Suppression of Pulsed Dynamic Nuclear Polarization by Many-Body Spin Dynamics

Abstract

We study a mechanism by which nuclear hyperpolarization due to the polarization transfer from a microwave-pulse-controlled electron spin is suppressed. From analytical and numerical calculations of the unitary dynamics of multiple nuclear spins, we uncover that, combined with the formation of the dark state within a cluster of nuclei, coherent higher-order nuclear spin dynamics impose limits on the efficiency of the polarization transfer even in the absence of mundane depolarization processes such as nuclear spin diffusion and relaxation. Furthermore, we show that the influence of the dark state can be partly mitigated by introducing a disentangling operation. Our analysis is applied to the nuclear polarizations observed in $^{13}$C nuclei coupled with a single nitrogen-vacancy center in diamond [Science 374, 1474 (2021) by J. Randall et al.]. Our work sheds light on collective engineering of nuclear spins as well as future designs of pulsed dynamic nuclear polarization protocols