“Ultracold gases of atoms provide wonderful, unique model systems in which to investigate macroscopic quantum phenomena such as superfluidity.”

The work by my group, and by others, has introduced ultracold Fermi gases of atoms as a new area of research. There has been considerable interest in this research because of the possibility, which was recently realized, of creating and observing a superfluid phase in a Fermi gas of atoms. Ultracold gases of atoms provide wonderful, unique model systems in which to investigate macroscopic quantum phenomena such as superfluidity. These low-density systems are relatively simple, extremely pure, and can be probed and manipulated in novel ways. Furthermore, the microscopic interaction between the atoms is theoretically well understood. The ultracold Fermi gas work grew out of the exciting achievement in 1995 of Bose-Einstein condensation in a dilute gas of atoms. The possibility of condensation and superfluidity in a gas of fermionic, rather than bosonic, atoms was extremely interesting because of the very close analogy to Cooper pairing and superconductivity.

My Ph.D. work with Thomas Rosenbaum at the University of Chicago focused on experiments studying heavy fermion superconductors. Following this I did a postdoc with Eric Cornell at JILA. I started my postdoc in the summer of 1995, just after the first dilute gas Bose-Einstein condensates were achieved by the JILA group. Creating and studying an ultracold Fermi gas of atoms was the natural next direction in the new field of quantum gases. Work on Fermi gases of atoms and in particular the goal of creating a superfluid with Cooper pairs of atoms meshed extremely well with my training and interests.

My group has done a number of pioneering experiments on ultracold Fermi gases of atoms, including the first realization of this quantum gas in 1999. A long-standing goal in this area of research was to explore the possibility of achieving a superfluid phase in the Fermi gas. In analogy with superconductivity, superfluidity would arise through the formation and condensation of Cooper pairs of atoms. We reported the creation and observation of such condensates of correlated pairs of atoms in 2004. This Fermi condensate is a superfluid phase that occurs in an extremely clean and precisely controllable dilute gas system. Furthermore, we found that the phase transition occurs at a remarkably high temperature relative to the Fermi temperature, and provides the experimental access to the predicted BCS-BEC crossover.

Experimental research in ultracold Fermi gases of atoms has advanced tremendously in the last seven years. Ultracold gases of fermionic atoms did not exist seven years ago. Magnetic-field Feshbach resonances, which are a crucial tool in the realization of Fermi condensates, had not yet been seen experimentally. Theoretical work on superfluidity in ultracold Fermi gases has also become much more sophisticated in recent years.

This is of course difficult to predict. There is a tremendous amount of work to be done in exploring the BCS-BEC crossover, both in terms of characterizing the unique properties of this new superfluid and in testing theoretical predictions. People are also very interested in pursuing the possibility of more exotic superfluid phases with non-s-wave pairing. Another exciting possibility is superfluidity of fermionic atoms in an optical lattice.

Deborah Jin, Ph.D.
JILA
University of Colorado
Boulder, CO, USA