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Superfluidity Of Ultracold Atomic Gases In An Optical Lattice With Defects

Posted on:2014-06-01Degree:MasterType:Thesis
Country:ChinaCandidate:Y JianFull Text:PDF
GTID:2250330422459921Subject:Theoretical Physics
Abstract/Summary:PDF Full Text Request
In recently years, the interplay between nonlinearity, disorder and discreteness has been the subject of intensive theoretical and experimental. This raises rich phenomena by the coupling of nonlinearity, disorder and discreteness, such as Anderson localization, Bose glass phase, etc. The atomic interaction plays a crucial role in the study of ultracold atomic gases. However, previous studies mainly concentrated in the short-range interac-tion of the BEC system. So the study of dipolar systems with long-range interactions and Fermi system is great significance. What we want to do is to discuss the superflu-idity of ultracold atomic gases in the Fermi system and dipole systems with long-range interactions.In the second part of our paper, superfluid Fermi gases in an optical lattice with random defects are discussed. We discuss the tunnelling of a plane wave in an annular optical lattice with defects, focusing on discussion of the interplay between defects and Fermi atomic interaction along the BCS-BEC crossover. Using a hydrodynamic scheme and a two-mode approximation, the dynamics of system maps on a nonrigid pendulum Hamiltonian. That is, the system with arbitrary defects can be considered as the case of a single defect. Through the analysis, we obtain critical atomic density of the system for supporting superfluidity at unitarity and in BEC limit. When the atomic density exceeds the critical value, the system becomes superfluid. We also find that due to the coupling of defects and the atomic, the superfluidity of the system strongly depends on the properties of defects and the atomic interaction. the system easily supports the superfluid states at unitarity than that in the BEC limit. Compared with the numerical solution and analysis result obtained by two mode approximation, we find they are consistent.In the third part of our paper, the dynamics of nonlocal discrete G-P equation with defects is investigated. We study some dynamics of dipolar gases. We also discuss the tunnelling of a plane wave in an annular optical lattice with defects. First of all, we an-alyze the energy stability and momentum stability of dipolar gas in pure lattice system. It shows that the dipoles can stabilize the gas because of repulsive nonlocal dipole-dipole interaction. Secondly, we study the superfluidity of dipole gases in lattice with defects and discuss the case of a single defect and the Gauss defect. Through two-mode ap-proximation, the analytical results are obtained and the system can be also considered as the case of a single defect. The critical scatter length for supporting superfluidity is obtained. Importantly, the critical condition strongly depend on the defects type, the local interaction, the quasimomentum of the plane wave and nonlocal interaction. The nonlocal dipolar interaction can enhance the superfluidity of the system. The analytical results are confirmed by numerical results.Finally, in fourth part, we present our main conclusions and make some prospects for future research.
Keywords/Search Tags:ultracold Fermi gases, ultracold dipolar gases, superfluidity, energystability, momentum stability
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