Composite-boson approach to molecular Bose-Einstein condensates in mixtures of ultracold Fermi gases

TL;DR

This paper demonstrates that an ansatz based on independent composite bosons accurately describes the condensate fraction in molecular Bose-Einstein condensates of ultracold Fermi gases, highlighting the role of entanglement in many-particle statistics.

Contribution

It introduces a composite-boson approach that effectively models the condensate fraction across interaction regimes, bridging theoretical methods and experimental possibilities.

Findings

Accurately describes condensate fraction matching previous methods.

Highlights entanglement as key to composite-boson behavior.

Enables exploration of BEC-BCS crossover physics.

Abstract

We show that an ansatz based on independent composite bosons [Phys. Rep. 463, 215 (2008)] accurately describes the condensate fraction of molecular Bose-Einstein condensates in ultracold Fermi gases. The entanglement between the fermionic constituents of a single Feshbach molecule then governs the many-particle statistics of the condensate, from the limit of strong interaction to close to unitarity. This result strengthens the role of entanglement as the indispensable driver of composite-boson behavior. The condensate fraction of fermion pairs at zero temperature that we compute matches excellently previous results obtained by means of fixed-node diffusion Monte Carlo methods and the Bogoliubov depletion approximation. This paves the way towards the exploration of the BEC-BCS crossover physics in mixtures of cold Fermi gases with an arbitrary number of fermion pairs as well as the implementation of Hong-Ou-Mandel-like interference experiments proposed within coboson theory.