The study of open quantum systems has a long story, however most discussions focus on oscillator bath models (which typically describe phonons, photons, magnons, electron-hole pairs, etc). Another universality class corresponds to spin bath models, where the bath is described by a discrete set of localized N-level systems. Importantly, in certain regimes the behavior of the spin bath can be radically different from the oscillator bath models (some examples of bath spins are lattice defects, dislocation modes, spin impurities, dangling bonds, nuclear spins and localized phonons/vibrons). In this talk I will motivate the importance of the spin bath to present experiments, and discuss its effect on the critical and dynamical properties of certain canonical spin models.
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