Mesure au-delà de la limite quantique standard de l'amplitude d'un champ électromagnétique dans le domaine micro-onde

Abstract : As an essential intermediary between theories and their experimental proofs, measurement is meaningfull if the precision of its results is high. The main emphasis of metrology in laboratories is therefore on increasing as much as possible the precision of the experimental evaluation of a parameter. Quantum noise that affects the measurement establishes a quantitative limit on the maximal precision that can be achieved with classical states: the standard quantum limit (SQL). Quantum metrology aims at using quantum features to beat this limit and to approach the physically ultimate limit called Heisenberg limit. This thesis presents a measurement strategy for an electromagnetic field containing less than one photon, which is based on the use of atom-field correlations in a cavity quantum electrodynamics experiment. The idea is to measure the amplitude of the small field by probing the disturbance caused on an entangled mesoscopic state that is already stored in the superconducting cavity. We demonstrated that our measurement strategy is in principle optimal thanks to two tools: the Fisher information (that depends on the measurement process) and the quantum Fisher information (that does not), which define the precision tanks to Cramér-Rao like equations. The measurement signal subsequently largely exceeded the level of accuracy obtained with classical states and we got as closed to the Heisenberg limit as the experimental imperfections allowed us.
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Mariane Penasa. Mesure au-delà de la limite quantique standard de l'amplitude d'un champ électromagnétique dans le domaine micro-onde. Physique Quantique [quant-ph]. Université Pierre et Marie Curie - Paris VI, 2016. Français. ⟨NNT : 2016PA066528⟩. ⟨tel-01529749⟩



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