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  1. High-contrast optically detected magnetic resonance is a valuable property for reading out the spin of isolated defect colour centres at room temperature. Spin-active single defect centres have been studied in wide bandgap materials including diamond, SiC and hexagonal boron nitride, each with associated advantages for applications. We report the discovery of optically detected magnetic resonance in two distinct species of bright, isolated defect centres hosted in GaN. In one group, we find negative optically detected magnetic resonance of a few percent associated with a metastable electronic state, whereas in the other, we find positive optically detected magnetic resonance of up to 30% associated with the ground and optically excited electronic states. We examine the spin symmetry axis of each defect species and establish coherent control over a single defect’s ground-state spin. Given the maturity of the semiconductor host, these results are promising for scalable and integrated quantum sensing applications. 
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    Free, publicly-accessible full text available February 12, 2025
  2. GaN has recently been shown to host bright, photostable, defect single-photon emitters in the 600–700 nm wavelength range that are promising for quantum applications. The nature and origin of these defect emitters remain elusive. In this work, we study the optical dipole structures and orientations of these defect emitters using the defocused imaging technique. In this technique, the far-field radiation pattern of an emitter in the Fourier plane is imaged to obtain information about the structure of the optical dipole moment and its orientation in 3D. Our experimental results, backed by numerical simulations, show that these defect emitters in GaN exhibit a single dipole moment that is oriented almost perpendicular to the wurtzite crystal c-axis. Data collected from many different emitters show that the angular orientation of the dipole moment in the plane perpendicular to the c-axis exhibits a distribution that shows peaks centered at the angles corresponding to the nearest Ga–N bonds and also at the angles corresponding to the nearest Ga–Ga (or N–N) directions. Moreover, the in-plane angular distribution shows little difference among defect emitters with different emission wavelengths in the 600–700 nm range. Our work sheds light on the nature and origin of these GaN defect emitters. 
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    Free, publicly-accessible full text available October 18, 2024
  3. Free, publicly-accessible full text available June 1, 2024
  4. Abstract

    The recently discovered spin-active boron vacancy (V$${}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$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 suggestive of symmetry-lowering of the defect system fromD3htoC2v. Additionally, the excited-state ODMR has strong temperature dependence of both contrast and transverse anisotropy splitting, enabling promising avenues for quantum sensing.

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