Micromechanical resonators affected by radiation pressure forces allow to address fundamental questions on quantum properties of mechanical objects, or, to explore quantum limits in measurement and amplification.
A promising setup for the purpose is an on-chip microwave cavity coupled to a micromechanical resonator. I will provide a review of this new field of "circuit optomechanics", and then discuss our work on these ideas. We demonstrate the possibility of building a mechanical microwave amplifier, with noise properties approaching the quantum regime. Under blue sideband irradiation to the microwave cavity, pump photons will be down-converted, transferring energy into the mechanical resonator.
Addition of a probe signal will induce coherent stimulated emission, leading to its amplification up to 30 dB. In the opposite regime, by pumping the red sideband, we cooled the 30 MHz mechanical mode very close to the ground state of motion, to thermal occupancy of only 1.8 quanta. Finally, it is shown how one can couple mechanical resonators via the cavity bus, thus allowing studies with multiple mechanical degrees of freedom near the quantum limit.