Collective strong coupling of cold atoms to an all-fiber ring cavity

Abstract

We experimentally demonstrate a ring geometry all-fiber cavity system for cavity quantum electrodynamics with an ensemble of cold atoms. The fiber cavity contains a nanofiber section which mediates atom-light interactions through an evanescent field. We observe well-resolved, vacuum Rabi splitting of the cavity transmission spectrum in the weak driving limit due to a collective enhancement of the coupling rate by the ensemble of atoms within the evanescent field, and we present a simple theoretical model to describe this. In addition, we demonstrate a method to control and stabilize the resonant frequency of the cavity by utilizing the thermal properties of the nanofiber.In the context of scalable quantum computing and quantum communication, one can envision a network of quantum systems, or nodes, linked together through appropriate quantum channels to form a quantum network [1][2][3]. These networks have a wide variety of applications, from quantum computation [4] to simulating many-body quantum systems [5]. The use of photons for quantum communication is well established [6], and hence quantum nodes require an efficient light-matter interface. Cavity quantum electrodynamics (QED) has been at the forefront of implementing strong, coherent atom-light interactions [7][8][9], and the ability of cavity QED systems to control and manipulate the quantum states of light and matter make them perfect candidates for quantum nodes [10]. For example, free-space Fabry-Pérot cavities have been used to implement an elementary quantum network consisting of two nodes [11].To overcome the complexity and poor scalability of free-space cavities, fiber-based alternatives are required in order to realize a large scale quantum network. When implementing an all-fiber quantum node, a useful component for achieving strong coupling between fiber guided light and atoms is an optical nanofiber. Such a nanofiber offers tight transversal-mode confinement and large evanescent fields, and therefore allows for efficient atom-light coupling [12,13], as well as nonlinear atomlight interactions at very low optical powers [14]. Recently, these nanofibers have been utilized to demonstrate a memory for light [15,16].The atom-light interaction can be further enhanced by the use of a fiber cavity. One such configuration utilizes a nanofiber section sandwiched between two fiberBragg gratings to form an all-fiber Fabry-Pérot cavity [17]. Strong optical coupling with a single cesium atom has been demonstrated in this system, with a moderate cavity finesse (F < 40), due to high quality trapping of the atom near to the nanofiber surface [18].An alternative ring geometry has been recently studied using a low finesse fiber cavity with a hot atomic vapor of rubidium, where it was seen that the cavity transmission varied as the probe frequency was scanned across the * sam.ruddell@auckland.ac.nz Doppler-broadened atomic resonance [19]. Furthermore, in a recent proposal, a ring cavity geometry has been suggested as a potential platform for studying multimode stro...

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