Anders Simonsen

A thesis for the degree of Doctor of Philosophy defended October 2019.

The PhD School of Science, Faculty of Science, Quantum Optics, Niels Bohr Institute, University of Copenhagen

Principal Supervisor:
Prof. Eugene Polzik

Sensitive electro-optical transduction Through resonant electro- and optomechanics

This thesis presents a scheme that transduce an electrical signal into and optical one, while simultaneously amplifying the signal. The transduction uses a coupling between an electrical and mechanical resonator, and experiments show that the coupling make the electrical signal dominate over thermal noise in the mechanical resonator, making the transduction scheme work as a low-noise preamplifier.

When operated at a Direct Current (DC) bias, the transduction reached an optical noise-temperature of 4K in a bandwidth of 3 kHz, and the noisetemperature projects to reach 90mK with better optical detection, a sensitivity that is competitive with conventional electronics. The initial transduction suffered from technical limitations, mostly from its assembly. These were addressed through a micro-fabrication process, a process that produced a new generation of transducers integrating both an electromechanical system and optical cavity on a single chip. The cavity interfaced directly with a fiber-network and greatly simplified the setup that is to operate the transducer. This technical innovation enabled an experiment where the transduction replaced a conventional electronic amplifier in a detection circuit for Magnetic Resonance Imaging (MRI), thus bringing the advantages of optical signal processing to the receiver chain of MRI scanners.