Equilibration rates and negative absolute temperatures for ultracold atoms in optical lattices

TL;DR

This paper explores how ultracold atoms in optical lattices can be used to realize and observe negative absolute temperatures, analyzing the conditions, signatures, and equilibration dynamics for both bosonic and fermionic systems.

Contribution

It provides a theoretical framework for creating stable T < 0 states in cold atom systems by reversing the confining potential and analyzes the equilibration timescales for fermions.

Findings

Stable superfluid condensates at T < 0 can be created with low entropy production.

Fermionic equilibration time scales grow with interaction strength and system size.

Negative temperature states serve as clear experimental signatures.

Abstract

As highly tunable interacting systems, cold atoms in optical lattices are ideal to realize and observe negative absolute temperatures, T < 0. We show theoretically that by reversing the confining potential, stable superfluid condensates at finite momentum and T < 0 can be created with low entropy production for attractive bosons. They may serve as `smoking gun' signatures of equilibrated T < 0. For fermions, we analyze the time scales needed to equilibrate to T < 0. For moderate interactions, the equilibration time is proportional to the square of the radius of the cloud and grows with increasing interaction strengths as atoms and energy are transported by diffusive processes.