Extended Data Fig. 7: Effect of calibration refinement.
From: Observation of topological phenomena in a programmable lattice of 1,800 qubits
a, b, Symmetries in the lattice dictate that each qubit should have an average magnetization of zero (a) and that each AFM coupler should be frustrated with the same probability as other couplers in its rotational symmetry equivalence class of 2L couplers (b). We use a gradient-descent shim method (code available from the corresponding author on reasonable request) to maintain degeneracy among qubits and equivalent couplers with flux offsets and small adjustments to specified coupling energies. Data are taken for L = 15, with 1,800 qubits and 1,290 AFM couplers, over 120 experiments with and without shim. Both magnetization and correlation distributions are tightened substantially. Outliers in shimmed spin–spin correlation are symmetry classes near the boundary of the lattice.
