Polarization gradient cooling of single atoms in optical dipole traps

TL;DR

This study demonstrates polarization gradient cooling of a single rubidium atom in an optical dipole trap, revealing the dependence of cooling efficiency on trap polarization and achieving temperatures around 10 microkelvin.

Contribution

It provides experimental insights into how trap polarization affects polarization gradient cooling limits and introduces methods to minimize heating during polarization switching.

Findings

Cooling limit is strongly polarization-dependent.

Achieved atom temperatures of approximately 10.4 microkelvin.

Switching trap polarization causes minimal heating.

Abstract

We experimentally investigate $\sigma^+$-$\sigma^-$ polarization gradient cooling~(PGC) of a single $^{87}$Rb atom in a tightly focused dipole trap and show that the cooling limit strongly depends on the polarization of the trapping field. For optimized cooling light power, the temperature of the atom reaches~$10.4(6)\,\mu$K in a linearly polarized trap, approximately five times lower than in a circularly polarized trap. The inhibition of PGC is qualitatively explained by the fictitious magnetic fields induced by the trapping field. We further demonstrate that switching the trap polarization from linear to circular after PGC induces only minor heating.