# Coherent single-atom superradiance

## TL;DR

This paper demonstrates cavity-mediated coherent superradiance from sequentially passing single atoms with predefined correlations, resulting in a steady-state coherent field with enhanced intensity, advancing understanding of collective atom-light interactions.

## Contribution

It introduces a method for achieving coherent superradiance with single atoms passing through a cavity sequentially, mediated by a long-lived cavity field, with precise atomic phase control.

## Key findings

- Steady-state coherent field generated with intensity proportional to the square of atom number.
- Over ten-fold enhancement in emission compared to noncollective cases.
- Atomic correlation achieved via nanometer-precision position control.

## Abstract

Quantum effects, prevalent in the microscopic scale, generally elusive in macroscopic systems due to dissipation and decoherence. Quantum phenomena in large systems emerge only when particles are strongly correlated as in superconductors and superfluids. Cooperative interaction of correlated atoms with electromagnetic fields leads to superradiance, the enhanced quantum radiation phenomenon, exhibiting novel physics such as quantum Dicke phase and ultranarrow linewidth for optical clocks. Recent researches to imprint atomic correlation directly demonstrated controllable collective atom-field interactions. Here, we report cavity-mediated coherent single-atom superradiance. Single atoms with predefined correlation traverse a high-Q cavity one by one, emitting photons cooperatively with the atoms already gone through the cavity. Such collective behavior of time-separated atoms is mediated by the long-lived cavity field. As a result, a coherent field is generated in the steady state, whose intensity varies as the square of the number of traversing atoms during the cavity decay time, exhibiting more than ten-fold enhancement from noncollective cases. The correlation among single atoms is prepared with the aligned atomic phase achieved by nanometer-precision position control of atoms with a nanohole-array aperture. The present work deepens our understanding of the collective matter-light interaction and provides an advanced platform for phase-controlled atom-field interactions.