Observation of Shapiro steps in an ultracold atomic Josephson junction

TL;DR

This paper reports the first observation of Shapiro steps in an ultracold atomic Josephson junction, revealing universal features and microscopic dissipative dynamics involving phonon emission and solitonic excitations.

Contribution

It demonstrates the occurrence of Shapiro steps in ultracold atomic systems and provides detailed insights into their microscopic dissipative mechanisms.

Findings

Shapiro steps observed in ultracold atomic Josephson junctions

Steps linked to phonon emission and soliton nucleation

Experimental results supported by classical-field simulations

Abstract

The current-voltage characteristic of a driven superconducting Josephson junction displays discrete steps. This phenomenon, called the Shapiro steps, forms today's voltage standard! Here, we report the observation of Shapiro steps in a driven Josephson junction in a gas of ultracold atoms. We demonstrate that the steps exhibit universal features, and provide insight into the microscopic dissipative dynamics that we directly observe in the experiment. We find that the steps are directly connected to phonon emission and nucleation of solitonic excitations, whose dynamics we follow in space and time. The experimental results are underpinned by extensive numerical simulations based on classical-field dynamics and may enable metrological and fundamental advances.