26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Laser-Threshold Magnetometry with Spin-1/2 and Spin-1 Quantum Sensors

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Quantum Science and Technology (QST)

Description

Magnetic-field sensing provides a non-invasive way to probe currents, spins and magnetic materials. Quantum magnetic sensors are attractive for this task because atomic-scale spin systems can convert weak magnetic field changes into optical signals with high spatial resolution. A central challenge is that conventional optically detected spin sensors often rely on small fluorescence-contrast changes, so their sensitivity can be limited by photon shot noise, collection efficiency, spin contrast and the practical trade-off between sensor volume and spatial resolution.

Laser-threshold magnetometry (LTM) offers a route to amplify weak spin-dependent optical changes in which the spin-dependent absorption or gain is embedded in an optical cavity operated close to threshold, where a small change in spin population can produce a large change in laser output. LTM for Spin-1 defect platforms [1-3] LTM has already been studied. Many spin-1/2 defects also respond strongly to magnetic fields, for example carbon impurities in hBN [4-5]. How LTM can be used with these spin-1/2 systems remains largely unexplored.

Here we show rate-equation models for LTM using both spin-1/2 and spin-1 quantum sensors. The models connect microwave-driven spin dynamics, optical cycling, shelving pathways and cavity photon number. In the present idealized seeded-cavity calculations, rate-engineered spin-1 designs reach sensitivities at the tens of fT Hz-1/2 level, while optimized spin-1/2 designs reach the few-hundred-fT Hz-1/2 level. These results suggest that LTM can broaden the design space for solid-state quantum magnetometers beyond established NV systems and provide guidance for emerging hBN, molecular and semiconductor spin sensors.

References
[1] J. Jan et al, New Journal of Physics 18, 013015 (2016).
[2] F. Schall et al, arXiv:2509.05204.
[3] S. Q. Lim et al, arXiv:2604.18937.
[4] N. Mendelson et al., Nature Materials, 20, 321 (2021).
[5] I. Robertson et al., Nature Physics 21, 1981 (2025).