Andrew Jayich

Strong dispersive coupling of a high-finesse cavity to a micromechanical membrane.

Macroscopic mechanical objects and electromagnetic degrees of freedom can couple to each other through radiation pressure. Optomechanical systems in which this coupling is sufficiently strong are predicted to show quantum effects and are a topic of considerable interest. Devices in this regime would offer new types of control over the quantum state of both light and matter, and would provide a new arena in which to explore the boundary between quantum and classical physics. Experiments so far have achieved sufficient optomechanical coupling to laser-cool mechanical devices, but have not yet reached the quantum regime. The outstanding technical challenge in this field is integrating sensitive micromechanical elements (which must be small, light and flexible) into high-finesse cavities (which are typically rigid and massive) without compromising the mechanical or optical properties of either. A second, and more fundamental, challenge is to read out the mechanical element’s energy eigenstate. Displacement measurements (no matter how sensitive) cannot determine an oscillator’s energy eigenstate, and measurements coupling to quantities other than displacement have been difficult to realize in practice. Here we present an optomechanical system that has the potential to resolve both of these challenges. We demonstrate a cavity which is detuned by the motion of a 50-nm-thick dielectric membrane placed between two macroscopic, rigid, high-finesse mirrors. This approach segregates optical and mechanical functionality to physically distinct structures and avoids compromising either. It also allows for direct measurement of the square of the membrane’s displacement, and thus in principle the membrane’s energy eigenstate. We estimate that it should be practical to use this scheme to observe quantum jumps of a mechanical system, an important goal in the field of quantum measurement.

Strong and tunable nonlinear optomechanical coupling in a low-loss system

An optical cavity coupled to a micrometre-sized mechanical resonator offers the opportunity to see quantum effects in relatively large structures. It is now shown that a variety of coupling mechanisms enable investigation of these fascinating systems in a number of different ways.

High quality mechanical and optical properties of commercial silicon nitride membranes

We have measured the optical and mechanical loss of commercial silicon nitride membranes. We find that 50nm thick, 1mm2 membranes have mechanical Q>106 at 293K, and Q>107 at 300mK, well above what has been observed in devices with comparable dimensions. The near-IR optical loss at 293K is less than 2×10−4. This combination of properties make these membranes attractive candidates for studying quantum effects in optomechanical systems.

Fiber-cavity-based optomechanical device

We describe an optomechanical device consisting of a fiber-based optical cavity containing a silicon nitride membrane. In comparison with typical free-space cavities, the fiber-cavitys small mode size (10 μm waist, 80 μm length) allows the use of smaller, lighter membranes and increases the cavity-membrane linear coupling to 3 GHz/nm and the quadratic coupling to 20 GHz/nm2. This device is also intrinsically fiber-coupled and uses glass ferrules for passive alignment. These improvements will greatly simplify the use of optomechanical systems, particularly in cryogenic settings. At room temperature, we expect these devices to be able to detect the shot noise of radiation pressure.

Cryogenic optomechanics with a Si 3 N 4 membrane and classical laser noise

We demonstrate a cryogenic optomechanical system comprising a flexible Si3N4 membrane placed at the center of a free-space optical cavity in a 400 mK cryogenic environment. We observe a mechanical quality factor Q > 4 x 10^6 for the 261-kHz fundamental drum-head mode of the membrane, and a cavity resonance halfwidth of 60 kHz. The optomechanical system therefore operates in the resolved sideband limit. We monitor the membranes thermal motion using a heterodyne optical circuit capable of simultaneously measuring both of the mechanical sidebands, and find that the observed optical spring and damping quantitatively agree with theory. The mechanical sidebands exhibit a Fano lineshape, and to explain this we develop a theory describing heterodyne measurements in the presence of correlated classical laser noise. Finally, we discuss the use of a passive filter cavity to remove classical laser noise, and consider the future requirements for laser cooling this relatively large and low-frequency mechanical element to very near its quantum mechanical ground state.

Stable, mode-matched, medium-finesse optical cavity incorporating a microcantilever mirror: Optical characterization and laser cooling

A stable optical resonator has been built using a 30-microm-wide, metal-coated microcantilever as one mirror. The second mirror was a 12.7-mm-diameter concave dielectric mirror. By positioning the two mirrors 75 mm apart in a near-hemispherical configuration, a Fabry-Perot cavity with a finesse equal to 55 was achieved. The finesse was limited by the optical loss in the cantilevers metal coating; diffraction losses from the small mirror were negligible. The cavity achieved passive laser cooling of the cantilevers Brownian motion.

Optomechanics in a fiber cavity

We have built an optomechanical device consisting of a fiber-based optical cavity and a silicon nitride membrane with the goal of observing radiation pressure shot noise and generating squeezed light at room temperature.

Nonlinear Optomechanical Couplings: Tools for Dealing with Solid Mechanical Objects in the Quantum Regime

We demonstrate several different forms of the optomechanical coupling (linear, quadratic, and quartic) realized at avoided crossings in the spectrum of an optical cavity containing a flexible dielectric membrane. Each coupling is tunable in situ.

Linear optical properties of a high-finesse cavity dispersively coupled to a micromechanical membrane

We present measurements of an optomechanical system in which the mechanical element is inside the cavity, and couples dispersively to the intracavity field. This geometry makes it easier to simultaneously achieve high optical finesse and high mechanical quality factor in an optomechanical device. We measured the linear optical properties of a such a device in which the mechanical element is a 50 nm thick silicon nitride membrane. We find that the devices finesse, resonant transmission and resonant reflection can be explained with a simple model which allows us to extract the membranes optical loss. Our results indicate that it should be possible to increase the finesse of these devices to 5 × 105 or higher.

Laser cooling of a microcantilever using a medium finesse optical cavity

A 75 mm optical cavity was formed using a microcantilever for one mirror. A finesse of 55 was achieved, not limited by diffraction around the cantilever. The microcantilever was passively laser cooled from 300 K to 50 K.