This paper derives the analytical expression of free energy for a weakly interacting Fermi gas in a weak magnetic field, by using the methods of quantum statistics as well as considering the relativistic effect. Based...This paper derives the analytical expression of free energy for a weakly interacting Fermi gas in a weak magnetic field, by using the methods of quantum statistics as well as considering the relativistic effect. Based on the derived expression, the thermodynamic properties of the system at both high and low temperatures are given and the relativistic effect on the properties of the system is discussed. It shows that, in comparison with a nonrelativistic situation, the relativistic effect changes the influence of temperature on the thermodynamic properties of the system at high temperatures, and changes the influence of particle-number density on them at extremely low temperature. But the relativistic effect does not change the influence of the magnetic field and inter-particle interactions on the thermodynamic properties of the system at both high and extremely low temperatures.展开更多
By using the Euler-MacLaurin formula, this paper studies the thermodynamic properties of an ideal Fermi gas confined in a D-dimensional rectangular container. The general expressions of the thermodynamic quantities wi...By using the Euler-MacLaurin formula, this paper studies the thermodynamic properties of an ideal Fermi gas confined in a D-dimensional rectangular container. The general expressions of the thermodynamic quantities with the finite-size corrections are given explicitly and the effects of the size and shape of the container on the properties of the system are discussed. It is shown that the corrections of the thermodynamic quantities due to the finite-size effects are significant to be considered for the case of strong degeneracy but negligible for the case of weak degeneracy or non-degeneracy. It is important to find that some familiar conclusions under the thermodynamic limit are no longer valid for the finite-size systems and there are some novel characteristics resulting from the finite-size effects, such as the nonextensivity of the system, the anisotropy of the pressure, and so on.展开更多
Based on the thermodynamic potential function of Fermi gas in a strong magnetic field, using the thermodynamics method, the integrated analytical expressions of thermodynamic quantities of the system at low temperatur...Based on the thermodynamic potential function of Fermi gas in a strong magnetic field, using the thermodynamics method, the integrated analytical expressions of thermodynamic quantities of the system at low temperatures are derived, and the effects of the magnetic field on the statistic properties of the system are analysed. It is shown that, as long as the temperature is not zero, the effects of the magnetic field on the thermodynamic quantities of the system contain both oscillatory and non-oscillatory parts. For the non-oscillatory part, compared with the situation of Fermi gas in a weak magnetic field, the influence of the magnetic field on the thermodynamic quantities is not exactly the same. For the oscillatory part, the period and amplitude of the oscillation are all related to the magnetic field. Due to the oscillation, the chemical potential may be greater than Ferim energy of the system, but the oscillation does not affect the thermodynamic stability of the system.展开更多
Due to the scale invariance, the thermodynamic laws of strongly interacting limit unitary Fermi gas can be similar to those of non-interacting ideal gas. For example, the virial theorem between pressure and energy den...Due to the scale invariance, the thermodynamic laws of strongly interacting limit unitary Fermi gas can be similar to those of non-interacting ideal gas. For example, the virial theorem between pressure and energy density of the ideal gas P = 2E/aV is still satisfied by the unitary Fermi gas. This paper analyses the sound velocity of unitary Fermi gases with the quasi-linear approximation. For comparison, the sound velocities for the ideal Boltzmann, Bose and Fermi gas are also given. Quite interestingly, the sound velocity formula for the ideal non-interacting gas is found to be satisfied by the unitary Fermi gas in different temperature regions.展开更多
The bipartite entanglement in Fermi gas without interaction is investigated when there ace three fermions in the system. The negativity and the yon Neumann entropy are employed to measure the entanglement of the syste...The bipartite entanglement in Fermi gas without interaction is investigated when there ace three fermions in the system. The negativity and the yon Neumann entropy are employed to measure the entanglement of the system. The position of the third fermion can affect the entanglement between the first and the second fermions. The entanglement can be enhanced or suppressed when the third fermion changes its position. When the two fermions are at the same position or when their distance is more than 2.0/kF, the third fermion cannot affect them.展开更多
Based on the theoretical results derived from pseudopotential method and local approximation, this paper studies the thermodynamic stability of a weakly interacting Fermi gas trapped in a harmonic potential by using a...Based on the theoretical results derived from pseudopotential method and local approximation, this paper studies the thermodynamic stability of a weakly interacting Fermi gas trapped in a harmonic potential by using analytical method of thermodynamics. The effects of the interparticle interactions as well as external potential on the thermodynamic stability of the system are discussed. It is shown that the system is stable as for the complete average, but as for local parts, the system is unstable anywhere. This instability shows that the stability conditions of mechanics cannot be satisfied anywhere, and the stability conditions of thermostatics cannot be satisfied somewhere. In addition, the interactions and external potential have direct effects on the local stability of the system.展开更多
We investigate the particle-hole fluctuation correction to the specific heat of an ultracold Fermi gas at unitarity within the framework of the non-self-consistent T-matrix approximation in the normal phase. We find g...We investigate the particle-hole fluctuation correction to the specific heat of an ultracold Fermi gas at unitarity within the framework of the non-self-consistent T-matrix approximation in the normal phase. We find good agreement between our theoretical predictions and the experimental data measured by the MIT group, apart from discrepancies near the transition temperature. At high temperature, our calculated specific heat has the tendency to approach the specific heat of the Boltzmann gas.展开更多
We study the possibility of stabilizing a Fulde-Ferrell-Larkin-Ovchinnikov(FFLO)state in an equally populated two-component Fermi gas trapped in a moving two-dimensional optical lattice.For a system with nearly half f...We study the possibility of stabilizing a Fulde-Ferrell-Larkin-Ovchinnikov(FFLO)state in an equally populated two-component Fermi gas trapped in a moving two-dimensional optical lattice.For a system with nearly half filling,we find that a finite pairing momentum perpendicular to the moving direction can be spontaneously induced for a proper choice of lattice velocity.As a result,the total pairing momentum is tilted towards the nesting vector to take advantage of the significant enhancement of the density of states.展开更多
Topological superfluid state is different from the normal superfluid one due to the excitation energy gap on the boundary.How to obtain the topological superfluid state by using spin-orbit coupling to control the s-wa...Topological superfluid state is different from the normal superfluid one due to the excitation energy gap on the boundary.How to obtain the topological superfluid state by using spin-orbit coupling to control the s-waves paired mass-imbalanced Fermi gas is a recent novel topic.In this paper,we study the topological superfluid phase diagram of two-dimensional mass-imbalanced Fermi gas with Rashba spin-orbit coupling at zero temperature.We find that due to the competition among mass imbalance,pairing interaction and spin-orbit coupling,there is a double-well structure in the thermodynamic potential,which affects the properties of the ground state of the system.We comprehensively give the phase diagrams of the system on the plane of spin-orbit coupling and chemical potential,and the phase diagrams on the plane of the reduced mass ratio and two-body binding energy.This study not only points out the stable region of topolog-ical superfluid state of mass-imbalanced Fermi gas,but also provides a detailed theoretical basis for better observation of topological superfluid state in experiments.展开更多
We study the properties of superfluid in a two-dimensional （2D） polarized Fermi gas with spin-orbit coupling and adiabatic rotation which are trapped in a harmonic potential. Due to the competition between polarizat...We study the properties of superfluid in a two-dimensional （2D） polarized Fermi gas with spin-orbit coupling and adiabatic rotation which are trapped in a harmonic potential. Due to the competition between polarization, spin-orbit coupling, and adiabatic rotation, the Fermi gas exhibits many intriguing phenomena. By using the Bardeen-Cooper-Schrieffer （BCS） mean-field method with local density approximation, we investigate the dependence of order parameter solution on the spin-orbit coupling strength and the rotation velocity. The energy spectra with different rotation velocities are studied in detail. Besides, the conditions for the zero-energy Majorana fermions in topological superfluid phase to be observed are obtained. By investigating distributions of number density, we find that the rotation has opposite effect on the distribution of number density with different spins, which leads to the enhancement of the polarization of Fermi gas. Here, we focus on the region of BCS pairing and ignore the Fulde-Ferrell-Larkin-Ovchinnikov state.展开更多
Based on the mean-field theory,we investigate the thermodynamic properties of the two-dimensional(2D)charged spin-1/2 Fermi gas.Lande′factor g is introduced to measure the strength of the paramagnetic effect.There is...Based on the mean-field theory,we investigate the thermodynamic properties of the two-dimensional(2D)charged spin-1/2 Fermi gas.Lande′factor g is introduced to measure the strength of the paramagnetic effect.There is a competition between diamagnetism and paramagnetism in the system.The larger the Lande′factor,the smaller the entropy and specific heat.Diamagnetism tends to increase the entropy,while paramagnetism leads to the decrease of the entropy.We find that there exists a critical value of Lande′factor for the transition point due to the competition.The entropy of the system increases with the magnetic field when g<0.58.With the growth of paramagnetism,when g>0.58,the entropy first decreases with the magnetic field,then reaches a minimum value,and finally increases again.Both the entropy and specific heat increase with the temperature,and no phase transition occurs.The specific heat tends to a constant value at the hightemperature limit,and it approaches to zero at very low temperatures,which have been proved by the analytical calculation.展开更多
We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases. A Kadomtsev-Petviashvili I （KPI） solitary wave has been realized for superfluid Fermi gases i...We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases. A Kadomtsev-Petviashvili I （KPI） solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen-Coope-Schrieffer （BCS） regime, Bose-Einstein condensate （BEC） reginle, and unitarity regime. One- lump solution as well as one-line soliton solutions for the KPI equation are obtained, and two-line soliton solutions with the same amplitude are also studied in the limited cases. The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity.展开更多
A theoretical study of the BCS-BEC crossover is presented. Starting from a two-channel Boson-Fermion resonance model, the BCS-Bogoiubov mean-field method and the Green＇s function method are adopted. The result shows ...A theoretical study of the BCS-BEC crossover is presented. Starting from a two-channel Boson-Fermion resonance model, the BCS-Bogoiubov mean-field method and the Green＇s function method are adopted. The result shows that we can end up with a BCS-type theory but with a composite order parameter. Calculation shows that the Bose condensate of BCS Cooper pairs is proportional to the molecular BEC of Bose molecules. The resonance superfluid phase is indicated by the energy spectrum with an obvious interpretation of the transition mechanism.展开更多
The Joule-Thomson effect reflects the interaction among constituent particles of macroscopic system.Forclassical ideal gas,the corresponding Joule-Thomson coefficient is vanishing while it is non-zero for ideal quantu...The Joule-Thomson effect reflects the interaction among constituent particles of macroscopic system.Forclassical ideal gas,the corresponding Joule-Thomson coefficient is vanishing while it is non-zero for ideal quantum gasdue to the quantum degeneracy.In recent years,much attention is paid to the unitary Fermi gas with infinite two-bodyscattering length.According to universal analysis,the thermodynamical law of unitary Fermi gas is similar to that ofnon-interacting ideal gas,which can be explored by the virial theorem P = 2E/3V.Based on previous works,we furtherstudy the unitary Fermi gas properties.The effective chemical potential is introduced to characterize the nonlinear levelscrossing effects in a strongly interacting medium.The changing behavior of the rescaled Joule-Thomson coefficientaccording to temperature manifests a quite different behavior from that for ideal Fermi gas.展开更多
We investigate the tunneling dynamics of the Fermi gases in an optical lattice in the Bose--Einstein condensation （BEC） regime. The three critical scattering lengths and the system energies are found in different ca...We investigate the tunneling dynamics of the Fermi gases in an optical lattice in the Bose--Einstein condensation （BEC） regime. The three critical scattering lengths and the system energies are found in different cases of Josephson oscillation （JO）, oscillating-phase-type self-trapping （OPTST）, running-phase-type self-trapping （RPTST）, and self-trapping （ST）. It is found that the s-wave scattering lengths have a crucial role on the tunneling dynamics. By adjusting the scattering length in the adiabatic condition, the transition probability changes with the adiabatic periodicity and a rectangular periodic pattern emerges. The periodicity of the rectangular wave depends on the system parameters such as the periodicity of the adjustable parameter, the s-wave scattering length.展开更多
We study the ferromagnetic transition of a two-component homogeneous dipolar Fermi gas with 1D spin-orbit coupling(SOC) at finite temperature.The ferromagnetic transition temperature is obtained as functions of dipola...We study the ferromagnetic transition of a two-component homogeneous dipolar Fermi gas with 1D spin-orbit coupling(SOC) at finite temperature.The ferromagnetic transition temperature is obtained as functions of dipolar constantλd,spin-orbit coupling constant λSOC and contact interaction constant λS.It increases monotonically with these three parameters.In the ferromagnetic phase,the Fermi surfaces of different components can be deformed differently.The phase diagrams at finite temperature are obtained.展开更多
The tunneling dynamics of superfluid Fermi gas in a triple-well potential in the unitarity regime is investigated in the present paper. The fixed points of the （0,0） mode and the （π, π） mode are given. We find t...The tunneling dynamics of superfluid Fermi gas in a triple-well potential in the unitarity regime is investigated in the present paper. The fixed points of the （0,0） mode and the （π, π） mode are given. We find that the interaction parameter U and the coupling strength k could have an extreme effect on the quantum tunneling dynamics. We also find that, in the zero mode, only Josophson oscillation appears. However, for the mode, the trapping phenomena take place. An irregular oscillation of the particle number in each well could appear by adjusting the scanning period T. It is noted that if the scanning period is less than a critical point T＊, the particle number will come back to the fixed point with small oscillation, while if T 〉 T＊ the particle number cannot come back to the fixed point, but with irregular oscillations. The dependence of the critical point T＊ on the system parameter of coupling strength k is numerically given.展开更多
We report on the optimal production of the Bose and Fermi mixtures with ^(87) Rb and ^(40)K in a crossed optical dipole trap(ODT).We measure the atomic number and lifetime of the mixtures in combination of the spin st...We report on the optimal production of the Bose and Fermi mixtures with ^(87) Rb and ^(40)K in a crossed optical dipole trap(ODT).We measure the atomic number and lifetime of the mixtures in combination of the spin state |F=9/2,m_(F)=9/2> of^(40)K and |1,1>of ^(87) Rb in the ODT,which is larger and longer compared with the combination of the spin state |9/2,9/2> of^(40)K and 12,2) of ^(87)Rb in the ODT.We observe the atomic numbers of ^(87)Rb and ^(40)K shown in each stage of the sympathetic cooling process while gradually reducing the depth of the optical trap.By optimizing the relative loading time of atomic mixtures in the MOT,we obtain the large atomic number of ^(40)K(~6 ×10^(6)) or the mixtures of atoms with an equal number(~1.6 × 10^(6)) at the end of evaporative cooling in the ODT.We experimentally investigate the evaporative cooling in an enlarged volume of the ODT via adding a third laser beam to the crossed ODT and found that more atoms(8 × 10^(6)) and higher degeneracy(T/T_(F)=0.25) of Fermi gases are obtained.The ultracold atomic gas mixtures pave the way to explore phenomena such as few-body collisions and the Bose-Fermi Hubbard model,as well as for creating ground-state molecules of ^(87)Rb^(40)K.展开更多
We investigate the itinerant ferromagnetism in a dipolar Fermi atomic system with the anisotropic spin–orbit coupling(SOC),which is traditionally explored with isotropic contact interaction.We first study the ferroma...We investigate the itinerant ferromagnetism in a dipolar Fermi atomic system with the anisotropic spin–orbit coupling(SOC),which is traditionally explored with isotropic contact interaction.We first study the ferromagnetism transition boundaries and the properties of the ground states through the density and spin-flip distribution in momentum space,and we find that both the anisotropy and the magnitude of the SOC play an important role in this process.We propose a helpful scheme and a quantum control method which can be applied to conquering the difficulties of previous experimental observation of itinerant ferromagnetism.Our further study reveals that exotic Fermi surfaces and an abnormal phase region can exist in this system by controlling the anisotropy of SOC,which can provide constructive suggestions for the research and the application of a dipolar Fermi gas.Furthermore,we also calculate the ferromagnetism transition temperature and novel distributions in momentum space at finite temperature beyond the ground states from the perspective of experiment.展开更多
We review some recent progresses on the study of ultracold Fermi gases with synthetic spin-orbit coupling.In particular,we focus on the pairing superfluidity in these systems at zero temperature.Recent studies have sh...We review some recent progresses on the study of ultracold Fermi gases with synthetic spin-orbit coupling.In particular,we focus on the pairing superfluidity in these systems at zero temperature.Recent studies have shown that different forms of spin-orbit coupling in various spatial dimensions can lead to a wealth of novel pairing superfluidity.A common theme of these variations is the emergence of new pairing mechanisms which are direct results of spin-orbit-coupling-modified single-particle dispersion spectra.As different configurations can give rise to single-particle dispersion spectra with drastic differences in symmetry,spin dependence and low-energy density of states,spin-orbit coupling is potentially a powerful tool of quantum control,which,when combined with other available control schemes in ultracold atomic gases,will enable us to engineer novel states of matter.展开更多
文摘This paper derives the analytical expression of free energy for a weakly interacting Fermi gas in a weak magnetic field, by using the methods of quantum statistics as well as considering the relativistic effect. Based on the derived expression, the thermodynamic properties of the system at both high and low temperatures are given and the relativistic effect on the properties of the system is discussed. It shows that, in comparison with a nonrelativistic situation, the relativistic effect changes the influence of temperature on the thermodynamic properties of the system at high temperatures, and changes the influence of particle-number density on them at extremely low temperature. But the relativistic effect does not change the influence of the magnetic field and inter-particle interactions on the thermodynamic properties of the system at both high and extremely low temperatures.
基金Project supported by the National Natural Science Foundation of China (Grant No 10875100)
文摘By using the Euler-MacLaurin formula, this paper studies the thermodynamic properties of an ideal Fermi gas confined in a D-dimensional rectangular container. The general expressions of the thermodynamic quantities with the finite-size corrections are given explicitly and the effects of the size and shape of the container on the properties of the system are discussed. It is shown that the corrections of the thermodynamic quantities due to the finite-size effects are significant to be considered for the case of strong degeneracy but negligible for the case of weak degeneracy or non-degeneracy. It is important to find that some familiar conclusions under the thermodynamic limit are no longer valid for the finite-size systems and there are some novel characteristics resulting from the finite-size effects, such as the nonextensivity of the system, the anisotropy of the pressure, and so on.
文摘Based on the thermodynamic potential function of Fermi gas in a strong magnetic field, using the thermodynamics method, the integrated analytical expressions of thermodynamic quantities of the system at low temperatures are derived, and the effects of the magnetic field on the statistic properties of the system are analysed. It is shown that, as long as the temperature is not zero, the effects of the magnetic field on the thermodynamic quantities of the system contain both oscillatory and non-oscillatory parts. For the non-oscillatory part, compared with the situation of Fermi gas in a weak magnetic field, the influence of the magnetic field on the thermodynamic quantities is not exactly the same. For the oscillatory part, the period and amplitude of the oscillation are all related to the magnetic field. Due to the oscillation, the chemical potential may be greater than Ferim energy of the system, but the oscillation does not affect the thermodynamic stability of the system.
基金supported by the National Natural Science Foundation of China (Grant No. 10875050)
文摘Due to the scale invariance, the thermodynamic laws of strongly interacting limit unitary Fermi gas can be similar to those of non-interacting ideal gas. For example, the virial theorem between pressure and energy density of the ideal gas P = 2E/aV is still satisfied by the unitary Fermi gas. This paper analyses the sound velocity of unitary Fermi gases with the quasi-linear approximation. For comparison, the sound velocities for the ideal Boltzmann, Bose and Fermi gas are also given. Quite interestingly, the sound velocity formula for the ideal non-interacting gas is found to be satisfied by the unitary Fermi gas in different temperature regions.
基金the Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No.20050285002National Natural Science Foundation of China under Grant No.10774108
文摘The bipartite entanglement in Fermi gas without interaction is investigated when there ace three fermions in the system. The negativity and the yon Neumann entropy are employed to measure the entanglement of the system. The position of the third fermion can affect the entanglement between the first and the second fermions. The entanglement can be enhanced or suppressed when the third fermion changes its position. When the two fermions are at the same position or when their distance is more than 2.0/kF, the third fermion cannot affect them.
文摘Based on the theoretical results derived from pseudopotential method and local approximation, this paper studies the thermodynamic stability of a weakly interacting Fermi gas trapped in a harmonic potential by using analytical method of thermodynamics. The effects of the interparticle interactions as well as external potential on the thermodynamic stability of the system are discussed. It is shown that the system is stable as for the complete average, but as for local parts, the system is unstable anywhere. This instability shows that the stability conditions of mechanics cannot be satisfied anywhere, and the stability conditions of thermostatics cannot be satisfied somewhere. In addition, the interactions and external potential have direct effects on the local stability of the system.
基金Supported by the Research Fund for Advanced Talents of Jiangsu University under Grant No 14JDG174the National Natural Science Foundation of China under Grants Nos 11447126,11275097,11475085 and 11535005the Natural Science Foundation of Jiangsu Province of China under Grant No BK20130078
文摘We investigate the particle-hole fluctuation correction to the specific heat of an ultracold Fermi gas at unitarity within the framework of the non-self-consistent T-matrix approximation in the normal phase. We find good agreement between our theoretical predictions and the experimental data measured by the MIT group, apart from discrepancies near the transition temperature. At high temperature, our calculated specific heat has the tendency to approach the specific heat of the Boltzmann gas.
基金supported by the Beijing Natural Science Foundation,China(Grant No.Z180013)the National Natural Science Foundation of China(Grant Nos.11522436,11774425,and 12074428)+1 种基金the National Key R&D Program of China(Grant No.2018YFA0306501)the Research Funds of Renmin University of China(Grant Nos.16XNLQ03 and 18XNLQ15)。
文摘We study the possibility of stabilizing a Fulde-Ferrell-Larkin-Ovchinnikov(FFLO)state in an equally populated two-component Fermi gas trapped in a moving two-dimensional optical lattice.For a system with nearly half filling,we find that a finite pairing momentum perpendicular to the moving direction can be spontaneously induced for a proper choice of lattice velocity.As a result,the total pairing momentum is tilted towards the nesting vector to take advantage of the significant enhancement of the density of states.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11875149, 11874127, 52061014, and 61565007)the Youth Jing-gang Scholars Program of Jiangxi Province, Chinathe Program of Qing-jiang Excellent Young Talents, Jiangxi University of Science and Technology
文摘Topological superfluid state is different from the normal superfluid one due to the excitation energy gap on the boundary.How to obtain the topological superfluid state by using spin-orbit coupling to control the s-waves paired mass-imbalanced Fermi gas is a recent novel topic.In this paper,we study the topological superfluid phase diagram of two-dimensional mass-imbalanced Fermi gas with Rashba spin-orbit coupling at zero temperature.We find that due to the competition among mass imbalance,pairing interaction and spin-orbit coupling,there is a double-well structure in the thermodynamic potential,which affects the properties of the ground state of the system.We comprehensively give the phase diagrams of the system on the plane of spin-orbit coupling and chemical potential,and the phase diagrams on the plane of the reduced mass ratio and two-body binding energy.This study not only points out the stable region of topolog-ical superfluid state of mass-imbalanced Fermi gas,but also provides a detailed theoretical basis for better observation of topological superfluid state in experiments.
文摘We study the properties of superfluid in a two-dimensional （2D） polarized Fermi gas with spin-orbit coupling and adiabatic rotation which are trapped in a harmonic potential. Due to the competition between polarization, spin-orbit coupling, and adiabatic rotation, the Fermi gas exhibits many intriguing phenomena. By using the Bardeen-Cooper-Schrieffer （BCS） mean-field method with local density approximation, we investigate the dependence of order parameter solution on the spin-orbit coupling strength and the rotation velocity. The energy spectra with different rotation velocities are studied in detail. Besides, the conditions for the zero-energy Majorana fermions in topological superfluid phase to be observed are obtained. By investigating distributions of number density, we find that the rotation has opposite effect on the distribution of number density with different spins, which leads to the enhancement of the polarization of Fermi gas. Here, we focus on the region of BCS pairing and ignore the Fulde-Ferrell-Larkin-Ovchinnikov state.
基金supported by the National Natural Science Foundation of China(Grant No.11774019)the Fundamental Research Funds for the Central Universities,China(Grant No.FRF-BR-16-014A)。
文摘Based on the mean-field theory,we investigate the thermodynamic properties of the two-dimensional(2D)charged spin-1/2 Fermi gas.Lande′factor g is introduced to measure the strength of the paramagnetic effect.There is a competition between diamagnetism and paramagnetism in the system.The larger the Lande′factor,the smaller the entropy and specific heat.Diamagnetism tends to increase the entropy,while paramagnetism leads to the decrease of the entropy.We find that there exists a critical value of Lande′factor for the transition point due to the competition.The entropy of the system increases with the magnetic field when g<0.58.With the growth of paramagnetism,when g>0.58,the entropy first decreases with the magnetic field,then reaches a minimum value,and finally increases again.Both the entropy and specific heat increase with the temperature,and no phase transition occurs.The specific heat tends to a constant value at the hightemperature limit,and it approaches to zero at very low temperatures,which have been proved by the analytical calculation.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 91026005 and 11047010)the Natural Science Foundation of Northwest Normal University of China (Grant No. NWNU-KJCXGC-03-48)
文摘We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases. A Kadomtsev-Petviashvili I （KPI） solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen-Coope-Schrieffer （BCS） regime, Bose-Einstein condensate （BEC） reginle, and unitarity regime. One- lump solution as well as one-line soliton solutions for the KPI equation are obtained, and two-line soliton solutions with the same amplitude are also studied in the limited cases. The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity.
文摘A theoretical study of the BCS-BEC crossover is presented. Starting from a two-channel Boson-Fermion resonance model, the BCS-Bogoiubov mean-field method and the Green＇s function method are adopted. The result shows that we can end up with a BCS-type theory but with a composite order parameter. Calculation shows that the Bose condensate of BCS Cooper pairs is proportional to the molecular BEC of Bose molecules. The resonance superfluid phase is indicated by the energy spectrum with an obvious interpretation of the transition mechanism.
基金Supported in part by Natural Science Foundation of China under Grant Nos.10875050,10675052MOE of China under Grant No.IRT0624
文摘The Joule-Thomson effect reflects the interaction among constituent particles of macroscopic system.Forclassical ideal gas,the corresponding Joule-Thomson coefficient is vanishing while it is non-zero for ideal quantum gasdue to the quantum degeneracy.In recent years,much attention is paid to the unitary Fermi gas with infinite two-bodyscattering length.According to universal analysis,the thermodynamical law of unitary Fermi gas is similar to that ofnon-interacting ideal gas,which can be explored by the virial theorem P = 2E/3V.Based on previous works,we furtherstudy the unitary Fermi gas properties.The effective chemical potential is introduced to characterize the nonlinear levelscrossing effects in a strongly interacting medium.The changing behavior of the rescaled Joule-Thomson coefficientaccording to temperature manifests a quite different behavior from that for ideal Fermi gas.
基金Project supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA01020304)the National Natural Science Foundation of China(Grant Nos.11275156,91026005,11365020,and 11047010)
文摘We investigate the tunneling dynamics of the Fermi gases in an optical lattice in the Bose--Einstein condensation （BEC） regime. The three critical scattering lengths and the system energies are found in different cases of Josephson oscillation （JO）, oscillating-phase-type self-trapping （OPTST）, running-phase-type self-trapping （RPTST）, and self-trapping （ST）. It is found that the s-wave scattering lengths have a crucial role on the tunneling dynamics. By adjusting the scattering length in the adiabatic condition, the transition probability changes with the adiabatic periodicity and a rectangular periodic pattern emerges. The periodicity of the rectangular wave depends on the system parameters such as the periodicity of the adjustable parameter, the s-wave scattering length.
基金Project supported by the National Key Research and Development Project of China(Grant No.2016YFA0301501).
文摘We study the ferromagnetic transition of a two-component homogeneous dipolar Fermi gas with 1D spin-orbit coupling(SOC) at finite temperature.The ferromagnetic transition temperature is obtained as functions of dipolar constantλd,spin-orbit coupling constant λSOC and contact interaction constant λS.It increases monotonically with these three parameters.In the ferromagnetic phase,the Fermi surfaces of different components can be deformed differently.The phase diagrams at finite temperature are obtained.
基金supported by the National Fundamental Research Program of China(Grant Nos.2007CB814800 and 2011CB921503)the National Natural Science Foundation of China(Grant Nos.11275156,91021021,and 10875098)the Natural Science Foundation of Northwest Normal University(Grant No.NWNU-KJCXGC-03-48)
文摘The tunneling dynamics of superfluid Fermi gas in a triple-well potential in the unitarity regime is investigated in the present paper. The fixed points of the （0,0） mode and the （π, π） mode are given. We find that the interaction parameter U and the coupling strength k could have an extreme effect on the quantum tunneling dynamics. We also find that, in the zero mode, only Josophson oscillation appears. However, for the mode, the trapping phenomena take place. An irregular oscillation of the particle number in each well could appear by adjusting the scanning period T. It is noted that if the scanning period is less than a critical point T＊, the particle number will come back to the fixed point with small oscillation, while if T 〉 T＊ the particle number cannot come back to the fixed point, but with irregular oscillations. The dependence of the critical point T＊ on the system parameter of coupling strength k is numerically given.
基金supported by the Innovation Program for Quantum Science and Technology (Grant No. 2021ZD0302003)the National Natural Science Foundation of China (Grant Nos. 12034011, U23A6004, 12374245,12322409, 92065108, 11974224, and 12022406)+1 种基金the National Key Research and Development Program of China (Grant Nos. 2022YFA1404101 and 2021YFA1401700)the Fund for Shanxi 1331 Project Key Subjects Construction。
文摘We report on the optimal production of the Bose and Fermi mixtures with ^(87) Rb and ^(40)K in a crossed optical dipole trap(ODT).We measure the atomic number and lifetime of the mixtures in combination of the spin state |F=9/2,m_(F)=9/2> of^(40)K and |1,1>of ^(87) Rb in the ODT,which is larger and longer compared with the combination of the spin state |9/2,9/2> of^(40)K and 12,2) of ^(87)Rb in the ODT.We observe the atomic numbers of ^(87)Rb and ^(40)K shown in each stage of the sympathetic cooling process while gradually reducing the depth of the optical trap.By optimizing the relative loading time of atomic mixtures in the MOT,we obtain the large atomic number of ^(40)K(~6 ×10^(6)) or the mixtures of atoms with an equal number(~1.6 × 10^(6)) at the end of evaporative cooling in the ODT.We experimentally investigate the evaporative cooling in an enlarged volume of the ODT via adding a third laser beam to the crossed ODT and found that more atoms(8 × 10^(6)) and higher degeneracy(T/T_(F)=0.25) of Fermi gases are obtained.The ultracold atomic gas mixtures pave the way to explore phenomena such as few-body collisions and the Bose-Fermi Hubbard model,as well as for creating ground-state molecules of ^(87)Rb^(40)K.
基金supported by the National Key R&D Program of China(Grant Nos.2021YFA1400900,2021YFA0718300,and 2021YFA1400243)the Key Scientific Research Project of colleges and Universities in Henan Province(Nos.20A140018 and 23A140001)+1 种基金the National Natural Science Foundatiion of China(Grant Nos.12074105,12074106,12074120,12247146,12104135,and 61835013)the Natural Science Foundation of Shanghai(Grant No.20ZR1418500).
文摘We investigate the itinerant ferromagnetism in a dipolar Fermi atomic system with the anisotropic spin–orbit coupling(SOC),which is traditionally explored with isotropic contact interaction.We first study the ferromagnetism transition boundaries and the properties of the ground states through the density and spin-flip distribution in momentum space,and we find that both the anisotropy and the magnitude of the SOC play an important role in this process.We propose a helpful scheme and a quantum control method which can be applied to conquering the difficulties of previous experimental observation of itinerant ferromagnetism.Our further study reveals that exotic Fermi surfaces and an abnormal phase region can exist in this system by controlling the anisotropy of SOC,which can provide constructive suggestions for the research and the application of a dipolar Fermi gas.Furthermore,we also calculate the ferromagnetism transition temperature and novel distributions in momentum space at finite temperature beyond the ground states from the perspective of experiment.
基金supported by National Fundamental Research Program of China(Grant Nos.2011CB921200 and 2011CBA00200)National Key Basic Research Program(Grant No.2013CB922000)+4 种基金National Natural Science Foundation(Grant No.60921091)National Science Foundation of China(Grant Nos.10904172,11104158,11374177,11105134,1127409and 11374283)the Fundamental Research Funds for the Central Universities(Grant No.WK2470000006)the Research Funds of Renmin University of China(Grant No.10XNL016)the programs of Chinese Academy of Sciences
文摘We review some recent progresses on the study of ultracold Fermi gases with synthetic spin-orbit coupling.In particular,we focus on the pairing superfluidity in these systems at zero temperature.Recent studies have shown that different forms of spin-orbit coupling in various spatial dimensions can lead to a wealth of novel pairing superfluidity.A common theme of these variations is the emergence of new pairing mechanisms which are direct results of spin-orbit-coupling-modified single-particle dispersion spectra.As different configurations can give rise to single-particle dispersion spectra with drastic differences in symmetry,spin dependence and low-energy density of states,spin-orbit coupling is potentially a powerful tool of quantum control,which,when combined with other available control schemes in ultracold atomic gases,will enable us to engineer novel states of matter.
