Number-resolved preparation of mesoscopic atomic ensembles

The analysis of entangled atomic ensembles and their application for interferometry beyond the standard quantum limit requires an accurate determination of the number of atoms. We present an accurate fluorescence detection technique for atoms that is fully integrated into an experimental apparatus for the production of many-particle entangled quantum states. Number-resolved fluorescence measurements with single-atom accuracy for 1 up to 30 atoms are presented. According to our noise analysis, we extrapolate that the single-atom accuracy extends to a limiting atom number of 390(20) atoms. We utilize the accurate atom number detection for a number stabilization of the laser-cooled atomic ensemble. For a target ensemble size of 7 atoms prepared on demand, we achieve a 92(2)% preparation fidelity and reach number fluctuations 18(1) dB below the shot noise level using real-time feedback on the magneto-optical trap.

Automated summary

The article discusses an accurate technique for determining the number of atoms in entangled atomic ensembles, which is essential for interferometry beyond the standard quantum limit. The fluorescence detection method presented allows for single-atom accuracy measurements, with extrapolated accuracy for up to 390 atoms. This accurate atom number detection is utilized for stabilizing laser-cooled atomic ensembles and achieving high preparation fidelity and low number fluctuations below shot noise level in a target ensemble of 7 atoms.