Dresden 2026 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 28: Superconducting Electronics: SQUIDs and other Josephson Circuits and Components
TT 28.11: Talk
Tuesday, March 10, 2026, 12:15–12:30, CHE/0089
Nonequilibrium plasmon fluid in a Josephson junction chain — Anton V. Bubis1, •Lucia Vigliotti1, Maksym Serbyn1, and Andrew P. Higginbotham2 — 1Institute of Science and Technology Austria, Am Campus 1, Klosterneuburg, 3400, Austria — 2James Franck Institute and Department of Physics, University of Chicago, 929 E 57th St, Chicago, Illinois 60637, USA
With the recent push towards the development of quantum technologies, multimode quantum systems, such as superconducting resonators, have drawn considerable attention. These systems can be generally described as weakly nonlinear bosonic modes coupled to a thermal bath and subject to coherent driving. As the number of modes grows and extrinsic decoherence is reduced, understanding the mode-to-mode interaction becomes increasingly relevant, especially far from equilibrium. We consider the interacting plasmonic modes emerging in a long chain of Josephson junctions (JJs), probed via multitone microwave spectroscopy. We investigate the nonequilibrium kinetics of the resulting one-dimensional quantum fluid both theoretically and experimentally, focusing on four-wave-mixing processes. Under two coherent drives, we observe cascaded coupling between plasmonic modes, reproduced using input-output theory applied to nonlinear mode multiplets. Under incoherent broadband drive, we explore the kinetics of weakly populated modes and numerically implement a kinetic equation that predicts the non-equilibrium steady state and captures the excess linewidth of non-driven modes. Our work establishes the key role of four-wave-mixing nonlinearities in the non-equilibrium response of JJ chains.
Keywords: Josephson-junction chain; Plasmonic modes; Superconducting circuits; Circuit QED; Nonequilibrium dynamics