Fast Feedback Control of Mechanical Motion Using Circuit Optomechanics

Measurement-based control, using an active-feedback loop, is a standard tool in technology. Feedback control is also emerging as a useful and fundamental tool in quantum technology and in related fundamental studies, where it can be used to prepare and stabilize pure quantum states in various quantum systems. Feedback cooling of center-of-mass micromechanical oscillators, which typically exhibit high thermal noise far above the quantum regime, has been particularly actively studied and has recently been shown to allow ground-state cooling by means of optical measurements. Here we realize measurement-based feedback operations in an electromechanical system, cooling the mechanical thermal noise down to three quanta, limited by added amplifier noise. We also obtain significant cooling when the system is pumped at the blue optomechanical sideband, where the system is unstable without feedback.