We theoretically investigate thermalization and spin diffusion driven by a quantum spin bath for a realistic solid-state NMR experiment. We consider polycrystalline L-alanine, and investigate how the spin polarization spreads among several 13C nuclear spins, which interact via dipole-dipole coupling with the bath of strongly dipolar-coupled 1H nuclear (proton) spins. We do this by using direct numerical simulation of the many-spin time-dependent Schr\"odinger equation. We find that, although the proton spins located near the carbon sites interact most strongly with the 13C spins, this interaction alone is not enough to drive spin diffusion and thermalize the 13C nuclear spins. We demonstrate that the thermalization within the 13C subsystem is driven by the collective many-body dynamics of the proton spin bath, and specifically, that the onset of thermalization among the 13C spins is directly related to the onset of chaotic behavior in the proton spin bath. Therefore, thermalization and spin diffusion within the 13C subsystem is controlled by the proton spins located far from the C sites. In spite of their weak coupling to the 13C spins, these far-away protons help produce a network of strongly coupled proton spins with collective dynamics, that drives thermalization.
@article{arxiv.1812.11638,
title = {Thermalization in Solid-State NMR Controlled by Quantum Chaos in Spin Bath},
author = {Walter Hahn and V. V. Dobrovitski},
journal= {arXiv preprint arXiv:1812.11638},
year = {2019}
}