Journal Article

FZJ-2026-00983

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Microwave-activated gates between a fluxonium and a transmon qubit

Ciani, A. (Corresponding author)FZJ* ; Varbanov, B. M. ; Jolly, N. ; Andersen, C. K. ; Terhal, B. M.

2022
APS College Park, MD

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Please use a persistent id in citations: doi:10.1103/PhysRevResearch.4.043127  doi:10.34734/FZJ-2026-00983

Abstract: We propose and analyze two types of microwave-activated gates between a fluxonium and a transmon qubit, namely a cross-resonance (CR) and a CPHASE gate. The large frequency difference between a transmon and a fluxonium makes the realization of a two-qubit gate challenging. For a medium-frequency fluxonium qubit, the transmon-fluxonium system allows for a cross-resonance effect mediated by the higher levels of the fluxonium over a wide range of transmon frequencies. This allows one to realize the cross-resonance gate by driving the fluxonium at the transmon frequency, mitigating typical problems of the cross-resonance gate in transmon-transmon chips related to frequency targeting and residual ZZ coupling. However, when the fundamental frequency of the fluxonium enters the low-frequency regime below 100 MHz, the cross-resonance effect decreases leading to long gate times. For this range of parameters, a fast microwave CPHASE gate can be implemented using the higher levels of the fluxonium. In both cases, we perform numerical simulations of the gate showing that a gate fidelity above 99% can be obtained with gate times between 100 and 300 ns. Next to a detailed gate analysis, we perform a study of chip yield for a surface code lattice of fluxonia and transmons interacting via the proposed cross-resonance gate. We find a much better yield as compared to a transmon-only architecture with the cross-resonance gate as native two-qubit gate.

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Contributing Institute(s):

1. Quantum Computing Analytics (PGI-12)

Research Program(s):

1. 5221 - Advanced Solid-State Qubits and Qubit Systems (POF4-522) (POF4-522)

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