Oxide-Nitride Heteroepitaxy for Low-Loss Dielectrics in Superconducting Quantum Circuits

Abstract

Superconducting qubits show great promise for the realization of fault-tolerant quantum computing, but lossy, amorphous dielectrics limit current technology. Identifying highly crystalline and stoichiometric dielectrics with intrinsically low microwave loss is therefore a central materials challenge, yet experimentally validated platforms remain scarce. This work integrates a crystalline dielectric into a heteroepitaxial TiN/$\gamma$-Al${}_2$O${}_3$/TiN trilayer grown via pulsed laser deposition. Correlative high-resolution imaging, diffraction, and spectroscopy measurements confirm the single-crystal quality and chemical integrity of all layers, with minimal defects and limited anion interdiffusion across the oxide-nitride interfaces. Using microwave lumped-element resonators with parallel-plate capacitors, this work establishes an experimentally-measured upper bound for the dielectric loss of $\gamma$-Al${}_2$O${}_3$, which has a low intrinsic two-level system loss of ${\delta }_{\text{TLS}}^0=(2.8\pm 0.1)\times 10^{-5}$. These results establish heteroepitaxial oxides on transition metal nitrides as an attractive materials platform for superconducting quantum circuits, particularly for integration into compact device architectures such as merged-element transmons and microwave kinetic inductance detectors.

arXiv commentThis document is the unedited Author's version of a Submitted Manuscript subsequently accepted for publication in ACS Nano, copyright (c) 2026 The Authors. Published By American Chemical Society. To access the final published article, see ACS Articles on Request. 37 pages, 6 figures, 1 table