Optimizing a Dynamical Decoupling Protocol for Solid-State Electronic Spin Ensembles in Diamond

TL;DR

This paper demonstrates significant enhancement of spin coherence times in diamond NV centers using optimized dynamical decoupling protocols, enabling advances in quantum sensing and collective spin state creation.

Contribution

It introduces a recursive concatenated XY8 dynamical decoupling protocol that preserves arbitrary spin states more effectively than previous methods.

Findings

Coherence time increased from 0.7 ms to 30 ms at 77 K.

Optimal control identified as a recursive XY8 protocol.

Enhanced coherence enables improved quantum sensing and dense spin state engineering.

Abstract

We demonstrate significant improvements of the spin coherence time of a dense ensemble of nitrogen-vacancy (NV) centers in diamond through optimized dynamical decoupling (DD). Cooling the sample down to $77$ K suppresses longitudinal spin relaxation $T_1$ effects and DD microwave pulses are used to increase the transverse coherence time $T_2$ from $\sim 0.7$ ms up to $\sim 30$ ms. We extend previous work of single-axis (CPMG) DD towards the preservation of arbitrary spin states. Following a theoretical and experimental characterization of pulse and detuning errors, we compare the performance of various DD protocols. We identify that the optimal control scheme for preserving an arbitrary spin state is a recursive protocol, the concatenated version of the XY8 pulse sequence. The improved spin coherence might have an immediate impact on improvements of the sensitivities of AC magnetometry. Moreover, the protocol can be used on denser diamond samples to increase coherence times up to NV-NV interaction time scales, a major step towards the creation of quantum collective NV spin states.