• Fermilab
• Quantum Computing
• Quantum Transduction
• Mechanical Design
• Variable Coupler

This thesis work is the result of activities carried out at Università di Pisa and the
traineeship at the Superconducting Radio-Frequency (SRF) department of Fermilab,
America’s premier laboratory for particle physics and accelerator research.
The superconducting qubits that are used in a quantum computer operate at millikelvin
temperature in a dilution refrigerator, and they have their quantum states
encoded in microwave photons, transfering that microwave quantum information
out of the refrigerator to a different quantum system would swamp the signal with
thermal noise when emerging to room temperature. A solution is to use a quantum
transducer that can convert the quantum signals from microwave to optical, and
send quantum information through fiber optics cables.
There are a few different approaches to quantum transduction, but the Superconducting
Quantum Materials and Systems Center (SQMS) is focusing on an electrooptic
quantum transducer for microwave-to-optical frequency conversion using a
lithium niobate WGM resonator and a diamond coupling prism.
Since the resonator system’s coupling strength is tunable by changing the distance
between the diamond prism and the resonator, this work has the purpose of developing
a mechanical design for a variable optical coupler which works in a dilution
refrigerator at 10 milli-kelvin.
This device will allow a micro-positioning of the prism with respect to the resonator,
to achieve the maximum optical coupling between the two.
In order to do that, the paper proposes:
• An experimental validation of the optical model to understand how many degrees
of freedom will be needed to the prism with a test bench at room temperature.
• The design of the mechanical device, needed to perform the micro-positioning
in operation with analysis using finite element software.
• Thermal analysis of the superconducting radio-frequency (SRF) cavity.
At the end of the analysis, the thesis illustrates the results of the research and work
activity, highlighting the performances of this new mechanical device which is a
big step in realizing a transducer that can be exploited for high-fidelity heralded
quantum entanglement generation between two distant quantum processing units,
as well as for high-precision microwave signal measurement and quantum sensing.