Amplified response of cavity-coupled quantum-critical systems

A quantum critical point develops when matter undergoes a continuous transformation between distinct ground states at absolute zero. It hosts pronounced quantum fluctuations, which render the system highly susceptible to external perturbations. While light-matter coupling has rapidly moved forward as a means to probe and control quantum materials, the capacity of quantum critical fluctuations in the photon-mediated responses has been largely unexplored. Here we advance the notion that directly coupling a quantum critical mode to a quantized cavity field dramatically facilitates the onset of superradiance. When the coupling between the two fields is bilinear, the transition is found to occur at vanishingly small light-matter coupling and is accompanied by strongly enhanced intrinsic squeezing. Our results identify a particularly favorable setting for realizing the elusive superradiant state, and point to a general principle by which quantum criticality amplifies photon-matter entanglement and enhances the associated metrological performance.