Association of Atoms into Universal Dimers using an Oscillating Magnetic Field

TL;DR

This paper derives a simple expression for the transition rate of atom pairing into dimers using an oscillating magnetic field in ultracold gases, highlighting effects of many-body physics and resonances.

Contribution

It introduces a new formula for the transition rate that incorporates many-body effects via the contact operator, applicable to thermal gases and Bose-Einstein condensates.

Findings

Transition rate peak width depends on temperature in thermal gases.

In a BEC, width is influenced by inelastic atom-dimer scattering.

Enhanced width near atom-dimer resonance indicates Efimov tetramers.

Abstract

In a system of ultracold atoms near a Feshbach resonance, pairs of atoms can be associated into universal dimers by an oscillating magnetic field with frequency near that determined by the dimer binding energy. We present a simple expression for the transition rate that takes into account many-body effects through a transition matrix element of the contact. In a thermal gas, the width of the peak in the transition rate as a function of the frequency is determined by the temperature. In a dilute Bose-Einstein condensate of atoms, the width is determined by the inelastic scattering rates of a dimer with zero-energy atoms. Near an atom-dimer resonance, there is a dramatic increase in the width from inelastic atom-dimer scattering and from atom-atom-dimer recombination. The recombination contribution provides a signature for universal tetramers that are Efimov states consisting of two atoms and a dimer.