Abstract
Precise optical control of microscopic particles has been mastered over the past three decades, with atoms, molecules and nano-particles now routinely trapped and cooled with extraordinary precision, enabling rapid progress in the study of quantum phenomena. Achieving the same level of control over macroscopic objects is expected to bring further advances in precision measurement, quantum information processing and fundamental tests of quantum mechanics. However, cavity optomechanical systems dominated by radiation pressure – so-called ‘optical springs’ – are inherently unstable due to the delayed dynamical response of the cavity. Here we demonstrate a fully stable, single-beam optical trap for a gram-scale mechanical oscillator. The interaction of radiation pressure with thermo-optic feedback generates damping that exceeds the mechanical loss by four orders of magnitude. The stability of the resultant spring is robust to changes in laser power and detuning, and allows purely passive self-locking of the cavity. Our results open up a new way of trapping and cooling macroscopic objects for optomechanical experiments.
Highlights
Optical springs have been proposed as a solution to the problem of mechanical coupling which impedes the operation of macroscopic objects in the quantum regime[1,2]
Cooling is achieved by rotating the optical spring quadrature using thermo-optic feedback, giving rise to a damping force several orders of magnitude stronger than the mechanical damping of the oscillator. This quadrature rotation produces a characteristic nonlinear dependence of damping on the cavity input power. We note that this effect is fundamentally different to the “photothermal pressure” observed in micro-mechanical oscillators[3,24,25,26], in which thermal expansion applies a force to the oscillator which may partially cancel radiation pressure
The mechanical oscillator comprises a high reflectivity 1/4′′ dielectric mirror glued to a silicon flexure with a 100 μm membrane
Summary
Optical springs have been proposed as a solution to the problem of mechanical coupling which impedes the operation of macroscopic objects in the quantum regime[1,2]. In addition to requiring two incident light fields, such methods work only at carefully chosen laser power and detuning, making them unsuitable for experiments in which these are critical tuning parameters Both thermoelastic and thermorefractive effects (known collectively as thermo-optic effects) can modify the dynamic behavior of an optomechanical system[19,20,21,22]. Cooling is achieved by rotating the optical spring quadrature using thermo-optic feedback, giving rise to a damping force several orders of magnitude stronger than the mechanical damping of the oscillator This quadrature rotation produces a characteristic nonlinear dependence of damping on the cavity input power. Our work illustrates how even a small amount of absorption, an unavoidable and generally considered detrimental effect in high-quality optics, can be exploited to stabilize an optomechanical cavity, and opens up a new way of trapping and cooling macroscopic objects using purely optical forces
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