Observation of collective atomic recoil motion in a momentum-squeezed, ultra-cold, degenerate fermion gas

TL;DR

This study demonstrates collective atomic recoil motion in an ultra-cold degenerate fermion gas, revealing wave-mixing processes despite Pauli blocking, and shows differences from bosonic systems in pump detuning effects.

Contribution

First observation of collective recoil motion in a fermionic quantum gas, highlighting wave-mixing without bosonic stimulation effects.

Findings

Clear recoil motion observed in fermions despite Pauli blocking

Simultaneous perpendicular wave-mixing processes detected

No red-blue pump detuning asymmetry unlike in Bose-Einstein condensates

Abstract

We demonstrate clear collective atomic recoil motion in a dilute, momentum-squeezed, ultra-cold degenerate fermion gas by circumventing the effects of Pauli blocking. Although gain from bosonic stimulation is necessarily absent because the quantum gas obeys Fermi-Dirac statistics, collective atomic recoil motion from the underlying wave-mixing process is clearly visible. With a single pump pulse of the proper polarization, we observe two mutually-perpendicular wave-mixing processes occurring simultaneously. Our experiments also indicate that the red-blue pump detuning asymmetry observed with Bose-Einstein condensates does not occur with fermions.