Metrology and metastability in quantum input-output systems

By Madalin Guta (University of Nottingham)
Abstract: Estimating unknown parameters with high accuracy is a key task in quantum metrology and quantum control. For open systems dynamics, the natural setting is the input-output formalism in which the output process can be monitored through continuous time measurements. For ergodic dynamics, the absolute precision limit is given by the quantum Fisher information, which scales linearly in the lont time limit. Of particular interest are systems which exhibit metastability, or dynamical phase transitions, for which the scaling is quadratic for times of the order of the coherence time. However, the quantum Fisher information is believed to be non-achievable with standard measurements such as photon counting, homodyne and heterodyne measurements. Therefore it is important to design and analyse measurement techniques which provide estimation precision comparable to the absolute limit. In this talk I will present preliminary results in this direction which use the idea of 'quantum output post-processing' by series product.
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