Weak continuous measurements require more work than strong ones

Abstract: We analyze a dynamical model for a quantum measurement process, able to capture nonideal (weak or inefficient) measurements. In this model, the irreversibility of the measurement dynamics is due to action of a reservoir at equilibrium, which cause decoherence between the states associated with different measurement results. We analyze the performance of measurement process generated by the model, by introducing figures of merits to quantify the strength of the measurement and its efficiency. We also derive and analyze a lower bound on the measurement work cost that we can relate to the measurement quality. We take as an illustration a qubit measurement owing to its coupling to a harmonic oscillator. We investigate the long sequences of extremely short and weak measurements (a.k.a continuous measurements), to find under which conditions they converge to an ndeal measurement and analyze their work cost. Surprisingly, we find that a sequence converging towards a projective measurement has a much larger work cost than a equivalent strong measurement obtained from a single intense interaction with the apparatus. We extend this result to a large class of models owing to scaling arguments. Our analysis offer new insights into the trade-offs between measurement strength, energy consumption, and information extraction in quantum measurement protocols.