This report estimates the potential for secondary emission processes induced by ionizing radiation to result in the generation of quasiparticles in superconducting circuits. These estimates are based on evaluation of data collected from a small superconducting detector and a fluorescence measurement of typical read-out circuit board materials. Specifically, we study cosmic ray muons interacting with substrate or mechanical support materials present within the vicinity of superconducting circuits. We evaluate the potential for secondary emission, such as scintillation and/or fluorescence, from these nearby materials to occur at sufficient energy (wavelength) and rate (photon flux) to ultimately lead to the breaking of superconducting Copper pairs (i.e., production of quasiparticles). This evaluation leads to a conclusion that material fluorescence in the vicinity of superconducting circuits is a potential contributor to undesirable elevated quasiparticle populations. A co-design approach evaluating superconducting circuit design and the material environment within the immediate vicinity of the circuit would prove beneficial for mitigating undesired environmentally-induced influences on superconducting device performance, such as in direct detection dark matter sensors or quantum computing bits (qubits).
This report estimates the potential for secondary emission processes induced by ionizing radiation to result in the generation of quasiparticles in superconducting circuits. These estimates are based on evaluation of data collected from a small superconducting detector and a fluorescence measurement of typical read-out circuit board materials. Specifically, we study cosmic ray muons interacting with substrate or mechanical support materials present within the vicinity of superconducting circuits. We evaluate the potential for secondary emission, such as scintillation and/or fluorescence, from these nearby materials to occur at sufficient energy (wavelength) and rate (photon flux) to ultimately lead to the breaking of superconducting Copper pairs (i.e., production of quasiparticles). This evaluation leads to a conclusion that material fluorescence in the vicinity of superconducting circuits is a potential contributor to undesirable elevated quasiparticle populations. A co-design approach evaluating superconducting circuit design and the material environment within the immediate vicinity of the circuit would prove beneficial for mitigating undesired environmentally-induced influences on superconducting device performance, such as in direct detection dark matter sensors or quantum computing bits (qubits).
Abstract Ionizing radiation has been shown to reduce the performance of superconducting quantum circuits. In this report, we evaluate the expected contributions of different sources of ambient radioactivity for typical superconducting qubit experiment platforms. Our assessment of radioactivity inside a typical cryostat highlights the importance of selecting appropriate materials for the experiment components nearest to qubit devices, such as packaging and electrical interconnects. We present a shallow underground facility (30-meter water equivalent) to reduce the flux of cosmic rays and a lead shielded cryostat to abate the naturally occurring radiogenic gamma-ray flux in the laboratory environment. We predict that superconducting qubit devices operated in this facility could experience a reduced rate of correlated multi-qubit errors by a factor of approximately 20 relative to the rate in a typical above-ground, unshielded facility. Finally, we outline overall design improvements that would be required to further reduce the residual ionizing radiation rate, down to the limit of current generation direct detection dark matter experiments.
Ionizing radiation in the form of α, β, γ, and additional high-energy particles can induce decoherence via phonon and quasiparticle poisoning in superconducting qubits. Recent studies have explored this effect using cosmic rays or controlled radioactive sources held in the proximity of a qubit package, and have concluded that reductions in such ``external'' environmental radiation may benefit stable operation of qubit devices. However, the effect of long-lived, unstable daughters of 222Rn that ``plate out'' directly on device and packaging surfaces has not been as extensively explored. This plate-out process, well-known to the dark matter direct detection field, occurs throughout the fabrication and testing lifecycle of a device and (separately) its packaging, and produces a local source of α-decays which can remain active for decades. As this scales with chip area, understanding and managing this source of ionizing radiation is relevant for successfully scaling quantum computing architectures to larger numbers of qubits in a radiation-robust way. We present a setup capable of accelerating and enhancing radon daughter plateout by a factor of 7×104 over ambient, in order to study, \textit{in situ}, the impact of these events on superconducting qubits. We also provide outlook on the potential impact of this source of ionizing radiation on current and future qubit arrays.
When a high-energy particle, such as a γ ray or muon, impacts the substrate of a superconducting qubit chip, large numbers of electron-hole pairs and phonons are created. The ensuing dynamics of the electrons and holes changes the local offset-charge environment for qubits near the impact site. The phonons that are produced have energy above the superconducting gap in the films that compose the qubits, leading to quasiparticle excitations above the superconducting ground state when the phonons impinge on the qubit electrodes. An elevated density of quasiparticles degrades qubit coherence, leading to errors in qubit arrays. Because these pair-breaking phonons spread throughout much of the chip, the errors can be correlated across a large portion of the array, posing a significant challenge for quantum error correction. In order to study the dynamics of γ -ray impacts on superconducting qubit arrays, we use a γ -ray source outside the dilution refrigerator to controllably irradiate our devices. By using charge-sensitive transmon qubits, we can measure both the offset-charge shifts and quasiparticle poisoning due to the γ irradiation at different doses. We study correlations between offset-charge shifts and quasiparticle poisoning for different qubits in the array and compare these with numerical modeling of charge and phonon dynamics following a γ -ray impact. We thus characterize the poisoning footprint of these impacts and quantify the performance of structures for mitigating phonon-mediated quasiparticle poisoning.
Correlated errors may devastate quantum error corrections that are necessary for the realization of fault-tolerant quantum computation. Recent experiments with superconducting qubits indicate that they can arise from quasiparticle (QP) bursts induced by cosmic-ray muons and γ-rays. Here, we use charge-parity jump and bit flip for monitoring QP bursts and two muon detectors in the dilution refrigerator for detecting muon events. We directly observe QP bursts leading to correlated errors that are induced solely by muons and separate the contributions of muons and γ-rays. We further investigate the dynamical process of QP burst and the impact of QP trapping on correlated errors and particle detection. The proposed method, which monitors multiqubit simultaneous charge-parity jumps, has high sensitivity to QP bursts and may find applications for the detection of cosmic-ray particles, low-mass dark matter, and far-infrared photons. The correlated errors in superconducting qubits have been linked to high-energy particle impacts from cosmic rays, but a direct observation has been lacking. Here, the authors measure the quasiparticle bursts and correlated errors and separate the contributions of cosmic-ray muons and γ-rays in a 63-qubit processor.
Ionizing radiation is a known source of correlated errors in superconducting quantum processors, inhibiting the functionality of quantum error correction surface codes. High-energy photons and charged particles deposit pair-breaking energy into these systems leading to excess quasiparticles near Josephson junctions that increase qubit decoherence. Previous investigations of this problem have relied on ambient, stochastic sources of ionizing radiation or alternative methods of quasiparticle generation. Here, we present a facility that couples an electron linear accelerator (linac) to a dilution refrigerator to study ionizing radiation in quantum systems. A single linac electron closely mimics the energy deposition characteristics of a typical cosmic-ray muon, and we demonstrate the facility's usefulness with a multi-qubit superconducting transmon chip. Characteristic radiation-induced relaxation errors are quickly and easily collected with the speed and timing information of the linac. Additionally, we present qubit excitation and detuning errors that can be difficult to detect without the on-demand source of ionizing radiation. These error signatures are shown to be dependent on the junction placement and surrounding superconducting gaps.
Radiation effects in electronic systems have been extensively studied within the context of classical micro- and nano-electronics, enabling reliable operation in space, nuclear, and other harsh environments through well-established concepts such as total ionizing dose, displacement damage, and single-event effects. Superconducting quantum technologies, however, operate in a fundamentally different regime, relying on macroscopic quantum coherence at millikelvin temperatures and energy scales many orders of magnitude smaller than those associated with ionizing radiation. Recent experiments have revealed that even rare radiation events, originating from cosmic rays or natural radioactivity, can generate quasiparticle bursts and non-equilibrium phonons, leading to decoherence and spatially correlated errors across multiple qubits. These phenomena challenge classical notions of radiation hardness and locality that underpin conventional mitigation strategies. This perspective bridges decades of radiation-effects knowledge from classical electronics with emerging insights from superconducting quantum devices, circuits, and qubits. The limitations of directly translating classical radiation-hardness concepts to quantum hardware and examining radiation interactions with superconducting materials and Josephson junctions are highlighted, and the distinct implications for quantum computing vs quantum sensing are discussed. Finally, critical gaps in testing, modeling, and multiscale simulation methodologies are identified, outlining directions toward radiation-aware quantum engineering that integrate materials science, device physics, and system-level design to enable robust, deployable quantum technologies.