An optomechanical lock-in amplifier with intracavity radiation pressure mediated gain*

Quantum metrology applications leveraging highly squeezed states of light, including next-generation gravitational wave detectors, can be limited by mode-matching, photodetection, and other optical losses in the readout chain. Phase-sensitive ponderomotive pre-amplification can protect quantum noise limited signals from such downstream losses without introducing excess input-referred loss. We describe a tabletop traveling wave cavity in which a 1550nm pump tuned on-resonance coherently mixes with amplitude sidebands of a homodyne probe field to drive a gram-scale silicon resonator. The resulting cavity length fluctuations induce phase fluctuations in the reflected pump, which are sensed through Pound-Drever-Hall locking. We present the audio-band gain performance and noise budget of the initial demonstration. Ongoing work may bring the amplifier's input-referred noise well below vacuum shot noise by canceling pump relative intensity noise through a balanced Mach-Zehnder configuration and reducing thermal noise through cryogenic (123K) operation.