Interaction-free interferometry carries half the Fisher information of direct probing for transmissivity, equal information per absorbed photon, and only beats direct schemes when distinguishing an object from empty space, at a rate growing like the number of Zeno cycles.
Optimal quantum estimation of loss in bosonic channels
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We address the estimation of the loss parameter of a bosonic channel probed by Gaussian signals. We derive the ultimate quantum bound on precision and show that no improvement may be obtained by having access to the environment degrees of freedom. We found that, for small losses, the variance of the optimal estimator is proportional to the loss parameter itself, a result that represents a qualitative improvement over the shot noise limit. An observable based on the symmetric logarithmic derivative is derived, which attains the ultimate bound and may be implemented using Gaussian operations and photon counting.
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Counterfactual Quantum Sensing: What Interaction-Free Measurement Can and Cannot Buy
Interaction-free interferometry carries half the Fisher information of direct probing for transmissivity, equal information per absorbed photon, and only beats direct schemes when distinguishing an object from empty space, at a rate growing like the number of Zeno cycles.