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Register a new userQuantum degenerate two-species Fermi-Fermi mixture coexisting with a Bose-Einstein condensate
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We report on the generation of a quantum degenerate Fermi-Fermi mixture of two different atomic species. The quantum degenerate mixture is realized employing sympathetic cooling of fermionic Li-6 and K-40 gases by an evaporatively cooled bosonic Rb-87 gas. We describe the combination of trapping and cooling methods that proved crucial to successfully cool the mixture. In particular, we study the last part of the cooling process and show that the efficiency of sympathetic cooling of the Li-6 gas by Rb-87 is increased by the presence of K-40 through catalytic cooling. Due to the differing physical properties of the two components, the quantum degenerate Li-6 K-40 Fermi-Fermi mixture is an excellent candidate for a stable, heteronuclear system allowing to study several so far unexplored types of quantum matter.
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We have produced a macroscopic quantum system in which a Li-6 Fermi sea coexists with a large and stable Na-23 Bose-Einstein condensate. This was accomplished using inter-species sympathetic cooling of fermionic Li-6 in a thermal bath of bosonic Na-23.
We report on the transport of mixed quantum degenerate gases of bosonic 87Rb and fermionic 40K in a harmonic potential provided by a modified QUIC trap. The samples are transported over a distance of 6 mm to the geometric center of the anti-Helmholtz coils of the QUIC trap. This transport mechanism was implemented by a small modification of the QUIC trap and is free of losses and heating. It allows all experiments using QUIC traps to use the highly homogeneous magnetic fields that can be created in the center of a QUIC trap and improves the optical access to the atoms, e.g., for experiments with optical lattices. This mechanism may be cascaded to cover even larger distances for applications with quantum degenerate samples.
We measure the temperature of a deeply degenerate Fermi gas, by using a weakly interacting sample of heavier bosonic atoms as a probe. This thermometry method relies on the thermalization between the two species and on the determination of the condensate fraction of the bosons. In our experimental implementation, a small sample of 41K atoms serves as the thermometer for a 6Li Fermi sea. We investigate the evaporative cooling of a 6Li spin mixture in a single-beam optical dipole trap and observe how the condensate fraction of the thermometry atoms depends on the final trap depth. From the condensate fraction, the temperature can be readily extracted. We show that the lowest temperature of 6.3(5)% of the Fermi temperature is obtained, when the decreasing trap depth closely approaches the Fermi energy. To understand the systematic effects that may in uence the results, we carefully investigate the role of the number of bosons and the thermalization dynamics between the two species. Our thermometry approach provides a conceptually simple, accurate, and general way to measure the temperature of deeply degenerate Fermi gases. Since the method is independent of the specific interaction conditions within the Fermi gas, it applies to both weakly and strongly interacting Fermi gases.
We give an overview of recent experiments on an ultracold Fermi-Bose quantum gas where the interspecies interaction can be tuned via magnetic Feshbach resonances. We first describe the various steps that have led to the observation of Feshbach resonances in the K-Rb system we investigate, and their accurate characterization. We then describe experiments in which Feshbach resonances are exploited to study interaction effects and to associate weakly bound KRb dimers.
We derive the criteria for the Thomas-Fermi regime of a dipolar Bose-Einstein condensate in cigar, pancake and spherical geometries. This also naturally gives the criteria for the mean-field one- and two-dimensional regimes. Our predictions, including the Thomas-Fermi density profiles, are shown to be in excellent agreement with numerical solutions. Importantly, the anisotropy of the interactions has a profound effect on the Thomas-Fermi/low-dimensional criteria.
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