Thermal noise in GW detectors

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Together with quantum noise, thermal noise forms the fundamental noise of GW detectors. Thermal noise has been studied in great detail for the most important components in GW detectors including electronics, suspensions, coatings, and substrates. We have contributed to this research with a study of thermal noise in so-called spring-antispring systems, which can be described with the same formalism applicable to all systems in thermal equilibrium, but where our intuitive understanding of how system parameters determine thermal fluctuations can fail [Harms, Mow-Lowry (2018)].

Open problems to be studied in the future are thermal fluctuations in stationary, non-equilibrium systems, e.g., systems with static temperature gradients, which is of relevance for detectors with cooled test masses (like KAGRA, or future detectors like Einstein Telescope and Cosmic Explorer). Furthermore, we know that stress can alter thermal fluctuations in a system. An interesting question is if stress in mirror coatings can be exploited to reduce coating thermal noise.