Cavity Optomechanics: Coherent coupling of light to mechanical oscillators
The mutual coupling of optical and mechanical degrees of freedom via radiation pressure has been a subject of interest in the context of quantum limited displacements measurements for Gravity Wave Detection for many decades, however light forces have remained experimentally unexplored in such systems. Recent advances in nano- and micro-mechanical oscillators have for the first time allowed the observation of radiation pressure phenomena in an experimental setting and constitute the emerging research field of Cavity Optomechanics(1).
Using on-chip micro-cavities that combine both optical and mechanical degrees of freedom in one and the same device(2), radiation pressure back-action of photons is shown to lead to effective cooling(3-6) of the mechanical oscillator mode using dynamical backaction, which has been predicted by Braginsky as early as 1969(4). This back-action cooling exhibits many close analogies to atomic laser cooling. For instance, it is shown theoretically that only in the resolved sideband regime, cooling to the quantum ground state is possible. With this novel technique the quantum mechanical ground state of a micromechanical oscillator can be reached. Using cryogenic precooling(7) to ca. 800 mK the preparation of a micromechanical oscillator to only 1.7 quanta is shown, occupying the quantum ground state ca. 40% of the time. Moreover it is possible in this regime to observe quantum coherent coupling in which the mechanical and optical mode hybridize and the coupling rate exceeds the mechanical and optical decoherence rate (http://arxiv.org/abs/1107.3761). This accomplishment enables a range of quantum optical experiments, including state transfer from light to mechanics.
Optomechanical systems also offer entirely new means to control the light field. Using the recently discovered phenomenon of optomechanically induced transparency(10) it is possible to enable devices that store light in mechanical excitations, or create optical delay lines with unpredecented delay time. Recent highlights of the literature of some of the emerging applications of cavity optomechanics will be reviewed.
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