LIGO Document P1300170-v1

Toward Quantum Opto-Mechanics in a Gram-Scale Suspended Mirror Interferometer

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A new generation of interferometric gravitational wave detectors, currently under construction, will closely approach the fundamental quantum limits of measurement, serving as a prominent example of quantum mechanics at the macroscale. Simultaneously, numerous experiments involving micro-mechanical oscillators are beginning to explore the quantum regime, with the help of optical cooling techniques.

We discuss the approach to the quantum regime in a gram-scale opto-mechanical experiment, and in large-scale gravitational wave detectors. The gram-scale experiment is designed so that radiation pressure forces completely dominate the dynamics of the mechanical mirror suspensions. We review a series of optical trapping and cooling techniques that we have demonstrated using this apparatus. A variant of these techniques is applied to a gravitational wave interferometer -- yielding an effective temperature of 1.4 microkelvin and a phonon occupation number of 234 in a kilogram-scale oscillator. Then we analyze the displacement noise spectrum in the gram-scale system, which is currently limited by thermally driven fluctuations of the mirror suspensions. We identify methods for improving the suspension, in order to reveal the quantum fluctuations attributable to back-action of a displacement measurement. Finally, we propose a scheme for exploiting the opto-mechanical coupling in this system to generate optical entanglement.

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