Quantum Behavior of Measurement Apparatus arXiv:1001.3032v2 [quant-ph] 31 May 2010 Taoufik Amri ∗ Laboratoire Kastler Brossel, UMR 8552 (ENS/UPMC/CNRS), 4 Place Jussieu Case 74, 75252 Paris Cedex 05, France (Dated: October 22, 2018) We precise for the first time the quantum behavior of a measurement apparatus in the framework of the usual interpretation of quantum physics. We show how such a behavior can also be studied by the retrodiction of pre-measurement states corresponding to its responses. We translate in terms of these states some interesting properties of the behavior of an apparatus, such as the projectivity, the fidelity, the non-Gaussian character, or the non-classicality of measurements performed by this one. We also propose an experimental procedure allowing the tomography of these pre-measurement states for optical detectors. We illustrate the relevance of these new notions for measurements, by evaluating them for two detectors widely used in quantum optics: the avalanche photodiode and the homodyne detection. PACS numbers: 03.65.Ta, 42.50.Dv, 03.65.Wj, 03.67.-a ∗ Corresponding author : amri.taoufik@gmail.com 1 Abstract