Quantitative simulation of a magneto-optical trap operating near the photon recoil limit

Niamh C. Keegan,Paul Huillery,Ryan K. Hanley,Danielle Boddy,Matthew P. A. Jones,Alistair D. Bounds,Riccardo Faoro

doi:10.1080/09500340.2017.1401679

Abstract

We present a quantitative model for magneto-optical traps operating on narrow transitions, where the transition linewidth and the recoil shift are comparable. We combine a quantum treatment of the light scattering process with a Monte-Carlo simulation of the atomic motion. By comparing our model to an experiment operating on the transition in strontium, we show that it quantitatively reproduces the cloud size, position, temperature and dynamics over a wide range of operating conditions, without any adjustable parameters. We also present an extension of the model that quantitatively reproduces the transfer of atoms into a far off-resonance dipole trap, highlighting its use as a tool for optimizing complex cold atom experiments.

Highlights

The advent of laser cooling and trapping [1,2,3,4] was a revolutionary advance leading to a plethora of ultra-cold atomic experiments
Since gravity is strong compared to the light-induced forces, the atoms fall under gravity until the resonance condition is met, forming an elliptically shaped narrow-line MOTs’ (nMOTs) (shown in Figure 1(c)) where the atoms predominantly interact with the beam that directly opposes gravity
As well as the equilibrium properties, we have considered whether our model can reproduce the outof-equilibrium dynamics of the nMOT

Summary

Introduction

The advent of laser cooling and trapping [1,2,3,4] was a revolutionary advance leading to a plethora of ultra-cold atomic experiments. In conventional magneto-optical traps operating on strong dipole allowed transitions η 1000 In this regime a single scattering event does not significantly alter the subsequent probability to scatter a photon, and the effects of individual scattering events can be averaged out, leading to the conventional semi-classical theory of Doppler cooling [10]. Since gravity is strong compared to the light-induced forces, the atoms fall under gravity until the resonance condition is met, forming an elliptically shaped nMOT (shown in Figure 1(c)) where the atoms predominantly interact with the beam that directly opposes gravity This regime enables the lowest temperatures, reaching half the photon recoil limit, which for 88Sr is 460 nK [24]

Modelling the cloud

Experimental configuration

Testing the model

Dipole trapping

Conclusions