Probing the optical conductivity of trapped charge-neutral quantum gases

¹ Department of Physics, Engineering Physics and Astronomy, Queen's University - Kingston, Ontario, K7L 3N6, Canada
² Department of Physics and Astronomy, McMaster University - Hamilton, Ontario, L8S 4M1, Canada

Received: 23 October 2014
Accepted: 3 April 2015

Abstract

We study a harmonically confined atomic gas which is subjected to an additional external potential such as an optical lattice. Using a linear response formulation, we determine the response of the gas to a small, time-dependent displacement of the harmonic trap and derive a simple exact relation showing that the centre-of-mass position of the atomic cloud is directly related to the global optical conductivity of the system. We demonstrate the usefulness of this approach by calculating the optical conductivity of bosonic atoms in an optical lattice. In the Mott insulating phase, there is clear evidence of an optical Mott gap, providing a proof-of-principle demonstration that the global optical conductivity gives high-quality information about the excitations of strongly correlated quantum gases.