Aurélien Kuhn

Deformable two-dimensional photonic crystal slab for cavity optomechanics

We have designed photonic crystal suspended membranes with optimized optical and mechanical properties for cavity optomechanics. Such resonators sustain vibration modes in the megahertz range with quality factors of a few thousand. Thanks to a two-dimensional square lattice of holes, their reflectivity at normal incidence at 1064 nm reaches values as high as 95%. These two features, combined with the very low mass of the membrane, open the way to the use of such periodic structures as deformable end mirrors in Fabry-Perot cavities for the investigation of cavity optomechanical effects.

A micropillar for cavity optomechanics

We have designed a micromechanical resonator suitable for cavity optomechanics. We have used a micropillar geometry to obtain a high-frequency mechanical resonance with a low effective mass and a very high quality factor. We have coated a 60-μm diameter low-loss dielectric mirror on top of the pillar and are planning to use this micromirror as part of a high-finesse Fabry-Perot cavity to laser cool the resonator down to its quantum ground state and to monitor its quantum position fluctuations by quantum-limited optical interferometry.

Free-space cavity optomechanics in a cryogenic environment

We present a free-space optomechanical system operating in the 1-K range. The device is made of a high mechanical quality factor micropillar with a high-reflectivity optical coating atop, combined with an ultra-small radius-of-curvature coupling mirror to form a high-finesse Fabry-Perot cavity embedded in a dilution refrigerator. The cavity environment as well as the cryostat have been designed to ensure low vibrations and to preserve micron-level alignment from room temperature down to 100 mK.

A micromechanical resonator to reach the quantum regime

We present a new micromechanical resonator designed for the observation of its quantum ground state (QGS). To reach QGS, a high frequency resonator with the lowest possible mass and the highest possible quality factor, coupled with an extremely sensitive measurement technique, has to be implemented. Using a high-finesse Fabry-Perot cavity with a mirror coated on the resonator, we expect benefits from the unique sensitivity of optical interferometry (10−38 m2/Hz) and from the optomechanical coupling between the light and the micro-resonator both to laser cool the resonator down to its ground state and to observe its residual quantum position fluctuations. We present the resonator we have developed for that purpose, which takes advantage from the high intrinsic quality factor of single crystal quartz and is designed to obtain a high resonance frequency (a few MHz) as well as a low mass (a few tens of µg). A length extension mode is used in order to avoid any deformation of the mirror surface and so to preserve the intrinsic quality factor of the resonator. A dedicated crystallographic orientation and a beam equilateral cross-section have been defined with respect to the quartz trigonal symmetry, allowing the micromachining of the resonator by wet etching. A beam cross-section area of 10−2 mm2 has been chosen to ease the deposit of the multilayered mirror. First mechanical characterizations of the resonator give a resonance frequency of 3.6 MHz, with a 25 µg mass and a quality factor of 390 000. Next steps will be the coating of the low-loss mirror on the resonator and its implementation in the Fabry-Perot cavity.

Cavity optomechanics with a nonlinear photonic-crystal nanomembrane

We have designed, fabricated and characterized a nanomembrane which could be used as a moving end mirror of a Fabry-Perot cavity. The high reflectivity and optimized mechanical properties of the membrane should allow us to demonstrate the mechanical ground state of the membrane. As any sub-micron mechanical resonator, our system demonstrates nonlinear dynamical effects. We characterize the mechanical response to a strong pump drive and observe a shift in the oscillation frequency and phase conjugation of the mechanical mode. Such nonlinear effects are expected to play a role in the quantum dynamics of the membrane as well.

Cavity optomechanics with micromirrors

We present a new generation of high Q (2 million) high-frequency (4 MHz) optomechanical resonators, designed for optical cooling and dilution fridge operation at 100 mK using a small-waist Fabry-Perot cavity.

Experimental Optomechanics with Single and Twin Moving Mirrors

We present experiments where the motion of micro-mirrors is optically monitored with a quantum-limited sensitivity. Direct effects of radiation pressure on single and twin-mirror cavities are experimentally demonstrated. Applications to quantum optics are discussed.