Qubit readout schemes often deviate from ideal projective measurements, introducing critical issues that limit quantum computing performance. In this work, we model charge-sensing-based readout for semiconductor spin qubits in double quantum dots, and identify key error mechanisms caused by the back-action of the charge sensor. We quantify how the charge noise of the sensor, residual tunneling, and g-tensor modulation degrade readout fidelity, induce a mixed post-measurement state, and cause leakage from the computational subspace. For state-of-the-art systems with strong spin-orbit interaction and electrically tunable g-tensors, we identify a readout sweet spot, that is, a special device configuration where readout is closest to projective. Our framework provides a foundation for developing effective readout error mitigation strategies, with broad applications for optimizing readout performance for a variety of charge-sensing techniques, advancing quantum protocols, and improving adaptive circuits for error correction.
@article{arxiv.2505.15878,
title = {Readout sweet spots for spin qubits with strong spin-orbit interaction},
author = {Domonkos Svastits and Bence Hetényi and Gábor Széchenyi and James Wootton and Daniel Loss and Stefano Bosco and András Pályi},
journal= {arXiv preprint arXiv:2505.15878},
year = {2025}
}