Fig. 5
From: One-dimensional quantum computing with a ‘segmented chain’ is feasible with today’s gate fidelities
Protocol for CNOT gates in a one-dimensional array of surface-code logical qubits. In the left column, squares denote surface-code qubits, red wavy lines denote rough boundaries, and green bold lines denote smooth boundaries. Any path connecting two rough (smooth) boundaries represents a Z (X) operator of the surface-code qubit. The controlled-NOT gate on two surface-code qubit can be realised following the procedure from a–e. In steps (a–c), the target qubit is deformed. In step (d) Control and Target qubits are merged, then they are splitted in step (e), as in usual lattice surgery.30 The right column illustrates the evolution of rough and smooth boundaries with time. In order to separate rough (smooth) boundaries with sufficient distance (so that the logical information is protected), three ancillary surface-code qubits A1, A2, and A3 are required. See Appendix for details
