Excited-state spin-resonance spectroscopy of V$_\text{B}^-$ defect centers in hexagonal boron nitride

TL;DR

This study characterizes the excited-state spin properties of V$_\text{B}^-$ defect centers in hexagonal boron nitride, revealing temperature-dependent features that enhance their potential for quantum sensing applications.

Contribution

It provides the first detailed temperature-dependent ODMR spectroscopy of the excited state, including the excited-state Hamiltonian and its implications for quantum sensing.

Findings

Room-temperature zero-field splitting of 2.1 GHz in the excited state

Confirmation of spin rotation in the excited state via pulsed ODMR

Observation of Zeeman-mediated level anti-crossings in both states

Abstract

The recently discovered spin-active boron vacancy (V$_\text{B}^-$) defect center in hexagonal boron nitride (hBN) has high contrast optically-detected magnetic resonance (ODMR) at room-temperature, with a spin-triplet ground-state that shows promise as a quantum sensor. Here we report temperature-dependent ODMR spectroscopy to probe spin within the orbital excited-state. Our experiments determine the excited-state spin Hamiltonian, including a room-temperature zero-field splitting of 2.1 GHz and a g-factor similar to that of the ground-state. We confirm that the resonance is associated with spin rotation in the excited-state using pulsed ODMR measurements, and we observe Zeeman-mediated level anti-crossings in both the orbital ground- and excited-state. Our observation of a single set of excited-state spin-triplet resonance from 10 to 300 K is consistent with an orbital-singlet, which has consequences for understanding the symmetry of this defect. Additionally, the excited-state ODMR has strong temperature dependence of both contrast and transverse anisotropy splitting, enabling promising avenues for quantum sensing.