Subhertz interferometry at the quantum noise limit

Significance 

Fundamental scientific research and applications such as metrology require high precision phase measurements, which require the use of highly sensitive optical interferometers such as the laser interferometer gravitational-wave observatory. Despite achieving remarkable shot-noise-limited sensitivity levels, interferometric measurements of low signals and gravitational waves have remained a great challenge. This can be attributed to the dominant classical noises i.e. seismic, optical and thermal at the low-frequency region. In recent literature, multifrequency interferometry has been employed to obtain uncontaminated interferometric signals and sub-shot-noise phase measurements w