Harmonic and Subharmonic Association and Dissociation of Universal Dimers in a Thermal Gas

TL;DR

This paper investigates how oscillating magnetic fields induce association and dissociation of universal dimers in ultracold atomic gases, revealing harmonic and subharmonic resonances and providing analytical transition rate calculations.

Contribution

It introduces a theoretical framework to calculate association and dissociation rates via contact operator transitions, including many-body effects, for the first time.

Findings

Harmonic resonance occurs near the dimer binding energy frequency.

Subharmonic resonance appears at half the binding energy frequency.

Analytical expressions for transition rates are derived for both processes.

Abstract

In a gas of ultracold atoms whose scattering length is controlled by a magnetic Feshbach resonance, atoms can be associated into universal dimers by an oscillating magnetic field. In addition to the harmonic resonance with frequency near that determined by the dimer binding energy, there is a subharmonic resonance with half that frequency. If the thermal gas contains dimers, they can be dissociated into unbound atoms by the oscillating magnetic field. We show that the transition rates for association and dissociation can be calculated by treating the oscillating magnetic field as a sinusoidal time-dependent perturbation proportional to the contact operator. Many-body effects are taken into account through transition matrix elements of the contact operator. We calculate both the harmonic and subharmonic transition rates analytically for association in a thermal gas of atoms and dissociation in a thermal gas of dimers.