Kerr-cat qubits are a promising candidate for fault-tolerant quantum
computers owing to the biased nature of errors. The ZZ coupling between the
qubits can be utilized for a two-qubit entangling gate, but the residual
coupling causes unnecessary always-on gates and crosstalk. 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 Rzz​(Θ) gate (ZZ rotation with angle
Θ), one of the two-qubit entangling gates. We numerically show that the
fidelity of the Rzz​(−π/2) gate is higher than 99.9% in a case of 16 ns
gate time and without decoherence.Comment: 8 pages, 5 figure