Quantum theory of feedback cooling of an anelastic macromechanical oscillator

Abstract

Conventional techniques for laser cooling, by coherent scattering off of internal states or through an optical cavity mode, have so far proved inefficient on mechanical oscillators heavier than a few nanograms. That is because larger oscillators vibrate at frequencies much too small compared to the scattering rates achievable by their coupling to auxiliary modes. Decoherence mechanisms typically observed in heavy low-frequency elastically suspended oscillators also differ markedly from what is assumed in conventional treatments of laser cooling. We show that for a low-frequency anelastic oscillator forming the mechanically compliant end mirror of a cavity, detuned optical readout, together with measurement-based feedback to stiffen and dampen it, can harness ponderomotively generated quantum correlations to realize efficient cooling to the motional ground state. This will pave the way for experiments that call for milligram-scale mechanical oscillators prepared in pure motional states, for example, for tests of gravity's effect on massive quantum systems.