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.
@article{arxiv.2409.03340,
title = {Observation of Shapiro steps in an ultracold atomic Josephson junction},
author = {Erik Bernhart and Marvin Röhrle and Vijay Pal Singh and Ludwig Mathey and Luigi Amico and Herwig Ott},
journal= {arXiv preprint arXiv:2409.03340},
year = {2026}
}