Resolving the positions of defects in superconducting quantum bits

TL;DR

This paper introduces a technique to locate defects in superconducting qubits by tuning defect resonance frequencies with electric fields, aiding in improving material quality and coherence in quantum devices.

Contribution

A novel method to determine the spatial location of defects in superconducting qubits using electric field tuning and simulation comparison, applicable to existing samples.

Findings

Able to identify defect locations relative to the qubit edge.

Applicable to various qubit types without additional design modifications.

Provides insights for material and fabrication improvements.

Abstract

Solid-state quantum coherent devices are quickly progressing. Superconducting circuits, for instance, have already been used to demonstrate prototype quantum processors comprising a few tens of quantum bits. This development also revealed that a major part of decoherence and energy loss in such devices originates from a bath of parasitic material defects. However, neither the microscopic structure of defects nor the mechanisms by which they emerge during sample fabrication are understood. Here, we present a technique to obtain information on locations of defects relative to the thin film edge of the qubit circuit. Resonance frequencies of defects are tuned by exposing the qubit sample to electric fields generated by electrodes surrounding the chip. By determining the defect's coupling strength to each electrode and comparing it to a simulation of the field distribution, we obtain the probability at which location and at which interface the defect resides. This method is applicable to already existing samples of various qubit types, without further on-chip design changes. It provides a valuable tool for improving the material quality and nano-fabrication procedures towards more coherent quantum circuits.