Inductively shunted transmon qubit for ZZ interaction cancellation*

To improve the cross-resonance (CR) gate fidelity between superconducting qubits, unwanted ZZ interaction has to be eliminated. Previously, it has been demonstrated that combining a capacitively shunted flux qubit (CSFQ) and a transmon can suppress the ZZ interaction when the anharmonicities of the two qubits are exactly opposite. However, this implementation has several challenges such as the CSFQ requires an external magnetic flux bias and it is difficult to achieve controlled anharmonicity at the flux-noise insensitive point. In light of this, here we present the so-called inductively shunted transmon that has a positive anharmonicity for the purpose of ZZ cancellation. The proposed qubit is easy to fabricate since it contains a single Josephson junction with junction parameters similar to that of the coupled transmon; Both frequency and anharmonicity of such qubit can be easily modelled and well controlled, enabling seamless integration with current CR-gate systems. Furthermore, by including a pi-junction or by trapping a flux in the qubit loop with a gradiometric design, one can fully eliminate the external magnetic flux for scaling up.