Thermometry of ultracold fermions by (super)lattice modulation spectroscopy

TL;DR

This paper proposes a method for measuring the temperature of ultracold fermions in optical lattices using lattice modulation spectroscopy, which reveals the Fermi distribution through quasimomentum-resolved atom excitations.

Contribution

It introduces a theoretical scheme for thermometry of ultracold fermions via lattice modulation spectroscopy, applicable to current experimental setups and effective at very low temperatures.

Findings

Atom excitation rate reflects the Fermi distribution and temperature.

Method is feasible with current experimental parameters.

Effective down to a few percent of the hopping amplitude.

Abstract

We theoretically consider non-interacting fermions confined to optical lattices and apply a lattice amplitude modulation that we choose to be either homogeneous or of superlattice geometry. We study the atom excitation rate to higher Bloch bands which can be measured by adiabatic band mapping. We find that the atom excitation rate shows a clear signature of the temperature dependent Fermi distribution in the lowest band of the equilibrium lattice as excitations are quasimomentum-resolved. Based on typical experimental parameters and incorporating a trapping potential, we find that thermometry of one- and two-dimensional systems is within the reach of nowadays experiments. Our scheme is valid down to temperatures of a few percent of the hopping amplitude comparable to the N\'eel temperature in interacting systems.