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Fluctuations quantiques et thermiques dans les transducteurs électromécaniques

Abstract : Fluctuations are present in any measurement and determine the ultimate sensitivity. This is particularly true for the fundamental fluctuations, namely thermal and quantum noise. The first objective of this thesis has been to develop a general method allowing us to treat measurement systems consisting of passive elements and active ones, the latter being used for amplification and feedback. This method, based on network theory and on the quantum scattering matrix formalism, is applicable to linear systems and, in a more general case, to systems linearisable around the working point. It can take into account all noise sources and can, therefore, describe accurately a non ideal, real, measurement. Its modular character is well-adapted for the treatment of complex systems. The second objective has been to study the influence of quantum and thermal fluctuations on electromecanical measurements. The noise in such systems is usually dominated by thermal fluctuations, but has been pushed towards the quantum limits by ambitious experimental studies requiring very high sensitivity (detection of gravitational waves, test of the equivalence principle in outer space) and due to the technological development in the field of cryogenics. The method developed in this thesis provides a consistent theoretical framework for the treatment of quantum and thermal fluctuations in these systems. In particular, results have been obtained for an accelerometer developed at ONERA for fundamental physical experiments in space, which has the specific feature of employing the mechanism of cold damping. The results allow for an estimate of the ultimate sensitivity limits of such an instrument.
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Submitted on : Tuesday, March 7, 2006 - 12:21:58 PM
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  • HAL Id : tel-00011777, version 1


Francesca Grassia. Fluctuations quantiques et thermiques dans les transducteurs électromécaniques. Physique Atomique [physics.atom-ph]. Université Pierre et Marie Curie - Paris VI, 1998. Français. ⟨tel-00011777⟩



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