Cavity cooling of a microlever

Abstract

The prospect of realizing entangled quantum states between macroscopic objects and photons¹ has recently stimulated interest in new laser-cooling schemes^2,3. For example, laser-cooling of the vibrational modes of a mirror can be achieved by subjecting it to a radiation² or photothermal⁴ pressure, actively controlled through a servo loop adjusted to oppose its brownian thermal motion within a preset frequency window. In contrast, atoms can be laser-cooled passively without such active feedback, because their random motion is intrinsically damped through their interaction with radiation^5,6,7,8. Here we report direct experimental evidence for passive (or intrinsic) optical cooling of a micromechanical resonator. We exploit cavity-induced photothermal pressure to quench the brownian vibrational fluctuations of a gold-coated silicon microlever from room temperature down to an effective temperature of 18 K. Extending this method to optical-cavity-induced radiation pressure might enable the quantum limit to be attained, opening the way for experimental investigations of macroscopic quantum superposition states¹ involving numbers of atoms of the order of 10¹⁴.