Observation of the Josephson plasma mode for a superfluid $^3$He weak link

TL;DR

This paper reports the direct observation of the Josephson plasma mode in superfluid helium-3, demonstrating how phase oscillations relate to the weak link's critical current and confirming theoretical predictions.

Contribution

First direct measurement of the Josephson plasma mode in superfluid helium-3, linking phase oscillation frequency to critical current with experimental validation.

Findings

Phase oscillation frequency decreases as phase approaches π.

Low amplitude frequency measures the critical current.

Experimental results agree with theoretical models.

Abstract

The quantum phase difference across a superfluid Josephson-like weak link may exhibit periodic motion describable by a nonlinear equation identical to that of a rigid pendulum. We have directly observed this mode and find that the phase oscillation frequency decreases toward zero as the phase amplitude increases toward $\pi$. We also find that the low amplitude frequency is a direct measure of the weak link's critical current in quantitative agreement with theory.