Onset of Fermi Degeneracy in a Trapped Atomic Gas

Abstract

An evaporative cooling strategy that uses a two-component Fermi gas was employed to cool a magnetically trapped gas of 7 x 10(5) (40)K atoms to 0.5 of the Fermi temperature T(F). In this temperature regime, where the state occupation at the lowest energies has increased from essentially zero at high temperatures to nearly 60 percent, quantum degeneracy was observed as a barrier to evaporative cooling and as a modification of the thermodynamics. Measurements of the momentum distribution and the total energy of the confined Fermi gas directly revealed the quantum statistics.

Schematic phase diagram and collective excitations in the collisional regime for trapped boson–fermion mixtures at zero temperature

“…A specific motivation for interest in boson-fermion mixtures is that the collisions between fermions and bosons can foster thermalization of the fermionic component and induce so-called sympathetic cooling [4,12]. Elastic collisions between fermions in a single hyperfine state are inhibited by the Pauli principle [13] and even in multi-component Fermi gases the collisions between atoms in different hyperfine states become ineffective at very low temperature because of Fermi factors [9].…”

Prospect of creating a composite Fermi–Bose superfluid

“…Given the problems encountered in the evaporative cooling of neutral fermion atoms [3], it may be of future interest to use coherent molecule formation in an alternative cooling scheme, such as the example we now discuss. In conclusion, we have pointed out that the coherent atom-molecule interactions available in present-day atom cooling experiments suggest the exciting prospect of creating a cold atom superfluid of novel structure, consisting of mutually coherent field components of different spin statistics.…”

“…In addition to the observed boson gas superfluids, the prospect of studying fermion superfluidity in the gas phase provides a powerful motivation [2] for the atom cooling efforts with fermion isotopes [3]. S-wave Cooper pairing -the most likely mechanism for achieving fermion superfluidity in the low-density gases -relies on the mutual attraction of two distinguishable types of fermions [4].…”

Heteronuclear quantum gas mixtures

“…n F (r) = (2m F ) 3/2 6π 2 3 max µ F −r 2 − g F B · n B (r), 0 3/2 (9) Note that the problem only depends onr = x 2 1 +x 2 2 +x 2 3 . In the new set of coordinates, equations (4) become …”