Surviving readout errors and incomplete postselection in monitored quantum circuits

arXiv:2610.20712v1 Announce Type: new Abstract: We study how readout errors affect dynamics in monitored quantum circuits. Such errors make postselection effectively incomplete, conditioning trajectories on imperfect rather than true records. Focusing on U(1)-symmetric circuits, we find that the charge-sharpening transition survives at a finite error rate, with the sharp phase's vanishing fluctuations replaced by a finite steady-state plateau. The charge fluctuations show a shallow minimum near the ideal transition point as a function of measurement rate, signaling the competition between measurement-induced purification and noise-induced mixing. By decomposing the fluctuations into quantum and classical contributions, we show the minimum marks where incomplete postselection still retains enough trajectory memory to attenuate noise-induced mixing, leaving a detectable signature of the transition even in a noisy setting. Mid-circuit measurements are far harder to mitigate against readout errors than standard end-of-circuit ones, because the errors corrupt the postselection itself; the decomposition therefore offers a minimal mitigation framework and a route to locate the transition directly from experimental data. Our results show that charge sharpening survives readout errors in a quantitative and experimentally accessible way.