Resonant enhancement of readout contrast of the V2 silicon vacancy in 4H-SiC

The V2 center in 4H-SiC is a well-studied silicon vacancy defect due to spin and optical properties that are promising for quantum technologies. However, for quantum sensing, it has relatively weak readout contrast using off-resonant laser excitation, typically about 0.5% for cw optically-detected magnetic resonance (ODMR) in ensembles. To address this problem, we investigate the resonant excitation of V2 ensembles in 4H-SiC samples at low temperatures and compare to off-resonant excitation. For relatively weak resonant excitation, we report a maximum ODMR contrast of 56%, yielding 50 times improvement over off-resonant excitation (~1.1%). While the PL from resonant excitation increases linearly with power over 2 orders of magnitude, the contrast decreases, approaching the non-resonant contrast. Although this limits the strength of the ODMR signal, the improved contrast still leads to an order of magnitude improvement in the estimated shot-noise-limited sensitivity. The reduced laser power requirements are also a significant advantage. We will also report on efforts to use this resonant approach for low-temperature, wide-field magnetic imaging of quantum materials and devices.