Dynamical Stabilization of Multiplet Supercurrents in Multi-terminal Josephson Junctions

TL;DR

This paper demonstrates that multiplet supercurrents in multi-terminal Josephson junctions can arise from purely dynamical phase correlations, with potential applications in topological matter and qubit design.

Contribution

It shows that multiplet resonances can be explained by a three-terminal circuit model, revealing a dynamical stabilization mechanism analogous to Kapitza's inverted pendulum.

Findings

Multiplet resonances observed in graphene Josephson junctions and circuit simulations.

Dynamical stabilization mechanism akin to Kapitza's inverted pendulum.

Presence of robust $ ext{cos}2 ext{phi}$ energy contributions for qubit engineering.

Abstract

The dynamical properties of multi-terminal Josephson junctions have recently attracted interest, driven by the promise of new insights into synthetic topological phases of matter and Floquet states. This effort has culminated in the discovery of Cooper multiplets, in which the splitting of a Cooper pair is enabled via a series of Andreev reflections that entangle four (or more) electrons. In this text, we show conclusively that multiplet resonances can also emerge as a consequence of the three terminal circuit model. The supercurrent appears due to the correlated phase dynamics at values that correspond to the multiplet condition $nV_1 = -mV_2$ of applied bias. The emergence of multiplet resonances is seen in i) a nanofabricated three-terminal graphene Josephson junction, ii) an analog three terminal Josephson junction circuit, and iii) a circuit simulation. The mechanism which stabilizes the state of the system under those conditions is purely dynamical, and a close analog to Kapitza's inverted pendulum problem. We describe parameter considerations that best optimize the detection of the multiplet lines both for design of future devices. Further, these supercurrents have a classically robust $\cos2\phi$ energy contribution, which can be used to engineer qubits based on higher harmonics.