Multiplet Supercurrents in a Josephson Circuit

TL;DR

This paper investigates a Josephson circuit with three superconducting electrodes, demonstrating multiplet resonances and a novel supercurrent, which could enable topologically protected states at higher energy scales than traditional multiterminal junctions.

Contribution

The study introduces a Josephson circuit with three electrodes that exhibits robust multiplet resonances and a new supercurrent, expanding the understanding of topological phenomena in simpler two-terminal systems.

Findings

Demonstrated dynamic generation of multiplet resonances.

Resonances are robust at elevated temperatures.

Observed a novel supercurrent coupling voltage-biased contacts.

Abstract

Multiterminal Josephson junctions are a promising platform to host synthetic topological phases of matter and Floquet states. However, the energy scales governing topological protection in these devices are on the order of the spacing between Andreev bound states. Recent theories suggest that similar phenomena may instead be explored in circuits composed of two-terminal Josephson junctions, allowing for the topological protection to be controlled by the comparatively large Josephson energy. Here, we explore a Josephson circuit, in which three superconducting electrodes are connected through Josephson junctions to a common superconducting island. We demonstrate the dynamic generation of multiplet resonances, which have previously been observed in multiterminal Josephson junctions. The multiplets are found to be robust to elevated temperatures and are confirmed by exhibiting the expected Shapiro step quantization under a microwave drive. We also find an unexpected novel supercurrent, which couples a pair of contacts that are both voltage-biased with respect to the common superconducting island. We show that this supercurrent results from synchronization of the phase dynamics and pose the question whether it should also carry a topological contribution.