Residual-$ZZ$-coupling suppression and fast two-qubit gate for Kerr-cat qubits based on level-degeneracy engineering

TL;DR

This paper presents a method to suppress residual $ZZ$-coupling in Kerr-cat qubits using level-degeneracy engineering, enabling high-fidelity, fast two-qubit gates crucial for scalable quantum computing.

Contribution

It introduces a $ZZ$-coupling scheme with a tunable coupler that leverages degeneracy control to switch coupling on and off, improving qubit interaction management.

Findings

Residual $ZZ$ coupling can be effectively suppressed.

Achieves $R_{ZZ}(-rac{ au}{2})$-gate fidelity over 99.9%.

Gate operation time is as short as 18 ns.

Abstract

Building large-scale quantum computers requires an interqubit-coupling scheme with a high on-off ratio to avoid unwanted crosstalk coming from residual coupling and to enable fast multi-qubit operations. We propose a $ZZ$-coupling scheme for two Kerr-cat qubits with a frequency-tunable coupler. By making four relevant states of the two Kerr-cat qubits quadruply degenerate, we can switch off the $ZZ$ coupling. By partially lifting the level degeneracy, we can switch it on. We theoretically show that an experimentally feasible circuit model suppresses the residual $ZZ$ coupling. Moreover, our circuit can realize $R_{ZZ}(-\pi/2)$-gate fidelity higher than $99.9\%$ within $18$ ns when decoherence is ignored. Our model includes the first-order terms in expansion beyond the rotating-wave approximation.