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Ultracold Chemical Reactions of a Single Rydberg Atom in a Dense Gas

Michael Schlagmüller, Tara Cubel Liebisch, Felix Engel, Kathrin S. Kleinbach, Fabian Böttcher, Udo Hermann, Karl M. Westphal, Anita Gaj, Robert Löw, Sebastian Hofferberth, Tilman Pfau, Jesús Pérez-Ríos, and Chris H. Greene
Phys. Rev. X 6, 031020 – Published 10 August 2016
Physics logo See Synopsis: Rydberg Atom Takes a Dip in the Cold Sea

Abstract

Within a dense environment (ρ1014atoms/cm3) at ultracold temperatures (T<1μK), a single atom excited to a Rydberg state acts as a reaction center for surrounding neutral atoms. At these temperatures, almost all neutral atoms within the Rydberg orbit are bound to the Rydberg core and interact with the Rydberg atom. We have studied the reaction rate and products for nS Rb87 Rydberg states, and we mainly observe a state change of the Rydberg electron to a high orbital angular momentum l, with the released energy being converted into kinetic energy of the Rydberg atom. Unexpectedly, the measurements show a threshold behavior at n100 for the inelastic collision time leading to increased lifetimes of the Rydberg state independent of the densities investigated. Even at very high densities (ρ4.8×1014cm3), the lifetime of a Rydberg atom exceeds 10μs at n>140 compared to 1μs at n=90. In addition, a second observed reaction mechanism, namely, Rb2+ molecule formation, was studied. Both reaction products are equally probable for n=40, but the fraction of Rb2+ created drops to below 10% for n90.

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  • Received 4 May 2016

DOI:https://doi.org/10.1103/PhysRevX.6.031020

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Atomic, Molecular & Optical

Synopsis

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Rydberg Atom Takes a Dip in the Cold Sea

Published 10 August 2016

A Rydberg atom immersed in a dense cloud of ultracold neutral atoms can undergo two chemical processes.

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Authors & Affiliations

Michael Schlagmüller, Tara Cubel Liebisch, Felix Engel, Kathrin S. Kleinbach, Fabian Böttcher, Udo Hermann, Karl M. Westphal, Anita Gaj, Robert Löw, Sebastian Hofferberth, and Tilman Pfau*

  • 5. Physikalisches Institut and Center for Integrated Quantum Science and Technology (IQST), Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany

Jesús Pérez-Ríos and Chris H. Greene

  • Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA

  • *t.pfau@physik.uni-stuttgart.de

Popular Summary

Because chemical reactions typically occur very rapidly (i.e., within a few femtoseconds) and on very small length scales of only a few nanometers, it is nearly impossible to observe these reactions in detail. Accordingly, it is desirable to slow down the reaction process, which we do here using ultracold atoms. In addition, the length scales are enlarged by utilizing Rydberg atoms to permit the use of state-of-the-art measurement devices. By combining the excitation of very high-lying Rydberg states (n>100) and the coldest and densest samples available in atomic physics (Bose-Einstein condensates), we attain a regime in which the reaction process between two atoms becomes observable.

We consider an ensemble of roughly two million rubidium atoms held below 1μK above absolute zero. When Rydberg atoms are excited in an ultracold atom cloud, everything slows down, including the motion of the Rydberg atom and the motion of the ultracold ground-state atoms. In the dense cloud, ground-state atoms might sit accidentally inside the orbit of the Rydberg electron. The arising reaction dynamics now occur in the microscopic regime and on microsecond time scales, which makes them more readily observable using current technologies. We observe and study two reaction channels: an angular-momentum change of the Rydberg electron and the formation of Rb2+ molecules. These reaction channels are explained from a fully quantum description of the involved energy landscape, yielding precise information about the ultracold chemical reactions taking place within this fascinating system. We show that it is possible to control the system such that, for the first time, a Rydberg orbit can be directly imaged in real space.

We expect that our work will have applications in Rydberg quantum optics, quantum simulation, and quantum computation.

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Vol. 6, Iss. 3 — July - September 2016

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It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 3.0 License. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

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