The realization of spin-orbit-coupled ultracold gases has driven a wide range of research and is typically based on the rotating wave approximation(RWA).By neglecting the counter-rotating terms,RWA characterizes a sin...The realization of spin-orbit-coupled ultracold gases has driven a wide range of research and is typically based on the rotating wave approximation(RWA).By neglecting the counter-rotating terms,RWA characterizes a single near-resonant spin-orbit(SO)coupling in a two-level system.Here,we propose and experimentally realize a new scheme for achieving a pair of two-dimensional(2D)SO couplings for ultracold fermions beyond RWA.This work not only realizes the first anomalous Floquet topological Fermi gas beyond RWA,but also significantly improves the lifetime of the 2D-SO-coupled Fermi gas.Based on pump-probe quench measurements,we observe a deterministic phase relation between two sets of SO couplings,which is characteristic of our beyond-RWA scheme and enables the two SO couplings to be simultaneously tuned to the optimum 2D configurations.We observe intriguing band topology by measuring two-ring band-inversion surfaces,quantitatively consistent with a Floquet topological Fermi gas in the regime of high Chern numbers.Our study can open an avenue to explore exotic SO physics and anomalous topological states based on long-lived SO-coupled ultracold fermions.展开更多
The relativistic quantum motions of the oscillator field(via the Klein–Gordon oscillator equation)under a uniform magnetic field in a topologically non-trivial space-time geometry are analyzed.We solve the Klein–Gor...The relativistic quantum motions of the oscillator field(via the Klein–Gordon oscillator equation)under a uniform magnetic field in a topologically non-trivial space-time geometry are analyzed.We solve the Klein–Gordon oscillator equation using the Nikiforov-Uvarov method and obtain the energy profile and the wave function.We discuss the effects of the non-trivial topology and the magnetic field on the energy eigenvalues.We find that the energy eigenvalues depend on the quantum flux field that shows an analogue of the Aharonov–Bohm effect.Furthermore,we obtain the persistent currents,the magnetization,and the magnetic susceptibility at zero temperature in the quantum system defined in a state and show that these magnetic parameters are modified by various factors.展开更多
Higher-order topological phases(HOTPs) are systems with topologically protected in-gap boundary states localized at their ed à nT-dimensional boundaries, with d the system dimension and n the order of the topolog...Higher-order topological phases(HOTPs) are systems with topologically protected in-gap boundary states localized at their ed à nT-dimensional boundaries, with d the system dimension and n the order of the topology. This work proposes a dynamics-based characterization of one large class of Z-type HOTPs without specifically relying on any crystalline symmetry considerations. The key element of our innovative approach is to connect quantum quench dynamics with nested configurations of the socalled band inversion surfaces(BISs) of momentum-space Hamiltonians as a sum of operators from the Clifford algebra(a condition that can be partially relaxed), thereby making it possible to dynamically detect each and every order of topology on an equal footing. Given that experiments on synthetic topological matter can directly measure the winding of certain pseudospin texture to determine topological features of BISs, the topological invariants defined through nested BISs are all within reach of ongoing experiments. Further, the necessity of having nested BISs in defining higher-order topology offers a unique perspective to investigate and engineer higher-order topological phase transitions.展开更多
The notion of a band gap is ubiquitous in the characterization of matter.Particularly interesting are pseudo-gaps,which are enigmatic regions of very low density of states that have been linked to novel phenomena like...The notion of a band gap is ubiquitous in the characterization of matter.Particularly interesting are pseudo-gaps,which are enigmatic regions of very low density of states that have been linked to novel phenomena like high temperature superconductivity.In this work,we discover a novel origin for pseudo-gaps when boundaries are introduced in a non-Hermitian lattice.It generically occurs due to the interference between two or more asymmetric pumping channels,and possess no analog in Hermitian systems.Mathematically,it can be visualized as being created by divergences of spectral flow in the complex energy plane,analogous to how sharp edges creates divergent electric fields near an electrical conductor.A non-Hermitian pseudo-gap can host symmetry-protected mid-gap modes like ordinary topological gaps,but the mid-gap modes are extended instead of edge-localized,and exhibit extreme sensitivity to symmetry-breaking perturbations.Surprisingly,pseudo-gaps can also host an integer number of edge modes even though the pseudo-bands possess fractional topological windings,or even no well-defined Chern number at all,in the marginal case of a phase transition point.Challenging conventional notions of topological bulk-boundary correspondences and even the very concept of a band,pseudo-gaps post profound implications that extend to many-body settings,such as fractional Chern insulators.展开更多
Generalized solutions of the standard gauge transformation equations are presented and discussed in physical terms. They go beyond the usual Dirac phase factors and they exhibit nonlocal quantal behavior, with the wel...Generalized solutions of the standard gauge transformation equations are presented and discussed in physical terms. They go beyond the usual Dirac phase factors and they exhibit nonlocal quantal behavior, with the well-known Relativistic Causality of classical fields affecting directly the phases of wavefunctions in the Schr?dinger Picture. These nonlocal phase behaviors, apparently overlooked in path-integral approaches, give a natural account of the dynamical nonlocality character of the various (even static) Aharonov-Bohm phenomena, while at the same time they seem to respect Causality. For particles passing through nonvanishing magnetic or electric fields they lead to cancellations of Aharonov-Bohm phases at the observation point, generalizing earlier semiclassical experimental observations (of Werner & Brill) to delocalized (spread-out) quantum states. This leads to a correction of previously unnoticed sign-errors in the literature, and to a natural explanation of the deeper reason why certain time-dependent semiclassical arguments are consistent with static results in purely quantal Aharonov-Bohm configurations. These nonlocalities also provide a remedy for misleading results propagating in the literature (concerning an uncritical use of Dirac phase factors, that persists since the time of Feynman’s work on path integrals). They are shown to conspire in such a way as to exactly cancel the instantaneous Aharonov-Bohm phase and recover Relativistic Causality in earlier “paradoxes” (such as the van Kampen thought-experiment), and to also complete Peshkin’s discussion of the electric Aharonov-Bohm effect in a causal manner. The present formulation offers a direct way to address time-dependent single- vs double-slit experiments and the associated causal issues—issues that have recently attracted attention, with respect to the inability of current theories to address them.展开更多
We obtained the ground-state energy level and associated geometric phase in the Dicke model with the dipoledipole interactions analytically by the Holstein-Primakoff transformation and the boson expansion approach in ...We obtained the ground-state energy level and associated geometric phase in the Dicke model with the dipoledipole interactions analytically by the Holstein-Primakoff transformation and the boson expansion approach in the thermodynamic limit. The nonadiabatic geometric phase induced by the photon field was derived with the time-dependent unitary transformation. It is shown that dipole-dipole interactions have a deep influence on scaled behavior of the geometric phase at the critical point.展开更多
The quantum phase effects for induced electric and magnetic dipole moments are investigated. It is shown that the phase shift received by the induced electric dipole has the same form as the one induced by magnetic di...The quantum phase effects for induced electric and magnetic dipole moments are investigated. It is shown that the phase shift received by the induced electric dipole has the same form as the one induced by magnetic dipole moment, therefore the total phase is a hybrid of these two types of phase. This feature indicates that to have a decisive measurement on either one of these two phases, it is necessary to measure the velocity dependence of the observed phase.展开更多
We theoretically investigate possible quantum Hall phases and corresponding edge states in graphene by taking a strong magnetic field, Zeeman splitting M, and sublattice potential △ into account but without spin–orb...We theoretically investigate possible quantum Hall phases and corresponding edge states in graphene by taking a strong magnetic field, Zeeman splitting M, and sublattice potential △ into account but without spin–orbit interaction. It was found that for the undoped graphene either a quantum valley Hall phase or a quantum spin Hall phase emerges in the system, depending on relative magnitudes of M and △. When the Fermi energy deviates from the Dirac point, the quantum spin-valley Hall phase appears and its characteristic edge state is contributed only by one spin and one valley species. The metallic boundary states bridging different quantum Hall phases possess a half-integer quantized conductance, like e^2/2h or3e^2/2h. The possibility of tuning different quantum Hall states with M and △ suggests possible graphene-based spintronics and valleytronics applications.展开更多
基金supported by the Chinese Academy of Sciences Strategic Priority Research Program(XDB35020100)the National Key Research and Development Program of China(2021YFA1400900 and 2018YFA0305601)+3 种基金the National Natural Science Foundation of China(11874073,12304564,11825401,12204187,12261160368)the Open Project of Shenzhen Institute of Quantum Science and Engineering(SIQSE202003)the Hefei National Laboratorythe Scientific and Technological Innovation 2030 Key Program of Quantum Communication and Quantum Computing(2021ZD0301903 and 2021ZD0302000)。
文摘The realization of spin-orbit-coupled ultracold gases has driven a wide range of research and is typically based on the rotating wave approximation(RWA).By neglecting the counter-rotating terms,RWA characterizes a single near-resonant spin-orbit(SO)coupling in a two-level system.Here,we propose and experimentally realize a new scheme for achieving a pair of two-dimensional(2D)SO couplings for ultracold fermions beyond RWA.This work not only realizes the first anomalous Floquet topological Fermi gas beyond RWA,but also significantly improves the lifetime of the 2D-SO-coupled Fermi gas.Based on pump-probe quench measurements,we observe a deterministic phase relation between two sets of SO couplings,which is characteristic of our beyond-RWA scheme and enables the two SO couplings to be simultaneously tuned to the optimum 2D configurations.We observe intriguing band topology by measuring two-ring band-inversion surfaces,quantitatively consistent with a Floquet topological Fermi gas in the regime of high Chern numbers.Our study can open an avenue to explore exotic SO physics and anomalous topological states based on long-lived SO-coupled ultracold fermions.
文摘The relativistic quantum motions of the oscillator field(via the Klein–Gordon oscillator equation)under a uniform magnetic field in a topologically non-trivial space-time geometry are analyzed.We solve the Klein–Gordon oscillator equation using the Nikiforov-Uvarov method and obtain the energy profile and the wave function.We discuss the effects of the non-trivial topology and the magnetic field on the energy eigenvalues.We find that the energy eigenvalues depend on the quantum flux field that shows an analogue of the Aharonov–Bohm effect.Furthermore,we obtain the persistent currents,the magnetization,and the magnetic susceptibility at zero temperature in the quantum system defined in a state and show that these magnetic parameters are modified by various factors.
基金the Singapore Ministry of Education Academic Research Fund Tier-3 Grant No.MOE2017T3-1-001(WBS.No.R-144-000-425-592)the Singapore National Research Foundation Grant No.NRF-NRFI2017-04(WBS No.R-144-000-378-281)。
文摘Higher-order topological phases(HOTPs) are systems with topologically protected in-gap boundary states localized at their ed à nT-dimensional boundaries, with d the system dimension and n the order of the topology. This work proposes a dynamics-based characterization of one large class of Z-type HOTPs without specifically relying on any crystalline symmetry considerations. The key element of our innovative approach is to connect quantum quench dynamics with nested configurations of the socalled band inversion surfaces(BISs) of momentum-space Hamiltonians as a sum of operators from the Clifford algebra(a condition that can be partially relaxed), thereby making it possible to dynamically detect each and every order of topology on an equal footing. Given that experiments on synthetic topological matter can directly measure the winding of certain pseudospin texture to determine topological features of BISs, the topological invariants defined through nested BISs are all within reach of ongoing experiments. Further, the necessity of having nested BISs in defining higher-order topology offers a unique perspective to investigate and engineer higher-order topological phase transitions.
基金funding support by the National Natural Science Foundation of China (12104519)the Guangdong Basic and Applied Basic Research Foundation (2020A1515110773)
文摘The notion of a band gap is ubiquitous in the characterization of matter.Particularly interesting are pseudo-gaps,which are enigmatic regions of very low density of states that have been linked to novel phenomena like high temperature superconductivity.In this work,we discover a novel origin for pseudo-gaps when boundaries are introduced in a non-Hermitian lattice.It generically occurs due to the interference between two or more asymmetric pumping channels,and possess no analog in Hermitian systems.Mathematically,it can be visualized as being created by divergences of spectral flow in the complex energy plane,analogous to how sharp edges creates divergent electric fields near an electrical conductor.A non-Hermitian pseudo-gap can host symmetry-protected mid-gap modes like ordinary topological gaps,but the mid-gap modes are extended instead of edge-localized,and exhibit extreme sensitivity to symmetry-breaking perturbations.Surprisingly,pseudo-gaps can also host an integer number of edge modes even though the pseudo-bands possess fractional topological windings,or even no well-defined Chern number at all,in the marginal case of a phase transition point.Challenging conventional notions of topological bulk-boundary correspondences and even the very concept of a band,pseudo-gaps post profound implications that extend to many-body settings,such as fractional Chern insulators.
文摘Generalized solutions of the standard gauge transformation equations are presented and discussed in physical terms. They go beyond the usual Dirac phase factors and they exhibit nonlocal quantal behavior, with the well-known Relativistic Causality of classical fields affecting directly the phases of wavefunctions in the Schr?dinger Picture. These nonlocal phase behaviors, apparently overlooked in path-integral approaches, give a natural account of the dynamical nonlocality character of the various (even static) Aharonov-Bohm phenomena, while at the same time they seem to respect Causality. For particles passing through nonvanishing magnetic or electric fields they lead to cancellations of Aharonov-Bohm phases at the observation point, generalizing earlier semiclassical experimental observations (of Werner & Brill) to delocalized (spread-out) quantum states. This leads to a correction of previously unnoticed sign-errors in the literature, and to a natural explanation of the deeper reason why certain time-dependent semiclassical arguments are consistent with static results in purely quantal Aharonov-Bohm configurations. These nonlocalities also provide a remedy for misleading results propagating in the literature (concerning an uncritical use of Dirac phase factors, that persists since the time of Feynman’s work on path integrals). They are shown to conspire in such a way as to exactly cancel the instantaneous Aharonov-Bohm phase and recover Relativistic Causality in earlier “paradoxes” (such as the van Kampen thought-experiment), and to also complete Peshkin’s discussion of the electric Aharonov-Bohm effect in a causal manner. The present formulation offers a direct way to address time-dependent single- vs double-slit experiments and the associated causal issues—issues that have recently attracted attention, with respect to the inability of current theories to address them.
文摘We obtained the ground-state energy level and associated geometric phase in the Dicke model with the dipoledipole interactions analytically by the Holstein-Primakoff transformation and the boson expansion approach in the thermodynamic limit. The nonadiabatic geometric phase induced by the photon field was derived with the time-dependent unitary transformation. It is shown that dipole-dipole interactions have a deep influence on scaled behavior of the geometric phase at the critical point.
基金Supported by the China Scholarship Councilthe Hanjiang Scholar Project of Shaanxi University of Technology
文摘The quantum phase effects for induced electric and magnetic dipole moments are investigated. It is shown that the phase shift received by the induced electric dipole has the same form as the one induced by magnetic dipole moment, therefore the total phase is a hybrid of these two types of phase. This feature indicates that to have a decisive measurement on either one of these two phases, it is necessary to measure the velocity dependence of the observed phase.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.1144721811274059+1 种基金11404278and 11447216)
文摘We theoretically investigate possible quantum Hall phases and corresponding edge states in graphene by taking a strong magnetic field, Zeeman splitting M, and sublattice potential △ into account but without spin–orbit interaction. It was found that for the undoped graphene either a quantum valley Hall phase or a quantum spin Hall phase emerges in the system, depending on relative magnitudes of M and △. When the Fermi energy deviates from the Dirac point, the quantum spin-valley Hall phase appears and its characteristic edge state is contributed only by one spin and one valley species. The metallic boundary states bridging different quantum Hall phases possess a half-integer quantized conductance, like e^2/2h or3e^2/2h. The possibility of tuning different quantum Hall states with M and △ suggests possible graphene-based spintronics and valleytronics applications.
