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Strong interaction between light and a single trapped atom without a cavity

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

Published May 4, 2008• 0 citations
Publisher

Abstract

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.

DOI
10.1109/qels.2008.4553171

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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.
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.
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.
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.
We characterize the interaction between a single atom or similar microscopic system and a light field via the scattering ratio. For this, we first derive the electrical field in a strongly focused Gaussian light beam, and then consider the atomic response. Following the simple scattering model, the fraction of scattered optical power for a weak coherent probe field leads to unphysical scattering ratios above 1 in the strong focusing regime. A refined model considering interference between the exciting and scattered field into finite-sized detectors or optical fibers is presented, and compared with experimental extinction measurements for various focusing strengths.
Cavity quantum electrodynamics (QED), the system of a single atom interacting with a single mode of a high finesse optical resonator, has tremendous potential for use in quantum logic, quantum information processing, and in enabling observation of quantum mechanical effects in the laboratory. The work of this thesis demonstrates a number of steps toward realizing these goals, by employing an experimental system with the strongest atom-field coupling achieved to date in optical cavity QED. The effects of strong coupling in cavity QED are studied for single cold atoms measured one at a time, in real time. The passage of single atoms through the cavity is employed to map out the frequency response of the system, and to demonstrate that quantum rather than semiclassical theory provides the correct theoretical model. The mechanical effects of strong coupling on single atoms are explored, these experiments demonstrating the first trapping of single atoms with single photons. Additionally, strong coupling enables high signal-to-noise ratio for monitoring atomic position at single photon field strengths; this capability is employed to investigate the motion of atoms trapped within the cavity. The transmitted cavity field is used to reconstruct the trajectories of single atoms, thereby realizing a new form of microscopy - the Atom-Cavity Microscope. Technical developments necessary to create the cavities used in this experiment are detailed. Ideas for future extensions to the experiment are proposed; a zero light-shift dipole force trap, and measurement of photon statistics of a single strongly coupled atom (which realizes a photon blockade device) are discussed.
Strong interactions between light and atoms at the single-quantum level are an important ingredient for quantum technologies, as well as for studies of fundamental effects in quantum optics. This thesis describes the development of a novel experimental platform that allows for trapping a single rubidium atom in the evanescent mode of a nano-fabricated optical cavity with sub-wavelength dimensions. By virtue of their small size, these cavities provide extremely large atom-photon coupling strengths and good prospects for scalability and integration into complex quantum optical circuits. Positioning the atom near the nano-structure is accomplished using a scanning optical tweezer dipole trap. As a first application, we have demonstrated a coherent optical switch, where a single gate photon controls the propagation of many subsequent signal photons, with the interaction mediated by the atom and cavity. We have also shown that the optical response of the combined atom-cavity system is nonlinear at the level of one or two photons.