Device for quantum transduction: optimization and development

This thesis aims to improve the design of a quantum electro-optical transducer, which operates in a dilution refrigerator at milli-kelvin temperatures. The transducer is used for frequency conversion from microwaves to optical photons, employing a superconducting radiofrequency (SRF) cavity and a lithium niobate coupling prism. The coupling between system components is adjustable by varying the distance between the crystal and the tuner. The research focused on developing a more robust design, less sensitive to component tolerances, while ensuring better heat dissipation and precise crystal alignment within the cavity. The work was structured into the following steps: 1. Analysis of the previous version of the transducer design and identification of its limitations. 2. Development of a new design to address the identified issues. 3. Analysis of experimental results to identify potential limitations in the simulation models. Throughout the development process, various design solutions based on alternative operating principles were explored. The final choice was to proceed with a design that required minimal changes compared to the previous version, for cost and time considerations. The results show that, although the components in the new design are subjected to higher stresses, they remain below the yield limits. Additionally, the temperature distribution between components is more uniform and lower, allowing for higher pumping powers, thereby increasing conversion efficiency and improving the quality factor. The new design also ensures more precise crystal alignment within the cavity, a feature not guaranteed by the previous design. Electromagnetic simulations further demonstrated improvements in the device’s performance, particularly with a wider tuning range and greater operational flexibility. The increase in the participation ratio contributed to a better coupling between the optical and microwave modes, further enhancing conversion efficiency.