Readout failures in superconducting qubits due to TLS-defects in tunnel junctions

TL;DR

This paper investigates how material defects, specifically TLS in tunnel junctions, cause readout failures in superconducting qubits by resonantly coupling with the readout resonator, affecting qubit performance.

Contribution

It demonstrates the strong coupling between TLS defects and the readout resonator, revealing a new mechanism for readout failure in superconducting qubits.

Findings

TLS-resonator coupling causes resonance frequency shifts

Material defects interfere with qubit readout signals

TLS in tunnel barriers impact qubit operation

Abstract

Material defects give rise to parasitic two-level systems (TLS) which present a major source of decoherence in superconducting qubits. Here, we study a strongly coupled TLS that resides in the tunnel barrier of transmon qubit. We use multi-photon spectroscopy and TLS strain tuning to explore the rich spectrum of the interacting three-partite system consisting of TLS, qubit, and its readout resonator. This reveals a strong effective resonant coupling between the TLS and the qubit's readout resonator which dresses the resonator states and results in a resonance frequency shift that spoils the readout signal. Our finding presents yet another way how material defects can interfere with qubit operation and hinder the realization of solid-state quantum processors.