Toward the quantum ground state of a gram-scale object
We describe an experiment in which coupling between intense optical fields and mirror oscillators is used for generating squeezed states of light, and also for optically cooling a gram-scale mirror oscillator. An intense radiation field impinging on a movable mirror can be used to correlate the intensity and phase "quadratures" of the light, leading to squeezed state generation. The radiation field can also be used to optically trap the mirror, cooling it to low enough energies that quantum effects become observable. We report on an experiment with optical field-mechanical oscillator coupling that is aimed at generating squeezed vacuum states, and may also lead to observable mirror-light entanglement. Some key features of the experiment are: (i) High stored optical power (10 kW); (ii) Low-mass (1 gram) mirrors suspended as high quality factor (Q 106), low stiffness (mechanical resonance at a few Hz) pendulums; (iii) a differential measurement to cancel out classical laser noise; and most importantly, (iv) a strong optical spring to reduce the coupling of classical force noises to the mirror and also to give a flat response in the measurement band. The optical spring effect arises from a radiation pressure induced restoring force, generated in an optical cavity that is detuned from resonance. In addition to optically cooling the 1 gram mirror, the optical spring effect has the further advantage that it can increase the number of oscillations before decoherence by several orders of magnitude. We describe some experimental milestones achieved using this technique, which include: (i) Optical rigidity corresponding to a Young's modulus of 1.2 TPa (20% stiffer than diamond); (ii) Minimum temperatures in the millikelvin range; (iii) Increase in the dynamical lifetime of the state by two orders of magnitude; and (iv) Observation and control of parametric instabilities. We conclude with description of an experimental path, using existing technologies, that that should culminate in observation of low energy quantum states, thereby exposing quantum effects in gram-scale objects. © 2005 Optical Society of America.