In this thesis I present a developing project to elaborate a scientific platform towards the realization of light-matter interaction based on tapered optical nanofiber (TNF) that enables optical fields to interface with trapped neutral atoms in their vicinity. In such a configuration, the guided light exhibits a large portion of evanescent field into the vacuum thus laser cooled atoms can couple to the fiber mode. By trapping and cooling atoms around the nanofiber I investigated the interaction of the atoms with the field. My work presented in this thesis includes: Calculating the evanescent modes propagating through our fiber; Implementing fiber pulling setup using oxyhydrogen flame and analyzing nanofiber’s thermal dynamics and degradation; Constructing a Rubidium 87 MOT and characterizing its critical parameters; Realizing some atom-light interface through an experiment on coupling spontaneously emitted photons from MOT into TNF; Calculating two-color dipole trap parameters for our nanofiber.
In this thesis I present a developing project to elaborate a scientific platform towards the realization of light-matter interaction based on tapered optical nanofiber (TNF) that enables optical fields to interface with trapped neutral atoms in their vicinity. In such a configuration, the guided light exhibits a large portion of evanescent field into the vacuum thus laser cooled atoms can couple to the fiber mode. By trapping and cooling atoms around the nanofiber I investigated the interaction of the atoms with the field. My work presented in this thesis includes: Calculating the evanescent modes propagating through our fiber; Implementing fiber pulling setup using oxyhydrogen flame and analyzing nanofiber’s thermal dynamics and degradation; Constructing a Rubidium 87 MOT and characterizing its critical parameters; Realizing some atom-light interface through an experiment on coupling spontaneously emitted photons from MOT into TNF; Calculating two-color dipole trap parameters for our nanofiber.
This project aims to develop scientific as well as technical foundations towards realization of a novel platform for light-matter interaction based on tapered optical nanofibers that enable to interface neutral atoms in their vicinity. A setup for magneto-optical trap (MOT) has been built. Tapered nanofibers (TNFs) of sub-wavelength diameter, with transmission of 95 percent have been fabricated and characterized. Next, a nanofiber is transferred into the MOT setup and installed inside the vacuum chamber. The MOT cloud and nanofiber are made to spatially overlap inside ultra-high vacuum (UHV). Coupling of fluorescence of MOT into the guided mode of TNF has been observed. This clearly shows the coupling of atoms with the fiber-guided mode and that our interface works. In addition, 65-70 percent absorption of a free space beam by the atomic cloud has been observed and the relevant MOT parameters are obtained from it. Our efforts are directed towards observing interaction of atoms with the fiber-guided light via evanescent field. Attempts have been made to observe absorption of a probe beam through the nanofiber by the MOT cloud and techniques for switching on-off the MOT beams, the probe beam and the magnetic field are developed for that purpose. Ultimately, the goal will be to trap atoms in the vicinity of a nanofiber enabling to reach a large optical depth accompanied by the ability to reach high intensities for low optical power. I will present my work on the development of this MOT-nanofiber interface - a new promising platform for research in nonlinear quantum optics, quantum information science and technology, quantum communication and hybrid quantum system.
Tapered optical fiber with subwavelength diameter waist, an optical nanofiber, provides a unique and versatile platform for manipulating atoms and photons. In the guided modes of the nanofibers, the optical field can be tightly confined in the transverse direction while enabling strong interaction with the surrounding medium in the evanescent region. Combining laser-cooled atoms with nanofibers has enabled surprising quantum optics experiments, e.g. the efficient channeling of emission from single atoms into the fiber-guided modes, spectroscopy of near-surface atoms, high optical depth with an array of atoms optically trapped around the nanofiber, atomic memories and Bragg reflectors for fiber-guided photons, chiral light-matter interaction etc. In addition, using moderate longitudinal confinement in nanofiber cavities has enabled strong coupling between a single atom and fiber-guided photons. In this article, I review some of the key experimental demonstrations on the “atom＋nanofiber” platform.
In this thesis, I present the realization of a fiber-optical interface using optically trapped cesium atoms, which is an efficient tool for coupling light and atoms. The basic principle of the presented scheme relies on the trapping of neutral cesium atoms in a two-color evanescent field surrounding a nanofiber. The strong confinement of the fiber guided light, which also protrudes outside the nanofiber, provides strong confinement of the atoms as well as efficient coupling to near-resonant light propagating through the fiber. In chapter 1, the necessary physical and mathematical background describing the propagation of light in an optical fiber is presented. The exact solution of Maxwell’s equations allows us to model fiber-guided light fields which give rise to the trapping potentials and the atom-light coupling in the close vicinity of a nanofiber. Chapter 2 gives the theoretical background of light-atom interaction. A quantum mechanical model of the light-induced shifts of the relevant atomic levels is reviewed, which allows us to quantify the perturbation of the atomic states due to the presence of the trapping light-fields. The experimental realization of the fiber-based atom trap is the focus of chapter 3. Here, I analyze the properties of the fiber-based trap in terms of the confinement of the atoms and the impact of several heating mechanisms. Furthermore, I demonstrate the transportation of the trapped atoms, as a first step towards a deterministic delivery of individual atoms. In chapter 4, I present the successful interfacing of the trapped atomic ensemble and fiber-guided light. Three different approaches are discussed, i.e., those involving the measurement of either near-resonant scattering in absorption or the emission into the guided mode of the nanofiber. In the analysis of the spectroscopic properties of the trapped ensemble we find good agreement with the prediction of theoretical model discussed in chapter 2. In addition, I introduce a non-destructive scheme for the interrogation of the atoms states, which is sensitive to phase shifts of far-detuned fiber-guided light interacting with the trapped atoms. The inherent birefringence in our system, induced by the atoms, changes the state of polarization of the probe light and can be thus detected via a Stokes vector measurement.
This thesis pertains to the synthesis and use of tapered nanofibers (TNF) in quantum optics experiments. TNFs are optical fibers which contain a region radially tapering down to a submicron diameter. The key feature of such fibers is that a significant portion of an internally propagating electromagnetic field is just outside the fiber in the form of an evanescent field. TNFs are used to substantially improve light-matter interactions by providing a constant small focus of light along millimeters or centimeters of length. Here we report the successful synthesis of a low-loss TNF of custom geometry both theoretically and experimentally. Additionally, we study the thermodynamics of such fibers, demonstrating the ability to measure their temperature resulting from a coupled laser. Finally, we demonstrate the ability to recover lost transmission, due to atoms adsorbed on the fiber's surface. We conclude with an outlook on future experiments with TNFs.
We are in the process of building an experimental setup for trapping and optically interfacing laser-cooled strontium atoms using the evanescent field surrounding an optical nanofiber [1]. The nanofiber is produced from a standard step-index optical fiber in a heat-pull process. It features a waist diameter of 230 nm where light is still efficiently guided while a significant part of the light propagates in the form of an evanescent field surrounding the nanofiber. Atoms are trapped in a one-dimensional (1D) optical lattice formed by two fiber-guided light-fields, red- and blue-detuned with respect to the strong transition at a wavelength of 461 nm. The aim is to realize a compensated trap, where the wavelengths of the trapping fields are magic for the 7.4 kHz wide intercombination line at 689 nm. This will allow us to implement advanced schemes for loading atoms into the 1D optical lattice and to investigate the phenomenon of selective radiance [2], where the atoms themselves can act as the waveguide. Here we will present our compact design for trapping strontium atoms from a laser ablated source with a “hot MOT” (operated at 461 nm wavelength), then transfer them to a “cold MOT” (operated at the intercombination line) and to the nanofiber trap.
Tapered optical fibers with a nanofiber waist are versatile tools for interfacing light and matter. In this context, laser-cooled atoms trapped in the evanescent field surrounding the optical nanofiber are of particular interest: They exhibit both long ground-state coherence times and efficient coupling to fiber-guided fields. Here, we demonstrate electromagnetically induced transparency, slow light, and the storage of fiber-guided optical pulses in an ensemble of cold atoms trapped in a nanofiber-based optical lattice. We measure a slow-down of light pulses to group velocities of 50 m/s. Moreover, we store optical pulses at the single photon level and retrieve them on demand in the fiber after 2 microseconds with an overall efficiency of (3.0 +/- 0.4) %. Our results show that nanofiber-based interfaces for cold atoms have great potential for the realization of building blocks for future optical quantum information networks.