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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Interfacing light and single atoms with a lens

Meng Khoon Tey, Syed Abdullah Aljunid, Florian Huber, Brenda Chng, Zilong Chen, Gleb Maslennikov, Christian Kurtsiefer

Published Dec 2, 2008• 7 citations

Abstract

Abstract. We investigate the interaction between a single atom and a light field in the strong focusing regime. Such a configuration is subject to recent experimental work not only with atoms but also molecules and other atom-like systems as quantum dots. We derive the scattering probability for a photon from such a microscopic object modeled by a two-level system, starting with a Gaussian beam as the spatial mode of the light field. The focusing by an ideal lens is modeled using spherical wave fronts of a field compatible with Maxwell equations. Using a semi-classical approach for the atom-field interaction, we predict scattering probability of photons by a single atom of up to 98% for realistic focusing parameters. Experimental results for different focusing strengths are compared with our theoretical model. PACS numbers: 42.50Ct, 42.50Ex, 42.25BsInterfacing light and single atoms with a lens 2 1.

DOI: 10.1117/12.810207

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We consider the near-resonant interaction between a single atom and a focused light mode, where the single atom localized at the focus of a lens can scatter a significant fraction of light. Complementary to previous experiments on extinction and phase shift effects of a single atom, here we report on the measurement of coherently backscattered light. The strength of the observed effect suggests combining strong focusing with a cavity to further enhance the field at the location of the atom. This could make scaling up to a network of several atom + cavity nodes more realistic due to significant technical simplification of the atom–light interface. We consider theoretically a nearly concentric cavity, which has a strongly focused optical mode. Simple estimates show that in such a case one can expect a significant single photon Rabi frequency.

We measured the extinction of a focused light beam by a single 87Rb atom localized in an optical dipole trap and found a value of 7.2% for a focused Gaussian beam resonantly interacting with an atomic two-level system. Various models describing interaction of an atom with a focused light field are compared to explain our experimental result. Our experiment suggests that a strong coupling may be achieved without cavity assistance. This opens new perspectives for a development of an efficient atom-photon interface for Quantum Information processing.

In order to observe substantial interaction between single atoms and photons, cavities with a high finesse can be used to enhance the field at the location of an atom. Alternatively, an attempt can be made to tailor the spatial mode of a photon to closely match the mode corresponding to an electrical dipole transition of an atom by strong focusing [1]. In this paper, we present our experimental work on measurements of extinction and phase shift of a weak coherent beam due to the presence of an atom in the strongly focused part of a Gaussian light beam.