Tuning the ZZ coupling between Kerr-cat qubits with transmon couplers*

A key feature of a Kerr-cat qubit [1, 2] is that its bit-flip rate is much smaller than its phase-flip one. This can reduce the number of qubits necessary to construct one logical qubit in a fault-tolerant quantum computer. A major obstacle to scaling up a fault-tolerant quantum computer is unwanted residual couplings between qubits, which prevent us from precisely operating a qubit locally and spread errors. One of the popular methods to suppress residual ZZ couplings between transmon qubits is to use tunable couplers [3]. However, this method has not been adapted for Kerr-cat qubits yet. We here theoretically propose a method to tune a ZZ coupling between two Kerr-cat qubits using two transmon couplers [4]. Our method allows not only the suppression of the residual ZZ coupling but also a fast and high-fidelity R_zz gate.

[1] S. Masuda, T. Kanao, H. Goto, Y. Matsuzaki, T. Ishikawa, and S. Kawabata, Phys. Rev. Appl. 18, 034076 (2022). [2] H. Chono, T. Kanao, and H. Goto, Phys. Rev. Res. 4, 043054 (2022). [3] H. Goto, Phys. Rev. Appl. 18, 034038 (2022). [4] T. Aoki, T. Kanao, H. Goto, S. Kawabata, and S. Masuda, arXiv:2303.16622 (2023).