Optomechanics

Mechanical technologies are everywhere in society, from oscillators in timekeeping devices to accelerometers and electronic filters in automobiles and cell phones. They also represent an indispensable set of tools for science: using tiny mechanical systems, it is possible to “feel around” surfaces at the atomic scale, detect chemical mass changes with single-proton resolution, and sense the gentle magnetic “tugs” from individual electron spins, persistent currents in a normal-metal ring, or even element-specific nanoscale clusters of nuclei (creating a 3D map!). Meanwhile, human-scale masses (positioned kilometres apart) currently “listen” to the passing waves of spacetime distortion emitted by violent high-gravity events across the universeIn the field of optomechanics, we have learned to exploit the forces exerted by light to gain an unprecedented level of control over these systems at all size scales, leading to a host of new functionalities for next-generation sensing applications, including experiments in which the laws of quantum mechanics play a central role.

Our research aims to create extremely sensitive micromechanical elements that are actuated in unique ways by light. In addition to creating new types of reconfigurable sensing technologies, these complementary efforts will enable fundamental studies of quantum motion at the macro scale, mechanical transduction of quantum information between a variety of “quantum bit” (“qubit”) technologies and light, and even the detection of zeptonewton forces.

Trampoline optomechanical systems: We fabricate delicate “micro-trampolines” that are among the lowest-noise mechanical sensors in the world and compatible with the world’s most sensitive optical cavities. This combination of properties corresponds to a regime in which the force exerted by an average of one photon — the smallest quantity of light allowed by nature — in our apparatus will profoundly influence their mechanical trajectories. This mechanical recoil will in-turn affect the light, enabling (among other things) a sensitive platform for creating quantum “squeezed” states of light that will be useful for enhancing the sensitivity of interferometers such as those used to measure gravitational waves to values below the standard quantum limit.

Optical levitation: Under carefully engineered conditions, light can exert a strong restoring force (a.k.a. an “optical spring”) to these and related mechanical systems. In so doing, the “traditional” flexible material supports are assisted / replaced with light (a low-noise alternative to matter), which can even further improve the sensitivity of these systems.

Toward strong control over mechanical geometry: Many major advances in the field rely on our ability to strongly control a mechanical element’s frequency and damping parameter, often by many orders of magnitude. To date, no comparably strong control over the remaining fundamental mechanical properties — shape and mass — has been demonstrated. To gain this control, we build toward a system in which light perturbs a so-called “phononic crystal” structure, enabling us to smoothly tune the spatial extent of a mechanical oscillation from the centimeter scale to the micron scale on chip, opening a significant new branch of possibilities to the field. Interestingly, due to a collective enhancement effect, a larger device is predicted to exhibit a larger response to a given level of light (in spite of its larger mass!), enabling a macroscopic response to single-photon light levels in a millimeter-scale device.