Abstract

Technological advancements over the last quarter-century have led to moving-mirror systems obtaining the most sensitive displacement measurements to date, with sensitivities of better than 10⁻²⁰ m/√Hz in both benchtop optomechanical experiments [1] and kilometre-scale interferometric gravitational-wave detectors [2]. In such systems, even if classical noise has been reduced, two quantum-noise sources are still present: quantum shot noise (QSN) and quantum radiation pressure noise (QRPN). These two quantum-noise sources are dominant in different Fourier frequency regimes, and their crossover creates a limit to the displacement sensitivity that one can achieve with a coherent laser beam: the standard quantum limit (SQL) [3].

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