VQE

VQE looks for the ground-state energy of a Hamiltonian. A parametrised circuit — the ansatz — prepares a state; the machine measures the energy in each needed basis; the parameters are tuned so the energy falls. The lowest value reachable is bounded below by the true ground state.

Where the Hamiltonian is small enough, the exact ground state is computed offline (up to 18 qubits in ROX OS) and every measured energy is judged by its distance to it. Above that size there is no exact reference: the run is judged head-to-head against the vendor default, and the record says so.

On the record: a 12-spin ring in two topologies, Hückel and Möbius, on a folding ladder to 432 two-qubit gates; both arms measured against the exact value; the forecast of the energy sealed before the run. Records on Proof.