Sub-Doppler laser cooling and magnetic trapping of natural-abundance fermionic potassium

Abstract

We demonstrate the largest number of 40K atoms that has ever been cooled to deeply sub-Doppler temperatures in a single-chamber apparatus without using an enriched source of potassium. With gray molasses cooling on the D 1-line following a standard D 2-line magneto-optical trap, we obtain 3×105 atoms at 10(2) µK. We reach densities high enough to measure the temperature via absorption imaging using the time-of-flight method. We magnetically trap a mixture of mF=−3/2,−5/2 and −7/2 Zeeman states of the F=7/2 hyperfine ground state confining 5×104 atoms with a lifetime of 0.6 s or ∼103 atoms with a lifetime of 2.8 s—depending on whether the temperature of the potassium dispensers was chosen to maximize the atom number or the lifetime. The background pressure-limited lifetime of 0.6 s is a reasonable starting point for proof-of-principle experiments with atoms and/or molecules in optical tweezers as well as for sympathetic cooling with another species if transport to a secondary chamber is implemented. Our results show that unenriched potassium can be used to optimize experimental setups containing 40K in the initial stages of their construction, which can effectively extend the lifetime of enriched sources. Moreover, the demonstration of sub-Doppler cooling and magnetic trapping of a relatively small number of potassium atoms might influence experiments with laser-cooled radioactive isotopes of potassium.