High-Contrast Z Z Interaction Using Superconducting Qubits with Opposite-Sign Anharmonicity

For building a scalable quantum processor with superconducting qubits, Z Z interaction is of great concern because its residual has a crucial impact to two-qubit gate fidelity. Two-qubit gates with fidelity meeting the criterion of fault-tolerant quantum computation have been demonstrated using Z Z interaction. However, as the performance of quantum processors improves, the residual static Z Z can become a performance-limiting factor for quantum gate operation and quantum error correction. Here, we introduce a superconducting architecture using qubits with opposite-sign anharmonicity, a transmon qubit, and a C -shunt flux qubit, to address this issue. We theoretically demonstrate that by coupling the two types of qubits, the high-contrast Z Z interaction can be realized. Thus, we can control the interaction with a high on-off ratio to implement two-qubit controlled-Z gates, or suppress it during two-qubit gate operation using X Y interaction (e.g., an iSWAP gate). The proposed architecture can also be scaled up to multiqubit cases. In a fixed coupled system, Z Z crosstalk related to neighboring spectator qubits could also be heavily suppressed.