TLS loss in superconducting resonators on epitaxial hBN thin films

The integration of low-loss dielectrics into superconducting circuits is of importance to the functionality of quantum computers and sensors. In this work, we fabricate and measure niobium resonators atop few-layer, epitaxial hexagonal boron nitride (hBN) grown by Molecular Beam Epitaxy on a sapphire substrate and compare against a control counterpart without hBN. We conduct radiofrequency measurements which probe the responses to power, temperature, and temporal fluctuations of two-level systems. The resonators integrating hBN maintain low dielectric loss with a low-power internal loss tangent on the order of 10^-6, and demonstrate hBN can be added to the conventional superconducting qubit stack with minimal degradation of the quality factor. This research represents a first step towards a materials-driven strategy to eliminate phonon-mediated correlated errors in solid-state quantum systems, which leverages the thermal properties of 2D materials to prevent athermal phonons excited in the device substrate from transmitting across the superconductor-substrate interface. The same technique applied to quantum sensors would maximize phonon collection by blocking phonons from entering passive metal films.