A High-Finesse Suspended Interferometric Sensor for Macroscopic Quantum Mechanics with Femtometre Sensitivity

We present an interferometric sensor for investigating macroscopic quantum mechanics on a table-top scale. The sensor consists of pair of suspended optical cavities with a finesse in excess of 100,000 comprising 10 g fused-silica mirrors. In the current room-temperature operation, we achieve a peak sensitivity of 0.5 in the acoustic frequency band, limited by the readout noise. With additional suppression of the readout noise, we will be able to reach the quantum radiation pressure noise, which would represent a novel measurement of the quantum back-action effect. Such a sensor can eventually be utilised for demonstrating macroscopic entanglement and testing semi-classical and quantum gravity models.