Early this year, when researchers at the University of Florence in Italy saw the oscillating pattern shown in the figure below, with a peak in intensity appearing first at one value of momentum and then at another, they knew that ultracold fermionic atoms were viable candidates for atom interferometry. 1
Fermions are somewhat surprising candidates for this application. Most attention to date has focused on Bose–Einstein condensates (BECs), which look especially promising for precision atom interferometry because all the atoms are in the same ground state and the macroscopic wavefunction can interfere with itself. As David Pritchard (MIT) puts it, BECs are to matter-wave interferometry what lasers are to optical interferometry: a coherent, single-mode, and brilliant source.
In the case of fermions, however, the Pauli principle prevents two atoms from simultaneously sharing the same state; thus there is no macroscopic coherence. What the Florence group, led by Massimo Inguscio, has...
