Laser Cooling of a Micromechanical Membrane to the Quantum Backaction Limit

TLDR

Radiation pressure can damp and cool a mechanical resonator, but shot noise imposes a quantum backaction limit on the minimum phonon occupation, analogous to the Doppler limit in atomic laser cooling. The study sideband cools a micromechanical membrane resonator to this quantum backaction limit. By monitoring optical sidebands, the authors directly observe the membrane reaching thermal equilibrium with the optical bath. This level of optomechanical coupling, surpassing intrinsic thermal decoherence, had not been achieved in prior ground‑state cooling experiments.

Abstract

The radiation pressure of light can act to damp and cool the vibrational motion of a mechanical resonator, but even if the light field has no thermal component, shot noise still sets a limit on the minimum phonon occupation. In optomechanical sideband cooling in a cavity, the finite off-resonant Stokes scattering defined by the cavity linewidth combined with shot noise fluctuations dictates a quantum backaction limit, analogous to the Doppler limit of atomic laser cooling. In our work, we sideband cool a micromechanical membrane resonator to the quantum backaction limit. Monitoring the optical sidebands allows us to directly observe the mechanical object come to thermal equilibrium with the optical bath. This level of optomechanical coupling that overwhelms the intrinsic thermal decoherence was not reached in previous ground-state cooling demonstrations.