  The sensitivity afforded by quantum sensors is limited by decoherence.
Quantum error correction (QEC) can enhance sensitivity by suppressing
decoherence, but it has a side-effect: it biases a sensor's output in realistic
settings. If unaccounted for, this bias can systematically reduce a sensor's
performance in experiment, and also give misleading values for the minimum
detectable signal in theory. We analyze this effect in the
experimentally-motivated setting of continuous-time QEC, showing both how one
can remedy it, and how incorrect results can arise when one does not.
