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Circuit-QED Lattice System with Flexible Connectivity and Gapped Flat Bands for Photon-Mediated Spin Models

Kellen O'Brien*, Maya Amouzegar, Won Chan Lee, and Martin Ritter

Alicia J. Kollár

  • *Contact author: kobrie@umd.edu
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PRX Quantum 7, 010321 – Published 30 January, 2026

DOI: https://doi.org/10.1103/z9n2-mmmf

Abstract

Quantum spin models are ubiquitous in solid-state physics, but classical simulation of them remains extremely challenging. Experimental testbed systems with a variety of spin-spin interactions and measurement channels are therefore needed. One promising potential route to such testbeds is provided by microwave-photon-mediated interactions between superconducting qubits, where native strong light-matter coupling enables significant interactions even for virtual-photon-mediated processes. In this approach, the spin-model connectivity is set by the photonic mode structure, rather than the spatial structure of the qubit. Lattices of coplanar-waveguide (CPW) resonators have been demonstrated to allow extremely flexible connectivities and can therefore host a huge variety of photon-mediated spin models. However, large-scale CPW lattices with nontrivial band structures have never before been successfully combined with superconducting qubits. Here we present the first such device featuring a quasi-1D CPW lattice with multiple transmon qubits. We demonstrate that superconducting-qubit readout and diagnostic techniques can be generalized to this highly multimode environment and observe the effective qubit-qubit interaction mediated by the bands of the resonator lattice. This device completes the toolkit needed to realize CPW lattices with qubits in one or two Euclidean dimensions, or negatively curved hyperbolic space, and paves the way to driven-dissipative spin models with a large variety of connectivities.

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Popular Summary

Photons are particles of light which exist across the electromagnetic spectrum, from radio and microwaves to visible and ultraviolet light. By making circuits out of superconductors which carry current without generating heat and cooling the devices to very low temperatures, it is possible to make microwave circuits where the photons move like electrons moving in a material. Instead of being limited by chemistry, the spatial structure and connectivity with which the photons move is instead limited by the ability to design precision circuits. In this work, the researchers harness arrays of superconducting microwave resonators to produce microwave metamaterials in which photons carry excitations between superconducting qubits.

The researchers have implemented and characterized a full-scale device featuring transmon qubits coupled to microwave photons moving in an unconventional lattice geometry which will give rise to interesting forms of qubit-qubit interaction and have adapted spectroscopic techniques to accurately characterize the performance of the device. This device and the methods developed here pave the way toward larger-scale implementations in which these newly created interactions will give rise to unconventional magnetism. Future projects plan to capitalize on the capability of the resonator lattice platform to realize non-Euclidean connectivities between qubits.

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PRX Quantum 7, 010321– Published 30 January, 2026
  • Received 8 July 2025
  • Revised 5 October 2025
  • Accepted 5 December 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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