Effects of Quantum and Thermal Fluctuations on Stability of Phase-locking in One-dimensional Long Josephson Junction Stacks

Giovanni Filatrella, Niels Grønbech‐Jensen, R. Monaco +6 more

Frank Schlawin, Anastasia S. D. Dietrich, Dieter Jaksch

We simulate the current-voltage relation of short layered superconductors, which we model as stacks of capacitively coupled Josephson junctions. The system is driven by external laser fields, in order to optically control the voltage drop across the junction. We identify parameter regimes in which supercurrents can be stabilized against thermally induced phase slips, thus reducing the effective voltage across the superconductor. Furthermore, single driven Josephson junctions are known to exhibit phase-locked states, where the superconducting phase is locked to the driving field. We numerically observe their persistence in the presence of thermal fluctuations and capacitive coupling between adjacent Josephson junctions. Our results indicate how macroscopic material properties can be manipulated by exploiting the large optical nonlinearities of Josephson plasmons.

David B. Haviland, Edmund Chow, Per Delsing

Alexey Vladimirovich Ustinov, H. Kohlstedt, Christoph Heiden

A system of two vertically stacked Nb/Al-AlOx/Nb long Josephson junctions is studied experimentally. The magnetic coupling between the junctions is provided by their common electrode of the thickness d∼λL. The current-voltage characteristics of the stack displays resonant steps which are understood to be the phase-locked flux-flow resonances of the two junctions. These modes can be tuned by the magnetic field in a broad voltage range which corresponds to the Josephson frequencies between 150 and 600 GHz. Our observations suggest a possibility of application of the stacked long Josephson junctions as local oscillators for millimeter and submillimeter wave circuits.

E. Goldobin, H. Kohlstedt, Alexey Vladimirovich Ustinov

A tuning technique for mutual phase locking of two vertically stacked long Josephson junctions is suggested and successfully tested. The technique is based on passing a current through the middle electrode between two tunnel barriers. Mutually synchronized oscillation modes in the Nb/Al–AlOx/Nb stack are found to be tunable in the frequency range from 180 to 420 GHz. Presented results extend the possibility of using stacked long Josephson junctions as coherently operating oscillators for millimeter and submillimeter wave bands.

Igor S. Beloborodov, F. W. J. Hekking, F. Pistolesi