## Critical thermalization of a disordered dipolar spin system in diamond

**Speaker:**Soonwon Choi, Harvard

**When:**September 23, 2016 (Fri), 12:00PM to 01:00PM (add to my calendar)

**Location:**SCI 352

**Hosted by:**Alexander Sushkov

*This event is part of the Biophysics/Condensed Matter Seminar Series. *

Nearly sixty years ago, Anderson predicted that the interplay between long-range couplings and disorder in quantum systems can lead to a novel regime of slow, sub-diffusive thermalization. This is in stark contrast to both conventional ergodic system and many-body localized systems. In this talk, we present both theory and experimental observation of such critical thermalization in a three dimensional ensemble of ~10^6 spins coupled via dipolar interactions. By coherently manipulating the spin states of nitrogen vacancy color centers in diamond, we observe that two groups of oppositely polarized spins approach their equilibrium state via slow, sub-exponential relaxation dynamics, that is consistent with power laws with disorder-dependent exponents. This behavior is modified at late time owing to many-body interactions. These observations are quantitatively explained by a resonance counting theory, which reveals the subtle role of long-range interactions in the system.