article published yes Lucia Vigliotti author 539e1e1a-e604-11ee-a1df-f02b018e5c8c Andrew P Higginbotham author 4AD6785A-F248-11E8-B48F-1D18A9856A870000-0003-2607-2363 Maksym Serbyn author 47809E7E-F248-11E8-B48F-1D18A9856A870000-0002-2399-5827 MaSe department AnHi department Center for Correlated Quantum Materials and Solid State Quantum Systems: Probing topology in circuits and quantum materials project 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. https://research-explorer.ista.ac.at/download/23029/23069/2026_PhysicalReviewB_Vigliotti.pdf application/pdfno https://creativecommons.org/licenses/by/4.0/ American Physical Society2026 eng 2469-9950 2469-9969 2603.0637110.1103/cw3m-thsw 11419 Vigliotti, Lucia, et al. “Plasmon Decay and Nonequilibrium Steady States in Josephson Junction Chains.” <i>Physical Review B</i>, vol. 114, no. 19, 194501, American Physical Society, 2026, doi:<a href="https://doi.org/10.1103/cw3m-thsw">10.1103/cw3m-thsw</a>. Vigliotti L, Higginbotham AP, Serbyn M. 2026. Plasmon decay and nonequilibrium steady states in Josephson junction chains. Physical Review B. 114(19), 194501. Vigliotti, Lucia, Andrew P Higginbotham, and Maksym Serbyn. “Plasmon Decay and Nonequilibrium Steady States in Josephson Junction Chains.” <i>Physical Review B</i>. American Physical Society, 2026. <a href="https://doi.org/10.1103/cw3m-thsw">https://doi.org/10.1103/cw3m-thsw</a>. Vigliotti L, Higginbotham AP, Serbyn M. Plasmon decay and nonequilibrium steady states in Josephson junction chains. <i>Physical Review B</i>. 2026;114(19). doi:<a href="https://doi.org/10.1103/cw3m-thsw">10.1103/cw3m-thsw</a> Vigliotti, L., Higginbotham, A. P., &#38; Serbyn, M. (2026). Plasmon decay and nonequilibrium steady states in Josephson junction chains. <i>Physical Review B</i>. American Physical Society. <a href="https://doi.org/10.1103/cw3m-thsw">https://doi.org/10.1103/cw3m-thsw</a> L. Vigliotti, A.P. Higginbotham, M. Serbyn, Physical Review B 114 (2026). L. Vigliotti, A. P. Higginbotham, and M. Serbyn, “Plasmon decay and nonequilibrium steady states in Josephson junction chains,” <i>Physical Review B</i>, vol. 114, no. 19. American Physical Society, 2026. 230292026-10-02T08:33:31Z2026-10-07T09:42:41Z