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.