Replica symmetry breaking in a cavity QED spin glass

Abstract: Spin glasses are canonical examples of complex matter.  Although much about their structure remains uncertain, they inform the description of a wide array of complex phenomena, ranging from magnetic ordering in metals with impurities to aspects of evolution, protein folding, climate models, and artificial intelligence, where spin glass theory forms a mathematical basis for neuromorphic computing.  Advancing experimental insight into their structure requires repeatable control over microscopic degrees of freedom.  We have recently achieved this at the atomic level using a quantum optical system comprised of ultracold gases of atoms coupled via photons resonating within a confocal cavity.  This realizes a transverse-field vector spin glass with all-to-all connectivity.  Spin configurations are observed in cavity emission. Configuration correlations reveal the emergence of replica symmetry breaking and nascent ultrametric structure as signatures of spin-glass order. The unusual driven-dissipative nature of the system manifests as a nonthermal Parisi distribution, in close correspondence with Monte Carlo simulations.  The controllability of this new spin-glass system, potentially down to the quantum-spin-level, enables the study of spin glass physics in novel regimes, with application to quantum neural network computing.

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