Tunable Local Thermalization of a Disordered, Floquet-Engineered Dipolar Ensemble

Ubiquity of local thermalization in ergodic quantum systems is a central paradigm of condensed matter physics. Unravelling the local relaxation dynamics in specific models however remains an open theoretical and experimental challenge. In this talk we report on recent advances in which dense ensembles of nitrogen vacancy centers in diamond are Floquet-engineered to modify the spin exchange anisotropy of their native dipolar interaction. In addition to standard Ramsey measurements as a global probe, we develop a novel technique to measure ensemble-averaged, infinite temperature autocorrelation functions of local operators. This technique, exploiting strong local disorder in the system, functions as an exquisite probe of local thermalization in the many-body system. As a function of the tunable exchange anisotropy, we show how both the timescale and shape of these measured spin autocorrelations are nontrivially modified, in striking contrast to the expectations set by the NMR literature. In particular, we show theoretically how the shape of the relaxation, as quantified by stretching exponents, encodes the correlation properties of the system's intrinsic spin bath that emerges to thermalize the system. In addition to providing novel physical heuristics to interpret the experimental results, our work establishes a general phenomenology for understanding out-of-equilibrium quench dynamics in disordered, long-range interacting systems.