Microwave optomechanics in the strong coupling regime

In the longstanding endeavor to access the quantum nature of macroscopic mechanical motion, the experimental challenge is not only that of state preparation, but also one of measurement. The flourishing field of cavity optomechanics, in which an electromagnetic resonance couples parametrically to a mechanical oscillator, addresses both of these challenges-providing a nearly ideal architecture for both manipulation and detection of mechanical motion at the quantum level. In this talk, I present experiments in which the motion of a high-Q, micromechanical membrane couples to a superconducting microwave resonator. When this `cavity´ is excited with coherent microwave photons near its resonance, the displacement of the membrane becomes encoded as modulation of this tone. The microwaves, in turn, also impart forces back on the oscillator, which enforce the Heisenberg limits on measurement and can also be exploited either to cool or amplify the motion. The unprecedented optomechanical coupling strength allows the driven system to enter the strong-coupling regime, where the normal modes are now hybrids of the original radio-frequency mechanical and the microwave electrical resonances. This normal-mode splitting is verified by direct spectroscopy of the `dressed states´ of the hybridized cavity resonance, showing excellent agreement with theoretical predictions. As all of these experiments take place in at a temperature below 40 mK, this system operates in the quantum-enabled regime where the thermal decoherence rate is small enough to allow sideband cooling of the mechanical mode to the ground state. By measuring the noise spectrum of this mechanical system with an efficient, nearly shot-noise limited microwave detection, the residual thermal motion of the membrane is easily resolvable above the measurement imprecision. The final part of this talk will quantify the thermal motion occupancy of the mechanical mode as it is cooled with radiation-pressure forces to below its- - quantum zero-point motion and enters the strong coupling regime.