Sub-Doppler laser cooling of fermionic 40K atoms in three-dimensional gray optical molasses

We demonstrate sub-Doppler cooling of 40K on the D1 atomic transition. Using a gray-molasses scheme, we efficiently cool a compressed cloud of 6.5 × 108 atoms from ~4 mK to 20 μK in 8 ms. After transfer to a quadrupole magnetic trap, we measure a phase space density of ~10−5. This technique offers a promising route for fast evaporation of fermionic 40K.