- Physical qubits
- The hardware qubits on the device, before any error correction.
- Atoms
- Neutral-atom vendors count the atoms trapped in the array; each one can act as a physical qubit.
- Algorithmic qubits (AQ)
- IonQ's own system-level metric: the widest circuit at which a fixed set of benchmark algorithms still succeeds. No other vendor publishes it.
- Logical qubits
- Error-corrected qubits, each encoded across many physical ones. The codes differ between demonstrations, so two records rarely mean the same thing.
- Quantum volume
- A system-level score (a power of two) from square random circuits. Vendors run it under their own assumptions.
- Two-qubit gate fidelity
- How often a two-qubit gate does what it should, as a percent. The cards show the best published figure, with its device and source.