Robust two-dimensional subrecoil Raman cooling by adiabatic transfer in a tripod atomic system

Abstract

We demonstrate two-dimensional robust Raman cooling in a four-level tripod system, in which velocity selective population transfer is achieved by a stimulated Raman adiabatic passage. In contrast to basic two-dimensional Raman cooling with square-envelope pulses [Phys. Rev. A 83, 023407 (2011)], the technique presented here allows for a wide variation in the pulse duration and amplitude once the adiabaticity criterion is satisfied. An efficient population transfer together with attainment of a narrow spread of the resonant-velocity group leads to the narrowing of the velocity-distribution spread down to $0.1{v}_{\mathrm{rec}}$, corresponding to an effective temperature equal to $0.01{T}_{\mathrm{rec}}$. This robust method opens additional possibilities for cooling of neutral atoms.