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arXiv:cond-mat/0306050 · Physical Review Letters

Fiftyfold Improvement in the Number of Quantum Degenerate Fermionic Atoms

Zoran Hadzibabic, Subhadeep Gupta, Claudiu Andrei Stan, Christian H. Schunck, Martin W. Zwierlein, Kai Dieckmann, Wolfgang Ketterle

Published Oct 16, 2003• 187 citations
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Abstract

We have produced a quantum degenerate $^{6}\mathrm{L}\mathrm{i}$ Fermi gas with up to $7\ifmmode\times\else\texttimes\fi{}{10}^{7}$ atoms, an improvement by a factor of 50 over all previous experiments with degenerate Fermi gases. This was achieved by sympathetic cooling with bosonic $^{23}\mathrm{N}\mathrm{a}$ in the $F=2$, upper hyperfine ground state. We have also achieved Bose-Einstein condensation of $F=2$ sodium atoms by direct evaporation.

DOI
10.1103/physrevlett.91.160401

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We have produced a quantum degenerate 6Li^{6}\mathrm{L}\mathrm{i}6Li Fermi gas with up to 7\ifmmode×\else\texttimes\fi1077\ifmmode\times\else\texttimes\fi{}{10}^{7}7\ifmmode×\else\texttimes\fi107 atoms, an improvement by a factor of 50 over all previous experiments with degenerate Fermi gases. This was achieved by sympathetic cooling with bosonic 23Na^{23}\mathrm{N}\mathrm{a}23Na in the F=2F=2F=2, upper hyperfine ground state. We have also achieved Bose-Einstein condensation of F=2F=2F=2 sodium atoms by direct evaporation.
Experimental methods of laser and evaporative cooling, used in the production of atomic Bose-Einstein condensates have recently been extended to realize quantum degeneracy in trapped Fermi gases. Fermi gases are a new rich system to explore the implications of Pauli exclusion on scattering properties of the system, and ultimately fermionic superfluidity. We have produced a new macroscopic quantum system, in which a degenerate Li-6 Fermi gas coexists with a large and stable Na-23 BEC. This was accomplished using inter-species sympathetic cooling of fermionic 6Li in a thermal bath of bosonic Na-23. We have achieved high numbers of both fermions (less than 10(exp 5) and bosons (less than 10(exp 6), and Li-6 quantum degeneracy corresponding to one half of the Fermi temperature. This is the first time that a Fermi sea was produced with a condensate as a "refrigerator".
Evaporative cooling of an atom gas of bosons, whereby the hottest atoms are progressively removed, is an effective and widely used method for forming Bose-Einstein condensates. For Fermi gases, however, collisions between identical fermions are forbidden, and new tricks, such as mixing two Fermi gases with different spin states, have been used to form Fermi condensates. Truscott et al. (p. 2570; see the Perspective by O'Hara and Thomas) now create quantum-degenerate Bose and Fermi condensates simultaneously from a boson-fermion mixture. Heat is removed from the fermions through elastic collisions with the bosons, a process called sympathetic cooling. They show that different statistics associated with the two types of gases can actually be visualized.
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 6Li and 40K gases by an evaporatively cooled bosonic 87Rb 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 6Li gas by 87Rb is increased by the presence of 40K through catalytic cooling. Because of the differing physical properties of the two components, the quantum degenerate 6Li-40K Fermi-Fermi mixture is an excellent candidate for a stable, heteronuclear system allowing the study of several so far unexplored types of quantum matter.
We have produced a macroscopic quantum system in which a 6Li{}^{6}\mathrm{Li}6Li Fermi sea coexists with a large and stable 23Na{}^{23}\mathrm{Na}23Na Bose-Einstein condensate. This was accomplished using interspecies sympathetic cooling of fermionic 6Li{}^{6}\mathrm{Li}6Li in a thermal bath of bosonic 23Na{}^{23}\mathrm{Na}23Na. The system features rapid thermalization and long lifetimes.
We report the first quantum degenerate dipolar Fermi gas, the realization of which opens a new frontier for exploring strongly correlated physics and, in particular, quantum liquid crystalline phases. A quantum degenerate Fermi gas of the most magnetic atom 161Dy is produced by laser cooling to 10 μK before sympathetically cooling with ultracold, bosonic 162Dy. The temperature of the spin-polarized 161Dy is a factor T/T(F)=0.2 below the Fermi temperature T(F)=300 nK. The cotrapped 162Dy concomitantly cools to approximately T(c) for Bose-Einstein condensation, thus realizing a novel, nearly quantum degenerate dipolar Bose-Fermi gas mixture. Additionally, we achieve the forced evaporative cooling of spin-polarized 161Dy without 162Dy to T/T(F)=0.7. That such a low temperature ratio is achieved may be a first signature of universal dipolar scattering.