Coupled oscillator model of a trapped Fermi gas at the BEC-BCS crossover

Abstract

We address theoretically the puzzling discontinuity of the radial quadrupole mode frequency observed in a trapped Fermi gas across the BEC-BCS crossover. We apply the scaling transformation to a two-channel model of a resonant Fermi superfluid and argue that the frequency downshift in the crossover region is due to Feshbach coupling of the molecular Bose-Einstein condensate (BEC) to the surrounding Fermi sea. The Bose and Fermi components of the gas act as coupled macroscopic oscillators. The frequency jump corresponds to the point where the closed-channel molecules are entirely converted into the Fermi sea. This implies linear scaling of the "critical" detuning between the scattering channels with the Fermi energy, which can be readily verified in an experiment.

5-pages main text with 1 figure

References in corpus (7)

• Theory of ultracold Fermi gases
• Weakly bound dimers of fermionic atoms
• Resonantly-paired fermionic superfluids
• Dynamics of a strongly interacting Fermi gas: the radial quadrupole mode
• Breathing Mode of a BEC Repulsively Interacting with a Fermionic Reservoir
• Temperature and finite-size effects in collective modes of superfluid Fermi gases
• Radial quadrupole and scissors modes in trapped Fermi gases across the BCS phase transition