Above 99.9% Fidelity Single-Qubit Gates, Two-Qubit Gates, and Readout in a Single Superconducting Quantum Device

TL;DR

This paper demonstrates a superconducting quantum device achieving over 99.9% fidelity in single-qubit gates, two-qubit gates, and readout simultaneously, advancing scalable quantum computing.

Contribution

It introduces a method to optimize coupling parameters in a superconducting circuit for high-fidelity operations without trade-offs, including a new calibration protocol.

Findings

Achieved 99.93% average CZ gate fidelity

Achieved 99.98% single-qubit gate fidelity

Readout fidelities over 99.94%

Abstract

Achieving high-fidelity single-qubit gates, two-qubit gates, and qubit readout is critical for building scalable, error-corrected quantum computers. However, device parameters that enhance one operation often degrade the others, making simultaneous optimization challenging. Here, we demonstrate that careful tuning of qubit-coupler coupling strengths in a superconducting circuit with two transmon qubits coupled via a tunable coupler enables high-fidelity single- and two-qubit gates, without compromising readout performance. As a result, we achieve a 40h-averaged CZ gate fidelity of 99.93%, simultaneous single-qubit gate fidelities of 99.98%, and readout fidelities over 99.94% in a single device. These results are enabled by optimized coupling parameters, an efficient CZ gate calibration experiment based on our new Phased-Averaged Leakage Error Amplification (PALEA) protocol, and a readout configuration compatible with high coherence qubits. Our results demonstrate a viable path toward scaling up superconducting quantum processors while maintaining consistently high fidelities across all core operations.