Quantum dynamics of Josephson fluxons

• Applicant: Professor Alexey V. Ustinov, Ph.D.
• Subject Area: Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405869393

• Final Report Year: 2024

Final Report Abstract

In this project, we have for the first time studied long Josephson junctions with electrodes made of a high kinetic inductance material. By using disordered granular aluminum as such a material, we experimentally demonstrated a drastic reduction of the Swihart velocity in a long Josephson junction. The corresponding reduction of the vortex size should facilitate the crossover to the quantum dynamics. The high kinetic inductance electrodes also enable scaling up the junction impedance and facilitate solving the long-standing problem of impedance matching LJJs to external circuits. The studied long Josephson junctions deposited on resonators showed interesting but complex physics with a clear and unambiguous signal of a quantum two-level dynamics. Spectroscopic and time-domain measurements indicated two-level systems interacting with the resonators with comparably long coherence times. The underlying physical process associated with these magnetically-tunable twolevel systems is not clear to date and requires more theoretical as well as experimental investigations.

Publications

• Quantum beats of a magnetic fluxon in a two-cell SQUID. Physical Review B, 103(22).
  Moskalenko, I. N.; Besedin, I. S.; Seidov, S. S.; Fistul, M. V. & Ustinov, A. V.
  
• Fluxons in high-impedance long Josephson junctions. Applied Physics Letters, 120(11).
  Wildermuth, Micha; Powalla, Lukas; Voss, Jan Nicolas; Schön, Yannick; Schneider, Andre; Fistul, Mikhail V.; Rotzinger, Hannes & Ustinov, Alexey V.
  
• Experimental Condensed Matter Physics Band 33: Quantum Tunneling of Josephson Vortices in High-Impedance Long Junctions. KIT Scientific Publishing
  Wildermuth, M. M.