Fig. 2

a A chain of ion traps. In each trap, qubits (ions, represented by circles and squares) are coupled to the same phonon modes, and two-qubit entangling gates (e.g., CNOT gates, represented by colour curves) can be performed on any pair of qubits. Traps are coupled by moving qubits (squares) between nearest neighbouring traps. b A chain of resonators. Similar to ion traps, in each resonator, qubits (e.g., superconducting qubits) are coupled to the same photon mode, and two-qubit entangling gates can be performed on any pair of qubits. Two nearest neighbouring resonators are coupled by sharing a qubit. c The surface code in a segmented chain qubit array. The upper panel illustrates the interaction network in the segmented chain qubit array. Each segment contains several data qubits (circles) and two shuttle qubits (squares). Qubits within the same segment are all-to-all connected, i.e., two-qubit entangling gates (e.g., CNOT gates) can be directly performed on any pair of qubits. Two nearest neighbouring segments are coupled by sharing one shuttle qubit. The lower panel illustrates the array of surface-code qubits. Qubits unused in the encoding (e.g., shuttle qubits) are not shown in the lower panel. A surface-code logical qubit is encoded in several segments, and each segment provides qubits in one column of the surface code. CNOT gates can be performed on neighbouring surface-code qubits. These logical qubits form a one-dimensional quantum computer with nearest neighbouring interactions