The imbalanced Fermi gas at unitarity

TL;DR

This paper extends Monte Carlo methods to study the imbalanced unitary Fermi gas, overcoming the sign problem to compute key physical properties at unbalanced conditions.

Contribution

It introduces a reweighting approach to adapt the worm algorithm for imbalanced Fermi gases, enabling first-principles calculations of their thermodynamic properties.

Findings

Critical temperature for imbalanced gas determined

Energy per particle quantified for various imbalances

Contact density computed across different imbalance levels

Abstract

Lattice field theory is a useful tool for studying strongly interacting theories in condensed matter physics. A prominent example is the unitary Fermi gas: a two-component system of fermions interacting with divergent scattering length. With Monte Carlo methods this system can be studied from first principles. In the presence of an imbalance (unequal number of particles in the two components) a sign problem arises, which makes conventional algorithms inapplicable. We will show how to apply reweighting techniques to generalise the recently developed worm algorithm to the imbalanced case, and present results for the critical temperature, the energy per particle, the chemical potential and the contact density for equal, as well as unequal number of fermions in the two spin components.