Ultracold atoms at unitarity within quantum Monte Carlo

TL;DR

This paper uses variational and diffusion quantum Monte Carlo methods to accurately calculate properties of a zero-temperature fermionic gas at unitarity, providing new insights into its energy, pair correlations, and condensate fraction.

Contribution

It presents the first detailed quantum Monte Carlo calculations of various properties of the fermionic gas at unitarity, including energy ratios and condensate fractions, with improved accuracy.

Findings

Energy ratio of 0.4339(1) from DMC calculations

Condensate fraction estimated at 0.51

Two-body density matrices show notable differences between VMC and DMC

Abstract

Variational and diffusion quantum Monte Carlo (VMC and DMC) calculations of the properties of the zero-temperature fermionic gas at unitarity are reported. The ratio of the energy of the interacting to the non-interacting gas for a system of 128 particles is calculated to be 0.4517(3) in VMC and 0.4339(1) in the more accurate DMC method. The spherically-averaged pair-correlation functions, momentum densities, and one-body density matrices are very similar in VMC and DMC, but the two-body density matrices and condensate fractions show some differences. Our best estimate of the condensate fraction of 0.51 is a little smaller than values from other quantum Monte Carlo calculations.