High-performance conditional-driving gate for Kerr parametric oscillator qubits

TL;DR

This paper improves the performance of a two-qubit gate for Kerr parametric oscillators by canceling flux pulse effects and optimizing control, achieving over 99.9% fidelity at faster speeds.

Contribution

It introduces a method to cancel AC-Zeeman shifts and employs shortcuts to adiabaticity to enhance gate speed and fidelity in Kerr parametric oscillator qubits.

Findings

Achieved over 99.9% average fidelity in gate operation.

Demonstrated twice faster gate performance with proposed methods.

Identified flux pulse-induced AC-Zeeman shift as a key error source.

Abstract

Kerr parametric oscillators (KPOs), two-photon driven Kerr-nonlinear resonators, can stably hold coherent states with opposite-sign amplitudes and are promising devices for quantum computing. Recently, we have theoretically proposed a two-qubit gate $R_{zz}$ for highly detuned KPOs and called it a conditional-driving gate [Chono $\textit{et al}$., Phys. Rev. Res. $\textbf{4}$, 043054 (2022)]. In this study, analyzing its superconducting-circuit model and deriving a corresponding static model, we find that an AC-Zeeman shift due to the flux pulse for the gate operation largely affects the gate performance. This effect becomes a more aggravating factor with shorter gate times, leading to an increase in the error rate. We thus propose a method to cancel this undesirable effect. Furthermore, through the use of shortcuts to adiabaticity and the optimization of flux pulses, we numerically demonstrate a conditional-driving gate with average fidelity exceeding 99.9$\%$ twice faster than that without the proposed method.