Benchmark: GHZ state size
Benchmarks / System level (whole processor)
The largest Greenberger-Horne-Zeilinger state (all qubits jointly 0 or jointly 1) a processor prepares and verifies: a test of multi-qubit entanglement.
- Level
- System level (whole processor)
- Maintained by
- No single maintainer; used by the KPI Comp 2b of the Quantum Flagship.
- European
- Not determined: Used as a European KPI; the benchmark itself has no single owner.
How it is measured
A circuit entangles all qubits; parity or coherence measurements estimate the state fidelity, and the state counts when the fidelity exceeds the threshold for genuine multipartite entanglement. Moses et al. (2023) report a 32-qubit GHZ state on a trapped-ion processor.
Limitations and criticisms
- Measures one specific state; it says little about arbitrary circuits.
- Verification methods and thresholds differ between reports.
Used in European procurements
- Used in: EuroHPC procurement Euro-Q-Exa (Required in the benchmark suite (scored under the award criteria))
- Used in: EuroHPC procurement EuroQCS-France (now Lucy) (Required in the benchmark suite (scored under the award criteria))
- Used in: EuroHPC procurement EuroQCS-Italy (now SOL) (Required in the benchmark suite (scored under the award criteria))
- Used in: EuroHPC procurement EuroSSQ-HPC (Required in the benchmark suite (scored under the award criteria))
- Used in: EuroHPC procurement MeluXina-Q (Required in the benchmark suite (scored under the award criteria))
As the tender documents state; how a benchmark is weighted against others is described in each procurement.
Sources
- Quantum Flagship Strategic Advisory Board (2025). Quantum Flagship Strategic Advisory Board: KPI booklet (March 2025). Booklet read for the KPI observatory. Read: booklet (see the KPI observatory), retrieved 2026-10-23.
- S. A. Moses et al. (2023). A Race Track Trapped-Ion Quantum Processor. Phys. Rev. X 13, 041052 (2023); arXiv:2305.03828. Read: abstract page, retrieved 2026-10-23.