Optical interface created by laser-cooled atoms trapped in the evanescent field surrounding an optical nanofiber

📝 Abstract

Trapping and optically interfacing laser-cooled neutral atoms is an essential requirement for their use in advanced quantum technologies. Here we simultaneously realize both of these tasks with cesium atoms interacting with a multi-color evanescent field surrounding an optical nanofiber. The atoms are localized in a one-dimensional optical lattice about 200 nm above the nanofiber surface and can be efficiently interrogated with a resonant light field sent through the nanofiber. Our technique opens the route towards the direct integration of laser-cooled atomic ensembles within fiber networks, an important prerequisite for large scale quantum communication schemes. Moreover, it is ideally suited to the realization of hybrid quantum systems that combine atoms with, e.g., solid state quantum devices.

💡 Analysis

Trapping and optically interfacing laser-cooled neutral atoms is an essential requirement for their use in advanced quantum technologies. Here we simultaneously realize both of these tasks with cesium atoms interacting with a multi-color evanescent field surrounding an optical nanofiber. The atoms are localized in a one-dimensional optical lattice about 200 nm above the nanofiber surface and can be efficiently interrogated with a resonant light field sent through the nanofiber. Our technique opens the route towards the direct integration of laser-cooled atomic ensembles within fiber networks, an important prerequisite for large scale quantum communication schemes. Moreover, it is ideally suited to the realization of hybrid quantum systems that combine atoms with, e.g., solid state quantum devices.

📄 Content

Optical interface created by laser-cooled atoms trapped in the evanescent field surrounding an optical nanofiber E. Vetsch, D. Reitz, G. Sagu´e, R. Schmidt, S. T. Dawkins, and A. Rauschenbeutel∗ Institut f¨ur Physik, Johannes Gutenberg-Universit¨at Mainz, 55099 Mainz (Dated: November 26, 2024) Trapping and optically interfacing laser-cooled neutral atoms is an essential requirement for their use in advanced quantum technologies. Here we simultaneously realize both of these tasks with cesium atoms interacting with a multi-color evanescent field surrounding an optical nanofiber. The atoms are localized in a one-dimensional optical lattice about 200 nm above the nanofiber surface and can be efficiently interrogated with a resonant light field sent through the nanofiber. Our technique opens the route towards the direct integration of laser-cooled atomic ensembles within fiber networks, an important prerequisite for large scale quantum communication schemes. Moreover, it is ideally suited to the realization of hybrid quantum systems that combine atoms with, e.g., solid state quantum devices. PACS numbers: 42.50.Ct, 37.10.Gh, 37.10.Jk Laser-trapped atoms are well isolated from their en- vironment and can be coherently manipulated as well as efficiently interrogated using resonant light [1]. This makes them prime candidates for the implementation of quantum memories and quantum repeaters, necessary, e.g., for the operation of long distance quantum com- munication networks [2–5]. At the same time, solid state quantum devices, such as quantum dots or superconduct- ing circuits, are readily miniaturized and integrated using well established technologies [6]. For these reasons, the possibility of combining atomic and solid state devices in so-called hybrid quantum systems, which combine the advantageous properties of both approaches, has recently attracted considerable interest [7–9]. Two prerequisites have to be fulfilled in order to realize such a hybrid quan- tum system. On the one hand, the atoms would have to be efficiently interfaced with resonant probe light for manipulation and interrogation. On the other hand, the atoms would have to be trapped in order to be placed in close vicinity of the charged or magnetized solid state devices in order to be coupled via electric or magnetic interaction. Here, we demonstrate that both tasks, trap- ping and optically interfacing neutral atoms, can be si- multaneously accomplished by means of tapered optical fibers with a nanofiber waist. The coupling of laser cooled atoms with light by means of optical fibers has been an active field of research over the past years. For this purpose, two types of optical fibers have been employed: In hollow core fibers, the atoms are funneled into a capillary in the centre of the fiber where they couple to the guided fiber mode [10, 11]. This implies that at least one end of the hollow core fiber has to terminate inside the vacuum chamber and that the device can thus not be directly connected to a fiber network. The situation is different when using op- tical nanofibers with a diameter smaller than the wave- length of the guided light. In this case, the atoms re- main at the outside of a fiber and couple to the evanes- FIG. 1: (a, black line) Potential as a function of distance from the surface of a 500-nm diameter nanofiber for a ground state cesium atom induced by a two-color evanescent field plus the van der Waals potential. The red and blue lines show the individual light induced potentials for a red- and blue-detuned field at 1064 nm and 780 nm respectively. We assumed a power of Pred = 2 × 2.2 mW (standing wave) and Pblue = 25 mW and orthogonal linear polarization of the red and blue fields. (b) Contour plots of the same potential as in (a). The red-detuned standing wave ensures axial confine- ment. (c) Azimuthal plot of the same potential as in (a) and (b). The planes of the plots in (a)–(c) are chosen to include the trapping minima. (d) Contour plot of the resulting array of trapping sites on both sides of the fiber showing equipoten- tial surfaces 40 µK and 125 µK above the trapping minimum. cent field surrounding the fiber [12, 13]. Such nanofibers can be realized as the waist of tapered optical fibers (TOFs) which allows one to optimally match the mode of a standard single mode optical fiber with the fundamen- tal nanofiber mode, thus ensuring high transmission of arXiv:0912.1179v2 [quant-ph] 7 May 2010 2 the device [14, 15] as well as direct integrability into fiber networks. Moreover, a nanofiber can be passed through an operating magneto-optical trap (MOT), thereby fa- cilitating the coupling of atoms and light [12, 16]. The ultimate goal in both lines of research is to combine the coupling scheme with three dimensional trapping of the atoms in order to maximize both the number of coupled atoms, resulting in the highest possible optical depth, as well as the interaction time. In this context, it has been proposed to realize a two-color optical dipole trap which mak

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