Breakdown of Kohn Theorem Near Feshbach Resonance

TL;DR

This paper investigates how collective excitation frequencies of a trapped 85Rb Bose-Einstein condensate are affected near a Feshbach resonance, revealing a violation of the Kohn theorem due to changes in the dipole mode frequency.

Contribution

It introduces a Gaussian variational approach to analyze the GP equation near Feshbach resonance, demonstrating the breakdown of the Kohn theorem in this regime.

Findings

Dipole mode frequency decreases near Feshbach resonance

Kohn theorem is violated in this regime

Method provides a new way to analyze BEC excitations

Abstract

We study the collective excitation frequencies of a harmonically trapped 85Rb Bose-Einstein condensate (BEC) in the vicinity of a Feshbach resonance. To this end, we solve the underlying Gross-Pitaevskii (GP) equation by using a Gaussian variational approach and obtain the coupled set of ordinary differential equations for the widths and the center of mass of the condensate. A linearization shows that the dipole mode frequency decreases when the bias magnetic field approaches the Feshbach resonance, so the Kohn theorem is violated.