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

TL;DR

This paper investigates how many-body nuclear spin dynamics and dark state formation limit the efficiency of pulsed dynamic nuclear polarization, proposing mitigation strategies and analyzing experimental implications.

Contribution

It reveals the role of dark states and higher-order nuclear spin dynamics in suppressing polarization transfer, offering insights for improving DNP protocols.

Findings

Dark state formation limits polarization transfer efficiency.

Disentangling operations can partly mitigate dark state effects.

Analysis applied to $^{13}$C nuclei with NV centers in diamond.

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.