# Deep laser cooling and efficient magnetic compression of molecules

## TL;DR

This paper presents a novel laser cooling scheme for molecules using dark states, achieving ultracold temperatures and efficient magnetic compression, with experimental validation of reaching 5.4 microkelvin.

## Contribution

The authors introduce a robust laser cooling method based on dark states applicable to molecules, demonstrating deep cooling and compression techniques with experimental results.

## Key findings

- Achieved molecular temperatures as low as 5.4 microkelvin.
- Developed a phase-space rotation method for measuring low temperatures.
- Demonstrated rapid magnetic compression of molecular clouds.

## Abstract

We introduce a scheme for deep laser cooling of molecules based on robust dark states at zero velocity. By simulating this scheme, we show it to be a widely applicable method that can reach the recoil limit or below. We demonstrate and characterise the method experimentally, reaching a temperature of 5.4(7) $\mu$K. We solve a general problem of measuring low temperatures for large clouds by rotating the phase-space distribution and then directly imaging the complete velocity distribution. Using the same phase-space rotation method, we rapidly compress the cloud. Applying the cooling method a second time, we compress both the position and velocity distributions.