John Teufel: Micromechanical Motion in the Quantum Regime

Abstract

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 opto- and electro-mechanics, 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 the circuit is excited with a coherent microwave tone near the cavity resonance, the displacement of the oscillator 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 to either cool or amplify the motion. The unprecedented electromechanical 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 at a temperature below 40 mK, this system also operates in the quantum-enabled regime where the thermal decoherence rate is small enough to permit sideband cooling of the mechanical mode to the ground state. The final part of this talk will quantify the thermal motion of the oscillator as it is cooled with microwave radiation-pressure forces into the quantum regime.