Motion-selective coherent population trapping by Raman sideband cooling along two paths in a $\Lambda$ configuration

TL;DR

This paper demonstrates a novel motion-selective coherent population trapping technique using Raman sideband cooling in a $\Lambda$ configuration, enhancing cooling efficiency for trapped $^{87}$Rb atoms and potentially for diatomic polar molecules.

Contribution

The paper introduces MSCPT, a new cooling scheme that selectively traps motional states via Raman transitions, extending the capabilities of sideband cooling.

Findings

Achieved a temperature dip near the CPT resonance condition.

Demonstrated MSCPT enhances Raman sideband cooling effectiveness.

Discussed potential applications to diatomic polar molecules.

Abstract

We report our experiment on sideband cooling with two Raman transitions in a $\Lambda$ configuration that allows selective coherent population trapping (CPT) of the motional ground state. The cooling method is applied to $^{87}$Rb atoms in a circularly-polarized one-dimensional optical lattice. Owing to the vector polarizability, the vibration frequency of a trapped atom depends on its Zeeman quantum number, and CPT resonance for a pair of bound states in the $\Lambda$ configuration depends on their vibrational quantum numbers. We call this scheme motion-selective coherent population trapping (MSCPT) and it is a trapped-atom analogue to the velocity-selective CPT developed for free He atoms. We observe a pronounced dip in temperature near a detuning for the Raman beams to satisfy the CPT resonance condition for the motional ground state. Although the lowest temperature we obtain is ten times the recoil limit owing to the large Lamb-Dicke parameter of 2.3 in our apparatus, the experiment demonstrates that MSCPT enhances the effectiveness of Raman sideband cooling and enlarges the range of its application. Discussions on design parameters optimized for MSCPT on $^{87}$Rb atoms and opportunities provided by diatomic polar molecules, whose Stark shift shows strong dependence on the rotational quantum number, are included.