Single-photon superradiance and subradiance in helical collectives of quantum emitters

Abstract

Collective emission of light from distributions of two-level systems (TLSs) was first predicted in 1954 by Robert Dicke, who showed that when $N$ quantum emitters absorb photons, their collective radiative decay rate can be enhanced (superradiance) or suppressed (subradiance) relative to a single emitter. In this work, we derive novel analytical expressions for the collective decay rates and Lamb shifts for the interaction of a single photon with a continuous distribution of TLSs on an infinite line and an infinite helix. We compare these solutions to collectives of TLSs on a cylinder, finding limits in which the eigenvalues of structures of different dimensions are equal. We also compare our solution with arrangements where the emitter distribution is discrete rather than continuous, and when short- ($1/r^3$), intermediate- ($1/r^2$), and long-range ($1/r$) interaction terms are included. We find important differences between the discrete vector and continuous scalar emitter cases, which do not agree in the limit where discrete spacing goes to 0. The analytical solution for the helix is then used to make estimates of the maximally superradiant state, thermally averaged collective decay rate, and percentage of trapped states of quantum emitter architectures in protein fibers. Given the differences between our idealized infinite helix and the numerical model describing protein fibers, our analytical estimates show excellent agreement with the numerical results for sparse arrangements of emitters in protein fibers. Our work thus bridges the gap between different formalisms for superradiance, aids the engineering of devices which harness quantum optical effects for computing with superradiant error correction and subradiant memories, and motivates the discovery and creation of flexible platforms for quantum information processing using the intrinsic helical geometries of biomatter.