-range spin interaction. For the nearest-neighbor and next-nearest neighbor spin interaction model, the analytic solutions are reduced from the general expressions. It is shown that the maximum spin squeezing is enhanced for the general arbitrary-range spin interaction compared with the nearest-neighbor interaction model as the long-range interaction with arbitrary sites enforces stronger correlation.
基金Project supported by UGC,NBHM,India in the form of major research projects,DAE-BRNS,India in the form of Young Scientist Research Award,ICTP,Italy in the form of Junior Associateship,and CSIR,India in the form of Senior Research Fellowship
文摘Information storage technology based on anisotropic ferromagnets with sufficiently high magneto-optical effects has received much attention in recent years.Magneto-optical recording combines the merits of magnetic and optical techniques.We investigate the magneto-optical effects on a biquadratic ferromagnet and show that the dynamics of the system are governed by a perturbed nonlinear Schro¨dinger equation.The evolutions of amplitude and velocity of the soliton are found to be time independent,thereby admitting the lossless propagation of the electromagnetic soliton in the medium,which may have potential applications in soliton based optical communication systems.We also exploit the role of perturbation,which has a significant impact on the propagation of an electromagnetic soliton.
基金Project supported by the Earmarked Research Grant from the Research Grants Council of HKSAR,China(Grant No.CUHK 401212)
文摘Fidelity measures the similarity between two states and is widely adapted by the condensed matter community as a probe of quantum phase transitions in many-body systems. Despite its success in witnessing quantum critical points, information about the fine structure of a quantum phase one can get from this approach is still limited. Here, we proposed a scheme called fidelity spectrum, By studying the fidelity spectrum, one can obtain information about the characteristics of a phase. In particular, we investigated the spectra in the one-dimensional transverse-field Ising model and the two- dimensional Kitaev model on a honeycomb lattice. It was found that the sPectra have qualitative differences in the critical and non-critical regions of the two models. From the distributions of them, the dominating k modes in a particular phase could also be captured.
基金the financial support by UGC,NBHM,India in the form of major research projectsBRNS in the form of Young Scientist Research Award,India+1 种基金the financial support from Periyar University,India in the form of University Research FellowshipJawaharlal Nehru Memorial Fund for providing funding for the doctoral study
文摘Magnetization dynamics in uniformly magnetized ferromagnetic media is studied by using Landau-Lifshitz-Gilbert equation. The nonlinear evolution equation is integrable with site-dependent and biquadratic exchange interaction by means of Landau-Lifshitz （LL） equation which is well understood. In the present work, we construct the exact solitary solutions of the nonlinear evolution equation, particularly, we employ the modified extended tangent hyperbolic function method. We show the shape changing property of solitons for the given integrable system in the presence of damping as well as inhomogeneities.
基金Project supported by Fundamental Research Funds for the Central Universities(Grant No.FRF-TP-19-013A3)。
文摘The infinite time-evolving block decimation algorithm(i TEBD)provides an efficient way to determine the ground state and dynamics of the quantum lattice systems in the thermodynamic limit.In this paper we suggest an optimized way to take the i TEBD calculation,which takes advantage of additional reduced decompositions to speed up the calculation.The numerical calculations show that for a comparable computation time our method provides more accurate results than the traditional i TEBD,especially for lattice systems with large on-site degrees of freedom.
文摘With the prevalent conception of self-replication (SR, a hallmark of living systems) as a non-equilibrium process subject to thermodynamic laws, a complementary approach derives the low energy quantum states arising from a Hamiltonian that appears to be specific for bio-systems by its containing some strongly binding terms. The bindings attract <em>properties</em> of the template (T) and the reactants to form a replicate (R). The criterion for SR that emerges from the theory is that second order (bi-linear) interaction terms between degrees of motion of T-R and the thermal bath dominate negatively over a linear self-energy term, and thereby provide a binding between the attributes of T and R. The formalism (reminiscent of the Kramers-Anderson mechanism for superexchange) is from first principles, but hinges on a drastic simplification by modelling the T, R and bath variables on interacting qubits and by congesting the attraction into a single (control) parameter. The development relies on further simplifying features, such as Random Phase Approximations and an Effective Hamiltonian formalism. The entropic balance to replication is considered and found to reside in the far surroundings.
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.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11404046,11347217,and 61201119)the Basic Research Foundation of Chongqing Education Committee,China(Grant No.KJ130615)the Chongqing Science&Technology Committee,China(Grant Nos.cstc2014jcyj A50013and cstc2013jj B50001)
文摘A comprehensive research of the antiferromagnetic （AFM） structures of perovskite-type EuZrO3 is carried out by use of the double-time Green＇s function. Two possible types of AFM configurations are considered, and theoretical results are compared with experimental results to extract the values of parameters J1, J2, and D. The obtained exchanges are employed to calculate the magnetic susceptibility, which is then in turn compared with the experimental one. Therefore, we think that the magnetic structure of EuZrO3 may be an isotropic G-type structure or an anisotropic A-type structure.
基金supported by the Nation Science Foundation of China (Grant no. 51920105011)Key R&D project of Liaoning Province of China (No. 2020JH2/10300079)Liao Ning revitalization talents program (XLYC1908034)。
文摘A bilayer nano-stanene-like structure with Ruderman-Kittel-Kasuya-Yoshida(RKKY)coupling described by the Ising model is proposed. The magnetic and thermodynamic properties are studied using the effective-field theory with correlations. The exchange coupling,longitudinal magnetic field, number of non-magnetic layers, and anisotropies had major influences on the magnetization, specific heat, and internal energy. Different saturation magnetizations are observed on the magnetization curve. The variation in the system blocking temperature is studied. The results provide theoretical guidance for the magnetic investigation of nanomaterials with RKKY coupling.
