Short answer: High-energy particles can strike a superconducting chip and release a burst of quasiparticles that disturbs many qubits at once, which breaks the assumption of independent errors that error correction relies on. A 2021 Nature Physics paper tracked such bursts across a large processor, a 2025 Nature Communications paper tied some of them to cosmic-ray muons, and a 2024 Physical Review Letters paper reports that gap engineering protects transmons. All three are laboratory studies of specific chips.
The problem
The Nature Physics abstract states the premise: logical error rates can be suppressed exponentially only if physical errors stay small and sufficiently uncorrelated as devices scale. It adds that impacts from cosmic rays and latent radioactivity violate those assumptions, because a particle can ionize the substrate and induce a burst of quasiparticles that destroys qubit coherence throughout the device.
2021: watching a burst spread
The authors use space- and time-resolved measurements on a large-scale quantum processor to identify bursts of quasiparticles produced by high-energy rays. They track events from their localized impact as they spread, simultaneously and severely limiting the energy coherence of all qubits and causing chip-wide failure. They say this highlights the need for mitigation to let quantum computing scale. The abstract describes high-energy radiation as already identified as an error source in pilot devices, with the effect on large-scale algorithms an open question.
2024: gap engineering as a defence
The Physical Review Letters abstract (2024) explains the mechanism: after an impact, phonons above the superconducting gap spread through the substrate and raise the quasiparticle density across the array. When quasiparticles tunnel across Josephson junctions, they cause correlated errors. Engineering different superconducting gaps across the junction offers resistance to this tunneling.
The authors fabricate all-aluminum transmons with both strong and weak gap engineering on the same substrate. Strongly gap-engineered qubits show no degradation during impact events, while weakly engineered ones show events of correlated degradation. The strongly engineered qubits are also robust to quasiparticle poisoning from increasing optical illumination intensity, whereas weakly engineered ones degrade rapidly. The authors conclude that gap engineering mitigates the threat of high-energy impacts to error correction in superconducting arrays. The specific quantity measured did not render in the retrieved abstract, so this post does not name it.
2025: linking bursts to muons
The Nature Communications paper uses charge-parity jumps and bit flips to monitor quasiparticle bursts, along with two muon detectors in the dilution refrigerator. The authors report directly observing bursts leading to correlated errors that are induced solely by muons, and they separate the contributions of muons and gamma rays. They also study the dynamics of a burst and the impact of quasiparticle trapping. They suggest the method of monitoring simultaneous charge-parity jumps could find applications in detecting cosmic-ray particles, low-mass dark matter and far-infrared photons, which is an outlook.
Limits
These are different chips, setups and shielding conditions. The gap engineering paper tests all-aluminum transmons and the abstract does not claim a full error-correction demonstration. No abstract here says the problem is solved.
FAQ
What is a quasiparticle burst?
A temporary surge of quasiparticles in a superconducting chip, which can reduce coherence of many qubits at once.
Why do correlated errors matter?
Error correction assumes errors are sufficiently uncorrelated, per the 2021 authors.
What is gap engineering?
Using different superconducting gaps across the junction to resist quasiparticle tunneling.
Do cosmic rays really cause this?
The 2025 authors report bursts induced solely by muons.
Is the issue fixed in processors?
Not according to these abstracts.
All field notes