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Google's team measured the error of an encoded T state at 1 to 2 in 10,000 or less. Gidney's 2025 RSA-2048 estimate assumes cultivated states about 1,000 times cleaner, followed by a further distillation step.
The team ran circuits with nearly 5,000 two-qubit gates and 5,000 mid-circuit resets and reproduced the predicted physics without error mitigation. It encoded no logical qubits, so it did not test error correction.
Google and MIT researchers spread error-correcting codes across small chip modules, with 42 to 116 physical qubits in their main examples. They have not tested the design on hardware or estimated what a complete algorithm would cost on it.
The Delft team tested its leakage reduction unit in error-correction experiments on five and seven physical qubits, with no runs discarded. The authors wrote that further research is required at larger code distances and for other codes.
Most of the 53 peer-reviewed experiments ran as simulations or quantum-inspired programs on ordinary computers. Their authors tested 41 only on toy or reduced datasets. The reviewers found no explicit demonstration of a quantum advantage.
Microsoft and Qolab researchers would call a logical qubit scalable only if a machine sustains it with repeated error correction and decodes errors in real time. DOE plans to pay for logical qubits under counting methods negotiated with each company.
The team measured how single photons move one step at a time, then multiplied those measurements into amplitudes for 1,419,857 paths. The authors wrote that more refined methods are needed to settle whether the paths are physically real.
Stuttgart physicists shielded single strontium atoms from thermal microwaves with coated glass plates and measured one state's room-temperature lifetime at about 21 times its free-space value. Qubit coherence in their setup remains at the 100-microsecond scale, they wrote.
The parallel gate took 14.8 microseconds and had an estimated fidelity of 0.92. The authors wrote that errors in preparing and reading out the qubits still limit the entangled states they can make.
Researchers lengthened a surface code in one direction on IBM Heron processors and reduced the matching type of logical error. With a measure that combined both error types, the team found no subthreshold scaling on its best-performing chip.
