High-fidelity dispersive spin sensing in a tunable unit cell of silicon MOS quantum dots

Metal–oxide–semiconductor (MOS) technology offers a promising route to scalable quantum computing based on spin qubits, but large-scale architectures require compact and sensitive sensors that preserve qubit connectivity and remain compatible with industrial fabrication. Here we demonstrate a dispersive spin–qubit sensor, a single-electron box (SEB), integrated within a bilinear unit cell of planar MOS quantum dots fabricated using an industrial 300-mm wafer process. Independent gate control of the SEB and double-quantum-dot tunnel rates enables optimization of the sensor, achieving state-of-the-art dispersive readout fidelities of 99.92% in 340 μs and 99% in 20 μs. We also develop a hidden Markov model of the two-electron spin dynamics, allowing a more accurate determination of the measurement outcome and corresponding fidelity. Our results show that the compactness and versatility of SEB-based charge sensing can be realized without compromising sensitivity, providing a scalable pathway for future MOS spin–qubit architectures.