Optimized mitigation of random-telegraph-noise dephasing by spectator-qubit sensing and control

Spectator qubits (SQs) are a tool to mitigate noise in hard-to-access data qubits. The SQ, designed be much more sensitive the noise, is measured frequently, and accumulated results used rarely correct For hardware-relevant example of dephasing from random telegraph we introduce Bayesian method employing complex linear maps which leads plausibly optimal adaptive measurement control protocol. suppression decoherence rate quadratic SQ sensitivity, establishing that paradigm works arbitrarily well right regime.