Demonstrating a four-qubit network for the surface code with superconducting qubits*

In the skew-symmetric layout of superconducting qubits and resonators for the surface-code error correction protocol, studying an inner ring structure of four qubits is a critical step towards demonstrating the core operations of a full plaquette tile. We show results for quantum devices consisting of twelve quantum degrees of freedom: four transmon qubits, coupled via four bus resonators, with four independent readout resonators. We discuss engineering challenges of such devices as well as benchmarked results for control and readout.