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报告内容
摘要
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The quantum characterization of detectors will be explored. The gravitational waves from a galactic or cosmic distance source have a very weak intensity to be observed on ground or space and thus requires extremely sensitive detectors. In fact, the intensity of gravitational waves may reach the standard quantum limit (SQL) and quantum nondemolition (QND) continuous measurements may be an important and inevitable technology in measuring gravitational waves. Quantum nondemolition measurements will be explained and a detector will be modeled by a suspended mass or a harmonic oscillator. A suspended mass or a harmonic oscillator under the influence of external driving forces exhibits variety of quantum states, such as coherent states, squeezed states and squeezed thermal states. The dissipation from classical or thermal noises may destroy the quantum coherence of the detector and prohibit any measurement from reaching the standard quantum limit. The Caldirola-Kanai oscillator and Bateman-Feshbach-Tikochinsky oscillator are used to model the dissipation. The measure of quantum coherence and decoherence is introduced and discussed in relation to gravitational wave detectors. The trajectory of the driven oscillator in squeezed thermal state is described by the Wigner function.
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