In this thesis, I present recent studies of cavity optomechanical physics using superconducting circuits. Optomechanical systems, in which an electromagnetic resonator couples to the motion of a moving object, have long been used as sensors of force, displacement, and mass. In the last decade, however, the field has matured as researchers have successfully taken mechanical resonators to the quantum regime, enabling applications like quantum-enhanced sensing, quantum state storage, and quantum-limited amplification. Many of these possible applications rely on the concept of parametric coupling, where, by driving the electrical resonance with a strong pump, the amplitude, frequency, and phase of the coupling between the electrical and mechanical resonators can be tuned. This work delves into the theory of parametric coupling and presents two experimental studies that test its limits and applications in superconducting optomechanical circuits.
In one experiment, we explore a fundamental limit of parametric coupling using a new architecture for cavity optomechanics where a micron-scale microfabricated membrane couples to the electric field of a centimeter-scale, three-dimensional microwave cavity. This device reaches the new regime of ultrastrong parametric coupling, where the coupling rate rivals the mechanical resonance frequency itself, possibly enabling new applications in quantum measurement and control of the mechanical mode.
One recent application of parametric coupling is the generation of nonreciprocity to enact one-way flow of information through a quantum network. In the second experiment presented here, we demonstrate nonreciprocity using the parametric coupling in a superconducting optomechanical circuit. We design and fabricate a circuit where two lumped element microwave resonances couple to two vibrational modes of a microfabricated membrane. By tuning the four parametric couplings, we ensure that microwave signals are transferred from one resonance to the other, but not in reverse. Crucially, we maintain relatively high efficiency in the forward direction, a metric that continues to be a challenge in alternative nonreciprocal devices.
I conclude with a snapshot of our ongoing work using Josephson parametric amplifiers to enable high-efficiency optomechanical measurements. This work will enable a host of future research directions in quantum measurement and control of mechanical resonators.
|Advisor:||Teufel, John D|
|Commitee:||Teufel, John D, Simmonds, Raymond W, Lehnert, Konrad W, Thompson, James K, Lasser, Gregor|
|School:||University of Colorado at Boulder|
|School Location:||United States -- Colorado|
|Source:||DAI 81/11(E), Dissertation Abstracts International|
|Subjects:||Physics, Quantum physics, Electrical engineering|
|Keywords:||Cavity optomechanics, Micromechanical systems, Optomechanics, Superconducting circuits|
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