Suppression of Qubit Crosstalk between Transmons and Capacitively Shunted Flux Qubits : Part1, Experiment

In multi-qubit cQED systems, the static ZZ crosstalk can be a limiting factor for high-fidelity two-qubit gates. Thus, mitigating such ZZ interactions becomes critically important for achieving high-fidelity entangling gates as the number of qubits increases. One potential way to suppress the static ZZ interaction involves combining different types of qubits. Capacitively shunted flux qubits (CSFQs), in contrast to transmon qubits, possess relatively large and positive anharmonicity. When they are paired with an appropriate detuning, the static ZZ term can be significantly suppressed for two-qubit gates based on the cross resonance interaction. We fabricated a two-qubit system consisting of a CSFQ and a fixed-frequency transmon coupled via a bus cavity. In this talk, we will present experimental results from these measurements, including the ZZ crosstalk and two-qubit gate fidelity versus detuning between the two qubits.