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The silicon vacancy center in Silicon Carbide (SiC) provides an optically addressable qubit at room temperature in its spin- 32 electronic state. However, optical spin initialization and readout are less efficient compared to those of spin-1 systems, such as nitrogen-vacancy centers in diamond, under non-resonant optical excitation. Spin-dependent fluorescence exhibits contrast only between | m= 3/2. and | m= 1/2. states, and optical pumping does not create a population difference between | +1/2. and | -1/2. states. Thus, operating one qubit (e. g. , \| +3/2. , | +1/2. \ states) leaves the population in the remaining state (| -1/2. ) unaffected, contributing to background in optical readout. To mitigate this problem, we propose a sensing scheme based on duplex qubit operation in the quartet, using microwave pulses with two resonant frequencies to simultaneously operate \| +3/2. , | +1/2. \ and \| -1/2. , | -3/2. \. Experimental results demonstrate that this approach doubles signal contrast in optical readout and improves sensitivity in AC magnetometry compared to simplex operation.
Tahara et al. (Sat,) studied this question.