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

Jay Deshmukh1,*,†, Srijita Das1, Binoy Nambiar2, Madhavi Chand1, Kishor V. Salunkhe1, Gautham Umasankar3,‡, Aneesh Kamat4,§, Kishan Bhowal5, Gaurav Agarwal6,‡ et al.

Lakshay Bharadwaj1, Eeshita Chawla1, Panya Jain1, Meghan P. Patankar1, and R. Vijay1,¶

  • *Contact author: jay.deshmukh@tifr.res.in
  • †Present address: Alice & Bob, Paris 75015, France.
  • ‡Present address: Department of Applied Physics, Yale University, New Haven, Connecticut 06520, USA.
  • §Present address: Department of Physics, RWTH Aachen University, Templergraben 55, Aachen 52062, Germany.
  • Contact author: r.vijay@tifr.res.in
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Phys. Rev. Research 8, 033049 – Published 13 July, 2026

DOI: https://doi.org/10.1103/6jdh-pm39

Abstract

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.

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Phys. Rev. Research 8, 033049– Published 13 July, 2026
  • Received 1 June 2025
  • Accepted 16 June 2026
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