Photoassociation dynamics in a Bose-Einstein condensate

TL;DR

This paper develops a comprehensive many-body theory for single-color photoassociation in Bose-Einstein condensates, addressing the limits of photoassociation rates and molecule formation under intense, rapidly varying laser fields.

Contribution

It introduces a dynamical many-body framework that surpasses mean field approaches, incorporating pair correlations and decay effects to better understand photoassociation limits.

Findings

Photoassociation rate is more limited than mean field predictions suggest.

The maximum stable ground state molecules are fewer due to many-body effects.

Decay of the excited molecular state significantly impacts the dynamics.

Abstract

A dynamical many body theory of single color photoassociation in a Bose-Einstein condensate is presented. The theory describes the time evolution of a condensed atomic ensemble under the influence of an arbitrarily varying near resonant laser pulse, which strongly modifies the binary scattering properties. In particular, when considering situations with rapid variations and high light intensities the approach described in this article leads, in a consistent way, beyond standard mean field techniques. This allows to address the question of limits to the photoassociation rate due to many body effects which has caused extensive discussions in the recent past. Both, the possible loss rate of condensate atoms and the amount of stable ground state molecules achievable within a certain time are found to be stronger limited than according to mean field theory. By systematically treating the dynamics of the connected Green's function for pair correlations the resonantly driven population of the excited molecular state as well as scattering into the continuum of non-condensed atomic states are taken into account. A detailed analysis of the low energy stationary scattering properties of two atoms modified by the near resonant photoassociation laser, in particular of the dressed state spectrum of the relative motion prepares for the analysis of the many body dynamics. The consequences of the finite lifetime of the resonantly coupled bound state are discussed in the two body as well as in the many body context. Extending the two body description to scattering in a tight trap reveals the modifications to the near resonant adiabatic dressed levels caused by the decay of the excited molecular state.