Based on the form of the n-dimensional generic power-law potential, the state equation and the heat capacity, the analytical expressions of the Joule-Thomson coefficient （3TC） for an ideal Bose gas are derived in n-...Based on the form of the n-dimensional generic power-law potential, the state equation and the heat capacity, the analytical expressions of the Joule-Thomson coefficient （3TC） for an ideal Bose gas are derived in n-dimensional potential. The effect of the spatial dimension and the external potential on the JTC are discussed, respectively. These results show that： （i） For the free ideal Bose gas, when n/s ≤ 2 （n is the spatial dimension, s is the momentum index in the relation between the energy and the momentum）, and T → Tc （Tc is the critical temperature）, the JTC can obviously improve by means of changing the throttle valve＇s shape and decreasing the spatial dimension of gases. （ii） For the inhomogeneous external potential, the discriminant △= [1 - y∏^ni=1（kT/εi）^1/tiГ（1/ti＋1）] （k is the Boltzmann Constant, T is the thermodynamic temperature, ε is the external field＇s energy）, is obtained. The potential makes the JTC increase when △ 〉 0, on the contrary, it makes the JTC decrease when A 〈△. （iii） In the homogenous strong external potential, the JTC gets the maximum on the condition of kTεi〈〈1.展开更多
We present a new method to identify the critical point for the Bose-Einstein condensation （BEC） of a trapped Bose gas. We calculate the momentum distribution of an interacting Bose gas near the critical temperature,...We present a new method to identify the critical point for the Bose-Einstein condensation （BEC） of a trapped Bose gas. We calculate the momentum distribution of an interacting Bose gas near the critical temperature, and find that it deviates significantly from the Gaussian profile as the temperature approaches the critical point. More importantly, the standard deviation between the calculated momentum spectrum and the Gaussian profile at the same temperature shows a turning point at the critical point, which can be used to determine the critical temperature. These predictions are also confirmed by our BEC experiment for magnetically trapped ST Rb gases.展开更多
In order to investigate the quantum phase transitions and the time-of-flight absorption pictures analyt- ically in a systematic way for ultracold Bose gases in bipartite optical lattices, we present a generalized Gree...In order to investigate the quantum phase transitions and the time-of-flight absorption pictures analyt- ically in a systematic way for ultracold Bose gases in bipartite optical lattices, we present a generalized Green＇s function method. Utilizing this method, we study the quantum phase transitions of ultracold Bose gases in two types of bipartite optical lattices, i.e., a hexagonal lattice with normal Bose-Hubbard interaction and a d-dimensional hypercubic optical lattice with extended Bose-Hubbard interaction. Furthermore, the time-of-flight absorption pictures of ultracold Bose gases in these two types of lat- tices are also calculated analytically. In hexagonal lattice, the time-of-flight interference patterns of ultracold Bose gases obtained by our analytical method are in good qualitative agreement with the exDerimental results of Soltan-Panahi, et al. [Nat. Phys. 7, 434 （2011）]. In square optical lattice, the emergence of peaks at（±π/a,±π/a） in the time-of-flight absorption pictures, which is believed to bea sort of evidence of the existence of a supersolid phase, is clearly seen when the system enters the compressible phase from charge-density-wave phase.展开更多
Weakly interacting quantum systems in low dimensions have been investigated for a long time,but there still remain a number of open questions and a lack of explicit expressions of physical properties of such systems.I...Weakly interacting quantum systems in low dimensions have been investigated for a long time,but there still remain a number of open questions and a lack of explicit expressions of physical properties of such systems.In this work,we find power-law scalings of thermodynamic observables in low-dimensional interacting Bose gases at quantum criticality.We present a physical picture for these systems with the repulsive interaction strength approaching zero;namely,the competition between the kinetic and interaction energy scales gives rise to power-law scalings with respect to the interaction strength in characteristic thermodynamic observables.This prediction is supported by exact Bethe ansatz solutions in one dimension,demonstrating a simple 1/3-power-law scaling of the critical entropy per particle.Our method also yields results in agreement with a non-perturbative renormalization-group computation in two dimensions.These results provide a new perspective for understanding many-body phenomena induced by weak interactions in quantum gases.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 present a cluster mean-field study for ground-state phase diagram and many-body dynamics of spin-1 bosons confined in a two-chain Bose-Hubbard ladder(BHL).For unbiased BHL,we find superfluid(SF)phase and integer fi...We present a cluster mean-field study for ground-state phase diagram and many-body dynamics of spin-1 bosons confined in a two-chain Bose-Hubbard ladder(BHL).For unbiased BHL,we find superfluid(SF)phase and integer filling Mott insulator(Int MI)phase.For biased BHL,in addition to the SF and Int MI phases,there appears half-integer filling Mott insulator(HInt MI)phase.The phase transition between the SF and Int MI phases can be first order at a part of phase boundaries,while the phase transition between the SF and HInt MI phases is always second order.By tuning the bias energy,we report on the change of the nature of SF-MI phase transitions.Furthermore,we study the effect of the spin-dependent interaction on the many-body population dynamics.The spin-dependent interaction can lead to rich dynamical behaviors,but does not influence the particle transfer efficiency.Our results indicate a way to tune the nature of the SF-MI phase transition and open a new avenue to study the many-body dynamics of spinor bosons in optical lattices.展开更多
We clarify some technical issues in the present generalized effective-potential Landau theory （GEPLT） to make the GEPLT more consistent and complete. Utilizing this clarified GEPLT, we analytically study the quantum...We clarify some technical issues in the present generalized effective-potential Landau theory （GEPLT） to make the GEPLT more consistent and complete. Utilizing this clarified GEPLT, we analytically study the quantum phase transitions of ultracold Bose gases in bipartite superlattices at zero temper- ature. The corresponding quantum phase boundaries are analytically calculated up to the third-order hopping, which are in excellent agreement with the quantum Monte Carlo （QMC） simulations.展开更多
We review our recent experimental realization and investigation of a spin orbit （SO） coupled Bose Einstein condensate （BEC） and quantum degenerate Fermi gas. By using two counter-propagathlg Ranlan lasers and cont...We review our recent experimental realization and investigation of a spin orbit （SO） coupled Bose Einstein condensate （BEC） and quantum degenerate Fermi gas. By using two counter-propagathlg Ranlan lasers and controlling the different frequency of two R,aman lasers to engineer the atom light interaction, we first study the SO coupling in BEC. Then we study SO coupling in Fermi gas. We, observe the spin dephasing in spin dynamics and momentum distribution asymmetry of the equilibrium state as halhnarks of SO coupling in a Fermi gas. To clearly reveal the, property of SO coupling Fermi gas, we also study the momentmn-resolved radio-frequency spectroscopy which characterizes the energy momentum dispersion and spin composition of the quantum states. We observe the change of errmion surfaces in different helieity branches with different atomic density, which indicates that a Lifshitz transition of the Fermi surface topology change can be found by further cooling the system. At last, we study the momentum-resolved Raman spectroscopy of an ultracoht Fermi gas.展开更多
基金Supported by Natural Science Foundation of Shaanxi Province under Grant No. 2007A02the Science Foundation of Baoji University of Science and Arts of China under Grant No. ZK0914
文摘Based on the form of the n-dimensional generic power-law potential, the state equation and the heat capacity, the analytical expressions of the Joule-Thomson coefficient （3TC） for an ideal Bose gas are derived in n-dimensional potential. The effect of the spatial dimension and the external potential on the JTC are discussed, respectively. These results show that： （i） For the free ideal Bose gas, when n/s ≤ 2 （n is the spatial dimension, s is the momentum index in the relation between the energy and the momentum）, and T → Tc （Tc is the critical temperature）, the JTC can obviously improve by means of changing the throttle valve＇s shape and decreasing the spatial dimension of gases. （ii） For the inhomogeneous external potential, the discriminant △= [1 - y∏^ni=1（kT/εi）^1/tiГ（1/ti＋1）] （k is the Boltzmann Constant, T is the thermodynamic temperature, ε is the external field＇s energy）, is obtained. The potential makes the JTC increase when △ 〉 0, on the contrary, it makes the JTC decrease when A 〈△. （iii） In the homogenous strong external potential, the JTC gets the maximum on the condition of kTεi〈〈1.
基金Supported by the National Natural Science Foundation of China under Grant No 11104322the National Key Basic Research and Development Program of China under Grant No 2011CB921503
文摘We present a new method to identify the critical point for the Bose-Einstein condensation （BEC） of a trapped Bose gas. We calculate the momentum distribution of an interacting Bose gas near the critical temperature, and find that it deviates significantly from the Gaussian profile as the temperature approaches the critical point. More importantly, the standard deviation between the calculated momentum spectrum and the Gaussian profile at the same temperature shows a turning point at the critical point, which can be used to determine the critical temperature. These predictions are also confirmed by our BEC experiment for magnetically trapped ST Rb gases.
基金Y.J. acknowledges Axel Pelster for his stimulating and fruitful discussions. Z.L. acknowledges inspir- ing discussions with Van Chen. This work was supported by the National Natural Science Foundation of China [Grant Nos. 11074043 （Z.L.）, 11274069 （Z.L.） and 11275119 （Y.J.）] and by the State Key Programs of China （Grant Nos. 2012CB921604 and 2009CB929204） （Z.L.）. This work was also supported by Ph.D. Programs Foundation of Ministry of Education of China under Grant No. 20123108110004 （Y.J.）.
文摘In order to investigate the quantum phase transitions and the time-of-flight absorption pictures analyt- ically in a systematic way for ultracold Bose gases in bipartite optical lattices, we present a generalized Green＇s function method. Utilizing this method, we study the quantum phase transitions of ultracold Bose gases in two types of bipartite optical lattices, i.e., a hexagonal lattice with normal Bose-Hubbard interaction and a d-dimensional hypercubic optical lattice with extended Bose-Hubbard interaction. Furthermore, the time-of-flight absorption pictures of ultracold Bose gases in these two types of lat- tices are also calculated analytically. In hexagonal lattice, the time-of-flight interference patterns of ultracold Bose gases obtained by our analytical method are in good qualitative agreement with the exDerimental results of Soltan-Panahi, et al. [Nat. Phys. 7, 434 （2011）]. In square optical lattice, the emergence of peaks at（±π/a,±π/a） in the time-of-flight absorption pictures, which is believed to bea sort of evidence of the existence of a supersolid phase, is clearly seen when the system enters the compressible phase from charge-density-wave phase.
基金supported by the National Key Research and Development Program of China under Grant No.2018YFA0305601the National Natural Science Foundation of China under Grant No.11874073+3 种基金the Chinese Academy of Sciences Strategic Priority Research Program under Grant No.XDB35020100the Hefei National Laboratory and the Scientific and Technological Innovation 2030 under Grant No.2021ZD0301903supported by the National Natural Science Foundation of China under key Grant No.12134015,and under Grants No.11874393 and No.12121004supported by the National Natural Science Foundation of China under Grant No.12104372.
文摘Weakly interacting quantum systems in low dimensions have been investigated for a long time,but there still remain a number of open questions and a lack of explicit expressions of physical properties of such systems.In this work,we find power-law scalings of thermodynamic observables in low-dimensional interacting Bose gases at quantum criticality.We present a physical picture for these systems with the repulsive interaction strength approaching zero;namely,the competition between the kinetic and interaction energy scales gives rise to power-law scalings with respect to the interaction strength in characteristic thermodynamic observables.This prediction is supported by exact Bethe ansatz solutions in one dimension,demonstrating a simple 1/3-power-law scaling of the critical entropy per particle.Our method also yields results in agreement with a non-perturbative renormalization-group computation in two dimensions.These results provide a new perspective for understanding many-body phenomena induced by weak interactions in quantum gases.
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Project supported by the Key-Area Research and Development Program of Guang Dong Province,China(Grant No.2019B030330001)the National Natural Science Foundation of China(Grant Nos.11874434 and 11574405)+1 种基金the Science and Technology Program of Guangzhou,China(Grant No.201904020024)the Guangzhou Science and Technology Projects(Grant No.202002030459)。
文摘We present a cluster mean-field study for ground-state phase diagram and many-body dynamics of spin-1 bosons confined in a two-chain Bose-Hubbard ladder(BHL).For unbiased BHL,we find superfluid(SF)phase and integer filling Mott insulator(Int MI)phase.For biased BHL,in addition to the SF and Int MI phases,there appears half-integer filling Mott insulator(HInt MI)phase.The phase transition between the SF and Int MI phases can be first order at a part of phase boundaries,while the phase transition between the SF and HInt MI phases is always second order.By tuning the bias energy,we report on the change of the nature of SF-MI phase transitions.Furthermore,we study the effect of the spin-dependent interaction on the many-body population dynamics.The spin-dependent interaction can lead to rich dynamical behaviors,but does not influence the particle transfer efficiency.Our results indicate a way to tune the nature of the SF-MI phase transition and open a new avenue to study the many-body dynamics of spinor bosons in optical lattices.
基金Z. L. acknowledges inspiring discussions with Yan Chen, Ying Jiang and also thanks Tao Wang for provid- ing the QMC data and useful discussions. Z. L. wishes also to thank Dan Bo Zhang for reading and providing useful comments on this manuscript. This work was supported by the State Key Programs of China （Grant Nos. 2017YFA0304204 and 2016YFA0300504）, and the National Natural Science Foundation of China （Grant Nos. 11625416, and 11474064）.
文摘We clarify some technical issues in the present generalized effective-potential Landau theory （GEPLT） to make the GEPLT more consistent and complete. Utilizing this clarified GEPLT, we analytically study the quantum phase transitions of ultracold Bose gases in bipartite superlattices at zero temper- ature. The corresponding quantum phase boundaries are analytically calculated up to the third-order hopping, which are in excellent agreement with the quantum Monte Carlo （QMC） simulations.
基金Acknowledgements This work was supported by the National Basic Research Program of China （Grant No. 2011CB921601）, the National Natural Science Foundation of China （NSFC, Grant No. 11234008）, NSFC Project for Excellent Research Team （Grant No. 61121064）, and Doctoral Program Foundation of the Ministry of Education China （Grant No. 20111401130001）.
文摘We review our recent experimental realization and investigation of a spin orbit （SO） coupled Bose Einstein condensate （BEC） and quantum degenerate Fermi gas. By using two counter-propagathlg Ranlan lasers and controlling the different frequency of two R,aman lasers to engineer the atom light interaction, we first study the SO coupling in BEC. Then we study SO coupling in Fermi gas. We, observe the spin dephasing in spin dynamics and momentum distribution asymmetry of the equilibrium state as halhnarks of SO coupling in a Fermi gas. To clearly reveal the, property of SO coupling Fermi gas, we also study the momentmn-resolved radio-frequency spectroscopy which characterizes the energy momentum dispersion and spin composition of the quantum states. We observe the change of errmion surfaces in different helieity branches with different atomic density, which indicates that a Lifshitz transition of the Fermi surface topology change can be found by further cooling the system. At last, we study the momentum-resolved Raman spectroscopy of an ultracoht Fermi gas.
