Fig. 1: Distance-2 surface code and qubit layout in the experiment.

a Two logical qubits of the distance-2 surface code and transversal CNOT gate. Each logical qubit is encoded by four data qubits and the logical CNOT gate between two logical qubits corresponds to the four physical CNOT gates between the corresponding data qubits. b The experiment uses eight physical qubits arranged in a 2 × 4 rectangular region on the superconducting quantum processor Wukong. The deep blue lines represent the topology of the processor, indicating the allowed two-qubit gates between physical qubits.