Observation of Tunable Superradiant Frequency Combs

TL;DR

This paper demonstrates tunable superradiant frequency combs in a driven spin ensemble coupled to a superconducting resonator, revealing a dynamical phase transition and establishing a link to continuous time crystals.

Contribution

It introduces a driven-dissipative cavity-QED model explaining periodic pulsed superradiance and shows how rare-earth ions enable dual-rail frequency combs in microwave and optical domains.

Findings

Observation of a dynamical phase transition from continuous-wave to pulsed superradiance.

Identification of a driven-dissipative model explaining the emergence of periodic superradiant phases.

Experimental demonstration of dual-rail superradiant frequency combs in rare-earth ion systems.

Abstract

Cavity quantum electrodynamics (QED) with quantum emitters coupled to resonators provides a powerful platform for engineering light-matter interactions and exploring collective phenomena. In particular, superradiance, arising from collective quantum interference among emitters, has been explored as a route to ultrastable continuous radiation. However, engineering superradiance in the time domain to realize periodic pulsed sources or frequency combs remains largely unexplored. Here, we investigate the non-equilibrium many-body dynamics of a driven spin ensemble coupled to an on-chip superconducting resonator and uncover a dynamical phase transition from continuous-wave to periodic pulsed superradiant emission. To quantitatively capture the observed dynamical phases, we introduce a driven-dissipative cavity-QED model that elucidates how the periodic pulsed superradiant phase emerges from collective, periodically repeating spin dynamics stabilized by the interplay of coherence growth, disorder, and dissipation. We also find that rare-earth ion spin systems exhibiting both optical and microwave transitions enable phase-synchronized, dual-rail superradiant frequency combs in both the microwave and optical domains. Our results not only open new avenues for dual-rail frequency-comb applications in quantum metrology and information processing, but also establish a fundamental connection between periodic pulsed superradiance and the emergence of a continuous time crystal as a novel nonequilibrium phase in driven open systems.