Abstract
Within a dense environment () at ultracold temperatures (), 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 Rydberg states, and we mainly observe a state change of the Rydberg electron to a high orbital angular momentum , with the released energy being converted into kinetic energy of the Rydberg atom. Unexpectedly, the measurements show a threshold behavior at for the inelastic collision time leading to increased lifetimes of the Rydberg state independent of the densities investigated. Even at very high densities (), the lifetime of a Rydberg atom exceeds at compared to at . In addition, a second observed reaction mechanism, namely, molecule formation, was studied. Both reaction products are equally probable for , but the fraction of created drops to below 10% for .
6 More- Received 4 May 2016
DOI:https://doi.org/10.1103/PhysRevX.6.031020
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Published by the American Physical Society
Physics Subject Headings (PhySH)
Synopsis
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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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 () 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 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 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.