Oxide-nitride heteroepitaxy for low-loss dielectrics in superconducting quantum circuits

TL;DR

This study demonstrates the integration of crystalline oxide-nitride heterostructures with low microwave loss into superconducting quantum circuits, advancing materials for fault-tolerant quantum computing.

Contribution

It reports the first direct measurement of low-loss epitaxial $ ext{γ}$-Al$_2$O$_3$ dielectric in a heteroepitaxial TiN-based trilayer, confirming its potential for quantum devices.

Findings

Epitaxial $ ext{γ}$-Al$_2$O$_3$ exhibits low two-level system loss ($ ext{δ}_{ ext{TLS}}^0 imes 10^{-5}$)

High-resolution imaging confirms single-crystal quality and minimal defects

Heteroepitaxial oxides on transition metal nitrides are promising for 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. In this work, we integrate 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, we report the first direct measurement of the dielectric loss of epitaxial $\gamma$-Al$_2$O$_3$, for which we find a low intrinsic two-level system loss, $\delta_{\text{TLS}}^0 = (2.8 \pm 0.1) \times 10^{-5}$. 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.