# Maltese cross coupling to individual cold atoms in free space

## TL;DR

This paper demonstrates a novel optical setup that captures fluorescence from a single cold atom from four directions simultaneously, enabling advanced quantum optics experiments with precise lens positioning.

## Contribution

It introduces a new four-directional fluorescence collection system for single cold atoms using interferometrically-guided lens placement, enhancing quantum optics capabilities.

## Key findings

- Observation of sub-Poissonian atom number statistics
- Detection of photon anti-bunching signals
- Stable and precise lens positioning achieved

## Abstract

We report on the simultaneous observation from four directions of the fluorescence of single $^{87}$Rb atoms trapped at the common focus of four high numerical aperture (${\rm NA}=0.5$) aspheric lenses. We use an interferometrically-guided pick-and-place technique to precisely and stably position the lenses along the four cardinal directions with their foci at a single central point. The geometry gives right angle access to a single quantum emitter, and will enable new trapping, excitation, and collection methods. The fluorescence signals indicate both sub-Poissonian atom number statistics and photon anti-bunching, showing suitability for cold atom quantum optics.