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Ranked by logical qubits, fault-tolerant applications look like a staircase. Ranked by the gates each one needs, the list within reach of announced machines is shorter. Elliptic-curve attacks come before every molecular ground-state estimate in Google's 2025 tables.
Are the qubits physical or logical? Is there a paper, and who checked it? A reader can judge a quantum computing announcement with seven questions, each shown here with a 2026 case and the document that answers it.
Alice & Bob's new count is about a quarter of its 2024 estimate. The authors assumed cat qubits that keep their value for about 100 years. Researchers have measured up to 22 seconds under full control.
The Sydney company said it cut its February estimate by about an order of magnitude in qubit-time with its Pinnacle 1.2 update. It has not published the circuits, the decoder, or the hardware behind its decoding speed.
NIST, the NSA, Britain's NCSC, the EU, Canada, and Australia all ask organizations to start post-quantum migration now. None claims a code-breaking quantum computer exists or gives it a known date. Their deadlines do not depend on either claim.
The circuit uses 24% fewer logical qubits and 18% fewer Toffoli gates than Google's low-qubit design. It covers a step that Shor's algorithm repeats. In a wider test, it failed 111 times in 360,960 additions.
None of the 24 agencies GAO audited had fully carried out three preparatory steps for post-quantum migration. At six sampled agencies, none could document the algorithms listed for every sampled system.
Polynomial-time quantum algorithms for factoring and quantum simulation are backed by complexity theory. Grover search gains are at most quadratic. Optimization and machine learning on ordinary data rely mostly on heuristics, and researchers have matched several claimed speedups classically.
The team restored error suppression in a stand-in test for logic gates by removing defective parts. The larger distance-5 code beat a distance-3 code only after the team discarded runs affected by leakage, and only in one basis.
A Sandia-led team scored Google, IBM, and Quantinuum processors and a logical-qubit machine on one scale. Helios-1 led at 1,504 without discarded runs, against about 250 million that the authors calculated for factoring RSA-2048.
