Phonon-assisted charge-cycling of nitrogen-vacancy centres in diamond

TL;DR

This paper investigates phonon-assisted processes affecting charge state control in nitrogen-vacancy centers in diamond, revealing specific phonon modes that influence charge cycling and implications for quantum sensing.

Contribution

It uncovers the role of phonon-assisted anti-Stokes excitation in NV charge state transitions and develops models identifying key phonon modes involved.

Findings

Sub-resonant charge transitions are phonon-assisted anti-Stokes processes.

Low energy acoustic phonons significantly contribute near the ZPL.

A 43 meV phonon mode impacts charge cycling at longer wavelengths.

Abstract

The nitrogen-vacancy (NV) centre in diamond is a leading platform for room-temperature quantum sensing. Improvements in sensitivity require precise control of the NV charge state. Transitions from the neutral NV$^0$ charge state to the negative NV$^-$ charge state can occur during excitation with photon energies below the ZPL transition of NV$^0$. These sub-resonant charge transitions limit modern initialisation protocols and have not been studied in full detail. In this paper we show that sub-resonant charge cycling arises from phonon-assisted anti-Stokes excitation. We further uncover the phonon states which contribute most strongly to the anti-Stokes transition via the development of novel quantitative models. The models indicate that low energy acoustic phonons strongly contribute to the transition close to the ZPL. At longer wavelengths a 43\,meV mode additionally impacts the charge cycling dynamics.