Abstract

Light-matter interactions are playing an increasingly crucial role in the understanding and engineering of new states of matter with relevance to the fields of quantum optics, solid state physics, chemistry and materials science. Experiments have shown that significant modifications of material properties and transport can occur in a cavity in the regime of collective strong light-matter coupling even without external irradiation – “in the dark”. In this talk we focus on paradigmatic models for disordered spins coupled to the photon field of cavity and discuss how collective light matter interactions can dramatically alter the many-particle spin wavefunctions in the limit of vanishingly small photon numbers. Subtle, permanent changes in the wavefunctions result from the combined effects of vacuum hybridization and long-range cavity-mediated couplings between the spins. A surprising, general, result is the realization of “semilocalization”, a famous and elusive effect usually associated to critical states of Anderson-like transitions. We discuss possible implications for energy transport mediated by collective light-matter dark states in molecular physics and quantum optical systems. We also provide evidence of novel many-particle phases and phase transitions that should occur in these systems at low energy, due to the combined effects of disorder and long-range couplings among spins.