Emergence of superradiance in dissipative dipolar-coupled spin systems

TL;DR

This paper demonstrates that dissipative dipolar-coupled spin systems can exhibit superradiance, with collective dissipation and quadratic scaling of radiation intensity, extending the understanding of superradiance beyond non-interacting atoms.

Contribution

It shows that dipolar interactions enable superradiance in spin systems, using a simplified model and a fluctuation-regulated quantum master equation, aligning with experimental observations.

Findings

Maximum radiation intensity scales as N^2.

Dipolar relaxation time scales as 1/N^2.

Superradiance observed under weak system-bath coupling.

Abstract

In the superradiance phenomenon, a collection of non-interacting atoms exhibits collective dissipation due to interaction with a common radiation field, resulting in a non-monotonic decay profile. This work shows that dissipative dipolar-coupled systems exhibit an identical collective dissipation aided by the nonsecular part of the dipolar coupling. We consider a simplified dipolar network where the dipolar interaction between the spin-pairs is assumed to be identical. Hence the dynamics remain confined in the block diagonal Hilbert spaces. For a suitable choice of the initial condition, the resulting dynamics require dealing with a smaller subspace which helps extend the analysis to a larger spin network. To include the nonsecular dipolar relaxation, we use a fluctuation-regulated quantum master equation. We note that a successful observation of superradiance in this system requires a weak system-bath coupling. Moreover, we find that for an ensemble of N spins, the maximum intensity of the radiation exhibits a nearly quadratic scaling (N^2), and the dipolar relaxation time follows an inverse square proportionality (1/N^2); these two observations help characterize the emergence of superradiance. Our results agree well with the standard results of pure spin superradiance observed experimentally in various systems.