Signatures of cooperative emission in photon coincidence: Superradiance versus measurement-induced cooperativity

TL;DR

This paper compares superradiance and measurement-induced cooperativity in quantum emitters, analyzing their signatures in photon coincidence signals and emphasizing the importance of time-dependent data to conclusively identify superradiance.

Contribution

It clarifies how photon coincidence signatures can arise from different cooperative mechanisms and highlights the need for time-resolved measurements to distinguish superradiance.

Findings

Anti-dip in photon coincidences indicates inter-emitter correlations.

Photon coincidences alone do not confirm superradiance.

Time-dependent data is essential for unambiguous superradiance detection.

Abstract

Indistinguishable quantum emitters confined to length scales smaller than the wavelength of the light become superradiant. Compared to uncorrelated and distinguishable emitters, superradiance results in qualitative modifications of optical signals such as photon coincidences. However, recent experiments revealed that similar signatures can also be obtained in situations where emitters are too far separated to be superradiant if correlations between emitters are induced by the wave function collapse during an emission-angle-selective photon detection event. Here, we compare two sources for cooperative emission, superradiance and measurement-induced cooperativity, and analyze their impact on time-dependent optical signals. We find that an anti-dip in photon coincidences at zero time delay is a signature of inter-emitter correlations in general but does not unambiguously prove the presence of superradiance. This suggests that photon coincidences at zero time delay alone are not sufficient and time-dependent data is necessary to clearly demonstrate a superradiant enhancement of the spontaneous radiative decay rate.