# Non-Markovian errors found in superconducting qubits and in Google Willow and IBM data

- Published: 2026-11-12 10:37 UTC
- Section: Digital & Computing › Quantum technology
- Tags: quantum error correction, non-Markovian errors, Markovian assumption, superconducting qubit, Google Willow, IBM Quantum, correlated noise, fault tolerance, qubit memory effects
- URL: https://realtech.media/news/rt-f4327036548ed6cd509720be_non_markovian_errors/

**Memory effects in errors, absent from standard error-correction models, have appeared in several experiments. How serious they become as qubit counts grow is unknown.**

![Non-Markovian errors found in superconducting qubits and in Google Willow and IBM data](https://realtech.media/media/2026/11/11599c075c20cd1b.jpg)
*Наука 2.0*

Several research groups report that errors in quantum computers can have memory, which contradicts the Markovian assumption behind quantum error correction (QEC), according to the outlet Nauka [1]. The assumption holds that errors occurring at different moments are unrelated to each other. Memory effects, however, keep showing up in experiments [1].

## Where memory effects were found

Ioan Pop of Karlsruhe Institute of Technology and colleagues found long-lived defects in the environment of a superconducting qubit, each of which can act as memory. "We directly show how this long-lived environment breaks one of the assumptions of error correction," he says [1]. The group of Rami Barends at Jülich Research Centre observed similar violations of the Markovian assumption on a different type of superconducting qubit [1].

The assumption was also tested on whole machines. In 2025, John Fidel Kam of the Agency for Science, Technology and Research in Singapore and co-authors analyzed a key error-correction experiment on Google's Willow computer. Part of the hard-to-correct errors matched a model in which the Markovian assumption does not hold [1]. Gregory Quiroz of Johns Hopkins University showed that a model with non-Markovian effects describes an IBM computer seven times better than standard noise models [1]. IBM Quantum said it redesigned its machines in light of the new data. Company researcher Alireza Seif said they continue to study non-Markovian effects on new hardware [1].

Lorenza Viola of Dartmouth College also found that the "remembering" parts of the environment can themselves behave as quantum systems and respond to the qubit. This is another type of error that QEC does not yet account for [1].

## What remains open

The work is preliminary. As the number of qubits grows, previously negligible effects may become more important. Kavan Modi, one of the authors of the Google Willow study, believes it is too early to sound the alarm, but there are no theoretical or experimental guarantees that the problem will not get worse. "We do not fully know where exactly it breaks," he says [1].

Theorems exist showing that fault tolerance can be achieved even with memory effects. How strong correlations can be before they become a problem remains an open question [1].

Pop believes QEC can be adapted to non-Markovian errors. A measurement method developed by his group may help find memory effects in devices and work around them. Kam adds that correlated errors can also be mitigated by tuning control and readout algorithms [1].

## Sources

1. [Наука 2.0](https://naukatv.ru/news/kvantovye_kompyutery_stolknulis_s_nemarkovskimi_oshibkami)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-f4327036548ed6cd509720be_non_markovian_errors/