Superradiance of entangled photon pairs from a high-density chip-scale Cs vapor cell

Superradiance is one of the most fundamental collective quantum phenomena in light-matter interactions and has been studied extensively since Dicke's seminal work.

However, its practical implementation remains challenging because superradiant enhancement requires strict experiment conditions for strong collective coupling among emitters.

Can superradiance emerge in a simple platform, such as an atomic vapor cell composed of thermally moving atoms?

To address this question, we identify the key signatures of superradiance in a hot atomic ensemble and find a use case of superradiance using an atomic vapor cell.

Here, the Photon-Pair SuperRadiance (PPSR) process in an atomic vapor cell provides a novel approach to generating superradiant quantum light from a practical atomic platform.

We experimentally demonstrate a superradiant entangled photon-pair generation via PPSR process in a high-density, 1-mm-long chip-scale Cs vapor cell.

The hot, dense atomic vapor cell allows the mean interatomic distance in the Doppler-broadened atomic ensemble to be reduced to 0.29 times the idler-photon wavelength, satisfying the condition for cooperative emission.

The thin chip-scale geometry enables high atomic densities while mitigating the reabsorption of emitted photons and maintaining moderate optical depth.

In this subwavelength regime, we clearly observe the temporal narrowing of the biphoton wavefunction from 0.60 ns to 0.17 ns due to a superradiant decay.

This pronounced temporal compression provides strong evidence of collective superradiant emission in the chip-scale Cs vapor cell.

Our PPSR source delivers a detected photon-pair rate exceeding 10^6 pairs/s while maintaining a high coincidence-to-accidental ratio of 280.