# Single-shot Non-destructive Detection of Rydberg Atom Ensembles by Transmission Measurement of a Microwave Cavity

## TL;DR

This paper demonstrates a non-destructive, single-shot method to detect Rydberg atom ensembles using microwave cavity transmission, enabling precise atom counting with minimal backaction.

## Contribution

It introduces a novel dispersive measurement technique for Rydberg atoms via microwave cavity transmission, achieving high-precision, non-destructive detection in a single shot.

## Key findings

- Achieved 13% precision in atom number detection for ~500 Rydberg atoms.
- Demonstrated minimal population transfer (~2%) during measurement.
- Enabled state population measurements in superposition states.

## Abstract

Rydberg atoms are at the core of an increasing number of experiments, which frequently rely on destructive detection methods, such as field ionization. Here, we present an experimental realization of single-shot non-destructive detection of ensembles of helium Rydberg atoms. We use the dispersive frequency shift of a superconducting microwave cavity interacting with the ensemble. By probing the transmission of the cavity and measuring the change in its phase, we determine the number of Rydberg atoms or the populations of Rydberg quantum states when the ensemble is prepared in a superposition. At the optimal probe power, determined by the critical photon number, we reach single-shot detection of the atom number with 13% precision for ensembles of about 500 Rydberg atoms with a measurement backaction characterized by approximately 2%-population transfer.