Narrow-Line Electric Quadrupole Cooling And Background-Free Imaging Of A Single Cs Atom With Spatially Structured Light

TL;DR

This paper demonstrates background-free imaging and sideband cooling of a single Cs atom using narrow-line electric quadrupole transitions and structured light, enhancing quantum control capabilities.

Contribution

It introduces a method for background-free imaging and cooling of a single atom with structured light and electric quadrupole transitions, expanding quantum control techniques.

Findings

Achieved 99.58% fidelity in background-free imaging.

Cooled atom to 5 microkelvin in a 1.1 millikelvin trap.

Controlled quadrupole transitions using orbital angular momentum of structured light.

Abstract

We demonstrate background-free imaging and sideband cooling of a single 133Cs atom via the narrow-line 6S1/2 to 5D5/2 electric quadrupole transition in a 1064 nm optical tweezer. The 5D5/2 state decays through the 6P3/2 state to the ground state, emitting an 852 nm wavelength photon that allows for background-free imaging. By encoding both spin and orbital angular momentum onto the 685 nm excitation light, we achieve background-free fluorescence histograms with 99.58(3)% fidelity by positioning the atom at the dark center of a vortex beam. Tuning the tweezer polarization ellipticity realizes a magic trap for the stretched F = 4, mF = 4 to F' = 6, mF' = 6 cycling transition. We cool to 5 uK in a 1.1 mK trap and outline a strategy for ground-state cooling. We compare cooling performance across different sideband regimes, while also exploring how the orbital angular momentum of structured light controls the selection rules for quadrupole transitions. These results expand the toolbox for high-fidelity quantum control and cooling in alkali-atom tweezer arrays.