Single atom counting in a two-color magneto-optical trap

TL;DR

This paper introduces a modified fluorescence detection scheme in a two-color magneto-optical trap that enables reliable single-atom counting with high fidelity, even in challenging experimental conditions.

Contribution

The authors develop a new method using a D1 transition and high-resolution microscopy to improve single-atom detection in a MOT, overcoming stray light issues.

Findings

Able to distinguish up to 17 atoms reliably

Achieved 95% classification fidelity

Enhanced detection in complex experimental setups

Abstract

Recording the fluorescence of a magneto-optical trap (MOT) is a standard tool for measuring atom numbers in experiments with ultracold atoms. When trapping few atoms in a small MOT, the emitted fluorescence increases with the atom number in discrete steps, which allows to measure the atom number with single-particle resolution. Achieving such single particle resolution requires stringent minimization of stray light from the MOT beams, which is very difficult to achieve in experimental setups that require in-vacuum components close to the atoms. Here, we present a modified scheme that addresses this issue: Instead of collecting the fluorescence on the MOT (D2) transition, we scatter light on an additional probing (D1) transition and collect this fluorescence with a high-resolution microscope while filtering out the intense MOT light. Using this scheme, we are able to reliably distinguish up to 17 $^{40}$K atoms with an average classification fidelity of 95 \%.