Surface science motivated by heating of trapped ions from the quantum ground state

TL;DR

This study investigates how surface contamination and treatments affect electric-field noise and ion heating in trapped ion quantum devices, revealing nonmonotonic behavior linked to surface properties.

Contribution

It provides a detailed surface analysis correlating ion heating rates with surface work functions and contamination, offering insights into the anomalous heating phenomenon.

Findings

Surface contamination influences ion heating rates.

Ion bombardment modifies surface work functions.

Nonmonotonic heating behavior relates to surface properties.

Abstract

For the past two and a half decades, anomalous heating of trapped ions from nearby electrode surfaces has continued to demonstrate unexpected results. Caused by electric-field noise, this heating of the ions' motional modes remains an obstacle for scalable quantum computation with trapped ions. One of the anomalous features of this electric-field noise is the reported nonmonotonic behavior in the heating rate when a trap is incrementally cleaned by ion bombardment. Motivated by this result, the present work reports on a surface analysis of a sample ion-trap electrode treated similarly with incremental doses of Ar$^+$ ion bombardment. Kelvin probe force microscopy and x-ray photoelectron spectroscopy were used to investigate how the work functions on the electrode surface vary depending on the residual contaminant coverage between each treatment. It is shown that the as-fabricated Au electrode is covered with a hydrocarbon film that is modified after the first treatment, resulting in work functions and core-level binding energies that resemble that of atomic-like carbon on Au. Changes in the spatial distribution of work functions with each treatment, combined with a suggested phenomenological coverage and surface-potential roughness dependence to the heating, appear to be related to the nonmonotonic behavior previously reported.