An extended ab initio theory of the V$_{\text{B}}^-$ center in hBN: excited states, Jahn-Teller distortion, and pressure dependence

TL;DR

This paper develops a comprehensive high-level quantum mechanical model of the V$_{ ext{B}}^-$ center in hBN, elucidating its excited states, Jahn-Teller effects, and pressure dependence to enhance quantum sensing applications.

Contribution

It introduces a detailed ab initio theoretical framework for the V$_{ ext{B}}^-$ center, including excited state analysis and stress effects, advancing understanding for quantum sensor development.

Findings

Clarified the excited state fine structure and Jahn-Teller effects.

Analyzed the stress dependence of the center's properties.

Provided insights into the optical and spin transition pathways.

Abstract

Ensembles of negatively charged boron vacancy (V$_{\text{B}}^-$) centers in hexagonal boron nitride (hBN) have emerged as a two-dimensional spin qubit system interfaced with optics to advance nanoscale quantum sensing. However, a comprehensive description of its optically detected magnetic resonance (ODMR) signal remains challenging due to the strongly correlated nature of the excited electronic states involved in its optical cycle. In this work, we model the energetics, structural relaxation, and transition rates of the V$_{\text{B}}^-$ center using a high-level wave-function-based electron correlation method (CASSCF-NEVPT2). We provide a thorough analysis of the excited state fine structure and pseudo Jahn-Teller effects, singlet-triplet quasi-degeneracies, photoluminescence parameters, intersystem crossing pathways, and stress-dependence of the fine structure and decay parameters. Our findings not only clarify the fundamental behavior of the V$_{\text{B}}^-$ center in hBN but also establish the theoretical foundation for advancing the V$_{\text{B}}^-$ center's readout for integrated 2D quantum sensors.