Quantum 2025 – scientific programme

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TUE: Tuesday Contributed Sessions

TUE 11: Quantum Optics and Quantum Computation

TUE 11.6: Talk

Tuesday, September 9, 2025, 15:30–15:45, ZHG104

Observation of Shapiro steps in an ultracold atomic Josephson junction — •Erik Bernhart¹, Marvin Röhrle¹, Florian Binoth¹, Vijay Pal Singh², Ludwig Mathey³, Luigi Amico^2,4, and Herwig Ott¹ — ¹Department of Physics and Research Center OPTIMAS, RPTU Kaiserslautern-Landau, Germany — ²Quantum Research Centre, Technology Innovation Institute, Abu Dhabi, UAE — ³Zentrum für Optische Quantentechnologien and Institut für Quantenphysik, Universität Hamburg — ⁴INFN-Sezione di Catania, Via S. Sofia 64, 95127 Catania, Italy

An ultracold atomic Josephson junction is an elementary example of quantum transport and offers a unique platform for quantum simulation of superconducting circuits. The related Josephson effect, where a dissipation-less supercurrent through a tunneling barrier is caused by a phase difference, is well known in superconductors. Is such a junction externally driven, the current-voltage characteristic displays discrete steps, named Shapiro steps, the basis of today’s voltage standard. We report on the experimental observation of Shapiro steps in a driven Josephson junction in a gas of ultracold atoms. We demonstrate the universal features of the steps, most noticeable the quantization of the step height. Our experiment provides insights in the microscopic dissipative dynamics, where we observe that the dynamics are caused by phonon emission and collective excitations. The experimental results are underpinned by extensive numerical simulations. Our work expands the understanding of the microscopic dynamics of Shapiro steps and it transfers the voltage standard to ultracold quantum gases.

Keywords: Ultracold Quantum Gases; Quantum Transport; Atomic Josephson Junction; Driven Superfluid Systems