Diversified vortex phase diagram for a rotating trapped two-band Fermi gas in the BCS-BEC crossover

Abstract

We report the equilibrium vortex phase diagram of a rotating two-band Fermi gas confined to a cylindrically symmetric parabolic trapping potential, using the recently developed finite-temperature effective field theory (Klimin et al 2016 Phys. Rev. A 94 023620). A non-monotonic resonant dependence of the free energy as a function of the temperature and the rotation frequency is revealed for a two-band superfluid. We particularly focus on novel features that appear as a result of interband interactions and can be experimentally resolved. The resonant dependence of the free energy is directly manifested in vortex phase diagrams, where areas of stability for both integer and fractional vortex states are found. The study embraces the BCS-BEC crossover regime and the entire temperature range below the critical temperature T c . Significantly different behavior of vortex matter as a function of the interband coupling is revealed in the BCS and BEC regimes. regime has also attracted much attention [27]. Vortex states in multiband quantum atomic gases have been studied to a far lesser extent.Therefore, in this work, the subject of our interest are fractional vortices in two-band Fermi gases of ultracold atoms in the BCS-BEC crossover. Although there is some similarity between superconductors and condensed atomic Fermi gases, the analogy is not complete. For one difference, cold gases certainly require an independent treatment by specific methods suitable in the entire BCS-BEC crossover range.Recently, the stability of different vortex states in a rotating trapped one-band Fermi gas has been theoretically studied in [14,15] using, respectively, the coarse-grained Bogoliubov-de Gennes (BdG) theory [28] (first applied to atomic Fermi gases in [29]) and the recently developed finite-temperature effective field theory (EFT) [30,31]. The finite-temperature EFT results agree with the results of the BdG theory and experiment for different manifestations: collective excitations and vortices [15,31], and solitons [32,33]. The finitetemperature EFT is aimed to find analytic results whenever possible. For example, for dark solitons in condensed Fermi gases, the finite-temperature EFT provides exact analytic solutions of the soliton equation of motion [32], while the BdG equations for the same problem have been solved only numerically.Besides our studies, there are several modifications of the EFT of condensed Fermi gases described in different publications and related to different ranges of external parameters (e.g., temperature and scattering length). They are developed either for the close vicinity to the critical temperature [34] or for the case T=0 (e.g., [35][36][37]). As analyzed in [31], the present finite-temperature EFT agrees with preceding works in all these limiting cases.At present, experimental data on vortices in two-band superfluid atomic Fermi gases are still lacking, in spite of the expected new physics stemming from the interband interactions in such a system. We report the first such theoretical study, to pave ...

Controlling the interaction of ultracold alkaline-earth atoms

“…This forces us to take into account the scattering state in the closed channel, that is to say, the so-called closed channel is not really "closed". The multi-orbital nature brings the physics into a new parameter regime that has not been explored before [39,[58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73]. Here we simply give couple examples.…”

“…First of all, the strong influence of the closed channel leads to a strong momentum dependence of the scattering amplitude, which can lead to an even higher transition temperature for forming Fermi superfluid, comparing to the single-channel wide resonance in alkaline-metal atom [58]. In the superfluid phase, since both two channels are occupied by the scattering states, it requires two order pairing order parameters to describes such a Fermi superfluid, which adds a new twist to the BEC-BCS crossover physics [39,[58][59][60][61][62][63][64][65]. This is reminiscent of multi-band superconductor in solid-state materials.…”

Tuning of non-paraxial effects of the Laguerre-Gaussian beam interacting with the two-component Bose–Einstein condensates

“…Considering different orbital angular momentum of the incident beam and using the angular momentum channels, one can create multiply quantized vortices in the twocomponent BEC [18,19]. These novel phenomenon of occurring multiply quantized vortices in BEC is observed in multicomponent superconductivity [64] or in rotating two-band Fermi gas [65]. The vortex-antivortex superpositions appear as the counter-rotating persistent currents in superconducting circuits [66,67] which are propitious candidates for qubits in quantum-information processing and quantum communication networks [68].…”

Vortices in Fermi gases with spin-dependent rotation potentials

“…Other techniques such as phase imprinting have also been used to achieve vortices in Bose-Einstein condensates (BECs) [18] and phase imprinting individual components of Fermi gases has been proposed for soliton creation [19]. Rotation and vortices in Fermi gases have been the subject of extensive theoretical study [20][21][22][23][24][25][26][27][28]; however, here we consider the rotation of both components at different frequencies.…”

“…Our approach is based on the effective field theory (EFT) for superfluid Fermi gases presented in Refs. [29][30][31], which has also been applied to the study of vortices [27,28]. Introduction of spin-dependent vector potentials for the two components in the microscopic action leads to a modification of the local chemical potential and spin-imbalance parameter and yields additional terms in the EFT action.…”