Work

Equal-spin and opposite-spin density-density correlations in the BCS-BEC crossover: Gauge symmetry, Pauli exclusion principle, Wick's theorem, and experiments

Year: 2026

Type: article

Abstract: We develop a general theory of -dependent density-density correlations, that is valid for any temperature, interactions, dimensions, and mass or population status of Fermi gases with two internal states. We use gauge invariance and the Pauli principle to establish constraints on the -dependent density-density correlations that are consistent with the fluctuation-dissipation and Wick's theorem. As an example, we study the -dependent density-density correlations from the BCS to the Bose regime in two dimensions at zero temperature, inspired by recent continuum quantum gas microscope experiments in Li 6 . We show that two-particle irreducible contributions, involving collective excitations, many-particle scattering, and vertex corrections, are essential to describe the experimental data. In particular, the two-particle irreducible terms are responsible for the emergence of an experimentally observed minimum in the opposite- density-density correlations.

Source: Physical Review A

DOI: 10.1103/xjhs-7z5w

Authors: Nikolai Kaschewski, Axel Pelster, Carlos A. R. Sá de Melo

Institutions: University of Kaiserslautern, Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau, Georgia Institute of Technology

Language: English

Topic: Cold Atom Physics and Bose-Einstein Condensates

Subfield: Atomic and Molecular Physics, and Optics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $2,675

Funder: Deutsche Forschungsgemeinschaft