Intrinsic Photon Loss at the Interface of Superconducting Devices

TL;DR

This paper develops a quantum theory explaining intrinsic photon loss at superconducting device interfaces due to piezoelectric effects, suggesting that defect-free interfaces could significantly improve qubit coherence times.

Contribution

It introduces a novel quantum model for dielectric energy loss at interfaces, highlighting the role of piezoelectric coupling even in perfect crystalline materials.

Findings

Intrinsic loss tangent can be explicitly calculated for various interfaces.

Defect-free interfaces could extend qubit $T_1$ times to around 10,000 microseconds.

Photon loss is primarily due to piezoelectric effects at interfaces, not defects.

Abstract

We present a quantum theory of dielectric energy loss arising from the piezoelectric coupling between photons and phonons in superconducting devices. Photon loss is shown to occur predominantly at the interface, where the piezoelectric effect is non-zero even when the materials are perfectly crystalline (epitaxial) and free of two-level system defects. We present explicit numerical calculations for the value of the intrinsic loss tangent at several interfaces to conclude that the $T_1$ of superconducting qubits may reach $10^{4}$ $\mu$s if the device is made with defect-free interfaces.