Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2503.10903 · Physical Review Research

Superconducting qubit-resonator quantum processor with effective all-to-all connectivity

Michael Renger, Jeroen Verjauw, Nicola Wurz, Amin Hosseinkhani, Caspar F. Ockeloen-Korppi, Wei Liu, Aniket Rath, Manish Thapa, Florian Vigneau, Elisabeth Wybo, Ville Bergholm, Chun Fai Chan, Bálint Csatári, Saga Dahl, Rakhim Davletkaliyev, Rakshyakar Giri, Daria Gusenkova, Hermanni Heimonen, Tuukka Hiltunen, Hao Hsu, Eric Hyyppä, Joni Ikonen, Tyler Jones, Shabeeb Khalid, Seung-Goo Kim, Miikka Koistinen, Anton A. Komlev, Janne Kotilahti, Vladimir Kukushkin, Julia Lamprich, Alessandro Landra, Lan-Hsuan Lee, Tianyi Li, Per Liebermann, Sourav Majumder, Janne Mäntylä, Fabian Marxer, Arianne Meijer - van de Griend, Vladimir Milchakov, Jakub Mrożek, Jayshankar Nath, Tuure Orell, Miha Papič, Matti Partanen, Alexander Plyushch, Stefan Pogorzalek, Jussi Ritvas, Pedro Figueroa Romero, Ville Sampo, Marko Seppälä, Ville Selinmaa, Linus Sundström, Ivan Takmakov, Brian Tarasinski, Jani Tuorila, Olli Tyrkkö, Alpo Välimaa, Jaap J. Wesdorp, Ping Yang, Liuqi Yu, Johannes Heinsoo, Antti P. Vepsäläinen, William Kindel, Hsiang-Sheng Ku, Frank Deppe

Published Dec 5, 2025• 5 citations
arXivHTMLPDF

Abstract

In this work, we introduce a superconducting quantum processor architecture that uses a transmission-line resonator to implement effective all-to-all connectivity between six transmon qubits. This architecture can be used as a test bed for algorithms that benefit from high connectivity. We show that the central resonator can be used as a computational element, which offers the flexibility to encode a qubit for quantum computation or to utilize its bosonic modes that further enables quantum simulation of bosonic systems. To operate the quantum processing unit (QPU), we develop and benchmark the qubit-resonator conditional Z gate and the qubit-resonator MOVE operation. The latter allows for transferring a quantum state between one of the peripheral qubits and the computational resonator. We benchmark the QPU performance and achieve a genuinely multiqubit entangled Greenberger-Horne-Zeilinger state over all six qubits with a readout-error mitigated fidelity of F | ψ 〉 GHZ = 0.86 .

DOI
10.1103/8x68-cx1w

Related papers

Coherent errors in a superconducting six-qubit network with beyond-nearest-neighbor connectivity

Jay Deshmukh, Srijita Das, Binoy Nambiar +11 more

Enhancing qubit connectivity in quantum processors is an important milestone for more efficient implementation of algorithms and novel error-correction protocols. While all-to-all connectivity has been demonstrated in quantum processors based on ion traps and neutral atoms, the exploration of enhanced connectivity in the superconducting qubit architecture has been a more recent endeavor. Here, we demonstrate the operation of a network comprising six superconducting transmon qubits with a novel, beyond-nearest-neighbor connectivity. We use a circular ring resonator with six qubits placed on the periphery at 60 ∘ spacing and capacitively coupled to it in a three-dimensional circuit-QED architecture. The ring resonator acts as a two-path coupler between each pair of qubits, and we present results demonstrating that each qubit has finite coupling to three other qubits with negligible coupling to the remaining two qubits. In this architecture, with fixed-frequency qubits and always-on coupling, we benchmark the single-qubit and two-qubit gates using randomized benchmarking. We find that our gate fidelities are strongly affected by the enhanced connectivity. We characterize the spread in qubit frequencies due to cross-Kerr terms and quantify its detrimental effect on the performance of single- and two-qubit gates. Finally, we analyze the effect of the spectator qubits using numerical simulations and propose a path toward optimizing this system and achieving > 99 % two-qubit gate fidelities across all connected qubit pairs.

Physical Review Research•Jun 16, 2026•0 citations

Modular Quantum Processor with an All-to-All Reconfigurable Router

Xuntao Wu, Haoxiong Yan, Gustav Andersson +10 more

Superconducting qubits provide a promising approach to large-scale fault-tolerant quantum computing. However, qubit connectivity on a planar surface is typically restricted to only a few neighboring qubits. Achieving longer-range and more flexible connectivity, which is particularly appealing in light of recent developments in error-correcting codes, however, usually involves complex multilayer packaging and external cabling, which is resource intensive and can impose fidelity limitations. Here, we propose and realize a high-speed on-chip quantum processor that supports reconfigurable all-to-all coupling with a large on-off ratio. We implement the design in a four-node quantum processor, built with a modular design comprising a wiring substrate coupled to two separate qubit-bearing substrates, each including two single-qubit nodes. We use this device to demonstrate reconfigurable controlled- Z gates across all qubit pairs, with a benchmarked average fidelity of 96.00 % ± 0.08 % and best fidelity of 97.14 % ± 0.07 % , limited mainly by dephasing in the qubits. We also generate multiqubit entanglement, distributed across the separate modules, demonstrating GHZ-3 and GHZ-4 states with fidelities of 88.15 % ± 0.24 % and 75.18 % ± 0.11 % , respectively. This approach promises efficient scaling to larger-scale quantum circuits and offers a pathway for implementing quantum algorithms and error-correction schemes that benefit from enhanced qubit connectivity. Published by the American Physical Society 2024

arXiv:2407.20134•Physical Review X•Nov 4, 2024•34 citations

Scalable High-Performance Fluxonium Quantum Processor

Long B. Nguyen, Gerwin Koolstra, Yosep Kim +12 more

The technological development of hardware heading toward universal fault-tolerant quantum computation requires a large-scale processing unit with high performance. While fluxonium qubits are promising with high coherence and large anharmonicity, their scalability has not been systematically explored. In this work, we propose a superconducting quantum information processor based on compact high-coherence fluxoniums with suppressed crosstalk, reduced design complexity, improved operational efficiency, high-fidelity gates, and resistance to parameter fluctuations. In this architecture, the qubits are readout dispersively using individual resonators connected to a common bus and manipulated via combined on-chip RF and DC control lines, both of which can be designed to have low crosstalk. A multi-path coupling approach enables exchange interactions between the high-coherence computational states and at the same time suppresses the spurious static ZZ rate, leading to fast and high-fidelity entangling gates. We numerically investigate the cross resonance controlled-NOT and the differential AC-Stark controlled-Z operations, revealing low gate error for qubit-qubit detuning bandwidth of up to 1 GHz. Our study on frequency crowding indicates high fabrication yield for quantum processors consisting of over thousands of qubits. In addition, we estimate low resource overhead to suppress logical error rate using the XZZX surface code. These results promise a scalable quantum architecture with high performance for the pursuit of universal quantum computation.

arXiv:2201.09374•Jan 23, 2022•2 citations

High-Fidelity Entangled States in a Connectivity-Four Fluxonium Quantum Processor

J. Schirk, N. Bruckmoser, S. M. Taubenberger +10 more

A central challenge in fluxonium-based quantum processors is the extension of the qubit connectivity to two-dimensional lattices compatible with quantum code-error correction. Here, we present a fluxonium quantum processor that employs lumped-element resonator couplers which realizes, for the first time, a connectivity-four unit cell with suppressed parasitic interactions. We achieve parallel single-qubit gate fidelities exceeding 99.9 % in simultaneous randomized benchmarking experiments, while maintaining residual static ZZ interactions below 1 kHz across all coupled qubit pairs. We implement resonator-induced phase (RIP) gates and benchmark two-qubit gate fidelities exceeding 99 % using interleaved randomized benchmarking. To cancel spectator errors observed in two-qubit operations, we implement a refocused RIP gate, recovering coherent control in the presence of multi-qubit connectivity. Furthermore, we prepare Greenberger-Horne-Zeilinger states of up to five qubits with a tomographic fidelity of 90 %, verifying multi-qubit entanglement within the unit cell. These results establish the fluxonium-resonator-fluxonium architecture as a viable approach to realizing densely connected fluxonium processors and provide a scalable path toward quantum error-correction-compatible processor architectures.

quant-pharXiv:2608.25503•Aug 27, 2026•0 citations

Implementing Grover Algorithm on Quantum Chip Architecture Optimized with QGHNN for Fidelity and Entanglement Preservation

Ahmad Salmanogli, Hesam Zandi

This study introduces a superconducting quantum chip architecture designed to simultaneously preserve entanglement and readout fidelity, addressing one of the key trade-offs in the development of scalable quantum hardware. In conventional quantum circuits, strong qubit qubit coupling enhances entanglement but often leads to undesired crosstalk, dephasing, and reduced measurement fidelity. To mitigate these effects, we propose a hybrid multiqubit configuration consisting of nine transmon qubits organized into interior and exterior groups, interconnected via a flux tunable qubit and a network of distributed resonators. The interior qubits along with tunable qubit form an entanglement core, while the exterior qubits operate in the dispersive regime under large detuning to enable readout. The degree of entanglement can be dynamically tuned by adjusting the coupling between the central tunable qubit and the interior qubits. The total Hamiltonian includes all significant coupling contributions, encompassing effective exchange interactions among interior and exterior qubits, as well as their mediated couplings through interface resonators. By numerically solving the complete Hamiltonian alongside the Lindblad master equation, the system dynamics are characterized, allowing evaluation of both spectroscopic features and separation fidelity. Simulation results demonstrate that the proposed design maintains strong entanglement by creating the avoided-crossing region while sustaining measurement fidelity around 0.995 under realistic noise conditions. These findings confirm that entanglement strength and readout fidelity can be co-optimized within a single, reconfigurable architecture, establishing a viable route toward high-performance and scalable superconducting quantum processors.

quant-pharXiv:2511.04194•Nov 7, 2025•0 citations

Ring-Resonator-Based Coupling Architecture for Enhanced Connectivity in a Superconducting Multiqubit Network

Sumeru Hazra, Anirban Bhattacharjee, Madhavi Chand +4 more

Qubit coherence and gate fidelity are typically considered the two most useful metrics for characterizing a quantum processor. An equally useful metric is interqubit connectivity as it minimizes gate count and allows implementing algorithms efficiently with reduced error. However, interqubit connectivity in superconducting processors tends to be limited to nearest neighbor due to practical constraints in typical planar realizations. Here, we introduce a superconducting architecture that uses a ring resonator as a multiqubit coupling element to provide beyond nearest-neighbor connectivity without compromising on coupling uniformity or introducing fabrication complexities. We theoretically analyze the interqubit coupling as a function of frequency for a pair of qubits placed at different positions along the ring resonator and show that for carefully chosen operating frequency and angular spacing between the qubits, the variation of coupling can be minimized. For an operating frequency between the first two resonances of the ring resonator and a ${30}^{\ensuremath{\circ}}$ angular spacing for qubits, we compute interqubit coupling for a device capable of supporting up to 12 qubits with each qubit connected to nine other qubits. Using four qubits positioned strategically in the ring-resonator coupler, we experimentally verify the theoretical prediction for all possible angular spacings between the two qubits and demonstrate good agreement. Just like the standard bus resonator coupler, the coupling in the ring-resonator coupler is mediated via virtual photons since the operating frequency is far away from the resonant modes of the ring coupler. This ensures that any small internal loss in the ring resonator does not introduce decoherence during the coupling operation. We also compute extensions of this idea involving larger ring resonators and a multiring system and show the possibility of highly connected networks with larger number of qubits. Apart from being plug and play for existing superconducting architectures, our concept is scalable, adaptable to other platforms and has the potential to significantly accelerate progress in quantum computing, annealing, simulations, and error correction.

arXiv:2012.09463•Physical Review Applied•Aug 11, 2021•37 citations
In this work, we introduce a superconducting quantum processor architecture that uses a transmission-line resonator to implement effective all-to-all connectivity between six transmon qubits. This architecture can be used as a test bed for algorithms that benefit from high connectivity. We show that the central resonator can be used as a computational element, which offers the flexibility to encode a qubit for quantum computation or to utilize its bosonic modes that further enables quantum simulation of bosonic systems. To operate the quantum processing unit (QPU), we develop and benchmark the qubit-resonator conditional Z gate and the qubit-resonator MOVE operation. The latter allows for transferring a quantum state between one of the peripheral qubits and the computational resonator. We benchmark the QPU performance and achieve a genuinely multiqubit entangled Greenberger-Horne-Zeilinger state over all six qubits with a readout-error mitigated fidelity of F | ψ 〉 GHZ = 0.86 .
Enhancing qubit connectivity in quantum processors is an important milestone for more efficient implementation of algorithms and novel error-correction protocols. While all-to-all connectivity has been demonstrated in quantum processors based on ion traps and neutral atoms, the exploration of enhanced connectivity in the superconducting qubit architecture has been a more recent endeavor. Here, we demonstrate the operation of a network comprising six superconducting transmon qubits with a novel, beyond-nearest-neighbor connectivity. We use a circular ring resonator with six qubits placed on the periphery at 60 ∘ spacing and capacitively coupled to it in a three-dimensional circuit-QED architecture. The ring resonator acts as a two-path coupler between each pair of qubits, and we present results demonstrating that each qubit has finite coupling to three other qubits with negligible coupling to the remaining two qubits. In this architecture, with fixed-frequency qubits and always-on coupling, we benchmark the single-qubit and two-qubit gates using randomized benchmarking. We find that our gate fidelities are strongly affected by the enhanced connectivity. We characterize the spread in qubit frequencies due to cross-Kerr terms and quantify its detrimental effect on the performance of single- and two-qubit gates. Finally, we analyze the effect of the spectator qubits using numerical simulations and propose a path toward optimizing this system and achieving > 99 % two-qubit gate fidelities across all connected qubit pairs.
Superconducting qubits provide a promising approach to large-scale fault-tolerant quantum computing. However, qubit connectivity on a planar surface is typically restricted to only a few neighboring qubits. Achieving longer-range and more flexible connectivity, which is particularly appealing in light of recent developments in error-correcting codes, however, usually involves complex multilayer packaging and external cabling, which is resource intensive and can impose fidelity limitations. Here, we propose and realize a high-speed on-chip quantum processor that supports reconfigurable all-to-all coupling with a large on-off ratio. We implement the design in a four-node quantum processor, built with a modular design comprising a wiring substrate coupled to two separate qubit-bearing substrates, each including two single-qubit nodes. We use this device to demonstrate reconfigurable controlled- Z gates across all qubit pairs, with a benchmarked average fidelity of 96.00 % ± 0.08 % and best fidelity of 97.14 % ± 0.07 % , limited mainly by dephasing in the qubits. We also generate multiqubit entanglement, distributed across the separate modules, demonstrating GHZ-3 and GHZ-4 states with fidelities of 88.15 % ± 0.24 % and 75.18 % ± 0.11 % , respectively. This approach promises efficient scaling to larger-scale quantum circuits and offers a pathway for implementing quantum algorithms and error-correction schemes that benefit from enhanced qubit connectivity. Published by the American Physical Society 2024
The technological development of hardware heading toward universal fault-tolerant quantum computation requires a large-scale processing unit with high performance. While fluxonium qubits are promising with high coherence and large anharmonicity, their scalability has not been systematically explored. In this work, we propose a superconducting quantum information processor based on compact high-coherence fluxoniums with suppressed crosstalk, reduced design complexity, improved operational efficiency, high-fidelity gates, and resistance to parameter fluctuations. In this architecture, the qubits are readout dispersively using individual resonators connected to a common bus and manipulated via combined on-chip RF and DC control lines, both of which can be designed to have low crosstalk. A multi-path coupling approach enables exchange interactions between the high-coherence computational states and at the same time suppresses the spurious static ZZ rate, leading to fast and high-fidelity entangling gates. We numerically investigate the cross resonance controlled-NOT and the differential AC-Stark controlled-Z operations, revealing low gate error for qubit-qubit detuning bandwidth of up to 1 GHz. Our study on frequency crowding indicates high fabrication yield for quantum processors consisting of over thousands of qubits. In addition, we estimate low resource overhead to suppress logical error rate using the XZZX surface code. These results promise a scalable quantum architecture with high performance for the pursuit of universal quantum computation.
A central challenge in fluxonium-based quantum processors is the extension of the qubit connectivity to two-dimensional lattices compatible with quantum code-error correction. Here, we present a fluxonium quantum processor that employs lumped-element resonator couplers which realizes, for the first time, a connectivity-four unit cell with suppressed parasitic interactions. We achieve parallel single-qubit gate fidelities exceeding 99.9 % in simultaneous randomized benchmarking experiments, while maintaining residual static ZZ interactions below 1 kHz across all coupled qubit pairs. We implement resonator-induced phase (RIP) gates and benchmark two-qubit gate fidelities exceeding 99 % using interleaved randomized benchmarking. To cancel spectator errors observed in two-qubit operations, we implement a refocused RIP gate, recovering coherent control in the presence of multi-qubit connectivity. Furthermore, we prepare Greenberger-Horne-Zeilinger states of up to five qubits with a tomographic fidelity of 90 %, verifying multi-qubit entanglement within the unit cell. These results establish the fluxonium-resonator-fluxonium architecture as a viable approach to realizing densely connected fluxonium processors and provide a scalable path toward quantum error-correction-compatible processor architectures.
This study introduces a superconducting quantum chip architecture designed to simultaneously preserve entanglement and readout fidelity, addressing one of the key trade-offs in the development of scalable quantum hardware. In conventional quantum circuits, strong qubit qubit coupling enhances entanglement but often leads to undesired crosstalk, dephasing, and reduced measurement fidelity. To mitigate these effects, we propose a hybrid multiqubit configuration consisting of nine transmon qubits organized into interior and exterior groups, interconnected via a flux tunable qubit and a network of distributed resonators. The interior qubits along with tunable qubit form an entanglement core, while the exterior qubits operate in the dispersive regime under large detuning to enable readout. The degree of entanglement can be dynamically tuned by adjusting the coupling between the central tunable qubit and the interior qubits. The total Hamiltonian includes all significant coupling contributions, encompassing effective exchange interactions among interior and exterior qubits, as well as their mediated couplings through interface resonators. By numerically solving the complete Hamiltonian alongside the Lindblad master equation, the system dynamics are characterized, allowing evaluation of both spectroscopic features and separation fidelity. Simulation results demonstrate that the proposed design maintains strong entanglement by creating the avoided-crossing region while sustaining measurement fidelity around 0.995 under realistic noise conditions. These findings confirm that entanglement strength and readout fidelity can be co-optimized within a single, reconfigurable architecture, establishing a viable route toward high-performance and scalable superconducting quantum processors.
Qubit coherence and gate fidelity are typically considered the two most useful metrics for characterizing a quantum processor. An equally useful metric is interqubit connectivity as it minimizes gate count and allows implementing algorithms efficiently with reduced error. However, interqubit connectivity in superconducting processors tends to be limited to nearest neighbor due to practical constraints in typical planar realizations. Here, we introduce a superconducting architecture that uses a ring resonator as a multiqubit coupling element to provide beyond nearest-neighbor connectivity without compromising on coupling uniformity or introducing fabrication complexities. We theoretically analyze the interqubit coupling as a function of frequency for a pair of qubits placed at different positions along the ring resonator and show that for carefully chosen operating frequency and angular spacing between the qubits, the variation of coupling can be minimized. For an operating frequency between the first two resonances of the ring resonator and a ${30}^{\ensuremath{\circ}}$ angular spacing for qubits, we compute interqubit coupling for a device capable of supporting up to 12 qubits with each qubit connected to nine other qubits. Using four qubits positioned strategically in the ring-resonator coupler, we experimentally verify the theoretical prediction for all possible angular spacings between the two qubits and demonstrate good agreement. Just like the standard bus resonator coupler, the coupling in the ring-resonator coupler is mediated via virtual photons since the operating frequency is far away from the resonant modes of the ring coupler. This ensures that any small internal loss in the ring resonator does not introduce decoherence during the coupling operation. We also compute extensions of this idea involving larger ring resonators and a multiring system and show the possibility of highly connected networks with larger number of qubits. Apart from being plug and play for existing superconducting architectures, our concept is scalable, adaptable to other platforms and has the potential to significantly accelerate progress in quantum computing, annealing, simulations, and error correction.