We present a quantum dynamics study on the isotope effects of hydro-gen transfer isomerization in the formic acid dimer,and this is achieved by multidimensional dy-namics calculations with an efficient quantum mechani...We present a quantum dynamics study on the isotope effects of hydro-gen transfer isomerization in the formic acid dimer,and this is achieved by multidimensional dy-namics calculations with an efficient quantum mechanical theoretical scheme developed by our group,on a full-dimensional neural network ab initio potential energy surface.The ground-state and fundamental tun-neling splittings for four deuterium isotopologues of formic acid dimer are considered,and the calculated results are in very good general agreement with the avail-able experimental measurements.Strong isotope effects are revealed,the mode-specific funda-mental excitation effects on the tunneling rate are evidently influenced by the deuterium sub-stitution of H atom with the substitution on the OH bond being more effective than on the CH bond.Our studies are helpful for acquiring a better understanding of isotope effects in the double-hydrogen transfer processes.展开更多
We study the non-Markovian dynamics of an open quantum system with machine learning.The observable physical quantities and their evolutions are generated by using the neural network.After the pre-training is completed...We study the non-Markovian dynamics of an open quantum system with machine learning.The observable physical quantities and their evolutions are generated by using the neural network.After the pre-training is completed,we fix the weights in the subsequent processes thus do not need the further gradient feedback.We find that the dynamical properties of physical quantities obtained by the dynamical learning are better than those obtained by the learning of Hamiltonian and time evolution operator.The dynamical learning can be applied to other quantum many-body systems,non-equilibrium statistics and random processes.展开更多
The reactive collisions of nitrogen ion with hydrogen and its isotopic variations have great significance in the field of astrophysics.Herein,the state-to-state quantum time-dependent wave packet calculations of N^(+)...The reactive collisions of nitrogen ion with hydrogen and its isotopic variations have great significance in the field of astrophysics.Herein,the state-to-state quantum time-dependent wave packet calculations of N^(+)(3P)+HD→NH^(+)/ND^(+)+D/H reaction are carried out based on the recently developed potential energy surface[Phys.Chem.Chem.Phys.2122203(2019)].The integral cross sections(ICSs)and rate coefficients of both channels are precisely determined at the state-to-state level.The results of total ICSs and rate coefficients present a dramatic preference on the ND+product over the NH^(+)product,conforming to the long-lived complex-forming mechanism.Product state-resolved ICSs indicate that both the product molecules are difficult to excite to higher vibrational states,and the ND^(+)product has a hotter rotational state distribution.Moreover,the integral cross sections and rate coefficients are precisely determined at the state-to-state level and insights are provided about the differences between the two channels.The present results would provide an important reference for the further experimental studies at the finer level for this interstellar chemical reaction.The datasets presented in this paper,including the ICSs and rate coefficients of the two products for the title reaction,are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00034.展开更多
The object of the paper is to formulate Quantum (Schrödinger) dynamics of spectrally bounded wavefunction. The Nyquist theorem is used to replace the wavefunction with a discrete series of numbers. Consequent...The object of the paper is to formulate Quantum (Schrödinger) dynamics of spectrally bounded wavefunction. The Nyquist theorem is used to replace the wavefunction with a discrete series of numbers. Consequently, in this case, Schrödinger dynamics can be formalized as a universal set of ordinary differential Equations, with universal coupling between them, which are related to Euler’s formula. It is shown that the coefficient (m, n) is inversely proportional to the distance between the points n and m. As far as we know, this is the first time that this inverse square law was formulated.展开更多
In this work, we discuss the topological transformation of quantum dynamics by showing the wave dynamics of a quantum particle on different types of topological structures in various dimensions from the fundamental po...In this work, we discuss the topological transformation of quantum dynamics by showing the wave dynamics of a quantum particle on different types of topological structures in various dimensions from the fundamental polygons of the corresponding universal covering spaces. This is not the view from different perspectives of an observer who simply uses different coordinate systems to describe the same physical phenomenon but rather possible geometric and topological structures that quantum particles are endowed with when they are identified with differentiable manifolds that are embedded or immersed in Euclidean spaces of higher dimension. We present our discussions in the form of Bohr model in one, two and three dimensions using linear wave equations. In one dimension, the fundamental polygon is an interval and the universal covering space is the straight line and in this case the standing wave on a finite string is transformed into the standing wave on a circle which can be applied into the Bohr model of the hydrogen atom. In two dimensions, the fundamental polygon is a square and the universal covering space is the plane and in this case, the standing wave on the square is transformed into the standing wave on different surfaces that can be formed by gluing opposite sides of the square, which include a 2-sphere, a 2-torus, a Klein bottle and a projective plane. In three dimensions, the fundamental polygon is a cube and the universal covering space is the three-dimensional Euclidean space. It is shown that a 3-torus and the manifold K?× S1?defined as the product of a Klein bottle and a circle can be constructed by gluing opposite faces of a cube. Therefore, in three-dimensions, the standing wave on a cube is transformed into the standing wave on a 3-torus or on the manifold K?× S1. We also suggest that the mathematical degeneracy may play an important role in quantum dynamics and be associated with the concept of wavefunction collapse in quantum mechanics.展开更多
After the Big Bang,chemical reactions of hydrogen with LiH and its isotopic variants played an important role in the late stage of recombination.Moreover,these reactions have attracted the attention of experts in the ...After the Big Bang,chemical reactions of hydrogen with LiH and its isotopic variants played an important role in the late stage of recombination.Moreover,these reactions have attracted the attention of experts in the field of molecular dynamics because of its simple structure.Electronically non-adiabatic effects play a key role in many chemical reactions,while the related studies in LiH2 reactive system and its isotopic variants are not enough,so the microscopic mechanism of this system has not been fully explored.In this work,the microscopic mechanism of H+LiD reaction are performed by comparing both the adiabatic and non-adiabatic results to study the non-adiabatic effects.The reactivity of R1(H+LiD→Li+HD)channel is inhibited,while that of R2(H+LiD→D+LiH)channel is enhanced when the non-adiabatic couplings are considered.For R1 channel,a direct stripping process dominates this channel and the main reaction mechanism is not influenced by the non-adiabatic effects.For R2 channel,at relatively low collision energy,the dominance changes from a rebound process to the complex-forming mechanism when the non-adiabatic effects are considered,whereas the rebound collision approach still dominates the reaction at relatively high collision energy in both calculations.The presented results provide a basis for further detailed study on this importantly astrophysical reaction system.展开更多
A branching random walk algorithm for many-body Wigner equations and its numerical applications for quantum dynamics in phase space are proposed and ana-lyzed in this paper.Using an auxiliary function,the truncated Wi...A branching random walk algorithm for many-body Wigner equations and its numerical applications for quantum dynamics in phase space are proposed and ana-lyzed in this paper.Using an auxiliary function,the truncated Wigner equation and its adjoint form are cast into integral formulations,which can be then reformulated into renewal-type equations with probabilistic interpretations.We prove that the first mo-ment of a branching random walk is the solution for the adjoint equation.With the help of the additional degree of freedom offered by the auxiliary function,we are able to produce a weighted-particle implementation of the branching random walk.In contrast to existing signed-particle implementations,this weighted-particle one shows a key ca-pacity of variance reduction by increasing the constant auxiliary function and has no time discretization errors.Several canonical numerical experiments on the 2D Gaussian barrier scattering and a 4D Helium-like system validate our theoretical findings,and demonstrate the accuracy,the efficiency,and thus the computability of the proposed weighted-particle Wigner branching random walk algorithm.展开更多
We study the quantum dynamics of an impurity-doped Bose–Einstein condensate(BEC) system.We show how to generate the macroscopic quantum superposition states(MQSSs) of the BEC by the use of projective measurements on ...We study the quantum dynamics of an impurity-doped Bose–Einstein condensate(BEC) system.We show how to generate the macroscopic quantum superposition states(MQSSs) of the BEC by the use of projective measurements on impurity atoms. It is found that the nonclassicality of MQSSs can be manipulated by changing the number of the impurities and their interaction with the BEC. It is shown that the BEC matter-wave field exhibits a collapse and revival phenomenon which reveals the quantum nature of the BEC matter-wave field. We investigate the micro-macro entanglement between the impurities and the BEC, and find enhancement of the micro-macro entanglement induced by the initial quantum coherence of the impurity atoms.展开更多
The dynamics of C+H_(2)→H+CH reaction is theoretically studied using the quasiclassical trajectory and quantum mechanical wave packet methods.The analysis of reaction probabilities,integral cross sections,and rate co...The dynamics of C+H_(2)→H+CH reaction is theoretically studied using the quasiclassical trajectory and quantum mechanical wave packet methods.The analysis of reaction probabilities,integral cross sections,and rate coefficients reveal the essential Coriolis coupling effects in the quantum mechanical wave packet calculations.The calculated polarizationdependent differential cross section,P(θ_(r))and P(Φ_(r))show that the j'of product rotational angular momentum is not only aligned along the y axis and the direction of the vector x+z,but also strongly oriented along the positive y axis.展开更多
Proton transport is one of the most important and interesting phenomena in living cells.The present work proposes a multiscale/multiphysics model for the understanding of the molecular mechanism of proton transport in...Proton transport is one of the most important and interesting phenomena in living cells.The present work proposes a multiscale/multiphysics model for the understanding of the molecular mechanism of proton transport in transmembrane proteins.We describe proton dynamics quantum mechanically via a density functional approach while implicitly model other solvent ions as a dielectric continuum to reduce the number of degrees of freedom.The densities of all other ions in the solvent are assumed to obey the Boltzmann distribution.The impact of protein molecular structure and its charge polarization on the proton transport is considered explicitly at the atomic level.We formulate a total free energy functional to put proton kinetic and potential energies as well as electrostatic energy of all ions on an equal footing.The variational principle is employed to derive nonlinear governing equations for the proton transport system.Generalized Poisson-Boltzmann equation and Kohn-Sham equation are obtained from the variational framework.Theoretical formulations for the proton density and proton conductance are constructed based on fundamental principles.The molecular surface of the channel protein is utilized to split the discrete protein domain and the continuum solvent domain,and facilitate the multiscale discrete/continuum/quantum descriptions.A number of mathematical algorithms,including the Dirichlet to Neumann mapping,matched interface and boundary method,Gummel iteration,and Krylov space techniques are utilized to implement the proposed model in a computationally efficient manner.The Gramicidin A(GA)channel is used to demonstrate the performance of the proposed proton transport model and validate the efficiency of proposed mathematical algorithms.The electrostatic characteristics of the GA channel is analyzed with a wide range of model parameters.The proton conductances are studied over a number of applied voltages and reference concentrations.A comparison with experimental data verifies the present model predictions and validates the proposed model.展开更多
Applicability of Feynman path integral approach to numerical simulations of quantum dynamics of an electron in real time domain is examined.Coherent quantum dynamics is demonstrated with one dimensional test cases(qua...Applicability of Feynman path integral approach to numerical simulations of quantum dynamics of an electron in real time domain is examined.Coherent quantum dynamics is demonstrated with one dimensional test cases(quantum dot models)and performance of the Trotter kernel as compared with the exact kernels is tested.Also,a novel approach for finding the ground state and other stationary sates is presented.This is based on the incoherent propagation in real time.For both approaches the Monte Carlo grid and sampling are tested and compared with regular grids and sampling.We asses the numerical prerequisites for all of the above.展开更多
Effective Hamiltonians in periodically driven systems have received widespread attention for realization of novel quantum phases, non-equilibrium phase transition, and Majorana mode. Recently, the study of effective H...Effective Hamiltonians in periodically driven systems have received widespread attention for realization of novel quantum phases, non-equilibrium phase transition, and Majorana mode. Recently, the study of effective Hamiltonian using various methods has gained great interest. We consider a vector differential equation of motion to derive the effective Hamiltonian for any periodically driven two-level system, and the dynamics of the spin vector are an evolution under the Bloch sphere. Here, we investigate the properties of this equation and show that a sudden change of the effective Hamiltonian is expected. Furthermore, we present several exact relations, whose expressions are independent of the different starting points. Moreover, we deduce the effective Hamiltonian from the high-frequency limit, which approximately equals the results in previous studies. Our results show that the vector differential equation of motion is not affected by a convergence problem, and thus, can be used to numerically investigate the effective models in any periodic modulating system. Finally, we anticipate that the proposed method can be applied to experimental platforms that require time-periodic modulation, such as ultracold atoms and optical lattices.展开更多
Floquet dynamical quantum phase transitions(DQPTs),which are nonanalytic phenomena recuring periodically in time-periodic driven quantum many-body systems,have been widely studied in recent years.In this article,the F...Floquet dynamical quantum phase transitions(DQPTs),which are nonanalytic phenomena recuring periodically in time-periodic driven quantum many-body systems,have been widely studied in recent years.In this article,the Floquet DQPTs in transverse XY spin chains under the modulation ofδ-function periodic kickings are investigated.We analytically solve the system,and by considering the eigenstate as well as the ground state as the initial state of the Floquet dynamics,we study the corresponding multiple Floquet DQPTs emerged in the micromotion with different kicking moments.The rate function of return amplitude,the Pancharatnam geometric phase and the dynamical topological order parameter are calculated,which consistently verify the emergence of Floquet DQPTs in the system.展开更多
Spin dynamics in several different types of ferromagnetic metal(FM)/10-nm-thick n-type GaAs quantum well(QW) junctions is studied by means of time-resolved Kerr rotation measurements. Compared with the MnGa/insitu dop...Spin dynamics in several different types of ferromagnetic metal(FM)/10-nm-thick n-type GaAs quantum well(QW) junctions is studied by means of time-resolved Kerr rotation measurements. Compared with the MnGa/insitu doped 10-nm-thick n-type GaAs QW junction, the spin lifetime of the MnGa/modulation-doped 10-nm-thick n-type GaAs QW junction is shorter by a factor of 5,consistent with the D'yakonov-Pcrel' spin relaxation mechanism. Meanwhile, compared with the spin lifetime of the MnAs/in-situ doped 10-nm-thick n-type GaAs QW junction, the MnGa/in-situ doped 10-nm-thick n-type GaAs QW junction is of a spin lifetime longer by a factor of 4.2. The later observation is well explained by the Rashba effect in the presence of structure inversion asymmetry, which acts directly on photo-excited eleetron spins. We demonstrate that MnGa-like FM/in-situ doped 10-nm-thick n-type GaAs QW junctions, which possess relatively low interfacial potential barriers, are able to provide long spin lifetimes.展开更多
As is well known,the quantum evolution speed of quantum state can never be accelerated in the Markovian regime without any operators on the system.The Hamiltonian corrections induced by the action of coherent driving ...As is well known,the quantum evolution speed of quantum state can never be accelerated in the Markovian regime without any operators on the system.The Hamiltonian corrections induced by the action of coherent driving forces are often used to fight dissipative and decoherence mechanisms in experiments.For this reason,considering three noisy channels(the phase-flip channel,the amplitude damping channel and the depolarizing channel),we propose a scheme of speedup evolution of an open system by controlling an external unitary coherent driving operator on the system.It is shown that,in the presence of the coherent driving,no-speedup evolution can be transformed into quantum speedup evolution in the Markovian dynamics process.Additionally,under the fixed coherent driving strength in the above three noisy channels,the best way to achieve the most degree of quantum speedup for the system has been acquired by rotating the system with appropriate driving direction angles,respectively.Finally,we conclude that the reason for this acceleration is not the nonMarkovian dynamical behavior of the system but due to the oscillation of geometric distance between the initial state and the target final state.展开更多
The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisciplinary interface that contributes to advancing the field...The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisciplinary interface that contributes to advancing the field of system autonomy,and pushes the engineering boundaries beyond the existing techniques.The present research adopts the experimental aspects of quantum entanglement and quantum cryptography,and integrates these established quantum capabilities into distributed robotic platforms,to explore the possibility of achieving increased autonomy for the control of multi-agent robotic systems engaged in cooperative tasks.Experimental quantum capabilities are realized by producing single photons(using spontaneous parametric down-conversion process),polarization of photons,detecting vertical and horizontal polarizations,and single photon detecting/counting.Specifically,such quantum aspects are implemented on network of classical agents,i.e.,classical aerial and ground robots/unmanned systems.With respect to classical systems for robotic applications,leveraging quantum technology is expected to lead to guaranteed security,very fast control and communication,and unparalleled quantum capabilities such as entanglement and quantum superposition that will enable novel applications.展开更多
We study the dynamical quantum phase transitions(DQPTs)in the XY chains with the Dzyaloshinskii-Moriya interaction and the XZY-YZX type of three-site interaction after a sudden quench.Both the models can be mapped to ...We study the dynamical quantum phase transitions(DQPTs)in the XY chains with the Dzyaloshinskii-Moriya interaction and the XZY-YZX type of three-site interaction after a sudden quench.Both the models can be mapped to the spinless free fermion models by the Jordan-Wigner and Bogoliubov transformations with the form■where the quasiparticle excitation spectraεkmay be smaller than 0 for some k and are asymmetrical■It is found that the factors of Loschmidt echo equal 1 for some k corresponding to the quasiparticle excitation spectra of the pre-quench Hamiltonian satisfyingε_(k)·ε_(-k)<0,when the quench is from the gapless phase.By considering the quench from different ground states,we obtain the conditions for the occurrence of DQPTs for the general XY chains with gapless phase,and find that the DQPTs may not occur in the quench across the quantum phase transitions regardless of whether the quench is from the gapless phase to gapped phase or from the gapped phase to gapless phase.This is different from the DQPTs in the case of quench from the gapped phase to gapped phase,in which the DQPTs will always appear.Moreover,we analyze the different reasons for the absence of DQPTs in the quench from the gapless phase and the gapped phase.The conclusion can also be extended to the general quantum spin chains.展开更多
This paper addresses the application of quantum entanglement and cryptography for automation and control of dynamic systems.A dynamic system is a system where the rates of changes of its state variables are not neglig...This paper addresses the application of quantum entanglement and cryptography for automation and control of dynamic systems.A dynamic system is a system where the rates of changes of its state variables are not negligible.Quantum entanglement is realized by the Spontaneous Parametric Down-conversion process.Two entangled autonomous systems exhibit correlated behavior without any classical communication in between them due to the quantum entanglement phenomenon.Specifically,the behavior of a system,Bob,at a distance,is correlated with a corresponding system,Alice.In an automation scenario,the"Bob Robot"is entangled with the"Alice Robot"in performing autonomous tasks without any classical connection between them.Quantum cryptography is a capability that allows guaranteed security.Such capabilities can be implemented in control of autonomous mechanical systems where,for instance,an"Alice Autonomous System"can control a"Bob Autonomous System"for applications of automation and robotics.The applications of quantum technologies to mechanical systems,at a scale larger than the atomistic scale,for control and automation,is a novel contribution of this paper.Notably,the feedback control transfer function of an integrated classical dynamic system and a quantum state is proposed.展开更多
In this review article,we first briefty introduce the transport theory and quantum molecular dynamics model applied in the study of the heavy ion collisions from low to intermediate energies.The developments of improv...In this review article,we first briefty introduce the transport theory and quantum molecular dynamics model applied in the study of the heavy ion collisions from low to intermediate energies.The developments of improved quantum molecular dynamics model(ImQMD)and ultra-relativistic quantum molecular dynamics model(UrQMD),are reviewed.The reaction mechanism and phenomena related to the fusion,multinucleon transrer,fragmentation,collective flow and particle production are reviewed and discussed within the framework of the two models.The constraints on the isospin asymmetric muclear equation of state and in-medium nucleon nucleon cross sections by comparing the heavy ion collision data with transport models calculations in last decades are also discussed,and the uncertainties of these constraints are analyzed as well.Finally,we discuss the future direction of the development of the transport models for improving the understanding of the reaction mechanism,the descriptions of various observables,the constraint on the nuclear equation of state,as well as for the constraint on in-medium nucleon-nucleon cross sections.展开更多
The isospin fractionations in 124Sn,107Sn+120Sn at 600 MeV/nucleon,and 136Xe,124Xe+208Pb at 1000 MeV/nucleon are investigated by the isospin-dependent quantum molecular dynamics model coupled with the statistical code...The isospin fractionations in 124Sn,107Sn+120Sn at 600 MeV/nucleon,and 136Xe,124Xe+208Pb at 1000 MeV/nucleon are investigated by the isospin-dependent quantum molecular dynamics model coupled with the statistical code GEMINI.The yield ratio as a function of the binding energy difference for light mirror nuclei 3H/3He,7Li/7Be,11B/11C,and 15N/15O is applied to estimate the ratio between neutrons and protons in the gas of the fragmenting system.By comparing the estimated values resulting from the simulations with and without the GEMINI code,it was found that the secondary decay distorts the signal of the isospin fractionation.To minimize the secondary decay effects,the yield ratio of the light mirror nuclei 3H/3He as well as its double ratio between two systems with different isospin asymmetries of the projectiles is recommended as robust isospin observables.展开更多
基金supported by the National Natural Sci-ence Foundation of China(No.21973098 and No.22133003)the Beijing National Laboratory for Molecular SciencesJianwei Cao acknowledges the Youth Innovation Promotion Association CAS(No.2018045).
文摘We present a quantum dynamics study on the isotope effects of hydro-gen transfer isomerization in the formic acid dimer,and this is achieved by multidimensional dy-namics calculations with an efficient quantum mechanical theoretical scheme developed by our group,on a full-dimensional neural network ab initio potential energy surface.The ground-state and fundamental tun-neling splittings for four deuterium isotopologues of formic acid dimer are considered,and the calculated results are in very good general agreement with the avail-able experimental measurements.Strong isotope effects are revealed,the mode-specific funda-mental excitation effects on the tunneling rate are evidently influenced by the deuterium sub-stitution of H atom with the substitution on the OH bond being more effective than on the CH bond.Our studies are helpful for acquiring a better understanding of isotope effects in the double-hydrogen transfer processes.
基金the National Program for Basic Research of the Ministry of Science and Technology of China(Grant Nos.2016YFA0300600 and 2016YFA0302104)the National Natural Science Foundation of China(Grant Nos.12074410,12047502,11934015,11975183,11947301,11774397,11775178,and 11775177)+3 种基金the Major Basic Research Program of the Natural Science of Shaanxi Province,China(Grant No.2017ZDJC-32)the Australian Research Council(Grant No.DP 190101529)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB33000000)the Double First-Class University Construction Project of Northwest University.
文摘We study the non-Markovian dynamics of an open quantum system with machine learning.The observable physical quantities and their evolutions are generated by using the neural network.After the pre-training is completed,we fix the weights in the subsequent processes thus do not need the further gradient feedback.We find that the dynamical properties of physical quantities obtained by the dynamical learning are better than those obtained by the learning of Hamiltonian and time evolution operator.The dynamical learning can be applied to other quantum many-body systems,non-equilibrium statistics and random processes.
基金Project supported by the National Natural Science Foundation of China(Grant No.11774043).
文摘The reactive collisions of nitrogen ion with hydrogen and its isotopic variations have great significance in the field of astrophysics.Herein,the state-to-state quantum time-dependent wave packet calculations of N^(+)(3P)+HD→NH^(+)/ND^(+)+D/H reaction are carried out based on the recently developed potential energy surface[Phys.Chem.Chem.Phys.2122203(2019)].The integral cross sections(ICSs)and rate coefficients of both channels are precisely determined at the state-to-state level.The results of total ICSs and rate coefficients present a dramatic preference on the ND+product over the NH^(+)product,conforming to the long-lived complex-forming mechanism.Product state-resolved ICSs indicate that both the product molecules are difficult to excite to higher vibrational states,and the ND^(+)product has a hotter rotational state distribution.Moreover,the integral cross sections and rate coefficients are precisely determined at the state-to-state level and insights are provided about the differences between the two channels.The present results would provide an important reference for the further experimental studies at the finer level for this interstellar chemical reaction.The datasets presented in this paper,including the ICSs and rate coefficients of the two products for the title reaction,are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00034.
文摘The object of the paper is to formulate Quantum (Schrödinger) dynamics of spectrally bounded wavefunction. The Nyquist theorem is used to replace the wavefunction with a discrete series of numbers. Consequently, in this case, Schrödinger dynamics can be formalized as a universal set of ordinary differential Equations, with universal coupling between them, which are related to Euler’s formula. It is shown that the coefficient (m, n) is inversely proportional to the distance between the points n and m. As far as we know, this is the first time that this inverse square law was formulated.
文摘In this work, we discuss the topological transformation of quantum dynamics by showing the wave dynamics of a quantum particle on different types of topological structures in various dimensions from the fundamental polygons of the corresponding universal covering spaces. This is not the view from different perspectives of an observer who simply uses different coordinate systems to describe the same physical phenomenon but rather possible geometric and topological structures that quantum particles are endowed with when they are identified with differentiable manifolds that are embedded or immersed in Euclidean spaces of higher dimension. We present our discussions in the form of Bohr model in one, two and three dimensions using linear wave equations. In one dimension, the fundamental polygon is an interval and the universal covering space is the straight line and in this case the standing wave on a finite string is transformed into the standing wave on a circle which can be applied into the Bohr model of the hydrogen atom. In two dimensions, the fundamental polygon is a square and the universal covering space is the plane and in this case, the standing wave on the square is transformed into the standing wave on different surfaces that can be formed by gluing opposite sides of the square, which include a 2-sphere, a 2-torus, a Klein bottle and a projective plane. In three dimensions, the fundamental polygon is a cube and the universal covering space is the three-dimensional Euclidean space. It is shown that a 3-torus and the manifold K?× S1?defined as the product of a Klein bottle and a circle can be constructed by gluing opposite faces of a cube. Therefore, in three-dimensions, the standing wave on a cube is transformed into the standing wave on a 3-torus or on the manifold K?× S1. We also suggest that the mathematical degeneracy may play an important role in quantum dynamics and be associated with the concept of wavefunction collapse in quantum mechanics.
基金supported by the National Natural Science Foundation of China(Grant No.11774043).
文摘After the Big Bang,chemical reactions of hydrogen with LiH and its isotopic variants played an important role in the late stage of recombination.Moreover,these reactions have attracted the attention of experts in the field of molecular dynamics because of its simple structure.Electronically non-adiabatic effects play a key role in many chemical reactions,while the related studies in LiH2 reactive system and its isotopic variants are not enough,so the microscopic mechanism of this system has not been fully explored.In this work,the microscopic mechanism of H+LiD reaction are performed by comparing both the adiabatic and non-adiabatic results to study the non-adiabatic effects.The reactivity of R1(H+LiD→Li+HD)channel is inhibited,while that of R2(H+LiD→D+LiH)channel is enhanced when the non-adiabatic couplings are considered.For R1 channel,a direct stripping process dominates this channel and the main reaction mechanism is not influenced by the non-adiabatic effects.For R2 channel,at relatively low collision energy,the dominance changes from a rebound process to the complex-forming mechanism when the non-adiabatic effects are considered,whereas the rebound collision approach still dominates the reaction at relatively high collision energy in both calculations.The presented results provide a basis for further detailed study on this importantly astrophysical reaction system.
基金This research was supported by grants from the National Natural Science Foundation of China(Nos.11471025,11421101,11822102).
文摘A branching random walk algorithm for many-body Wigner equations and its numerical applications for quantum dynamics in phase space are proposed and ana-lyzed in this paper.Using an auxiliary function,the truncated Wigner equation and its adjoint form are cast into integral formulations,which can be then reformulated into renewal-type equations with probabilistic interpretations.We prove that the first mo-ment of a branching random walk is the solution for the adjoint equation.With the help of the additional degree of freedom offered by the auxiliary function,we are able to produce a weighted-particle implementation of the branching random walk.In contrast to existing signed-particle implementations,this weighted-particle one shows a key ca-pacity of variance reduction by increasing the constant auxiliary function and has no time discretization errors.Several canonical numerical experiments on the 2D Gaussian barrier scattering and a 4D Helium-like system validate our theoretical findings,and demonstrate the accuracy,the efficiency,and thus the computability of the proposed weighted-particle Wigner branching random walk algorithm.
基金supported by the National Natural Science Foundation of China under Grants No. 11775075No.1143011 and No. 11935006。
文摘We study the quantum dynamics of an impurity-doped Bose–Einstein condensate(BEC) system.We show how to generate the macroscopic quantum superposition states(MQSSs) of the BEC by the use of projective measurements on impurity atoms. It is found that the nonclassicality of MQSSs can be manipulated by changing the number of the impurities and their interaction with the BEC. It is shown that the BEC matter-wave field exhibits a collapse and revival phenomenon which reveals the quantum nature of the BEC matter-wave field. We investigate the micro-macro entanglement between the impurities and the BEC, and find enhancement of the micro-macro entanglement induced by the initial quantum coherence of the impurity atoms.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11904394 and 12004216)the Natural Science Foundation of Shandong Province,China(Grant No.ZR2020QA064)。
文摘The dynamics of C+H_(2)→H+CH reaction is theoretically studied using the quasiclassical trajectory and quantum mechanical wave packet methods.The analysis of reaction probabilities,integral cross sections,and rate coefficients reveal the essential Coriolis coupling effects in the quantum mechanical wave packet calculations.The calculated polarizationdependent differential cross section,P(θ_(r))and P(Φ_(r))show that the j'of product rotational angular momentum is not only aligned along the y axis and the direction of the vector x+z,but also strongly oriented along the positive y axis.
基金supported in part by NSF grant CCF-0936830NIH grant R01GM-090208MSU Competitive Discretionary Funding Program grant 91-4600.
文摘Proton transport is one of the most important and interesting phenomena in living cells.The present work proposes a multiscale/multiphysics model for the understanding of the molecular mechanism of proton transport in transmembrane proteins.We describe proton dynamics quantum mechanically via a density functional approach while implicitly model other solvent ions as a dielectric continuum to reduce the number of degrees of freedom.The densities of all other ions in the solvent are assumed to obey the Boltzmann distribution.The impact of protein molecular structure and its charge polarization on the proton transport is considered explicitly at the atomic level.We formulate a total free energy functional to put proton kinetic and potential energies as well as electrostatic energy of all ions on an equal footing.The variational principle is employed to derive nonlinear governing equations for the proton transport system.Generalized Poisson-Boltzmann equation and Kohn-Sham equation are obtained from the variational framework.Theoretical formulations for the proton density and proton conductance are constructed based on fundamental principles.The molecular surface of the channel protein is utilized to split the discrete protein domain and the continuum solvent domain,and facilitate the multiscale discrete/continuum/quantum descriptions.A number of mathematical algorithms,including the Dirichlet to Neumann mapping,matched interface and boundary method,Gummel iteration,and Krylov space techniques are utilized to implement the proposed model in a computationally efficient manner.The Gramicidin A(GA)channel is used to demonstrate the performance of the proposed proton transport model and validate the efficiency of proposed mathematical algorithms.The electrostatic characteristics of the GA channel is analyzed with a wide range of model parameters.The proton conductances are studied over a number of applied voltages and reference concentrations.A comparison with experimental data verifies the present model predictions and validates the proposed model.
文摘Applicability of Feynman path integral approach to numerical simulations of quantum dynamics of an electron in real time domain is examined.Coherent quantum dynamics is demonstrated with one dimensional test cases(quantum dot models)and performance of the Trotter kernel as compared with the exact kernels is tested.Also,a novel approach for finding the ground state and other stationary sates is presented.This is based on the incoherent propagation in real time.For both approaches the Monte Carlo grid and sampling are tested and compared with regular grids and sampling.We asses the numerical prerequisites for all of the above.
基金supported by the National Natural Science Foundation of China (Grant No. 11774328)。
文摘Effective Hamiltonians in periodically driven systems have received widespread attention for realization of novel quantum phases, non-equilibrium phase transition, and Majorana mode. Recently, the study of effective Hamiltonian using various methods has gained great interest. We consider a vector differential equation of motion to derive the effective Hamiltonian for any periodically driven two-level system, and the dynamics of the spin vector are an evolution under the Bloch sphere. Here, we investigate the properties of this equation and show that a sudden change of the effective Hamiltonian is expected. Furthermore, we present several exact relations, whose expressions are independent of the different starting points. Moreover, we deduce the effective Hamiltonian from the high-frequency limit, which approximately equals the results in previous studies. Our results show that the vector differential equation of motion is not affected by a convergence problem, and thus, can be used to numerically investigate the effective models in any periodic modulating system. Finally, we anticipate that the proposed method can be applied to experimental platforms that require time-periodic modulation, such as ultracold atoms and optical lattices.
基金supported by the National Natural Science Foundation of China(Grant No.11475037)the Fundamental Research Funds for the Central Universities(Grant No.DUT19LK38)。
文摘Floquet dynamical quantum phase transitions(DQPTs),which are nonanalytic phenomena recuring periodically in time-periodic driven quantum many-body systems,have been widely studied in recent years.In this article,the Floquet DQPTs in transverse XY spin chains under the modulation ofδ-function periodic kickings are investigated.We analytically solve the system,and by considering the eigenstate as well as the ground state as the initial state of the Floquet dynamics,we study the corresponding multiple Floquet DQPTs emerged in the micromotion with different kicking moments.The rate function of return amplitude,the Pancharatnam geometric phase and the dynamical topological order parameter are calculated,which consistently verify the emergence of Floquet DQPTs in the system.
文摘Spin dynamics in several different types of ferromagnetic metal(FM)/10-nm-thick n-type GaAs quantum well(QW) junctions is studied by means of time-resolved Kerr rotation measurements. Compared with the MnGa/insitu doped 10-nm-thick n-type GaAs QW junction, the spin lifetime of the MnGa/modulation-doped 10-nm-thick n-type GaAs QW junction is shorter by a factor of 5,consistent with the D'yakonov-Pcrel' spin relaxation mechanism. Meanwhile, compared with the spin lifetime of the MnAs/in-situ doped 10-nm-thick n-type GaAs QW junction, the MnGa/in-situ doped 10-nm-thick n-type GaAs QW junction is of a spin lifetime longer by a factor of 4.2. The later observation is well explained by the Rashba effect in the presence of structure inversion asymmetry, which acts directly on photo-excited eleetron spins. We demonstrate that MnGa-like FM/in-situ doped 10-nm-thick n-type GaAs QW junctions, which possess relatively low interfacial potential barriers, are able to provide long spin lifetimes.
基金Project supported by the Shandong Provincial Natural Science Foundation,China(Grant No.ZR2020MA086)the National Natural Science Foundation of China(Grant Nos.61675115 and 11974209)。
文摘As is well known,the quantum evolution speed of quantum state can never be accelerated in the Markovian regime without any operators on the system.The Hamiltonian corrections induced by the action of coherent driving forces are often used to fight dissipative and decoherence mechanisms in experiments.For this reason,considering three noisy channels(the phase-flip channel,the amplitude damping channel and the depolarizing channel),we propose a scheme of speedup evolution of an open system by controlling an external unitary coherent driving operator on the system.It is shown that,in the presence of the coherent driving,no-speedup evolution can be transformed into quantum speedup evolution in the Markovian dynamics process.Additionally,under the fixed coherent driving strength in the above three noisy channels,the best way to achieve the most degree of quantum speedup for the system has been acquired by rotating the system with appropriate driving direction angles,respectively.Finally,we conclude that the reason for this acceleration is not the nonMarkovian dynamical behavior of the system but due to the oscillation of geometric distance between the initial state and the target final state.
文摘The intersection of Quantum Technologies and Robotics Autonomy is explored in the present paper.The two areas are brought together in establishing an interdisciplinary interface that contributes to advancing the field of system autonomy,and pushes the engineering boundaries beyond the existing techniques.The present research adopts the experimental aspects of quantum entanglement and quantum cryptography,and integrates these established quantum capabilities into distributed robotic platforms,to explore the possibility of achieving increased autonomy for the control of multi-agent robotic systems engaged in cooperative tasks.Experimental quantum capabilities are realized by producing single photons(using spontaneous parametric down-conversion process),polarization of photons,detecting vertical and horizontal polarizations,and single photon detecting/counting.Specifically,such quantum aspects are implemented on network of classical agents,i.e.,classical aerial and ground robots/unmanned systems.With respect to classical systems for robotic applications,leveraging quantum technology is expected to lead to guaranteed security,very fast control and communication,and unparalleled quantum capabilities such as entanglement and quantum superposition that will enable novel applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.11975126 and 11575087)。
文摘We study the dynamical quantum phase transitions(DQPTs)in the XY chains with the Dzyaloshinskii-Moriya interaction and the XZY-YZX type of three-site interaction after a sudden quench.Both the models can be mapped to the spinless free fermion models by the Jordan-Wigner and Bogoliubov transformations with the form■where the quasiparticle excitation spectraεkmay be smaller than 0 for some k and are asymmetrical■It is found that the factors of Loschmidt echo equal 1 for some k corresponding to the quasiparticle excitation spectra of the pre-quench Hamiltonian satisfyingε_(k)·ε_(-k)<0,when the quench is from the gapless phase.By considering the quench from different ground states,we obtain the conditions for the occurrence of DQPTs for the general XY chains with gapless phase,and find that the DQPTs may not occur in the quench across the quantum phase transitions regardless of whether the quench is from the gapless phase to gapped phase or from the gapped phase to gapless phase.This is different from the DQPTs in the case of quench from the gapped phase to gapped phase,in which the DQPTs will always appear.Moreover,we analyze the different reasons for the absence of DQPTs in the quench from the gapless phase and the gapped phase.The conclusion can also be extended to the general quantum spin chains.
文摘This paper addresses the application of quantum entanglement and cryptography for automation and control of dynamic systems.A dynamic system is a system where the rates of changes of its state variables are not negligible.Quantum entanglement is realized by the Spontaneous Parametric Down-conversion process.Two entangled autonomous systems exhibit correlated behavior without any classical communication in between them due to the quantum entanglement phenomenon.Specifically,the behavior of a system,Bob,at a distance,is correlated with a corresponding system,Alice.In an automation scenario,the"Bob Robot"is entangled with the"Alice Robot"in performing autonomous tasks without any classical connection between them.Quantum cryptography is a capability that allows guaranteed security.Such capabilities can be implemented in control of autonomous mechanical systems where,for instance,an"Alice Autonomous System"can control a"Bob Autonomous System"for applications of automation and robotics.The applications of quantum technologies to mechanical systems,at a scale larger than the atomistic scale,for control and automation,is a novel contribution of this paper.Notably,the feedback control transfer function of an integrated classical dynamic system and a quantum state is proposed.
基金Yingxun Zhang acknowledges the supports in part by the National Natural Science Foundation of China(Grant Nos.11875323,11875125,11475262,10675172,11075215,11475262,11790323,11790324,11790325,and 11961141003)the National Key R&D Program of China(Grant No.2018YFA0404404)+15 种基金the Continuous Basic Scientific Research Project(No.WDJC-2019-13)Ning Wang acknowledges the supports in part by the National Natural Science Foundation of China(Nos.U1867212 and 11422548)the Guangxi Natural Science Foundation(Nos.2015G XNSFDA139004,2017G XNSFG A198001)Qingfeng Li acknowledges the supports in part by the National Natural Science Foundation of China(Nos.11875125,11847315,11375062,11505057,11947410,and 11747312)the Zhejiang Provincial Natural Science Foundation of China(No.LY18A050002)the“Ten-Thousand Talent Program”of Zhejiang ProvinceJunlong Tian acknowledges the supports in part by the National Science Foundation of China(Nos.11961131010 and 11475004)Li Ou acknowledges the supports in part by the National Natural Science Foundation of China(No.11965004)the Natural Science Foundation of Guangxi Province(No.2016GXNSFFA380001)Foundation of Guangxi Innovative Team and Distinguished Scholar in Institutions of Higher EducationMin Liu acknowledges the supports in part by the National Natural Science Foundation of China(No.11875323)Kai Zhao acknowledges the supports in part by the National Natural Science Foundation of China(Nos.11675266,11005155,11475262,11275052,11375062,11547312,and 11275068)the National Key Basic Research Developm ent Program of China(Nos.2007CB209900 and 2013CB834404)Xizhen Wu acknowledges the supports in part by the National Natural Science Foundation of China(Nos.10235020,10979023,11005155,11365004,11475004,and 11675266)Zhuxia Li acknowledges the supports in part by the National Natural Science Foundation of China(Nos.19975073,10175093,10175089,10235030,11275052,11375062,11475262,11475004,11875323,and 11875125)the National Key Basic Research Development Program of China(Nos.G20000774 and 2007CB209900).
文摘In this review article,we first briefty introduce the transport theory and quantum molecular dynamics model applied in the study of the heavy ion collisions from low to intermediate energies.The developments of improved quantum molecular dynamics model(ImQMD)and ultra-relativistic quantum molecular dynamics model(UrQMD),are reviewed.The reaction mechanism and phenomena related to the fusion,multinucleon transrer,fragmentation,collective flow and particle production are reviewed and discussed within the framework of the two models.The constraints on the isospin asymmetric muclear equation of state and in-medium nucleon nucleon cross sections by comparing the heavy ion collision data with transport models calculations in last decades are also discussed,and the uncertainties of these constraints are analyzed as well.Finally,we discuss the future direction of the development of the transport models for improving the understanding of the reaction mechanism,the descriptions of various observables,the constraint on the nuclear equation of state,as well as for the constraint on in-medium nucleon-nucleon cross sections.
基金the Natural Science Foundation of China under(Nos.U2032137 and U1832182)the Natural Science Foundation of Guangdong Province,China(No.18zxxt65)Fundamental Research Funds for the Central Universities(No.19lgpy306).
文摘The isospin fractionations in 124Sn,107Sn+120Sn at 600 MeV/nucleon,and 136Xe,124Xe+208Pb at 1000 MeV/nucleon are investigated by the isospin-dependent quantum molecular dynamics model coupled with the statistical code GEMINI.The yield ratio as a function of the binding energy difference for light mirror nuclei 3H/3He,7Li/7Be,11B/11C,and 15N/15O is applied to estimate the ratio between neutrons and protons in the gas of the fragmenting system.By comparing the estimated values resulting from the simulations with and without the GEMINI code,it was found that the secondary decay distorts the signal of the isospin fractionation.To minimize the secondary decay effects,the yield ratio of the light mirror nuclei 3H/3He as well as its double ratio between two systems with different isospin asymmetries of the projectiles is recommended as robust isospin observables.
