Atomic Pair-State Interferometer: Controlling and Measuring an Interaction-Induced Phase Shift in Rydberg-Atom Pairs

Abstract

We present experiments measuring an interaction-induced phase shift of Rydberg atoms at Stark-tuned Förster resonances. The phase shift features a dispersive shape around the resonance, showing that the interaction strength and sign can be tuned coherently. We use a pair-state interferometer to measure the phase shift. Although the coupling between pair states is coherent on the time scale of the experiment, a loss of visibility occurs as a pair-state interferometer involves three simultaneously interfering paths and only one of them is phase shifted by the mutual interaction. Despite additional dephasing mechanisms, a pulsed Förster coupling sequence allows for observation of coherent dynamics around the Förster resonance.

DOI: http://dx.doi.org/10.1103/PhysRevX.2.031011

Received 20 February 2012
Published 15 August 2012

Published by the American Physical Society 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

Authors & Affiliations

J. Nipper, J. B. Balewski, A. T. Krupp, S. Hofferberth, R. Löw, and T. Pfau

5. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany

Popular Summary

Rydberg atoms are atoms in which one or more electrons are excited to high atomic orbits. In addition to being one of the workhorses of atomic and optical physics, Rydberg atoms have recently become a favored candidate for neutral-atom-based quantum information processing, serving both as single qubits and as components of basic quantum logical gates where coherent control of the phases of the Rydberg atoms becomes essential. This applicability originated in the fact that the interaction between two Rydberg atoms can be turned on and off with a strength contrast of many orders of magnitude by varying their distance. In this experimental paper, we add a new and promising tool for controlling the strength and character of the two-atom interaction, and in turn, shifting the quantum phases of the atoms, by exploiting the Förster resonant energy transfer between the atoms and tuning the resonance with small electric fields (Stark tuning).

The Förster resonant energy transfer occurs between two Rydberg atoms when they are at the right distance and in the right states. An easy way to understand the effect qualitatively in this context is to see the two atoms as two oscillating dipoles that interact with each other. And this interaction can be tuned by a small applied electric field. We start with a cloud of ultracold rubidium atoms and optically excite the atoms to one of their Rydberg states. By applying a small static electric field and increasing its strength gradually, we can make the Rydberg atoms interact with each other more strongly. The field-dependent, and distance-dependent, interaction between two atoms either flips the states of the atoms to different ones or shifts the phase of the original pair state coherently. A tailored laser-pulse sequence allows us to map the coherent evolution of the interaction effects onto the number of Rydberg atoms, which can then be easily detected.

Our proof-of-concept demonstration of a coherently controlled quantum phase shift in Rydberg atoms could open a new possibility for developing quantum phase gates and stimulate further advances in neutral-atom-based quantum information processing.

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Physical Review X

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