CPM Seminar

Quantum measurement of motion using a microwave interferometer

Konrad Lehnert

JILA - University of Colorado & NIST

Can the zero-point motion of a macroscopic mechanical oscillator be observed? While quantum mechanics places limits on how well the position of any oscillator can be measured, reaching those limits for macroscopic mechanical motion is technically challenging. Overcoming those challenges will bring to acoustics the kind of quantum control and measurement associated with quantum optics. For low-energy degrees of freedom, such as nuclear spins in mesoscopic systems, quantum acoustics may provide the kind of interface that cavity quantum electrodynamics provides for atoms. In this talk, I will describe our progress in realizing these notions, where we detect the motion of a nanomechanical oscillator using a microwave interferometer. The apparent disadvantage of using lower energy microwave photons is more than overcome by working with low-mass, low-dissipation mechanical oscillators that have been cooled in a cryostat to temperatures below 100 mK. I will show that the apparent motion of the mechanical oscillator due the interferometers noise is now substantially less than its zero-point motion. Furthermore, I will demonstrate that microwave “light” can cool the mechanical oscillator towards its motional ground state. Finally, the mechanical oscillator and microwave interferometer form an extraordinarily sensitive force detector, with 0.5 aN/Hz^1/2 force sensitivity.