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  • Open Access

Investigating spectral dynamics and spin signatures of a mechanically isolated quantum emitter in hBN

Sajedeh Shahbazi*, Alexander Pachl*, Kathrin Schwer, Patrick Maier, and Alexander Kubanek†

  • *These authors contributed equally to this work.
  • †Contact author: alexander.kubanek@uni-ulm.de
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Phys. Rev. Applied 26, 034041 – Published 18 September, 2026

DOI: https://doi.org/10.1103/m3gt-9g4v

Abstract

Mechanically isolated defect centers in hexagonal boron nitride are promising coherent quantum emitters, yet spectral instabilities persist, and their spin-related nature remains unclear. Here we investigate a single mechanically isolated quantum emitter in hBN integrated onto a coplanar waveguide. The emitter exhibits exceptionally bright photoluminescence excitation signals with saturation count rates exceeding 10 Mc/s. High-resolution spectroscopy reveals two closely spaced zero-phonon-line transitions originating from the same defect complex. Time-resolved spectroscopy shows that these transitions exhibit markedly different spectral diffusion dynamics, consistent with distinct donor-acceptor-pair-like recombination pathways with different sensitivities to local electrostatic fluctuations. Off-resonant blue illumination redistributes emission between the two transitions and increases the emission duty cycle without significantly modifying the dominant spectral diffusion rates at low temperature, indicating repumping from long-lived shelving states. Magnetic-field-dependent photoluminescence, optically detected magnetic resonance, and pump-probe measurements reveal millisecond-scale relaxation dynamics and magnetic-field-dependent fluorescence contrast, demonstrating spin-dependent population dynamics in the metastable shelving state. These results clarify how charge-driven spectral fluctuations and spin-dependent shelving jointly shape the optical cycling dynamics.

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Phys. Rev. Applied 26, 034041– Published 18 September, 2026
  • Received 17 April 2026
  • Revised 6 July 2026
  • Accepted 24 August 2026
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