IonQ's single-number application metric, the largest width at which a six-algorithm circuit suite clears a 1/e fidelity bar, retired in 2025 in favor of industry-standard metrics.
Algorithmic Qubits (#AQ) was IonQ’s headline performance metric from 2022 through 2025: a single number meant to capture the largest useful application circuit a machine can run. IonQ sketched it in its December 2020 scaling roadmap as a successor to log2-style summaries of Quantum Volume and made it operational in February 2022 on top of the QED-C application suite. No other vendor adopted it.
How it works
#AQ pins a six-algorithm subset of the QED-C suite: quantum Fourier transform, phase estimation, amplitude estimation, Monte Carlo sampling, VQE, and Hamiltonian simulation. A machine scores #AQ = n if every suite circuit with width up to n and up to n^2 two-qubit CX gates achieves normalized output fidelity, minus statistical error, above 1/e ≈ 0.37. Only two-qubit gates count toward the budget; results are typically drawn as a pass region on a volumetric-benchmarking-style plot. Error mitigation is allowed if disclosed; IonQ’s headline numbers used debiasing by default. The authoritative definition is IonQ’s web spec and the AQ.md file in IonQ’s QED-C fork; no peer-reviewed paper defines the metric.
Strengths and limitations
Scoring application-style circuits rather than random ones was the appeal; being vendor-defined and vendor-reported was the weakness. Quantinuum’s “Debunking algorithmic qubits” argues that error mitigation and aggressive compilation dominate the score (Forte at AQ 9 versus H2-1 at AQ 26 when both run unmitigated; a 992-entangling-gate benchmark compiled down to 141 gates) and notes that upstream QED-C methodology forbids those techniques, so #AQ scores are not comparable to unmitigated QED-C results; the 1/e threshold is also criticized as a low bar. IonQ countered that mitigation reflects real usage. Despite the name, #AQ counts neither physical nor logical qubits.
Notable results
IonQ reported Aria at #AQ 20 (2022), Forte at #AQ 29 (2023), #AQ 35 and 36 (2024), and Tempo at #AQ 64 in October 2025, the roadmap endpoint. In the same announcement IonQ retired #AQ as its headline number, saying it will instead report industry-standard metrics (physical qubits, median two-qubit gate fidelity, logical qubits, and logical error rates) plus application-specific benchmarks.