Implementation of Conditional-Phase Gates based on tunable ZZ-Interactions

TL;DR

This paper demonstrates a fast, high-fidelity CZ gate in superconducting qubits using a tunable ZZ-interaction via a flux-tunable coupler, offering a new approach to two-qubit gate implementation.

Contribution

It introduces a novel method for implementing conditional-phase gates using tunable ZZ-interactions controlled by a flux-tunable coupler, achieving high speed and fidelity.

Findings

Achieved a 38 ns CZ gate with 97.9% fidelity.

Controlled ZZ-coupling over three orders of magnitude.

Low leakage rate of 0.14%.

Abstract

High fidelity two-qubit gates exhibiting low crosstalk are essential building blocks for gate-based quantum information processing. In superconducting circuits two-qubit gates are typically based either on RF-controlled interactions or on the in-situ tunability of qubit frequencies. Here, we present an alternative approach using a tunable cross-Kerr-type ZZ-interaction between two qubits, which we realize by a flux-tunable coupler element. We control the ZZ-coupling rate over three orders of magnitude to perform a rapid (38 ns), high-contrast, low leakage (0.14 %) conditional-phase CZ gate with a fidelity of 97.9 % without relying on the resonant interaction with a non-computational state. Furthermore, by exploiting the direct nature of the ZZ-coupling, we easily access the entire conditional-phase gate family by adjusting only a single control parameter.