Simultaneous sub-Doppler laser cooling of fermionic Li 6 and K 40 on the D1 line: Theory and experiment

Abstract

We report on simultaneous sub-Doppler laser cooling of fermionic Li6 and K40 using the D1 optical transitions. We compare experimental results to a numerical simulation of the cooling process applying a semiclassical Monte Carlo wave-function method. The simulation takes into account the three-dimensional optical molasses setup and the dipole interaction between atoms and the bichromatic light field driving the D1 transitions. We discuss the physical mechanisms at play, identify the important role of coherences between the ground-state hyperfine levels, and compare D1 and D2 sub-Doppler cooling. In 5 ms, the D1 molasses phase greatly reduces the temperature for both Li6 and K40 at the same time, with final temperatures of 44 and 11μK, respectively. For both species this leads to a phase-space density close to 10-4. These conditions are well suited to direct loading of an optical or magnetic trap for efficient evaporative cooling to quantum degeneracy.