Cosmic rays and correlated errors in superconducting qubits

Short answer: Cosmic rays and natural radioactivity can break Cooper pairs in a superconducting chip, creating bursts of quasiparticles that disturb many qubits at once, which is a threat to error correction. A 2020 Nature paper presents evidence that ionizing radiation raises quasiparticle density and that shielding improves energy relaxation time. A 2021 Nature Physics paper tracks bursts across a large processor, and a 2025 Nature Communications paper links correlated errors directly to muons. These are experimental findings.

Why correlated errors matter

The 2025 abstract notes that correlated errors may devastate the quantum error correction needed for fault-tolerant computation. The 2021 abstract explains why: error correction depends on physical errors staying small and sufficiently uncorrelated as devices scale, so that logical error rates can be suppressed exponentially. It says cosmic rays and latent radioactivity violate these assumptions.

2020: ionizing radiation raises quasiparticle density

The Nature abstract says the coherence of superconducting qubits is affected by the breaking of Cooper pairs, which creates quasiparticles. The observed quasiparticle density is orders of magnitude above the equilibrium value predicted by Bardeen-Cooper-Schrieffer theory. Infrared photons were known to raise it, yet it stays higher than expected even in well-isolated systems. The authors provide evidence that ionizing radiation from environmental radioactive materials and cosmic rays contributes to the difference. They predict this would ultimately limit coherence times for qubits of the type measured to milliseconds. They also demonstrate that radiation shielding reduces the flux of ionizing radiation and thereby increases the energy-relaxation time. They call it a small effect for today's qubits but say mitigation will be critical for fault-tolerant superconducting quantum computers.

2021: bursts across a chip

The Nature Physics paper says an impinging particle can ionize the substrate and induce a burst of quasiparticles that destroys qubit coherence throughout the device. It notes that high-energy radiation had been identified as a source of error in pilot devices but that the effect on large-scale algorithms and error correction was an open question. The authors use space- and time-resolved measurements of a large-scale processor to identify bursts of quasiparticles produced by high-energy rays. They track events from their initial localized impact as they spread, simultaneously and severely limiting the energy coherence of all qubits and causing chip-wide failure. They conclude that mitigation is necessary for quantum computing to scale.

2025: separating muons from gamma rays

The Nature Communications paper monitors quasiparticle bursts using charge-parity jumps and bit flips, with two muon detectors in the dilution refrigerator to detect muon events. The authors say they directly observe quasiparticle bursts causing correlated errors induced solely by muons, and separate the contributions of muons and gamma rays. They also investigate the burst dynamics and the effect of quasiparticle trapping on correlated errors and particle detection. They suggest the method, which watches simultaneous charge-parity jumps on several qubits, might also detect cosmic-ray particles, low-mass dark matter and far-infrared photons. That is an outlook.

Limits

The 2020 authors describe the effect on today's qubits as small, while the 2021 authors describe chip-wide failures for individual burst events. These describe different measurements and conditions, so they are not in conflict. The mitigation claims are limited to shielding results in the 2020 paper.

FAQ

What is a quasiparticle burst?

A sudden group of broken Cooper pairs created when a particle ionizes the substrate.

Does shielding help?

The 2020 authors report that radiation shielding increases the energy-relaxation time.

Why is this a problem for error correction?

It produces correlated errors across many qubits, which violates the assumption of mostly independent errors.

Which particles cause it?

Cosmic-ray muons and gamma rays from environmental radioactivity, per the 2025 paper.

Are today's qubits badly affected?

The 2020 authors call the effect small for today's qubits and say it will matter at scale.