Quantum mechanics is a profoundly successful theory; enabling both the description of microscopic phenomena with exquisite precision, and important new physical technologies. However, the observation and manipulation of quantum properties of macroscopic systems is notoriously difficult. Recently, due to the development of new nanofabrication techniques and a series of ground-breaking experiments it has become apparent that this regime may be realisable in cavity opto-mechanical systems where a complex dynamical interaction is achieved between optical and mechanical degrees of freedom via radiation pressure.
The central initial goal of this new field is cooling of a macroscopic mechanical degree-of-freedom to its quantum ground state. In this colloquium I will present experiments towards this goal with integrated microresonators. In particular, I will report the first implementation of a cavity optoelectromechanical system; integrating electrical actuation capabilities of nanoelectromechanical devices with ultrasensitive mechanical transduction achieved via intracavity optomechanical coupling. The integration of electrical actuation into opto-mechanical devices is an enabling step towards the regime of quantum nonlinear dynamics, and provides new capabilities for quantum control of mechanical motion. In our system we observe electrical gradient forces as large as 0.40 microN, larger than any other cryogenically compatible optomechanical system; with simultaneous mechanical transduction sensitivity below 10-18 m/rtHz, representing a 3 orders of magnitude improvement over any nanoelectromechanical system to date. Using this system we have achieved active cooling of an integrated cavity opto-mechanical system for the first time, with final temperature limited to 25 K by optical shotnoise. The use of whispering gallery optical resonances allows convenient motion transduction with multiple independent probe fields at different wavelengths. This enables the first direct comparison between temperature inferences made via in-loop and out-of-loop transduced signals. Stark differences are observed, with serious over-estimation of cooling possible in the standard in-loop inference. Finally, we will discuss the route to ground-state cooling in this system.