25 May 2000 Ž . Optics Communications 179 2000 129–135 www.elsevier.comrlocateroptcom Requirements for coherent atom channeling 1 Claudia Keller a,b, ) , Jorg Schmiedmayer b , Anton Zeilinger a,b ¨ a Institut fur Experimentalphysik, UniÕersitat Wien, Boltzmanngasse 5, A-1090 Wien, Austria ¨ ¨ b Institut fur Experimentalphysik, UniÕersitat Innsbruck, Technikerstraße, 25 A-6020 Innsbruck, Austria ¨ ¨ Received 30 September 1999; received in revised form 19 January 2000; accepted 24 January 2000 Abstract The evolution of atomic de Broglie waves inside strong periodic potentials can be described as channeling and exhibits both particle and wave effects. Using a beam of metastable Argon atoms interacting with an intense standing light wave we detect an interference pattern arising from the coherent guiding of the atoms through the light channels. In analogy to light optics these interference effects are only visible, if certain requirements for longitudinal and transverse coherence are fulfilled. We experimentally study the influence of the velocity selection and the collimation of the Argon atoms. As well as an another factor determining the coherence of the evolution – the spontaneous emission. q 2000 Elsevier Science B.V. All rights reserved. PACS: 39.20.qq; 03.75.Be; 42.25.Kb; 03.75.Dg 1. Introduction The interaction of waves with periodic potentials is an extensively studied subject. In the case of long interaction times, the evolution inside the potential cannot be neglected. This arises particularly for X-ray and neutron diffraction at solid crystals. There the coupling between the incident wave and the periodic potential is small and the typical phenomenon of Bragg diffraction is observed. For special incidence angles Bragg diffraction is observed and in general ) Corresponding author. E-mail: claudia.keller@univie.ac.at 1 This paper is dedicated to Professor Marlan O. Scully at the occasion of his 60th birthday. only one diffracted peak is observed. This regime can also be realized with atoms in standing light w x waves and has already been studied in detail 1–3 . Using the interaction of an atomic beam with near resonant light in a standing light wave it is possible to increase the coupling strength enormously, far beyond anything possible for X-rays or neutrons. The potential height for the atoms is proportional to the intensity of the light field and inversely propor- tional to the detuning of the light from the atomic resonance. If the coupling is very strong the atoms can no longer pass over the potential maxima, as in the case of Bragg diffraction, and are confined be- tween the maxima of the light potential. In each such channel they have to evolve independently. This evolution is analogous to the behaviour of light in an 0030-4018r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0030-4018 00 00528-9