Above 99.9% Fidelity Single-Qubit Gates, Two-Qubit Gates, and Readout in a Single Superconducting Quantum Device
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.
Cite
@article{arxiv.2508.16437,
title = {Above 99.9% Fidelity Single-Qubit Gates, Two-Qubit Gates, and Readout in a Single Superconducting Quantum Device},
author = {Fabian Marxer and Jakub Mrożek and Joona Andersson and Leonid Abdurakhimov and Janos Adam and Ville Bergholm and Rohit Beriwal and Chun Fai Chan and Saga Dahl and Soumya Ranjan Das and Frank Deppe and Olexiy Fedorets and Zheming Gao and Alejandro Gomez Frieiro and Daria Gusenkova and Andrew Guthrie and Tuukka Hiltunen and Hao Hsu and Eric Hyyppä and Joni Ikonen and Sinan Inel and Shan W. Jolin and Azad Karis and Seung-Goo Kim and William Kindel and Anton Komlev and Miikka Koistinen and Roope Kokkoniemi and Snigdha Kumar and Hsiang-Sheng Ku and Julia Lamprich and Sami Laine and Alessandro Landra and Lan-Hsuan Lee and Nizar Lethif and Per Liebermann and Wei Liu and Kunal Mitra and Tuomas Mylläri and Caspar Ockeloen-Korppi and Tuure Orell and Alexander Plyshch and Jukka Räbinä and Arthur Rebello and Michael Renger and Outi Reentilä and Jussi Ritvas and Sampo Saarinen and Otto Salmenkivi and Matthew Sarsby and Mykhailo Savytskyi and Ville Selinmaa and Matthew Steggles and Eelis Takala and Ivan Takmakov and Brian Tarasinski and Jani Tuorila and Alpo Välimaa and Jeroen Verjauw and Jaap Wesdorp and Nicola Wurz and Wei Qiu and Lihuang Zhu and Juha Hassel and Johannes Heinsoo and Attila Geresdi and Antti Vepsäläinen},
journal= {arXiv preprint arXiv:2508.16437},
year = {2026}
}