Superfluid condensate fraction and pairing wave function of the unitary Fermi gas

He, Rongzheng; Li, Ning; Lu, Bing-Nan; Lee, Dean

doi:10.1103/physreva.101.063615

Title: Superfluid condensate fraction and pairing wave function of the unitary Fermi gas

Journal Article · Thu Jun 11 00:00:00 EDT 2020 · Physical Review A

DOI:https://doi.org/10.1103/physreva.101.063615· OSTI ID:1803442

He, Rongzheng ^[1];

^[1]; Lu, Bing-Nan ^[1];

^[1]

Michigan State Univ., East Lansing, MI (United States)

The unitary Fermi gas is a many-body system of two-component fermions with zero-range interactions tuned to infinite scattering length. Despite much activity and interest in unitary Fermi gas and its universal properties, there have been great difficulties in performing accurate calculations of the superfluid condensate fraction and pairing wave function. In this paper, we present auxiliary-field lattice Monte Carlo simulations using a lattice interaction which accelerates the approach to the continuum limit, thereby allowing for robust calculations of these difficult observables. As a benchmark test, we compute the ground-state energy of 33 spin-up and 33 spin-down particles. As a fraction of the free Fermi gas energy $$E_{\text{FG}}$$, we find $$E_0/E_{\text{FG}}$$ = 0.369(2), 0.372(2), using two different definitions of the finite-system energy ratio, in agreement with the latest theoretical and experimental results. We then determine the condensate fraction by measuring off-diagonal long-range order in the two-body density matrix. We find that the fraction of condensed pairs is α = 0.43(2). Further, we also extract the pairing wave function and find the pair correlation length to be $$ζ_pk_F$$ = 1.8(3)ℏ, where $$k_F$$ is the Fermi momentum. Provided that the simulations can be performed without severe sign oscillations, the methods we present here can be applied to superfluid neutron matter as well as more exotic $$\textit{P}$$-wave and $$\textit{D}$$-wave superfluids.

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Research Organization:: Michigan State Univ., East Lansing, MI (United States); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States).

Sponsoring Organization:: USDOE Office of Science (SC)

Grant/Contract Number:: SC0018638; AC52-06NA25396

OSTI ID:: 1803442

Journal Information:: Physical Review A, Vol. 101, Issue 6; ISSN 2469-9926

Publisher:: American Physical Society (APS)Copyright Statement

Country of Publication:: United States

Language:: English

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