The silicon vacancy center in Silicon Carbide (SiC) provides an optically addressable qubit at room temperature in its spin- \(\frac{3}{2}\) 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 \(| m=\pm 3/2\left.\right\rangle\) and \(| m=\pm 1/2\left.\right\rangle\) states, and optical pumping does not create a population difference between \(| +1/2\left.\right\rangle\) and \(| -1/2\left.\right\rangle\) states. Thus, operating one qubit (e.g., \(\left\{| +3/2\left.\right\rangle ,| +1/2\left.\right\rangle \right\}\) states) leaves the population in the remaining state ( \(| -1/2\left.\right\rangle\) ) 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 \(\left\{| +3/2\left.\right\rangle ,| +1/2\left.\right\rangle \right\}\) and \(\left\{| -1/2\left.\right\rangle ,| -3/2\left.\right\rangle \right\}\) . Experimental results demonstrate that this approach doubles signal contrast in optical readout and improves sensitivity in AC magnetometry compared to simplex operation.
