Laser trapping and interfacing of laser-cooled atoms in an optical fiber network is an important capability for quantum information science. Following the pioneering work of Balykin et al. and Vetsch et al., we propose a robust method of trapping single Cesium atoms with a two-color state-insensitive evanescent wave around a dielectric nanofiber. Specifically, we show that vector light shifts (i.e., effective inhomogeneous Zeeman broadening of the ground states) induced by the inherent ellipticity of the forward-propagating evanescent wave can be effectively canceled by a backward-propagating evanescent wave. Furthermore, by operating the trapping lasers at the magic wavelengths, we remove the differential scalar light shift between ground and excited states, thereby allowing for resonant driving of the optical D2 transition. This scheme provides a promising approach to trap and probe neutral atoms with long trap and coherence lifetimes with realistic experimental parameters.
Laser trapping and interfacing of laser-cooled atoms in an optical fiber network is an important capability for quantum information science. Following the pioneering work of Balykin et al. and Vetsch et al., we propose a robust method of trapping single Cesium atoms with a two-color state-insensitive evanescent wave around a dielectric nanofiber. Specifically, we show that vector light shifts (i.e., effective inhomogeneous Zeeman broadening of the ground states) induced by the inherent ellipticity of the forward-propagating evanescent wave can be effectively canceled by a backward-propagating evanescent wave. Furthermore, by operating the trapping lasers at the magic wavelengths, we remove the differential scalar light shift between ground and excited states, thereby allowing for resonant driving of the optical D2 transition. This scheme provides a promising approach to trap and probe neutral atoms with long trap and coherence lifetimes with realistic experimental parameters.
We report the experimental realization of an optical trap that localizes single Cs atoms $\ensuremath{\simeq}215\text{ }\text{ }\mathrm{nm}$ from the surface of a dielectric nanofiber. By operating at magic wavelengths for pairs of counterpropagating red- and blue-detuned trapping beams, differential scalar light shifts are eliminated, and vector shifts are suppressed by $\ensuremath{\approx}250$. We thereby measure an absorption linewidth $\ensuremath{\Gamma}/2\ensuremath{\pi}=5.7\ifmmode\pm\else\textpm\fi{}0.1\text{ }\text{ }\mathrm{MHz}$ for the Cs 6S1/2, $F=4\ensuremath{\rightarrow}6{P}_{3/2}$, ${F}^{\ensuremath{'}}=5$ transition, where ${\ensuremath{\Gamma}}_{0}/2\ensuremath{\pi}=5.2\text{ }\text{ }\mathrm{MHz}$ in free space. An optical depth $d\ensuremath{\simeq}66$ is observed, corresponding to an optical depth per atom ${d}_{1}\ensuremath{\simeq}0.08$. These advances provide an important capability for the implementation of functional quantum optical networks and precision atomic spectroscopy near dielectric surfaces.
Neutral atoms trapped in the evanescent optical potentials of nanotapered optical fibers are a promising platform for developing quantum technologies and exploring fundamental science, such as quantum networks and quantum electrodynamics. Building on the successful advancements with trapped alkali atoms, here we demonstrate a state-insensitive optical dipole trap for strontium-88, an alkaline-earth atom, using the evanescent fields of a nanotapered optical fiber. Leveraging the low laser-cooling temperatures of ∼1μK readily achievable with strontium, we demonstrate trapping in record low trap depths corresponding to ∼3μK. Further, employing a double magic wavelength trapping scheme, we realize state-insensitive trapping on the kilohertz-wide 5s21S0−5s5p3P1,∣m∣=1 cooling transition, which we verify by performing near-surface high-resolution spectroscopy of the atomic transition. This allows us to experimentally find and verify the state insensitivity of the trap nearby a theoretically predicted magic wavelength of 435.827(25) nm. Given the non-magnetic ground state and low collisional scattering length of strontium-88, this work also lays the foundation for developing versatile and robust matter-wave atomtronic circuits over nanophotonic waveguides.
Neutral atoms that are optically trapped using the evanescent fields surrounding optical nanofibers are a promising platform for developing quantum technologies and exploring fundamental science, such as quantum networks and many-body physics of interacting photons.Building on the successful advancements with trapped alkali atoms, here we trap strontium-88 atoms, an alkaline-earth element, in a state-insensitive, nanofiber-based optical dipole trap using the evanescent fields of an optical nanofiber.Employing a two-color, double magic-wavelength trapping scheme, we realize state-insensitive trapping of the atoms for the kilohertz-wide 5s 2 1 S 0 -5s5p 3 P 1,|m|=1 intercombination transition, which we verify by performing high-resolution spectroscopy for an atom-surface distance of about 300 nm.This allows us to experimentally find and verify the state insensitivity of the trap nearby a theoretically predicted magic wavelength of 435.827(25) nm, a necessary step to confirm precision atomic physics calculations.Alkaline-earth atoms also exhibit nonmagnetic ground states and ultranarrow linewidth transitions making them ideal candidates for atomic clocks and precision metrology applications, especially with state-insensitive traps.Additionally, given the low collisional scattering length specific to strontium-88, this work also lays the foundation for developing versatile and robust matter-wave atomtronic circuits over nanophotonic waveguides.
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.
We have recently demonstrated a new experimental platform for trapping and optically interfacing laser-cooled cesium atoms. The scheme uses a two-color evanescent field surrounding an optical nanofiber to localize the atoms in a one-dimensional optical lattice 200 nm above the nanofiber surface [1]. In order to use this fiber-coupled ensemble of trapped atoms for applications in the context of quantum communication and quantum information processing, non-classical states of the atomic spins have to be prepared and should live long enough to allow one to apply successive quantum gates. The close proximity of the trapped atoms to the nanofiber surface and the strong polarization gradients of nanofiber-guided light fields are potentially important sources of decoherence. Here, we present our latest experimental results on the coherence properties of atomic spins in our nanofiber-based trap. Using a microwave field to drive the clock transition, we determine inhomogeneous and homogeneous dephasing times by Ramsey and spin echo techniques, respectively. Our results constitute the first measurement of the coherence properties of atoms trapped in the vicinity of a nanofiber and represent a fundamental step towards establishing nanofiber-based traps for cold atoms as a building block in a quantum network.
Towards the Observation of Collective Radiance Phenomena in a One-Dimensional Array of Waveguide-Coupled Atoms with Sub −λ/2 Spacing
Recently, it has been shown theoretically that the fidelity of photon storage and retrieval in quantum memories scales exponentially better with the number of emitters if one harnesses the collective response of closely spaced atoms ordered in an array [1]. The improved scaling relies on the effect of selective radiance, that is, destructive interference that suppresses scattering into undesired modes. This occurs when the period of an array of emitters is less than half of the atomic resonant wavelength of the probe laser(d<λ/2). In order to realize this situation, we trap and optically interface laser-cooled cesium atoms using a two-color nanofiber-based dipole trap [2]. It is composed of a blue-detuned partial standing wave and two red-detuned running wave light fields, which counter-propagate in the fiber to compensate the inhomgenous broadening due to the vector light shift [3]. The resulting trapping potential consists of two 1D-arrays of trapping sites on the opposite sides of the nanofiber, where the axial period isd≃0.35λ. Radially, the minima of the trapping potential are located at a distance of 300nm from the fibers surface. We characterize the trap by measuring the trap frequencies, the total number of stored atoms, the fraction of sites filled with a single atom in the collisional blockade regime, and the lifetime of the atoms.