New directions in optomechanics: Brillouin cooling and Microsphere gas

I will review our recent experimental results in levitating optomechanics and cooling via the energy exchange between light and sound. In more details:

 

Brillouin Cooling

Although bolometric- and ponderomotive-induced deflection of device boundaries are widely used for laser cooling, the electrostrictive Brillouin  scattering of light from sound was considered an acousto-optical amplification-only process. It was suggested that cooling could be possible in multiresonance Brillouin systems when phonons experience lower damping than light. However, this regime was not accessible in electrostrictive Brillouin systems as backscattering enforces high acoustical frequencies associated with high mechanical damping. Recently, forward Brillouin scattering in microcavities has allowed access to low-frequency acoustical modes where mechanical dissipation is lower than optical dissipation, in accordance with the requirements for cooling. Here we experimentally demonstrate cooling via such a forward Brillouin process in a microresonator. We show two regimes of operation for the electrostrictive Brillouin process: acoustical amplification as is traditional and an electrostrictive Brillouin cooling regime. Cooling is mediated by resonant light in one pumped optical mode, and spontaneously scattered resonant light in one anti-Stokes optical mode, that beat and electrostrictively attenuate the Brownian motion of the mechanical mode.

 

Microspheres Gas:

An optically levitating sphere was suggested for quantum experiments at room temperature as its center-of-mass motion is coolable while being minimally coupled with the thermal environment. Extending such an optical trap to contain many microspheres, as done with atoms, is attractive but was studied pioneeringly mostly in a viscous environment and with multiple-minima traps where each particle clings to a fringe. Here we experimentally demonstrate microspheres gas in an optical trap and theoretically analyze the observed repulsion-attraction long-range dynamics. Our optical tweezers have a single minimum with additional minima born by the added particles. The diversity of the trapped-particles sizes and shapes together with their varying dynamics that ranges from periodic to random and dimension that span from 1D crystal to 3D gas stands in contrast with the simplicity of our single optical-beam experiment.  We believe that our optomechanical gas can impact light-matter studies by providing a many-body testbed that is self-coolable and free from clamping-loss or material-dissipation of mechanical energy.