Quantum optomechanics with a stable Fabry-Perot cavity in a microwave-to-optical transducer

Continued development of complementary capabilities in two quantum technologies—informa-

tion processing with microwave-frequency superconducting circuits and networks based on optical-

frequency photonic links—have motivated an effort to bridge the frequency gap between them with

a transducer capable of preserving quantum signals. At the same time, mechanical resonators

have been engineered to interact with electromagnetic waves across the spectrum in a variety of

tailorable physical implementations. This thesis describes advances in a transducer using the me-

chanical mode of a silicon nitride membrane as an intermediary permitting coupling between a

superconducting resonant LC circuit and a Fabry-P´erot optical cavity. With this choice of archi-

tecture, we have developed transducers of unparalleled efficiency and the unique capability to run

continuously without appreciably degrading the performance of the superconductor from scattered

optical photons. We have been able to laser-cool the mechanical mode to an occupation of less than

one photon, and achieved transducer performance capable of converting a single microwave photon

to optical frequencies with a signal-to-noise ratio of 1/3. Furthermore, operating the transducer

does not cause appreciable heating of a superconducting transmon qubit linked to its microwave

input port. With progress towards a quantum-enabled interface, we have started to develop ca-

pabilities towards implementing protocols that optically verify the quantum performance of the

transducer.