Unveiling the Zero-Phonon Line of the Boron Vacancy Center by Cavity Enhanced Emission

TL;DR

This study successfully measures the zero-phonon line of boron vacancies in hexagonal boron nitride using cavity-enhanced emission, revealing strong coupling effects and potential for quantum interface applications.

Contribution

First direct measurement of the ZPL of $V_B^-$ in hBN at room temperature via cavity coupling, demonstrating cavity-emitter interaction and Purcell enhancement.

Findings

Measured ZPL at 773 nm with high precision.

Observed Purcell effect maximum at cavity midpoint.

Confirmed theoretical predictions of cavity-emitter coupling.

Abstract

Negatively charged boron vacancies ($V_B^-$) in hexagonal boron nitride (hBN) exhibit a broad emission spectrum due to strong electron-phonon coupling and Jahn-Teller mixing of electronic states. As such, the direct measurement of zero-phonon line (ZPL) of $V_B^-$ has remained elusive. Here, we measure the room-temperature ZPL wavelength to be $773\pm2$ nm by coupling the hBN layer to the high-Q nanobeam cavity. As the wavelength of cavity mode is tuned, we observe a pronounced intensity resonance, indicating the coupling to $V_B^-$. Our observations are consistent with the spatial redistribution of $V_B^-$ emission. Spatially resolved measurements show a clear Purcell effect maximum at the midpoint of the nanobeam, in accord with the optical field distribution of the cavity mode. Our results are in good agreement with theoretical calculations, opening the way to using $V_B^-$ as cavity spin-photon interfaces.