Kerr cat qubits are a promising candidate for fault-tolerant quantum computers owing to the biased nature of their errors. The $ZZ$ coupling between the qubits can be utilized for a two-qubit entangling gate, but the residual coupling called $ZZ$ crosstalk is detrimental to precise computing. In order to resolve this problem, we propose a tunable $ZZ$-coupling scheme using two transmon couplers. By setting the detunings of the two couplers at opposite values, the residual $ZZ$ couplings via the two couplers cancel each other out. We also apply our scheme to the $R_{ZZ}(\mathrm{\Theta })$ gate ($ZZ$ rotation with angle $\mathrm{\Theta }$), one of the two-qubit entangling gates. We numerically show that the fidelity of the $R_{ZZ}(-\pi /2)$ gate is higher than 99.9% in a case of 16-ns gate time and without decoherence.

• Received 31 March 2023
• Revised 14 November 2023
• Accepted 13 December 2023

DOI:https://doi.org/10.1103/PhysRevApplied.21.014030