Probing individual tunneling fluctuators with coherently controlled tunneling systems

TL;DR

This paper investigates individual atomic tunneling fluctuators in aluminium oxide Josephson junctions by using superconducting qubits to detect and analyze their spectral switching behavior over a wide range of timescales.

Contribution

It introduces a method to probe single tunneling fluctuators with high sensitivity, extending measurable switching times from minutes to milliseconds.

Findings

Detection of telegraphic switching of tunneling systems

Extension of measurable switching times to milliseconds

Observation of interactions between fluctuators and coherent tunneling systems

Abstract

Josephson junctions made from aluminium and its oxide are the most commonly used functional elements for superconducting circuits and qubits. It is generally known that the disordered thin-film AlOx contains atomic tunneling systems. Coherent tunneling systems may couple strongly to a qubit via their electric dipole moment, giving rise to spectral level repulsion. In addition, slowly fluctuating tunneling systems are observable when they are located close to coherent ones and distort their potentials. This interaction causes telegraphic switching of the coherent tunneling systems' energy splitting. Here, we measure such switching induced by individual fluctuators on time scales from hours to minutes using a superconducting qubit as a detector. Moreover, we extend the range of measurable switching times to millisecond scales by employing a highly sensitive single-photon qubit swap spectroscopy and statistical analysis of the measured qubit states.