Eur. Phys. J. B 68, 401-415 (2009)
https://doi.org/10.1140/epjb/e2009-00040-8

Number of closed-channel molecules in the BEC-BCS crossover

Laboratoire Kastler Brossel, École Normale Supérieure, UPMC and CNRS, 24 rue Lhomond, 75231 Paris Cedex 05, France

Corresponding author: ^a werner@physics.umass.edu

Received: 2 July 2008
Revised: 9 December 2008
Published online: 10 February 2009

Abstract

Using a two-channel model, we show that the number of closed-channel molecules in a two-component Fermi gas close to a Feshbach resonance is directly related to the derivative of the energy of the gas with respect to the inverse scattering length. We extract this quantity from the fixed-node Monte Carlo equation of state and we compare to the number of closed-channel molecules measured in the Rice experiment with lithium [Partridge et al., Phys. Rev. Lett. 95, 020404 (2005)]. We also discuss the effect of a difference between the trapping potentials seen by a closed-channel molecule and by an open-channel pair of atoms in terms of an effective position-dependent scattering length.