Compensating fictitious magnetic field gradients in optical microtraps by using elliptically polarized dipole light

TL;DR

This paper demonstrates that adding a small elliptical polarization component to optical microtraps effectively compensates for fictitious magnetic field gradients, significantly improving trap lifetime and atom stability.

Contribution

The study introduces a novel method of using elliptical polarization to mitigate vector light shifts in optical microtraps, enhancing trap performance without large external magnetic fields.

Findings

Trap lifetime improved by up to a factor of 11.

Monte-Carlo simulations match experimental results.

Method applicable to various experiments with non-negligible longitudinal polarization.

Abstract

Tightly focused optical dipole traps induce vector light shifts ("fictitious magnetic fields") which complicate their use for single-atom trapping and manipulation. The problem can be mitigated by adding a larger, real magnetic field, but this solution is not always applicable; in particular, it precludes fast switching to a field-free configuration. Here we show that this issue can be addressed elegantly by deliberately adding a small elliptical polarization component to the dipole beam. In our experiments with single $^{87}$Rb atoms in a chopped trap, we observe improvements up to a factor 11 of the trap lifetime compared to the standard, seemingly ideal linear polarization. This effect results from a modification of heating processes via spin-state diffusion in state-dependent trapping potentials. We develop Monte-Carlo simulations of the evolution of the atom's internal and motional states and find that they agree quantitatively with the experimental data. The method is general and can be applied in all experiments where the longitudinal polarization component is non-negligible.