$\Lambda$-enhanced gray-molasses loading and EIT cooling of neutral atoms in nanophotonic traps

TL;DR

This paper demonstrates a method to significantly increase the number of atoms loaded into nanophotonic traps and extend their storage time using $ ext{Lambda}$-enhanced gray-molasses cooling and EIT-assisted cooling techniques.

Contribution

The authors introduce $ ext{Lambda}$-enhanced gray-molasses cooling to improve atom loading efficiency and show that EIT cooling extends trap lifetime with minimal optical power.

Findings

Six-fold increase in loaded atoms with $ ext{Lambda}$GM cooling.

Loaded about 4000 Cesium atoms in a small trap.

Trap storage time extended to 400 ms with EIT cooling.

Abstract

Nanophotonic traps for cold atoms typically have trap volumes that are orders of magnitude smaller than, e.g., free-space optical tweezers. This makes efficient loading of these traps challenging, thereby limiting the total number of atoms coupled to the nanophotonic waveguide. Here, we demonstrate that $\Lambda$-enhanced gray-molasses ($\Lambda$GM) can substantially increase the number of trapped atoms in a nanofiber-based cold-atom setup. Specifically, we observe a six-fold increase in the number of loaded atoms compared to conventional red-detuned polarization gradient cooling. Despite the unusually small depth of our optical trap of only 24 $\mu$K, we load about 4000 individual Cesium atoms, achieving optical depths exceeding 140 and reaching the collisional blockade regime over a length of approximately 1 mm. After loading, we perform efficient EIT-assisted cooling that is found to increase the trap storage time to 400(9) ms. This is a 5-fold improvement over the passive storage time. Remarkably, EIT-cooling also works with two co-propagating nanofiber-guided light fields and requiries only about a few hundred picowatt of optical power. Our results provide an efficient method to boost both the number of loaded atoms and the storage time of nanophotonic atom traps.