High-fidelity iSWAP gate with Double Transmon Coupler

TL;DR

This paper demonstrates a high-fidelity, fast parametric iSWAP gate between superconducting transmon qubits using a double transmon coupler, achieving over 99.8% fidelity without numerical optimization.

Contribution

It introduces a novel use of the double transmon coupler for high-fidelity, fast entangling gates with robust calibration methods, advancing superconducting qubit technology.

Findings

Achieved 99.827% gate fidelity in 40ns

Utilized robust phase estimation for calibration

Demonstrated extensibility to other gate types and qubit modalities

Abstract

Entangling operations are at the heart of all approaches to quantum information processing. Parametric gates, in particular, offer a versatile solution to strongly couple off-resonant superconducting qubits with suppressed parasitic crosstalk to spectator qubits due to frequency-selective activation. In this work, we demonstrate a parametric iSWAP gate between two transmon qubits using the recently developed double transmon coupler (DTC). The DTC supports robust internally-defined cancellation point (``off'' state) for static interactions, while simultaneously mediating a fast parametric coupling between data qubits that can be deployed for high-fidelity two-qubit operations. We use robust phase estimation to calibrate non-commuting error terms in the parametric iSWAP gate, and achieve a 99.827% gate fidelity in 40ns without any numerical optimization. The circuit architecture and calibration techniques developed here are extensible to other gate implementations and qubit modalities, paving the way towards resource-efficient quantum information processing.