Long-Distance Transmon Coupler with cz -Gate Fidelity above 99.8 %

Fabian Marxer, Antti Vepsäläinen, Shan W. Jolin, Jani Tuorila, Alessandro Landra, Caspar Ockeloen-Korppi, Wei Liu, Olli Ahonen, Adrian Auer, Lucien Belzane, Ville Bergholm, Chun Fai Chan, Kok Wai Chan, Tuukka Hiltunen, Juho Hotari, Eric Hyyppä, Joni Ikonen, David Janzso, Miikka Koistinen, Janne KotilahtiTianyi Li, Jyrgen Luus, Miha Papic, Matti Partanen, Jukka Räbinä, Jari Rosti, Mykhailo Savytskyi, Marko Seppälä, Vasilii Sevriuk, Eelis Takala, Brian Tarasinski, Manish J. Thapa, Francesca Tosto, Natalia Vorobeva, Liuqi Yu, Kuan Yen Tan, Juha Hassel, Mikko Möttönen, Johannes Heinsoo

Research output: Contribution to journalArticleScientificpeer-review

15 Citations (Scopus)


Tunable coupling of superconducting qubits has been widely studied due to its importance for isolated gate operations in scalable quantum processor architectures. Here, we demonstrate a tunable qubit-qubit coupler based on a floating transmon device, which allows us to place qubits at least 2 mm apart from each other while maintaining over 50-MHz coupling between the coupler and the qubits. In the introduced tunable-coupler design, both the qubit-qubit and the qubit-coupler couplings are mediated by two waveguides instead of relying on direct capacitive couplings between the components, reducing the impact of the qubit-qubit distance on the couplings. This leaves space for each qubit to have an individual readout resonator and a Purcell filter, which is needed for fast high-fidelity readout. In addition, simulations show that the large qubit-qubit distance significantly lowers unwanted non-nearest-neighbor coupling and allows multiple control lines to cross over the structure with minimal crosstalk. Using the proposed flexible and scalable architecture, we demonstrate a controlled-Z gate with (99.81±0.02)% fidelity.
Original languageEnglish
Article number010314
JournalPRX Quantum
Issue number1
Publication statusPublished - Jan 2023
MoE publication typeA1 Journal article-refereed


We acknowledge Matthew Sarsby, Roope Kokkoniemi, Ali Yurtalan Jean-Luc Orgiazzi, Lucas Ortega, Jorge Santos, Jaakko Jussila, Illari Kuronen, Jaakko Salo, Tiina Naaranoja, Otto Koskinen, and Tero Somppi for supporting the conceptualization, construction, and maintenance of the experimental setup, Ferenc Dósa-Rácz, Janne Mäntylä, Sinan Inel, and Leon Wubben for additional software support, and Olli-Pentti Saira for valuable discussions. We would additionally like to thank the rest of the IQM team for creating the entire infrastructure, laying the foundation of this work. The work was partly supported by the European Innovation Council (EIC) under Prometheus (Grant No. 959521), by Business Finland (Grant No. 7547/31/2021), and by the German Federal Ministry of Education and Research (BMBF) under the projects Q-Exa (Grant No. 13N16062), QSolid (Grant No. 13N16161), and MUNIQC-SC (Grant No. 13N16185). M.M. is partly supported by the Academy of Finland through its Centers of Excellence Program (Project No. 336810) and by the European Research Council under Advanced Grant ConceptQ (Grant No. 101053801). Parts of this work are included in patents applications filed by IQM Finland Oy. This work has used resources from the OtaNano Micronova cleanroom.


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