Experiments

Cavity opto-mechanics

The subject of the research is the opto-mechanical interaction between light and macroscopic mechanical oscillators, and includes topics of classical and quantum optics, nonlinear dynamics and chaos, quantum measurements (of interest for gravitational wave detectors).
Our experiments are currently focused on ponderomotive squeezing (quadrature squeezed light at the output of a cavity, induced by the radiation pressure interaction between the optical mode and an oscillating mirror) and on the confinement of a macroscopic mechanical oscillator in a squeezed state. The core of the first experiment is a micro-mechanical oscillator embedded in a high Finesse optical cavity. Crucial properties are the mechanical quality factor of the oscillator (to reduce the effect of thermal noise with respect to quantum fluctuations of the radiation pressure), the optical quality, the operation in a cryogenic environment with good mechanical isolation. Our micro-mirrors, developed in collaboration with Trento (University, CNR and FBK) and Delft (DIMES), show mechanical quality factors up to few 10⁶ at cryogenic temperature and optical losses around 10 ppm. These features make our resonators particularly suitable for the production of ponderomotive squeezing in the 100 KHz-range.
The second setup is based on a high-finesse cavity containing a nano-mechanical membrane. As recently demonstrated, such systems open the possibility to prepare macroscopic oscillators close to their fundamental quantum state. The goal of our experiment is the creation of a qualitatively different quantum state: a mechanical squeezed state. We have conceived and implemented an experimental scheme based on the parametric feedback control of the oscillator motion, which allows us to confine an optomechanical micro-mirror in a squeezed thermal state and to surpass the -3 dB physical limit in the noise reduction. In a moderately cooled system our technique could allow squeezing of a macroscopic mechanical oscillator below the zero-point motion. We are also realizing a series of optomechanical experiments, in the framework of a collaboration with INFN, devoted to testing and limiting possible quantum gravity effects in the dynamics of the oscillator.

SEM image of the front side of an oscillating micro-mirror with intgrated isolation stage

Phase space probability density functions (PDFs) for the mechanical oscillator in a thermal state (left) and in a squeezed thermal state (right))