Below the Seismic Noise Floor: From Micromechanical Oscillators to Gravitational Wave Detectors

Optomechanical systems, ranging in size from nano-mechanical oscillators to km-scale gravitational-wave detectors, nowadays allow to measure mechanical displacements close to the fundamental limits of physics. In this joint talk, we will discuss how limitations from seismic noise can be overcome in these mechanical systems and what other noise sources limit sensing displacements below the level of seismic noise. For gravitational-wave detectors, we will present an overview of the challenges and strategies to reduce the impact of seismic noise, from the monitoring arrays and isolation systems within current detector instruments, to the research activities for cancelling noise in future detector upgrades. In micromechanical oscillators, seismic noise is negligible at resonance frequencies in the kHz- to GHz-range. The motion of these low-mass systems is then dominated by thermal noise. We will present current worldwide experimental efforts to decrease the thermal noise as much as possible, both by working in low-temperature environments and by engineering low-dissipation oscillators with mechanical quality factors up to a billion. These efforts have recently enabled to asses the ultimate noise source in displacement measurements: the zero-point motion of the mechanical oscillator.