Multimode cavity setup for studying the thermalization of dielectric materials

Dielectric materials such as PTFE (Teflon), printed circuit boards (PCB), and Eccosorb, which are commonly used in solid state quantum computing experiments, are widely believed to thermalize poorly at millikelvin temperatures due to their small thermal conductivities. Consequently, these materials can remain warmer than the dilution refrigerator base temperature. This increases the thermal populations of coupled readout resonators, thereby limiting qubit coherence times through shot-noise dephasing. 

In this talk, we describe a multimode cavity (MMC) platform for measuring frequency-dependent dielectric constants, loss tangents, and temperatures of various target materials. We insert a dielectric sample into a multimode cavity, where its loss and temperature influence each mode’s decay and heating rates. We read out the individual mode populations by interfacing the MMC with a buffer cavity through a tunable SNAIL coupler. Photons swapped into the buffer using the SNAIL are detected with a coupled transmon whose coherence is protected from the sample’s elevated temperature. We will present preliminary measurements of the thermal properties of Teflon, indicating that its temperature remains 100 mK above the base temperature.