We investigate ultracold fermionic atoms in the trilayer honeycomb lattice. In the low energy approximation, we derive an effective Hamiltonian for pseudospins. The energy spectrum shows a cubic form of the wavevector...We investigate ultracold fermionic atoms in the trilayer honeycomb lattice. In the low energy approximation, we derive an effective Hamiltonian for pseudospins. The energy spectrum shows a cubic form of the wavevector and is gapless. The quasiparticles and quasiholes are ehiral and show Berry＇s phase π when the wavevector adiabatically evolves along a closed circle, Furthermore, the experimental detection of the energy spectrum is proposed with Bragg scattering techniques.展开更多
We report an effective method for enhancing the photoassociation of ultracold atoms using a non-resonant magnetic field,which enables the manipulation of the coupling between the wavefunctions of the colliding atomic ...We report an effective method for enhancing the photoassociation of ultracold atoms using a non-resonant magnetic field,which enables the manipulation of the coupling between the wavefunctions of the colliding atomic pairs and the excited molecules.A series of photoassociation spectra are measured for different magnetic fields.We show that the photoassociation rate is significantly dependent on the non-resonant magnetic field.A qualitatively theoretical explanation is provided,and shows a good agreement with the experimental result.展开更多
We propose a new method to control the directed quantum transport of ultracold atoms in a one-dimensional optical lattice. In this proposal, the effective tunneling between the neighboring sites can be adjusted via co...We propose a new method to control the directed quantum transport of ultracold atoms in a one-dimensional optical lattice. In this proposal, the effective tunneling between the neighboring sites can be adjusted via coherent destruction of tunneling by tuning the phase of the external field, instead of using the driving field intensity or the frequency, thus the directed quantum transport of ultracold atoms can be coherently controlled in a nmch easier manner. Our proposal overcomes the major drawback of the method used by Creffield et al [Phys. Rev. Lett. 99 （2007） 110501], and can be implemented, in principle, in any one-dimensional optical lattice. Some potential applications of the scheme are also discussed.展开更多
We experimentally observe the dynamic evolution of atoms in the evaporative cooling, by in-situ imaging the plugged hole of ultracold atoms. Ultracold rubidium atoms confined in a magnetic trap are plugged using a blu...We experimentally observe the dynamic evolution of atoms in the evaporative cooling, by in-situ imaging the plugged hole of ultracold atoms. Ultracold rubidium atoms confined in a magnetic trap are plugged using a blue-detuned laser beam with a waist of 20 m at a wavelength of 767 nm. We probe the variation of the atomic temperature and width versus the radio frequency in the evaporative cooling. Both the behaviors are in good agreement with the calculation of the trapping potential dressed by the rf signal above the threshold temperature,while deviating from the calculation near the phase transition. To accurately obtain the atomic width, we use the plugged hole as the reference to optimize the optical imaging system by precisely minimizing the artificial structures due to the defocus effect.展开更多
Quantum simulation is a powerful tool to study a variety of problems in physics, ranging from high-energy physics to condensed-matter physics. In this article, we review the recent theoretical and experimental progres...Quantum simulation is a powerful tool to study a variety of problems in physics, ranging from high-energy physics to condensed-matter physics. In this article, we review the recent theoretical and experimental progress in quantum simulation of Dirac equation with tunable parameters by using ultracold neutral atoms trapped in optical lattices or subject to light-induced synthetic gauge fields. The effective theories for the quasiparticles become relativistic under certain conditions in these systems, making them ideal platforms for studying the exotic relativistic effects. We focus on the realization of one, two, and three dimensional Dirac equations as well as the detection of some relativistic effects, including particularly the well-known Zitterbewegung effect and Klein tunneling. The realization of quantum anomalous Hall effects is also briefly discussed.展开更多
We systematically investigate the polarization gradient cooling （PGC） process in an optical molasses of ultracold cesium atoms. The SR mode for changing the cooling laser, which means that the cooling laser frequenc...We systematically investigate the polarization gradient cooling （PGC） process in an optical molasses of ultracold cesium atoms. The SR mode for changing the cooling laser, which means that the cooling laser frequency is stepped to the setting value while its intensity is ramped, is found to be the best for the PGC, compared with other modes studied. We verify that the heating effect of the cold atoms, which appears when the cooling laser intensity is lower than the saturation intensity, arises from insufficient polarization gradient cooling. Finally, an exponential decay function with a statistical explanation is introduced to explain the dependence of the cold atom temperature on the PGC interaction time.展开更多
We review recent developments in the use of magnetic lattices as a complementary tool to optical lattices for trapping periodic arrays of ultracold atoms and degenerate quantum gases. Recent advances include the reali...We review recent developments in the use of magnetic lattices as a complementary tool to optical lattices for trapping periodic arrays of ultracold atoms and degenerate quantum gases. Recent advances include the realisation of Bose–Einstein condensation in multiple sites of a magnetic lattice of one-dimensional microtraps, the trapping of ultracold atoms in square and triangular magnetic lattices,and the fabrication of magnetic lattice structures with submicron period suitable for quantum tunnelling experiments.Finally, we describe a proposal to utilise long-range interacting Rydberg atoms in a large spacing magnetic lattice to create interactions between atoms on neighbouring sites.展开更多
Tight-binding models for ultracold atoms in optical lattices can be properly defined by using the concept of maximally localized Wannier functions for composite bands. The basic principles of this approach are reviewe...Tight-binding models for ultracold atoms in optical lattices can be properly defined by using the concept of maximally localized Wannier functions for composite bands. The basic principles of this approach are reviewed here, along with different applications to lattice potentials with two minima per unit cell, in one and two spatial dimensions. Two independent methods for computing the tight-binding coefficients—one ab initio, based on the maximally localized Wannier functions, the other through analytic expressions in terms of the energy spectrum—are considered. In the one dimensional case, where the tight-binding coefficients can be obtained by designing a specific gauge transformation, we consider both the case of quasi resonance between the two lowest bands, and that between s and p orbitals. In the latter case, the role of the Wannier functions in the derivation of an effective Dirac equation is also reviewed. Then, we consider the case of a two dimensional honeycomb potential, with particular emphasis on the Haldane model, its phase diagram, and the breakdown of the Peierls substitution. Tunable honeycomb lattices, characterized by movable Dirac points, are also considered. Finally, general considerations for dealing with the interaction terms are presented.展开更多
The ground states of the ultracold spin-1 atoms superlattice in a weak magnetic field are obtained. It is shown trapped in a deep one-dimensional double-weU optical that the ground-state diagrams of the reduced double...The ground states of the ultracold spin-1 atoms superlattice in a weak magnetic field are obtained. It is shown trapped in a deep one-dimensional double-weU optical that the ground-state diagrams of the reduced double- well model are remarkably different for the antiferromagnetic and ferromagnetic condensates. The transition between the singlet state and nematic state is observed for the antiferromagnetic interaction atoms, which can be realized by modulating the tunneling parameter or the quadratic Zeeman energy. An experiment to distinguish the different spin states is suggested.展开更多
Due to the fundamental position of spin-orbit coupled ultracold atoms in the simulation of topological insulators, the gain/loss effects on these systems should be evaluated when considering the measurement or the cou...Due to the fundamental position of spin-orbit coupled ultracold atoms in the simulation of topological insulators, the gain/loss effects on these systems should be evaluated when considering the measurement or the coupling to the environment. Here, incorporating the mature gain/loss techniques into the experimentally realized spin-orbit coupled ultracold atoms in two-dimensional optical lattices, we investigate the corresponding non-Hermitian tight-binding model and evaluate the gain/loss effects on various properties of the system, revealing the interplay of the non-Hermiticity and the spin-orbit coupling. Under periodic boundary conditions, we analytically obtain the topological phase diagram, which undergoes a non-Hermitian gapless interval instead of a point that the Hermitian counterpart encounters for a topological phase transition. We also unveil that the band inversion is just a necessary but not sufficient condition for a topological phase in two-level spin-orbit coupled non-Hermitian systems. Because the nodal loops of the upper or lower two dressed bands of the Hermitian counterpart can be split into exceptional loops in this non-Hermitian model, a gauge-independent Wilson-loop method is developed for numerically calculating the Chern number of multiple degenerate complex bands. Under open boundary conditions, we find that the conventional bulk-boundary correspondence does not break down with only on-site gain/loss due to the lack of non-Hermitian skin effect, but the dissipation of chiral edge states depends on the boundary selection, which may be used in the control of edge-state dynamics. Given the technical accessibility of state-dependent atom loss, this model could be realized in current cold-atom experiments.展开更多
We study the quantum phase transition of ultracold atoms in the honeycomb optical lattice. The Hamiltonian of ultracold bosonic atoms in the honeycomb optical lattice is derived. We take the mean-field approximation a...We study the quantum phase transition of ultracold atoms in the honeycomb optical lattice. The Hamiltonian of ultracold bosonic atoms in the honeycomb optical lattice is derived. We take the mean-field approximation and further solve the Hamiltonian with the numerical diagonalization method. We obtain the phase diagram and find that the Mort-insulator （MI）, density wave （DW） and modulated superfluid （MS） phases appear. Furthermore, the phase diagram is analyzed according to the order parameter and the average number of particles.展开更多
We investigate the unconventional Landau levels of ultracold fermionic atoms on the two-dimensionalhoneycomb optical lattice subjected to an effective magnetic field,which is created with optical means.In the presence...We investigate the unconventional Landau levels of ultracold fermionic atoms on the two-dimensionalhoneycomb optical lattice subjected to an effective magnetic field,which is created with optical means.In the presenceof the effective magnetic field,the energy spectrum of the unconventional Landau levels is calculated.Furthermore,wepropose to detect the unconventional Landau levels with Bragg scattering techniques.展开更多
This paper reports that ultracold atoms are populated into different nS and nD Rydberg states （n=25-52） by two-photon excitation. The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-...This paper reports that ultracold atoms are populated into different nS and nD Rydberg states （n=25-52） by two-photon excitation. The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-optical trap by using the method of pulse field ionization. This denotes nS and nD states in the ionization spectrum and fits the data of energy levels of different Rydberg states to obtain quantum defects of nS and nD states.展开更多
The idea of manipulating the interaction between ultracold fermionic alkaline-earth(like)atoms via a laser-induced periodical synthetic magnetic field was proposed in Kanász-Nagy et al(2018 Phys.Rev.B 97,155156)....The idea of manipulating the interaction between ultracold fermionic alkaline-earth(like)atoms via a laser-induced periodical synthetic magnetic field was proposed in Kanász-Nagy et al(2018 Phys.Rev.B 97,155156).In that work,it was shown that in the presence of the shaking synthetic magnetic field,two atoms in^(1)S_(0)and^(3)P_(0) states experience a periodical interaction in a rotated frame,and the effective inter-atomic interaction was approximated as the time-averaged operator of this time-dependent interaction.This technique is supposed to be efficient for ^(173) Yb atoms which have a large natural scattering length.Here we examine this time-averaging approximation and derive the rate of the two-body loss induced by the shaking of the synthetic magnetic field,by calculating the zero-energy inter-atomic scattering amplitude corresponding to the explicit periodical interaction.We find that for the typical cases with shaking angular frequencyλof the synthetic magnetic field being of the order of(2π)kHz,the time-averaging approximation is applicable only when the shaking amplitude is small enough.Moreover,the two-body loss rate increases with the shaking amplitude,and is of the order of 10^(-10)cm^(3)·s^(-1) or even larger when the time-averaging approximation is not applicable.Our results are helpful for the quantum simulations with ultracold gases of fermionic alkaline-earth(like)atoms.展开更多
The vortex dynamics after the initial ring dark solitons in two-component ultracold Rydberg atomic systems have been investigated.The two parameters characterizing the Rydberg long-range interaction—namely,the Rydber...The vortex dynamics after the initial ring dark solitons in two-component ultracold Rydberg atomic systems have been investigated.The two parameters characterizing the Rydberg long-range interaction—namely,the Rydberg strength and the blockade radius—along with the initial depth,are identified as the main factors that affect the vortex dynamics.In the absence of Rydberg soft-core potential and spin-orbit coupling,the late vortex dipoles move along x-or y-axis first.However,this work demonstrates that,with certain Rydberg strength and blockade radius,the late vortex dipoles move towards the edge at an oblique angle to the coordinate axes,and it reveals that the Rydberg nonlocal nonlinear interaction shortens the lifetime of late vortices.When the intra-component and inter-component Rydberg strengths are different,the backgrounds of the two components gradually complement each other,and the lifetime of late vortices is significantly shortened.The presented results show that the Rydberg dressing breaks the rule that the initial average depth determines the number and paths of vortices.The motion features of vortex dipoles in the ultracold Rydberg atomic system have been ascertained,and their directions of movement can be predicted to some degree based on the rotation directions and initial positions of the vortices.展开更多
We have employed recoil-induced resonance（RIR） with linewidth on the order of 10 k Hz to demonstrate the fast thermometry for ultracold atoms. We theoretically calculate the absorption spectrum of RIR which agrees w...We have employed recoil-induced resonance（RIR） with linewidth on the order of 10 k Hz to demonstrate the fast thermometry for ultracold atoms. We theoretically calculate the absorption spectrum of RIR which agrees well with the experimental results. The temperature of the ultracold sample derived from the RIR spectrum is T = 84 ± 4.5 μK, which is close to 85 μK that measured by the method of time-of-flight absorption imaging. To exhibit the fast measurement advantage in applying RIR to the ultracold atom thermometry, we study the dependence of ultracold sample temperature on the trapping beam frequency detuning. This method can be applied to determine the translational temperature of molecules in photoassociation dynamics.展开更多
The evidences of three-body and four-body bound states have been reported in a series of very recent experiments with ultracold atoms.Here we study coherent creation of polyatomic molecules via a generalized atom-mole...The evidences of three-body and four-body bound states have been reported in a series of very recent experiments with ultracold atoms.Here we study coherent creation of polyatomic molecules via a generalized atom-molecule dark-state technique.By keeping the intermediate trimer or tetramer state essentially unpopulated,the constructive quantum two-channel interference is shown to play an important role in,e.g.coherent atom-pentamer conversion at ultracold temperature.展开更多
Liquid helium 4 had been the only bosonic superfluid available in experiments for a long time. This situation was changed in 1995, when a new superfluid was born with the realization of the Bose-Einstein condensation ...Liquid helium 4 had been the only bosonic superfluid available in experiments for a long time. This situation was changed in 1995, when a new superfluid was born with the realization of the Bose-Einstein condensation in ultracold atomic gases. The liquid helium 4 is strongly interacting and has no spin; there is almost no way to change its parameters, such as interaction strength and density. The new superfluid, Bose-Einstein condensate （BEC）, offers various advantages over liquid helium. On the one hand, BEC is weakly interacting and has spin degrees of freedom. On the other hand, it is convenient to tune almost all the parameters of a BEC, for example, the kinetic energy by spin--orbit coupling, the density by the external potential, and the interaction by Feshbach resonance. Great efforts have been devoted to studying these new aspects, and the results have greatly enriched our understanding of superfluidity. Here we review these developments by focusing on the stability and critical velocity of various superfluids. The BEC systems considered include a uniform superfluid in free space, a superfluid with its density periodically modulated, a superfluid with artificially engineered spinorbit coupling, and a superfluid of pure spin current. Due to the weak interaction, these BEC systems can be well described by the mean-field Gross-Pitaevskii theory and their superfluidity, in particular critical velocities, can be examined with the aid of Bogoliubov excitations. Experimental proposals to observe these new aspects of superfluidity are discussed.展开更多
We calculate the energy spectrum of three identical fermionic ultracold atoms in two different internal states confined in a two-dimensional anisotropic harmonic trap.Using the solutions of the corresponding two-body ...We calculate the energy spectrum of three identical fermionic ultracold atoms in two different internal states confined in a two-dimensional anisotropic harmonic trap.Using the solutions of the corresponding two-body problems obtained in our previous work(Chen et al 2020 Phys.Rev.A 101,053624),we derive the explicit transcendental equation for the eigen-energies,from which the energy spectrum is derived.Our results can be used for the calculation of the 3rd Virial coefficients or the studies of few-body dynamics.展开更多
We report a detailed study of magnetically levitated loading of ultracold ^(133)Cs atoms in a dimple trap.The atomic sample was produced in a combined red-detuned optical dipole trap and dimple trap formed by two smal...We report a detailed study of magnetically levitated loading of ultracold ^(133)Cs atoms in a dimple trap.The atomic sample was produced in a combined red-detuned optical dipole trap and dimple trap formed by two small waist beams crossing a horizontal plane.The magnetic levitation for the ^(133)Cs atoms forms an effective potential for a large number of atoms in a high spatial density.Dependence of the number of atoms loaded and trapped in the dimple trap on the magnetic field gradient and bias field is in good agreement with the theoretical analysis.This method has been widely used to obtain the Bose–Einstein condensation atoms for many atomic species.展开更多
基金Supported by the Teaching and Research Foundation for the Outstanding Young Faculty of Southeast University
文摘We investigate ultracold fermionic atoms in the trilayer honeycomb lattice. In the low energy approximation, we derive an effective Hamiltonian for pseudospins. The energy spectrum shows a cubic form of the wavevector and is gapless. The quasiparticles and quasiholes are ehiral and show Berry＇s phase π when the wavevector adiabatically evolves along a closed circle, Furthermore, the experimental detection of the energy spectrum is proposed with Bragg scattering techniques.
基金the National Key Research and Development Program of China(Grant No.2017YFA0304203)the National Natural Science Foundation of China(Grant Nos.61722507,61675121,and 61705123),PCSIRT,China(Grant No.IRT17R70),111 Project,China(Grant No.D18001)+2 种基金the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi(OIT),Chinathe Applied Basic Research Project of Shanxi Province,China(Grant Nos.201801D221004,201901D211191,and 201901D211188)the Shanxi 1331 KSC,and Collaborative Grant by the Russian Foundation for Basic Research and the National Natural Science Foundation of China(Grant Nos.6191101339 and 20-53-53025 in the RFBR classification)。
文摘We report an effective method for enhancing the photoassociation of ultracold atoms using a non-resonant magnetic field,which enables the manipulation of the coupling between the wavefunctions of the colliding atomic pairs and the excited molecules.A series of photoassociation spectra are measured for different magnetic fields.We show that the photoassociation rate is significantly dependent on the non-resonant magnetic field.A qualitatively theoretical explanation is provided,and shows a good agreement with the experimental result.
基金Supported by the National Basic Research Program of China under Grant No 2011CBA00200the National Natural Science Foundation of China under Grant No 11074244+3 种基金ARO(W911NF-12-1-0334)DARPA-YFA(N66001-10-1-4025)AFOSR(FA9550-11-1-0313)NSF-PHY(1104546)
文摘We propose a new method to control the directed quantum transport of ultracold atoms in a one-dimensional optical lattice. In this proposal, the effective tunneling between the neighboring sites can be adjusted via coherent destruction of tunneling by tuning the phase of the external field, instead of using the driving field intensity or the frequency, thus the directed quantum transport of ultracold atoms can be coherently controlled in a nmch easier manner. Our proposal overcomes the major drawback of the method used by Creffield et al [Phys. Rev. Lett. 99 （2007） 110501], and can be implemented, in principle, in any one-dimensional optical lattice. Some potential applications of the scheme are also discussed.
基金Supported by the National Key Research and Development Program of China under Grant No 2016YFA0301503the National Natural Science Foundation of China under Grant Nos 11674358 and 11434015the Instrument Project of the Chinese Academy of Sciences under Grant No YJKYYQ20170025
文摘We experimentally observe the dynamic evolution of atoms in the evaporative cooling, by in-situ imaging the plugged hole of ultracold atoms. Ultracold rubidium atoms confined in a magnetic trap are plugged using a blue-detuned laser beam with a waist of 20 m at a wavelength of 767 nm. We probe the variation of the atomic temperature and width versus the radio frequency in the evaporative cooling. Both the behaviors are in good agreement with the calculation of the trapping potential dressed by the rf signal above the threshold temperature,while deviating from the calculation near the phase transition. To accurately obtain the atomic width, we use the plugged hole as the reference to optimize the optical imaging system by precisely minimizing the artificial structures due to the defocus effect.
文摘Quantum simulation is a powerful tool to study a variety of problems in physics, ranging from high-energy physics to condensed-matter physics. In this article, we review the recent theoretical and experimental progress in quantum simulation of Dirac equation with tunable parameters by using ultracold neutral atoms trapped in optical lattices or subject to light-induced synthetic gauge fields. The effective theories for the quasiparticles become relativistic under certain conditions in these systems, making them ideal platforms for studying the exotic relativistic effects. We focus on the realization of one, two, and three dimensional Dirac equations as well as the detection of some relativistic effects, including particularly the well-known Zitterbewegung effect and Klein tunneling. The realization of quantum anomalous Hall effects is also briefly discussed.
基金supported by the National Basic Research Program of China(Grant Nos.2012CB921603 and 2010CB923103)the International Science &Technology Cooperation Program of China(Grant No.2011DFA12490)+2 种基金the National Natural Science Foundation of China(Grant Nos.11304189,61378015,and 61275209)the Project for Excellent Research Team of the National Natural Science Foundation of China(Grant No.61121064)the Program for Changjiang Scholars,China,and the Innovative Research Team in University,China(Grant No.IRT13076)
文摘We systematically investigate the polarization gradient cooling （PGC） process in an optical molasses of ultracold cesium atoms. The SR mode for changing the cooling laser, which means that the cooling laser frequency is stepped to the setting value while its intensity is ramped, is found to be the best for the PGC, compared with other modes studied. We verify that the heating effect of the cold atoms, which appears when the cooling laser intensity is lower than the saturation intensity, arises from insufficient polarization gradient cooling. Finally, an exponential decay function with a statistical explanation is introduced to explain the dependence of the cold atom temperature on the PGC interaction time.
基金supported by an Australian Research Council Discovery Project Grant(DP130101160)
文摘We review recent developments in the use of magnetic lattices as a complementary tool to optical lattices for trapping periodic arrays of ultracold atoms and degenerate quantum gases. Recent advances include the realisation of Bose–Einstein condensation in multiple sites of a magnetic lattice of one-dimensional microtraps, the trapping of ultracold atoms in square and triangular magnetic lattices,and the fabrication of magnetic lattice structures with submicron period suitable for quantum tunnelling experiments.Finally, we describe a proposal to utilise long-range interacting Rydberg atoms in a large spacing magnetic lattice to create interactions between atoms on neighbouring sites.
基金supported by the Universidad del Pais Vasco/Euskal Herriko Unibertsitatea (Grant No. UFI 11/55)the Ministerio de Economia y Competitividad (Grant No. FIS2012-36673-C03-03)+2 种基金the Basque Government (Grant No. IT472-10)the Helmholtz Gemeinschaft Deutscher-Young Investigators Group (Grant No. VH-NG-717, Functional Nanoscale Structure and Probe Simulation Laboratory)the Impuls und Vernetzungsfonds der HelmholtzGemeinschaft Postdoc Programme
文摘Tight-binding models for ultracold atoms in optical lattices can be properly defined by using the concept of maximally localized Wannier functions for composite bands. The basic principles of this approach are reviewed here, along with different applications to lattice potentials with two minima per unit cell, in one and two spatial dimensions. Two independent methods for computing the tight-binding coefficients—one ab initio, based on the maximally localized Wannier functions, the other through analytic expressions in terms of the energy spectrum—are considered. In the one dimensional case, where the tight-binding coefficients can be obtained by designing a specific gauge transformation, we consider both the case of quasi resonance between the two lowest bands, and that between s and p orbitals. In the latter case, the role of the Wannier functions in the derivation of an effective Dirac equation is also reviewed. Then, we consider the case of a two dimensional honeycomb potential, with particular emphasis on the Haldane model, its phase diagram, and the breakdown of the Peierls substitution. Tunable honeycomb lattices, characterized by movable Dirac points, are also considered. Finally, general considerations for dealing with the interaction terms are presented.
基金Supported by the National Natural Science Foundation of China under Grant No.11274095the Program of Innovation Scientists and Technicians Troop Construction Projects in Henan Province under Grant No.114100510021+1 种基金the Natural Science Basic Research Plan in Henan Province of China under Grant No.2011B140010the Innovative Research Team(in Science and Technology)in University of Henan Province under Grant No.2010IRTSTHN002
文摘The ground states of the ultracold spin-1 atoms superlattice in a weak magnetic field are obtained. It is shown trapped in a deep one-dimensional double-weU optical that the ground-state diagrams of the reduced double- well model are remarkably different for the antiferromagnetic and ferromagnetic condensates. The transition between the singlet state and nematic state is observed for the antiferromagnetic interaction atoms, which can be realized by modulating the tunneling parameter or the quadratic Zeeman energy. An experiment to distinguish the different spin states is suggested.
基金supported by the National Natural Science Foundation of China(Grant No.11904109)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2019A1515111101)+2 种基金the Science and Technology Program of Guangzhou(Grant No.2019050001)supported by the Key-Area Research and Development Program of Guangdong Province(Grant No.2019B030330001)the National Natural Science Foundation of China(Grant Nos.12074180,and U1801661)。
文摘Due to the fundamental position of spin-orbit coupled ultracold atoms in the simulation of topological insulators, the gain/loss effects on these systems should be evaluated when considering the measurement or the coupling to the environment. Here, incorporating the mature gain/loss techniques into the experimentally realized spin-orbit coupled ultracold atoms in two-dimensional optical lattices, we investigate the corresponding non-Hermitian tight-binding model and evaluate the gain/loss effects on various properties of the system, revealing the interplay of the non-Hermiticity and the spin-orbit coupling. Under periodic boundary conditions, we analytically obtain the topological phase diagram, which undergoes a non-Hermitian gapless interval instead of a point that the Hermitian counterpart encounters for a topological phase transition. We also unveil that the band inversion is just a necessary but not sufficient condition for a topological phase in two-level spin-orbit coupled non-Hermitian systems. Because the nodal loops of the upper or lower two dressed bands of the Hermitian counterpart can be split into exceptional loops in this non-Hermitian model, a gauge-independent Wilson-loop method is developed for numerically calculating the Chern number of multiple degenerate complex bands. Under open boundary conditions, we find that the conventional bulk-boundary correspondence does not break down with only on-site gain/loss due to the lack of non-Hermitian skin effect, but the dissipation of chiral edge states depends on the boundary selection, which may be used in the control of edge-state dynamics. Given the technical accessibility of state-dependent atom loss, this model could be realized in current cold-atom experiments.
基金Supported by the Teaching and Research Foundation for the Outstanding Young Faculty of Southeast University
文摘We study the quantum phase transition of ultracold atoms in the honeycomb optical lattice. The Hamiltonian of ultracold bosonic atoms in the honeycomb optical lattice is derived. We take the mean-field approximation and further solve the Hamiltonian with the numerical diagonalization method. We obtain the phase diagram and find that the Mort-insulator （MI）, density wave （DW） and modulated superfluid （MS） phases appear. Furthermore, the phase diagram is analyzed according to the order parameter and the average number of particles.
基金Supported by the Teaching and Research Foundation for the Outstanding Young Faculty of Southeast University
文摘We investigate the unconventional Landau levels of ultracold fermionic atoms on the two-dimensionalhoneycomb optical lattice subjected to an effective magnetic field,which is created with optical means.In the presenceof the effective magnetic field,the energy spectrum of the unconventional Landau levels is calculated.Furthermore,wepropose to detect the unconventional Landau levels with Bragg scattering techniques.
基金supported by the 973 Program of China(Grant No 2006CB921603)the National Natural Science Foundation of China (Grant Nos 10574084,60678003 and 60778008)+1 种基金the Special Foundation for State Major Basic Research Program of China(Grant No 2005CCA06300)the Scholarship Foundation of Shanxi Province,China
文摘This paper reports that ultracold atoms are populated into different nS and nD Rydberg states （n=25-52） by two-photon excitation. The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-optical trap by using the method of pulse field ionization. This denotes nS and nD states in the ionization spectrum and fits the data of energy levels of different Rydberg states to obtain quantum defects of nS and nD states.
文摘The idea of manipulating the interaction between ultracold fermionic alkaline-earth(like)atoms via a laser-induced periodical synthetic magnetic field was proposed in Kanász-Nagy et al(2018 Phys.Rev.B 97,155156).In that work,it was shown that in the presence of the shaking synthetic magnetic field,two atoms in^(1)S_(0)and^(3)P_(0) states experience a periodical interaction in a rotated frame,and the effective inter-atomic interaction was approximated as the time-averaged operator of this time-dependent interaction.This technique is supposed to be efficient for ^(173) Yb atoms which have a large natural scattering length.Here we examine this time-averaging approximation and derive the rate of the two-body loss induced by the shaking of the synthetic magnetic field,by calculating the zero-energy inter-atomic scattering amplitude corresponding to the explicit periodical interaction.We find that for the typical cases with shaking angular frequencyλof the synthetic magnetic field being of the order of(2π)kHz,the time-averaging approximation is applicable only when the shaking amplitude is small enough.Moreover,the two-body loss rate increases with the shaking amplitude,and is of the order of 10^(-10)cm^(3)·s^(-1) or even larger when the time-averaging approximation is not applicable.Our results are helpful for the quantum simulations with ultracold gases of fermionic alkaline-earth(like)atoms.
基金supported by the Natural Science Foundation of Hubei Province of China(Grant No.2025AFB370)。
文摘The vortex dynamics after the initial ring dark solitons in two-component ultracold Rydberg atomic systems have been investigated.The two parameters characterizing the Rydberg long-range interaction—namely,the Rydberg strength and the blockade radius—along with the initial depth,are identified as the main factors that affect the vortex dynamics.In the absence of Rydberg soft-core potential and spin-orbit coupling,the late vortex dipoles move along x-or y-axis first.However,this work demonstrates that,with certain Rydberg strength and blockade radius,the late vortex dipoles move towards the edge at an oblique angle to the coordinate axes,and it reveals that the Rydberg nonlocal nonlinear interaction shortens the lifetime of late vortices.When the intra-component and inter-component Rydberg strengths are different,the backgrounds of the two components gradually complement each other,and the lifetime of late vortices is significantly shortened.The presented results show that the Rydberg dressing breaks the rule that the initial average depth determines the number and paths of vortices.The motion features of vortex dipoles in the ultracold Rydberg atomic system have been ascertained,and their directions of movement can be predicted to some degree based on the rotation directions and initial positions of the vortices.
基金Project supported by the National Basic Research Development Program of China(Grant No.2012CB921603)the National High Technology Research and Development Program of China(Grant No.2011AA010801)+1 种基金the National Natural Science Foundation of China(Grant Nos.61275209,11304189,61378015,and 11434007)Program for Changjiang Scholars and Innovative Research Team in Universities of China(Grant No.IRT13076)
文摘We have employed recoil-induced resonance（RIR） with linewidth on the order of 10 k Hz to demonstrate the fast thermometry for ultracold atoms. We theoretically calculate the absorption spectrum of RIR which agrees well with the experimental results. The temperature of the ultracold sample derived from the RIR spectrum is T = 84 ± 4.5 μK, which is close to 85 μK that measured by the method of time-of-flight absorption imaging. To exhibit the fast measurement advantage in applying RIR to the ultracold atom thermometry, we study the dependence of ultracold sample temperature on the trapping beam frequency detuning. This method can be applied to determine the translational temperature of molecules in photoassociation dynamics.
基金Supported by the New-Century Excellent Talents Plrogram of the Ministry of Education of China the Natural Science Foundation of China under Grant No.10974045
文摘The evidences of three-body and four-body bound states have been reported in a series of very recent experiments with ultracold atoms.Here we study coherent creation of polyatomic molecules via a generalized atom-molecule dark-state technique.By keeping the intermediate trimer or tetramer state essentially unpopulated,the constructive quantum two-channel interference is shown to play an important role in,e.g.coherent atom-pentamer conversion at ultracold temperature.
基金supported by the National Basic Research Program of China(Grant Nos.2013CB921903 and 2012CB921300)the National Natural Science Foundation of China(Grant Nos.11274024,11334001,and 11429402)
文摘Liquid helium 4 had been the only bosonic superfluid available in experiments for a long time. This situation was changed in 1995, when a new superfluid was born with the realization of the Bose-Einstein condensation in ultracold atomic gases. The liquid helium 4 is strongly interacting and has no spin; there is almost no way to change its parameters, such as interaction strength and density. The new superfluid, Bose-Einstein condensate （BEC）, offers various advantages over liquid helium. On the one hand, BEC is weakly interacting and has spin degrees of freedom. On the other hand, it is convenient to tune almost all the parameters of a BEC, for example, the kinetic energy by spin--orbit coupling, the density by the external potential, and the interaction by Feshbach resonance. Great efforts have been devoted to studying these new aspects, and the results have greatly enriched our understanding of superfluidity. Here we review these developments by focusing on the stability and critical velocity of various superfluids. The BEC systems considered include a uniform superfluid in free space, a superfluid with its density periodically modulated, a superfluid with artificially engineered spinorbit coupling, and a superfluid of pure spin current. Due to the weak interaction, these BEC systems can be well described by the mean-field Gross-Pitaevskii theory and their superfluidity, in particular critical velocities, can be examined with the aid of Bogoliubov excitations. Experimental proposals to observe these new aspects of superfluidity are discussed.
基金supported in part by the National Key Research and Development Program of China Grant No.2018YFA0306502NSAF(Grant No.U1930201)+1 种基金supported by the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China under Grant No.21XNH088。
文摘We calculate the energy spectrum of three identical fermionic ultracold atoms in two different internal states confined in a two-dimensional anisotropic harmonic trap.Using the solutions of the corresponding two-body problems obtained in our previous work(Chen et al 2020 Phys.Rev.A 101,053624),we derive the explicit transcendental equation for the eigen-energies,from which the energy spectrum is derived.Our results can be used for the calculation of the 3rd Virial coefficients or the studies of few-body dynamics.
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.62020106014,62175140,12034012,and 92165106)the Natural Science Young Foundation of Shanxi Province(Grant No.202203021212376).
文摘We report a detailed study of magnetically levitated loading of ultracold ^(133)Cs atoms in a dimple trap.The atomic sample was produced in a combined red-detuned optical dipole trap and dimple trap formed by two small waist beams crossing a horizontal plane.The magnetic levitation for the ^(133)Cs atoms forms an effective potential for a large number of atoms in a high spatial density.Dependence of the number of atoms loaded and trapped in the dimple trap on the magnetic field gradient and bias field is in good agreement with the theoretical analysis.This method has been widely used to obtain the Bose–Einstein condensation atoms for many atomic species.
