Nonlocal long-range synchronization of planar Josephson junction arrays

TL;DR

This study demonstrates long-range synchronization in planar Josephson junction arrays due to nonlocal electrodynamics, revealing enhanced coupling and complex phenomena like bi-stability and incorrect Shapiro steps.

Contribution

It provides new insights into nonlocal interactions in planar Josephson junction arrays, showing their role in enabling large-scale phase-locking and complex dynamic behaviors.

Findings

Robust phase-locking despite large inter-junction distances

Observation of bi-stable critical currents and re-entrant superconductivity

Detection of incorrect Shapiro steps due to nonlocal electrodynamics

Abstract

We study arrays of planar Nb Josephson junctions with contacts to intermediate electrodes, which allow measurements of individual junctions and, thus, provide an insight into intricate array dynamics. We observe a robust phase-locking of arrays, despite a significant inter-junction separation. Several unusual phenomena are reported, such as a bi-stable critical current with re-entrant superconductivity upon switching of nearby junctions; and incorrect Shapiro steps, occurring at mixing frequencies between the external RF radiation and the internal Josephson frequency in nearby junctions. Our results reveal a surprisingly strong and long-range inter-junction interaction. It is attributed to nonlocality of planar junction electrodynamics, caused by the long-range spreading of stray electromagnetic fields. The nonlocality greatly enhances the high-frequency interjunction coupling and enables large-scale synchronization. Therefore, we conclude that planar geometry is advantageous for realization of coherent Josephson electronics.