@article{23029,
  abstract     = {Josephson junction (JJ) chains combine the coherence of superconductivity with the controllability of microwave-frequency circuits, making them a powerful platform for circuit quantum electrodynamics. In this work, we consider a long JJ chain that effectively realizes a multimode cavity with nonlinear dispersion and additional multimode interactions. Individual modes appearing due to the finite size of the chain can be experimentally probed via microwave spectroscopy, both in equilibrium and in driven far-from-equilibrium settings. We study the role of multimode interactions in degrading internal coherence—observable as excess linewidth—in both equilibrium and driven regimes. Focusing on two-into-two mode scattering as the leading relaxation process, we classify the relevant scattering processes and derive their expected temperature- and frequency-scaling under equilibrium conditions. For experimentally relevant parameters, we show that the equilibrium decay rate is dominated by nonresonant processes, however, weakly driving a particular set of modes out of equilibrium enhances resonant scattering, leading to observable signatures in the distribution function and linewidth. Finally, in the strong nonequilibrium regime, we report a crossover to a qualitatively different nonequilibrium steady state.},
  author       = {Vigliotti, Lucia and Higginbotham, Andrew P and Serbyn, Maksym},
  issn         = {2469-9969},
  journal      = {Physical Review B},
  number       = {19},
  publisher    = {American Physical Society},
  title        = {{Plasmon decay and nonequilibrium steady states in Josephson junction chains}},
  doi          = {10.1103/cw3m-thsw},
  volume       = {114},
  year         = {2026},
}

@article{21340,
  abstract     = {Equilibrium quantum systems are often described by a gas of weakly interacting normal modes. Bringing such systems far from equilibrium, however, can drastically enhance mode-to-mode interactions. Understanding the resulting liquid is a fundamental question for quantum statistical mechanics and a practical question for engineering driven quantum devices. To tackle this question, we probe the non-equilibrium kinetics of one-dimensional plasmons in a long chain of Josephson junctions. We introduce multimode spectroscopy to controllably study the departure from equilibrium, witnessing the evolution from pairwise coupling between plasma modes at weak driving to dramatic, high-order, cascaded couplings at strong driving. Scaling to many-mode drives, we stimulate interactions between hundreds of modes, resulting in near-continuum internal dynamics. Imaging the resulting non-equilibrium plasmon populations, we then resolve the nonlocal redistribution of energy in the response to a weak perturbation—an explicit verification of the emergence of a strongly interacting, non-equilibrium liquid of plasmons.},
  author       = {Bubis, Anton and Vigliotti, Lucia and Serbyn, Maksym and Higginbotham, Andrew P},
  issn         = {2375-2548},
  journal      = {Science Advances},
  number       = {7},
  publisher    = {AAAS},
  title        = {{Non-equilibrium plasmon liquid in a Josephson junction chain}},
  doi          = {10.1126/sciadv.ady7222},
  volume       = {12},
  year         = {2026},
}