Synchronization in the quaternionic Kuramoto model

TL;DR

This paper extends the Kuramoto model to quaternions, analyzing synchronization phenomena under various coupling strengths, revealing new periodic orbits, stability properties, and conjecturing universal synchronization in quaternionic oscillators.

Contribution

It introduces a quaternionic Kuramoto model, establishes synchronization conditions, and uncovers novel periodic orbits and stability characteristics unique to quaternionic oscillators.

Findings

Synchronization occurs under strong coupling for all N≥2.

New periodic orbits emerge at weak coupling for N=2.

Quaternionic synchronization persists even at super weak coupling for N=3.

Abstract

In this paper, we propose an $N$ oscillators Kuramoto model with quaternions $\mathbb{H}$. In case the coupling strength is strong, a sufficient condition of synchronization is established for general $N\geqslant 2$. On the other hand, we analyze the case when the coupling strength is weak. For $N=2$, when coupling strength is weak (below the critical coupling strength $\lambda_c$), we show that new periodic orbits emerge near each equilibrium point, and hence phase-locking state exists. This phenomenon is different from the real Kuramoto system since it is impossible to arrive at any synchronization when $\lambda<\lambda_c$. We prove a theorem that states a set of closed and dense contour forms near each equilibrium point, resembling a tree's growth rings. In other words, the trajectory of phase difference lies on a $4D$-torus surface. Therefore, this implies that the phase-locking state is Lyapunov stable but not asymptotically stable. The proof uses a new infinite buffer method (``$\delta/n$ criterion") and a Lyapunov function argument. This has been studied both analytically and numerically. For $N=3$, we consider the ``Lion Dance flow", the analog of Cherry flow for our model, to demonstrate that the quaternionic synchronization exists even when the coupling strength is ``super weak" (when $\lambda/\omega <0.85218915...$). Also, numerical evaluation reveals that when $N>3$, the stable manifold of Lion Dance flow exists, and the number of these equilibria is $\lfloor \frac{N-1}{2}\rfloor$. Therefore, we conjecture that Lyapunov stable quaternionic synchronization always exists.