The Emergence of Subradiance in Ensembles of Quantum Optical Emitters

Several of the leading quantum technologies are built around harnessing the intrinsic dynamics and interactions between single atoms. One of the key characteristics of these elementary building blocks is their spontaneous decay rate, which quantifies the time that the atom can store energy or information. As predicted by Purcell in 1946 [1], this rate can modified by engineering the environment of the atoms. Alternatively, in complex systems comprising several excited atoms, the decay rate can be similarly increased through the process known as Dicke superradiance [2]. However, decreasing the spontaneous emission rate, and thus increasing the time for which atoms remain excited, turns out to be a difficult challenge. In this work, we attempt to address that challenge, by theoretically investigating the emergence of subradiance – the suppression of dissipation rates from a collection of atomic emitters. To this end, we build a simplified model of relevant experimental systems, such as ensembles of nitrogen-vacancy defects in diamond, as a collection of interacting two-level systems. We trace the dynamics of such systems, and identify the so-called dissipative coupling between emitters as the necessary element for the emergence of the subradiance. We then develop a numerical model for tracing the dynamics of an atomic ensemble in the limit of weak excitations, and use it to study several idealised systems, such as a 1D chain, as well as the more realistic models of a random 2D ensembles of atoms. We identify the subradiance in all these setups, and characterise it as a function of physically-relevant parameters like the number, and spacing between atoms. Our work sets up a larger research program into identifying, and harnessing the subradiant states of atomic ensembles as new elementary building blocks for complex quantum systems.