optomechanical

Optomechanics is the study of the interaction between optical fields and mechanical motion, typically realized with light confined in optical resonators that couple to movable mechanical elements. In these systems a confined optical mode exerts radiation pressure or photothermal forces on a mechanical object such as a movable mirror, a membrane, a cantilever, or a levitated particle, while the mechanical motion modulates the optical resonance. This bidirectional coupling enables control, cooling, and readout of mechanical motion using light.

Key concepts include the optomechanical coupling rate, the cavity decay rate, and the mechanical frequency. The single-photon coupling rate, g0, characterizes the interaction strength between a single photon and a single phonon. The cooperativity, C, describes the ratio of coherent coupling to losses. In the resolved-sideband regime, where the cavity linewidth is smaller than the mechanical frequency, laser cooling can bring the mechanical mode toward its quantum ground state, enabling quantum control and measurement of motion.

Applications span precision sensing, force and displacement measurements, and explorations of quantum phenomena in mesoscopic systems. Demonstrations include optomechanical cooling, preparation of nonclassical states, and entanglement between light and mechanics. Common platforms include Fabry-Pérot cavities with movable mirrors, membranes in high-Q resonators, nanoscale optomechanical resonators, optomechanical crystals, and levitated optomechanical systems.

Challenges remain, notably thermal noise and decoherence at ambient temperatures, technical noise, and fabrication limits. Advances often rely on cryogenic cooling, high-quality factors, and improved isolation. Optomechanics bridges quantum optics and mechanical sensing, offering insights into fundamental physics and potential ultra-sensitive transducers.