Optimal Strategies in Post-Selected Quantum Metrology

Post-selected quantum metrology uses filters to allow detectors to operate at lower intensities without reducing the input rate of quantum information about unknown parameters of interest [1, 2, 3]. In this talk, I will present the optimal family of filters that achieves this lossless compression of information [4]. I will also show that optimal post-selection can always increase the (Fisher) information per output state, even in the presence of strong depolarising noise. This is true irrespectively of whether detector saturation or post-processing costs are dominant. Our optimal filter depends on the underlying parameters to be estimated. Thus, the best way to distil quantum information involves an adaptive strategy [5]. I will present our efforts towards constructing such an optimal adaptive strategy. Finally, I will explore potential applications of post-selection in metrology.