Experiments

Optomechanical tailoring of squeezed light

An optical resonant cavity with a mechanical oscillator as end mirror is an optomechanical system where the mechanical degrees of freedom couple with the optical field modes via the radiation pressure force, Fig. 1. A striking consequence of the optomechanical interaction is the coupling induced between light’s amplitude and phase fluctuations. Indeed, amplitude noise of the impinging beam, randomly drives the mechanical element, whose motion, in turn, induces phase fluctuations on the reflected beam.
The interplay between mechanical and cavity optical modes gives rise to a variety of effects which, in the quantum regime, may enable the exploration of quantum mechanics in entirely new ways. Quantum optomechanical oscillators could be used as an interface between microwave and photonic circuits and are also promising for quantum metrology and sensing applications beyond the standard quantum limit.
Our work (in collaboration with CNR-IMEM) aims at demonstrating the possibility of manipulating and controlling the spectral dependence of the field quadratures fluctuations of squeezed light by effect of opto-mechanical interaction. The optomechanical system we propose to investigate is a single-ended high-finesse Fabry-Pérot cavity whose end mirror is a mechanical microresonator supported by a silicon spring. The cavity resonantly enhances the circulating light intensity, while makes the intensity strongly dependent on the mirror position.
A first target is the realization of an optical squeezer capable of generating a squeezed vacuum state with a significant squeezing level in the spectral region around 100-300 kHz. The squeezer will be based on a degenerate optical parametric oscillator (OPO), operating below the threshold, thus generating a vacuum squeezed state of light at spectral frequencies of interest.
A second target is the development of a family of optomechanical micro-oscillators optimized for the production of variable-quadrature squeezed light. The micro-mirror, Fig. 2, must have a high mechanical susceptibility to increase the effect of radiation pressure, and a very low mechanical dissipation to increase the coherence time and reduce the thermal noise. High cavity finesse increases the radiation pressure acting on the movable mirror. In the development of the optomechanical devices, we will follow an approach focused on relatively thick silicon oscillators with high reflectivity coating. The relatively high mass (about 100 μg) is compensated by the ability to manage high power at low temperatures. These mechanical resonators can reach quality factors up to 2 x 106, if designed with features specific for keeping mechanical losses under control.
The final goal is to assemble the complete setup for the interrogation of the optomechanical cavity and homodyne detection of the reflected squeezed light.

Conceptual picture of an optomechanical cavity.

A FEM simulation of a Si₃N₄ mechanical micro-resonator (CNR-­IMEM).