Limits in interferometric measurements
Interferometry is widely used in measuring small displacements with very high sensitivity values. However, even if all classical sources of error have been eliminated from the measurement process, quantum noise is limiting gravitational wave or table-top interferometer sensitivities. To further study this phenomenon, the EU-funded project 'Quantum optics with optomechanical systems' (QOOMS) developed an optomechanical resonator where quantum radiation pressure noise (QRPN) prevailed over thermal noise. The resonator's highly reflective mirror surfaces allowed high optical finesse and increased the intracavity intensity fluctuations that give rise to QRPN. Scientists used a set-up where correlations between two light beams were created and sent into a high-finesse optical Fabry-Perot cavity. Monitoring correlations between the intensity of the first beam and the phase of the probe beam enabled them to demonstrate the QRPN effects. As contamination was apparent in measurements, scientists operated the cavity in a cryostat, thus reducing thermal noise by two orders of magnitude. QOOMS also developed a quartz micro-mechanical resonator and integrated it in the set-up. Several techniques were developed for coating the high-reflectivity mirror on top of the resonator. The high optical finesse provided by such low-loss coatings dramatically increased both displacement sensitivity and QRPN effects. Project work significantly enhanced knowledge about quantum noise in interferometric measurements.
Keywords
Radiation pressure, laser, matter interaction, interferometry, quantum noise, gravitational wave, quantum optics, optomechanical resonator, quantum radiation pressure noise, thermal noise, optical finesse, Fabry-Perot cavity, displacement sensitivity
