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arXiv:1609.08216 · Physical Review Letters

Critical Thermalization of a Disordered Dipolar Spin System in Diamond

Georg Kucsko, Soonwon Choi, Joonhee Choi, Peter C. Maurer, Hengyun Zhou, Renate Landig, Hitoshi Sumiya, Shinobu Onoda, Junichi Isoya, Fedor Jelezko, Eugene Demler, Norman Y. Yao, Mikhail D. Lukin

Published Jul 9, 2018• 179 citations
arXivHTMLPDF

Abstract

Statistical mechanics underlies our understanding of macroscopic quantum systems. It is based on the assumption that out-of-equilibrium systems rapidly approach their equilibrium states, forgetting any information about their microscopic initial conditions. This fundamental paradigm is challenged by disordered systems, in which a slowdown or even absence of thermalization is expected. We report the observation of critical thermalization in a three dimensional ensemble of ∼10^{6} electronic spins coupled via dipolar interactions. By controlling the spin states of nitrogen vacancy color centers in diamond, we observe slow, subexponential relaxation dynamics and identify a regime of power-law decay with disorder-dependent exponents; this behavior is modified at late times owing to many-body interactions. These observations are quantitatively explained by a resonance counting theory that incorporates the effects of both disorder and interactions.

DOI
10.1103/physrevlett.121.023601

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Statistical mechanics underlies our understanding of macroscopic quantum systems. It is based on the assumption that out-of-equilibrium systems rapidly approach their equilibrium states, forgetting any information about their microscopic initial conditions. This fundamental paradigm is challenged by disordered systems, in which a slowdown or even absence of thermalization is expected. We report the observation of critical thermalization in a three dimensional ensemble of ∼10^{6} electronic spins coupled via dipolar interactions. By controlling the spin states of nitrogen vacancy color centers in diamond, we observe slow, subexponential relaxation dynamics and identify a regime of power-law decay with disorder-dependent exponents; this behavior is modified at late times owing to many-body interactions. These observations are quantitatively explained by a resonance counting theory that incorporates the effects of both disorder and interactions.
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One of the central challenges of modern statistical physics is understanding the thermalization dynamics of quantum many-body systems at the microscopic level. In this thesis, we describe an experimental study of individual spin dynamics in a two-dimensional ensemble of electron spins on the surface of a diamond crystal. A near-surface NV center is used as a nanoscale magnetic sensor to probe individual spin correlation dynamics in a dipolar interacting spin ensemble. For each spin, the rate of relaxation of spin projection along the bias magnetic field is consistently much slower than the dipolar interaction strengths with its nearest neighbors and is strongly correlated with the timescale of the local magnetic field fluctuation. We present a quantitative model based on dynamic resonance counting arguments that explains these observations. Furthermore, we use resonant spin-lock driving to control the effective strength of the local magnetic fields and demonstrate the role of dynamical disorder in different regimes. In the regime of suppressed extrinsic disorder, we use dynamic mean field methods to explain our experimental observations. The work presented in this thesis paves the way towards a microscopic study of quantum thermalization in two-dimensional strongly interacting disordered spin ensembles.
We study the depolarization dynamics of a dense ensemble of dipolar interacting spins, associated with nitrogen-vacancy centers in diamond. We observe anomalously fast, density-dependent, and nonexponential spin relaxation. To explain these observations, we propose a microscopic model where an interplay of long-range interactions, disorder, and dissipation leads to predictions that are in quantitative agreement with both current and prior experimental results. Our results pave the way for controlled many-body experiments with long-lived and strongly interacting ensembles of solid-state spins.
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