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arXiv · 2508.16437

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

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

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Fabian Marxer, Jakub Mrożek, Joona Andersson, Leonid Abdurakhimov, Janos Adam, Ville Bergholm, Rohit Beriwal, Chun Fai Chan, Saga Dahl, Soumya Ranjan Das, Frank Deppe, Olexiy Fedorets, Zheming Gao, Alejandro Gomez Frieiro, Daria Gusenkova, Andrew Guthrie, Tuukka Hiltunen, Hao Hsu, Eric Hyyppä, Joni Ikonen, Sinan Inel, Shan W. Jolin, Azad Karis, Seung-Goo Kim, William Kindel, Anton Komlev, Miikka Koistinen, Roope Kokkoniemi, Snigdha Kumar, Hsiang-Sheng Ku, Julia Lamprich, Sami Laine, Alessandro Landra, Lan-Hsuan Lee, Nizar Lethif, Per Liebermann, Wei Liu, Kunal Mitra, Tuomas Mylläri, Caspar Ockeloen-Korppi, Tuure Orell, Alexander Plyshch, Jukka Räbinä, Arthur Rebello, Michael Renger, Outi Reentilä, Jussi Ritvas, Sampo Saarinen, Otto Salmenkivi, Matthew Sarsby, Mykhailo Savytskyi, Ville Selinmaa, Matthew Steggles, Eelis Takala, Ivan Takmakov, Brian Tarasinski, Jani Tuorila, Alpo Välimaa, Jeroen Verjauw, Jaap Wesdorp, Nicola Wurz, Wei Qiu, Lihuang Zhu, Juha Hassel, Johannes Heinsoo, Attila Geresdi, Antti Vepsäläinen. 2025-08-22. Above 99.9% Fidelity Single-Qubit Gates, Two-Qubit Gates, and Readout in a Single Superconducting Quantum Device. https://doi.org/10.1103/n86s-2b88

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