Low-temperature, high-density magneto-optical trapping of potassium using the open 4S-5P transition at 405 nm

TL;DR

This paper demonstrates a novel low-temperature, high-density magneto-optical trap for potassium using an open 4S-5P transition at 405 nm, achieving record low temperatures and increased atom density for quantum gas applications.

Contribution

It introduces the first implementation of potassium MOT on the open 4S-5P transition at 405 nm, significantly reducing temperature and increasing density compared to traditional methods.

Findings

Achieved temperatures as low as 63 microkelvin.

Observed a twenty-fold increase in phase space density.

Measured a two-body loss coefficient of 2 x 10^-10 cm^3/s.

Abstract

We report the laser cooling and trapping of neutral potassium on an open transition. Fermionic 40K is captured using a magneto-optical trap (MOT) on the closed 4S-4P transition at 767 nm and then transferred, with unit efficiency, to a MOT on the open 4S-5P transition at 405 nm. Because the 5P state has a smaller line width than the 4P state, the Doppler limit is reduced. We observe temperatures as low as 63(6) microkelvin, the coldest potassium MOT reported to date. The density of trapped atoms also increases, due to reduced temperature and reduced expulsive light forces. We measure a two-body loss coefficient of 2 x 10^-10 cm^3/s, and estimate an upper bound of 8x10^-18 cm^2 for the ionization cross section of the 5P state at 405 nm. The combined temperature and density improvement in the 405 nm MOT is a twenty-fold increase in phase space density over our 767 nm MOT, showing enhanced pre-cooling for quantum gas experiments. A qualitatively similar enhancement is observed in a 405 nm MOT of bosonic 41K.