OpenAI reports a QAC⁰ parity lower bound

For every fixed depth, polynomial qubit bound and ε>0, sufficiently large measured-output quantum circuits using arbitrary one-qubit and unbounded-arity Toffoli gates have some input on which parity succeeds with probability below 1/2+ε.

Sources for this record

What was already known

Parity has classical constant-depth circuit lower bounds. The corresponding measured-output quantum setting with polynomially many zero-initialized ancillas and unrestricted final garbage remained Moore’s parity conjecture.

AI involvement AI-led

OpenAI credits itself as manuscript author and states that its internal frontier model produced the results in this release. Individual human input is not detailed enough to establish task-only autonomy.

OpenAI is named as author on the manuscript, and its release attributes the results to an internal frontier model. The individual human input is not detailed enough to establish autonomy.

Importance Major

Resolves Moore’s QAC⁰ parity conjecture under the stated measured-output circuit model.

Limitations

The lower bound is worst-case over inputs and assumes constant depth, polynomially many qubits, zero-initialized ancillas and one measured output qubit.

Technical verification Formal (Lean 4)

OpenAI reports a Lean proof matching the selected claim.

Formal checking

The pinned Lean note proves this parity consequence, including a strict-below-2/3 specialization.

Checker
OpenAI-reported Lean 4 / Comparator
Scope
For every fixed depth, polynomial qubit bound and ε>0, sufficiently large measured-output quantum circuits using arbitrary one-qubit and unbounded-arity Toffoli gates have some input on which parity succeeds with probability below 1/2+ε.
Basis
Reported by the linked checker
Evidence source

Checking a formal statement does not establish that it matches the original problem.

Human understanding Few

Few is the default when evidence for a higher level is insufficient. No named person is documented as explaining the central argument for this assessed contribution.

Correction and publication history

2026-10-18 · publication

Primary manuscript, attribution, prior-work, and scoped checking review for non-notifying local inclusion.

Read this published revision