Ultralong Dephasing Times in Solid-State Spin Ensembles via Quantum Control

TL;DR

This paper demonstrates methods to significantly extend the spin dephasing time ($T_2^*$) in solid-state NV ensembles, enabling more sensitive and precise quantum sensors at room temperature.

Contribution

It introduces combined quantum control techniques that suppress dephasing mechanisms and enhance coherence times in NV spin ensembles, surpassing previous records.

Findings

Achieved over an order of magnitude increase in $T_2^*$.

Demonstrated the longest $T_2^*$ in solid-state spins at room temperature.

Outlined potential for highly sensitive NV-diamond magnetometers.

Abstract

Quantum spin dephasing is caused by inhomogeneous coupling to the environment, with resulting limits to the measurement time and precision of spin-based sensors. The effects of spin dephasing can be especially pernicious for dense ensembles of electronic spins in the solid-state, such as for nitrogen-vacancy (NV) color centers in diamond. We report the use of two complementary techniques, spin bath control and double quantum coherence, to enhance the inhomogeneous spin dephasing time ($T_2^*$) for NV ensembles by more than an order of magnitude. In combination, these quantum control techniques (i) eliminate the effects of the dominant NV spin ensemble dephasing mechanisms, including crystal strain gradients and dipolar interactions with paramagnetic bath spins, and (ii) increase the effective NV gyromagnetic ratio by a factor of two. Applied independently, spin bath control and double quantum coherence elucidate the sources of spin dephasing over a wide range of NV and spin bath concentrations. These results demonstrate the longest reported $T_2^*$ in a solid-state electronic spin ensemble at room temperature, and outline a path towards NV-diamond magnetometers with broadband femtotesla sensitivity.