We study cold collisions between trapped ions and trapped atoms in the semiclassical (Langevin) regime. Using Yb+ ions confined in a Paul trap and Yb atoms in a magneto-optical trap, we investigate charge-exchange collisions of several isotopes over three decades of collision energies down to 3 mueV (k_{B}x35 mK). The minimum measured rate coefficient of 6x10;{-10} cm;{3} s;{-1} is in good agreement with that derived from a Langevin model for an atomic polarizability of 143 a.u.

We present a novel method of machining optical fiber surfaces with a CO₂ laser for use in Fiber-based Fabry-Perot Cavities (FFPCs). Previously FFPCs were prone to large birefringence and limited to relatively short cavity lengths (≤ 200 μm). These characteristics hinder their use in some applications such as cavity quantum electrodynamics with trapped ions. We optimized the laser machining process to produce large, uniform surface structures. This enables the cavities to achieve high finesse even for long cavity lengths. By rotating the fibers around their axis during the laser machining process the asymmetry resulting from the laser's transverse mode profile is eliminated. Consequently we are able to fabricate fiber mirrors with a high degree of rotational symmetry, leading to remarkably low birefringence. Through measurements of the cavity finesse over a range of cavity lengths and the polarization dependence of the cavity linewidth, we confirmed the quality of the produced fiber mirrors for use in low-birefringence FFPCs.

We report on a novel single-photon source using a single calcium ion trapped between the end facets of two optical fibers. The optical fibers act as photonic channels, and in addition their metallic jackets provide a trapping electric field for the ion. Our system successfully combines a stable single-atom emitter with fiber optics, demonstrating remarkable compactness and scalability. In consequence, it is very well suited for use in quantum networks, where single ions interface with single photons traveling through optical fibers. We have demonstrated the non-classical character of the photons generated by this efficient source in continuous as well as pulsed mode. Contents

Abstract:We have produced high transmission sub-wavelength tapered optical fibers for the purpose of whispering gallery mode coupling in fused silica microcavities at 780 nm. A detailed analysis of the fiber transmittance evolution during tapering is demonstrated to reflect precisely the mode coupling and cutoff in the fiber. This allows to control the final size, the number of guided modes and their effective index. These results are checked by evanescent wave mapping measurements on the resulting taper.