Tunable Inductive Coupler for High-Fidelity Gates between Fluxonium Qubits

Helin Zhang; Chunyang Ding; D. K. Weiss; Ziwen Huang; Yuwei Ma; Charles Guinn; Sara Sussman; Sai Pavan Chitta; Danyang Chen; Andrew A. Houck; Jens Koch; David I. Schuster

doi:10.1103/PRXQuantum.5.020326

Tunable Inductive Coupler for High-Fidelity Gates between Fluxonium Qubits

Helin Zhang, Chunyang Ding, D. K. Weiss, Ziwen Huang, Yuwei Ma, Charles Guinn, Sara Sussman, Sai Pavan Chitta, Danyang Chen, Andrew A. Houck, Jens Koch, David I. Schuster^*

^*Corresponding author for this work

Physics and Astronomy

Research output: Contribution to journal › Article › peer-review

16 Scopus citations

Abstract

The fluxonium qubit is a promising candidate for quantum computation due to its long coherence times and large anharmonicity. We present a tunable coupler that realizes strong inductive coupling between two heavy-fluxonium qubits, each with approximately 50-MHz frequencies and approximately 5-GHz anharmonicities. The coupler enables the qubits to have a large tuning range of XX coupling strengths (-35 to 75 MHz). The ZZ coupling strength is <3 kHz across the entire coupler bias range and <100 Hz at the coupler off position. These qualities lead to fast high-fidelity single- and two-qubit gates. By driving at the difference frequency of the two qubits, we realize a iSWAP gate in 258 ns with fidelity 99.72%, and by driving at the sum frequency of the two qubits, we achieve a bSWAP gate in 102 ns with fidelity 99.91%. This latter gate is only five qubit Larmor periods in length. We run cross-entropy benchmarking for over 20 consecutive hours and measure stable gate fidelities, with bSWAP drift (2σ) <0.02% and iSWAP drift <0.08%.

Original language	English (US)
Article number	020326
Journal	PRX Quantum
Volume	5
Issue number	2
DOIs	https://doi.org/10.1103/PRXQuantum.5.020326
State	Published - Apr 2024

Funding

We would like to thank Sho Uemera, Leandro Stefanazzi, and Gustavo Cancelo for their help with the RFSoC, and Kevin He, Kan-Heng Lee, Ziqian Li, Tanay Roy, and Rachel Dey for useful discussions. This work was supported by the Army Research Office under Grant No. W911NF1910016. This work is funded in part by Enabling Practical-Scale Quantum Computation (EPiQC), a National Science Foundation (NSF) Expedition in Computing, under Grant No. CCF1730449. This work was partially supported by the University of Chicago Materials Research Science and Engineering Center, which is funded by the NSF under Award No. DMR-1420709. The devices were fabricated in the Pritzker Nanofabrication Facility at the University of Chicago, which receives support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), a node of the NSF\u2019s National Nanotechnology Coordinated Infrastructure. S.S. was supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program. We would like to thank Sho Uemera, Leandro Stefanazzi, and Gustavo Cancelo for their help with the RFSoC, and Kevin He, Kan-Heng Lee, Ziqian Li, Tanay Roy, and Rachel Dey for useful discussions. This work was supported by the Army Research Office under Grant No. W911NF1910016. This work is funded in part by Enabling Practical-Scale Quantum Computation (EPiQC), a National Science Foundation (NSF) Expedition in Computing, under Grant No. CCF1730449. This work was partially supported by the University of Chicago Materials Research Science and Engineering Center, which is funded by the NSF under Award No. DMR-1420709. The devices were fabricated in the Pritzker Nanofabrication Facility at the University of Chicago, which receives support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), a node of the NSF's National Nanotechnology Coordinated Infrastructure. S.S. was supported by the Department of Defense (DoD) through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program.

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials
General Computer Science
Mathematical Physics
General Physics and Astronomy
Applied Mathematics
Electrical and Electronic Engineering

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10.1103/PRXQuantum.5.020326

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abstract = "The fluxonium qubit is a promising candidate for quantum computation due to its long coherence times and large anharmonicity. We present a tunable coupler that realizes strong inductive coupling between two heavy-fluxonium qubits, each with approximately 50-MHz frequencies and approximately 5-GHz anharmonicities. The coupler enables the qubits to have a large tuning range of XX coupling strengths (-35 to 75 MHz). The ZZ coupling strength is <3 kHz across the entire coupler bias range and <100 Hz at the coupler off position. These qualities lead to fast high-fidelity single- and two-qubit gates. By driving at the difference frequency of the two qubits, we realize a iSWAP gate in 258 ns with fidelity 99.72%, and by driving at the sum frequency of the two qubits, we achieve a bSWAP gate in 102 ns with fidelity 99.91%. This latter gate is only five qubit Larmor periods in length. We run cross-entropy benchmarking for over 20 consecutive hours and measure stable gate fidelities, with bSWAP drift (2σ) <0.02% and iSWAP drift <0.08%.",

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AU - Guinn, Charles

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AU - Chitta, Sai Pavan

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AU - Schuster, David I.

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N2 - The fluxonium qubit is a promising candidate for quantum computation due to its long coherence times and large anharmonicity. We present a tunable coupler that realizes strong inductive coupling between two heavy-fluxonium qubits, each with approximately 50-MHz frequencies and approximately 5-GHz anharmonicities. The coupler enables the qubits to have a large tuning range of XX coupling strengths (-35 to 75 MHz). The ZZ coupling strength is <3 kHz across the entire coupler bias range and <100 Hz at the coupler off position. These qualities lead to fast high-fidelity single- and two-qubit gates. By driving at the difference frequency of the two qubits, we realize a iSWAP gate in 258 ns with fidelity 99.72%, and by driving at the sum frequency of the two qubits, we achieve a bSWAP gate in 102 ns with fidelity 99.91%. This latter gate is only five qubit Larmor periods in length. We run cross-entropy benchmarking for over 20 consecutive hours and measure stable gate fidelities, with bSWAP drift (2σ) <0.02% and iSWAP drift <0.08%.

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Tunable Inductive Coupler for High-Fidelity Gates between Fluxonium Qubits

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