Emergence of a molecular Bose–Einstein condensate from a Fermi gas

A. Swarup, B. Cowan

Markus Greiner, Cindy A. Regal, Deborah Jin

The realization of fermionic superfluidity in a dilute gas of atoms, analogous to superconductivity in metals, is a long-standing goal of ultracold gas research. Beyond being a new example of this fascinating quantum phenomenon, fermionic superfluidity in an atomic gas holds the promise of adjustable interactions and the ability to tune continuously from BCS-type superfluidity to Bose-Einstein condensation (BEC). This crossover between BCS superfluidity of correlated atom pairs in momentum space and BEC of local pairs has long been of theoretical interest, motivated in part by the discovery of high Tc superconductors. In atomic Fermi gas experiments superfluidity has not yet been demonstrated; however recent experiments have made remarkable progress toward this goal. Starting from an ultracold Fermi gas experimenters have used Feshbach resonances to reversibly create molecules, i.e. composite bosons consisting of local fermion pairs. Furthermore, the experiments have shown that the resulting diatomic molecules can have surprisingly long lifetimes. Here we report the conversion of a Fermi sea of atoms into a molecular BEC. In addition to being the first molecular condensate in thermal equilibrium, this BEC represents one extreme of the predicted BCS-BEC continuum.

Zhendong Zhang, Liangchao Chen, Kai-Xuan Yao +1 more

Using the theoretical formalism of R A Duine and H T C Stoof (arXiv: cond-mat/0303230v) 22 March 2003), we have theoretically evaluated magnetic field and density dependence of the Josephson frequency in coherence atom-molecule oscillation in Bose-Einstein condensed gas.Our theoretically obtained results show that Josephson frequency increases with both magnetic field for constant condensate density and also with condensate density for fixed magnetic field.Our theoretically evaluated results are in good agreement with the experimental data and also with other theoretical workers.Using the theoretical formalism of Markes Greiner etal (Nature, 26 Nov (2005)) , we have studied the emergence of molecular Bose-Einstein condensate from a Fermi gas of 6 Li atoms.The study has been performed with the help of Feshbach resonance.We have evaluated molecular condensate fraction N0/N as a function of (T/TC) and as a function of (T/TF).We have also evaluated scattering length 'a' in unit of a0, of mixture of two lowest hyperfine states of 6 Li atom, temperature (µK) all as a function of magnetic field (mT) near the crossing of the An evaluation …

M. Bartenstein, A. Altmeyer, S. Riedl +4 more

We demonstrate a reversible conversion of a 6Li2 molecular Bose-Einstein condensate to a degenerate Fermi gas of atoms by adiabatically crossing a Feshbach resonance. By optical in situ imaging, we observe a smooth change of the cloud size in the crossover regime. On the Feshbach resonance, the ensemble is strongly interacting and the measured cloud size is 75(7)% of the one of a noninteracting zero-temperature Fermi gas. The high condensate fraction of more than 90% and the adiabatic crossover suggest our Fermi gas to be cold enough to form a superfluid.