$\Lambda$-Enhanced Gray Molasses Cooling of $^{85}$Rb Atoms in Tweezers Using the D$_2$ Line

TL;DR

This paper demonstrates a novel $$-enhanced gray molasses cooling technique for $^{85}$Rb atoms in optical tweezers, achieving lower temperatures and longer coherence times with an alignment-free method.

Contribution

Introduces a $$-enhanced gray molasses cooling method on the D$_2$ line of $^{85}$Rb, improving cooling efficiency and coherence time without requiring alignment.

Findings

Achieved atomic temperatures of 4.0(2) μK.

Extended $T_2^*$ coherence time by 1.5 times.

Validated results with a semi-classical numerical model.

Abstract

We demonstrate the implementation of $\Lambda$-enhanced gray molasses cooling on the D$_2$ line of $^{85}$Rb atoms in an optical tweezer array. This technique yields lower atomic temperatures of 4.0(2) $\mu$K compared to red-detuned polarization gradient cooling, and consequently extends the $T_2^*$ coherence time of the hyperfine clock qubit by a factor of 1.5. The method is alignment-free and can be readily implemented on laser beams used for magneto-optical trapping, as it only requires frequency and phase modulation control. Our experimental observations are corroborated by a numerical model based on a semi-classical force approach extended to a four-level system, including two hyperfine states of the upper manifold that are 120 MHz apart.