Speaker
Description
Environmental radioactivity has been increasingly recognized as a limiting factor in the performance of superconducting quantum devices. Trace-level contamination in materials comprising dilution refrigerators and qubit packaging can produce ionizing radiation that generates quasiparticles, contributing to correlated error bursts and decoherence. Understanding and mitigating these effects requires both a thorough characterization of the radioactive content of common cryogenic materials, finding lower radioactivity alternatives, and controlled methods for studying the response of quantum devices to specific forms of radiation.
We present results from a systematic radioassay campaign leveraging Pacific Northwest National Laboratory's extensive ultralow-background measurement capability. A broad survey of materials commonly found in dilution refrigerators and superconducting qubit assemblies was conducted using inductively coupled plasma mass spectrometry (ICP-MS) or high-purity germanium gamma-ray spectroscopy. Drawing on decades of experience in radiopure materials selection for rare-event physics, we triaged the material inventory to prioritize components of highest radiological concern, which we will discuss in this work.
In parallel, we discuss the design and development of well-characterized alpha-emitting calibration sources suitable for deployment inside dilution refrigerators. These sources enable controlled exposure of superconducting devices to alpha-radiation, allowing the systematic study of upset events and the disentanglement of contributions from alpha particles versus from sources of beta radiation and gamma rays to qubit error rates. Together, these efforts support the broader community goal of understanding and mitigating radiation-induced decoherence in next-generation quantum processors.
