How Subradiance Enables Nonlinearity in Weakly Driven Quantum Arrays

TL;DR

This paper reveals that atom-thin quantum arrays exhibit strong nonlinear responses at very low light intensities due to subradiant states, enabling quantum correlations and squeezing without high power or thick samples.

Contribution

It demonstrates that subradiance enables nonlinear quantum effects in weakly driven, atom-thin arrays, challenging previous assumptions about classical behavior at low intensities.

Findings

Nonlinear responses persist at arbitrarily weak drive intensities.

Subradiant states dominate the nonlinear behavior.

Predicted generation of quantum correlations and multimode squeezing.

Abstract

Harnessing the nonlinear response of a medium is essential for applications including frequency conversion and light amplification, as well as for the generation of quantum many-body correlations of light or matter. However, achieving these effects typically requires high drive intensities and thick samples, which induce undesired heating effects that typically suppress quantum correlations. In this work, we demonstrate that atom-thin arrays of quantum emitters exhibit a robust nonlinear response even at arbitrarily weak drive intensities. This discovery challenges the long-held assumption that weakly driven ensembles behave classically; instead, we reveal that subradiant states provide a dominant nonlinear contribution that persists in the low-intensity limit. Using a Dynamical Mean-Field Theory (DMFT) approach, we predict that these nonlinearities generate a quantum-correlated steady state composed of interacting pairs of subradiant excitations, characterized by long-range correlations and multi-mode squeezing. Our findings establish a new frontier for nonlinear quantum optics at minimal power, and provide a scalable protocol for preparing multimode squeezing, offering potential for applications in quantum metrology.