Efficient two-dimensional subrecoil Raman cooling of atoms in a tripod configuration

Abstract

We present an efficient method for subrecoil cooling of neutral atoms by applying Raman cooling in two dimensions to a four-level tripod system. The atoms can be cooled simultaneously in two directions using only three laser beams. We describe the cooling process with a simple model showing that the momentum distribution can be rapidly narrowed to velocity spread down to 0.1v rec , corresponding to effective temperature equal to 0.01T rec . This method opens new possibilities for cooling of neutral atoms.

Theory of robust subrecoil cooling by stimulated Raman adiabatic passage

“…Although such a π-pulse operates efficiently on atoms corresponding to the resonant velocity group, the process requires extreme control of the pulse amplitude and duration. Even though some optimization can be obtained for the method [27], an approach based on adiabatic passage is of definite interest due to its robustness regarding pulse amplitudes and durations. However, the use of adiabatic passage in Raman cooling is not possible without having an exact understanding of its velocity-selective properties.…”

“…Ref. [27]), and b) using STIRAP pulses of substantially different amplitudes, but not changing their duration and amplitude during the pulse cycle series. In the latter case, the amplitudes are adjusted to transfer the wing of the velocity distribution together with the possibility to cool the atomic ensemble below the recoil limit.…”

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

“…This approach extends into 2D the recently proposed 1D cooling method [25], providing strong transverse cooling below the recoil limit. In contrast to the normal 2D Raman cooling [24], the method is robust and versatile as long as the adiabaticity criterion is satisfied. Strong and efficient cooling is especially attainable at the limit of large detuning from the upper state in the tripod configuration.…”

“…Although tight confinement and the subsequent discrete motional state structure for atoms offers many methods for further cooling in a manner similar to the cooling of trapped ions [16][17][18] and open possibilities for other interesting studies as quantum computing [19,20] and entanglement [21][22][23], alternative approaches are needed in order to apply cooling at a more general setting such as free space. This is the motivation for developing further purely light-based methods for reaching similar temperatures as with evaporative cooling, as discussed also in our previous work on the topic [24,25].…”

“…Our recent suggestion of cooling in a tripod atomic level system not only reduces the number of Raman beams by a factor of two, but also allows one, in principle, to reach temperatures as low as 0.01T rec . However, more cooling cycles are required in 2D Raman cooling as compared with 1D, which imposes strict demands on the velocity precision of the Raman transfer [24].…”