Improving the lifetime of aluminum-based superconducting qubits through atomic layer etching and deposition

TL;DR

This paper introduces a combined atomic layer etching and deposition process to improve the lifetime and performance of aluminum-based superconducting qubits by reducing dielectric loss and TLS defect density.

Contribution

The study demonstrates a novel surface treatment process that significantly enhances qubit coherence times and device stability by reversing fabrication-induced surface damage.

Findings

Two-fold reduction in dielectric loss in treated resonators and qubits

Median qubit $Q$ of $3.69 imes 10^6$ and $T_1$ of 196 μs achieved

Improvements are durable over several months

Abstract

We present a dry surface treatment combining atomic layer etching and deposition (ALE and ALD) to mitigate dielectric loss in fully fabricated superconducting quantum devices formed from aluminum thin films on silicon. The treatment, performed as a final processing step prior to device packaging, starts by conformally removing the native metal oxide and fabrication residues from the exposed surfaces through ALE before \textit{in situ} encapsulating the metal surfaces with a thin dielectric layer using ALD. We measure a two-fold reduction in loss attributed to two-level system (TLS) absorption in treated aluminum-based resonators and planar transmon qubits. Treated transmons with compact capacitor plates and gaps achieve median $Q$ and $T_1$ values of $3.69 \pm 0.42 \times 10^6$ and $196 \pm 22$~$\mu$s, respectively. These improvements were found to be sustained over several months. We discuss how the combination of ALE and ALD reverses fabrication-induced surface damages to significantly and durably improve device performance via a reduction of the TLS defect density in the capacitive elements.