Seminarium Optyczne

Resolution in imaging is bounded by measurement design, detectors sensitivity, light source noise and, ultimately, the quantum nature of light. Quantum metrology provides the framework to compute the ultimate precision limit on the estimation of any parameter encoded in a beam of light. In particular, the Cramér-Rao bound indicates the minimum variance of any unbiased estimator for a given measurement setting, and its quantum counterpart its optimisation over all measurements allowed by quantum mechanics. This limit is used has a benchmark to evaluate the performances of actual measurements. As a consequence, before considering any purely quantum effects, one has to ascertain saturation of the QCRB with classical sources. This is a key point that should become a strategy when optimising or proposing new imaging systems.After introducing these general concepts and their implication to optical parameter estimation, we will take the example of the quantum-metrology-inspired approach for estimating the separation between two incoherent sources. We will show experimentally how spatial mode decomposition allows for ultra-sensitive estimation.