Dicke superradiance and many-body decay in generic baths*

Dicke superradiance is a fascinating phenomenon that has inspired swathes of research in quantum optics. Perhaps unsurprisingly, as it checks all the boxes of a great piece of physics: it is a genuinely quantum many-body non-equilibrium effect that can be understood in a simple toy model and that on top can be observed in stunning experiments that show the emergence of a superradiance burst of light.

While the original model proposed by Dicke is permutation invariant, reality isn't, and yet experiments still show superradiance. Understanding when superradiance is robust and when it is not is a tricky business, as it requires one to move away from the easy permutation-invariant, Markovian limit. Moreover, what should be the criterion that determines whether a perturbation breaks superradiance? Recent years have seen a revival of interest as numerical and analytical methods to study this problem have improved. 

Here, we argue that a perturbation breaks superradiance if it removes the scaling of the burst in the limit of large emitter numbers. From this point of view, we evaluate a number of different "non-idealities" such as disorder, noise, interaction range, non-Markovianity (retardation), making an effort to distil simple toy models that encapsulate a specific effect and then proving (or numerically demonstrating) whether or not superradiance survives.