Enhancement of the quadrupole interaction of an atom with guided light of an ultrathin optical fiber

We investigate the electric quadrupole interaction of an alkali-metal atom with guided light in the fundamental and higher-order modes of a vacuum-clad ultrathin optical fiber. We calculate the quadrupole Rabi frequency, the quadrupole oscillator strength, and their enhancement factors. In the example of a rubidium-87 atom, we study the dependencies of the quadrupole Rabi frequency on the quantum numbers of the transition, the mode type, the phase circulation direction, the propagation direction, the orientation of the quantization axis, the position of the atom, and the fiber radius. We find that the root-mean-square (rms) quadrupole Rabi frequency reduces quickly but the quadrupole oscillator strength varies slowly with increasing radial distance. We show that the enhancement factors of the rms Rabi frequency and the oscillator strength do not depend on any characteristics of the internal atomic states except for the atomic transition frequency. The enhancement factor of the oscillator strength can be significant even when the atom is far away from the fiber. We show that, in the case where the atom is positioned on the fiber surface, the oscillator strength for the quasicircularly polarized fundamental mode HE$_{11}$ has a local minimum at the fiber radius $a\simeq 107$ nm, and is larger than that for quasicircularly polarized higher-order hybrid modes, TE modes, and TM modes in the region $a<498.2$ nm

Facile and time-resolved chemical growth of nanoporous CaxCoO2 thin films for flexible and thermoelectric applications

CaxCoO2 thin films can be promising for widespread flexible thermoelectric applications in a wide temperature range from room-temperature self-powered wearable applications (by harvesting power from body heat) to energy harvesting from hot surfaces (e.g., hot pipes) if a cost-effective and facile growth technique is developed. Here, we demonstrate a time resolved, facile and ligand-free soft chemical method for the growth of nanoporous Ca0.35CoO2 thin films on sapphire and mica substrates from a water-based precursor ink, composed of in-situ prepared Ca2+-DMF and Co2+-DMF complexes. Mica serves as flexible substrate as well as sacrificial layer for film transfer. The grown films are oriented and can sustain bending stress until a bending radius of 15 mm. Despite the presence of nanopores, the power factor of Ca0.35CoO2 film is found to be as high as 0.50 x 10-4 Wm-1K-2 near room temperature. The present technique, being simple and fast to be potentially suitable for cost-effective industrial upscaling.Comment: 16 pages, 5 figure

A simple, narrow, and robust atomic frequency reference at 993 nm exploiting the rubidium (Rb) 5S1/25\mathit{S}_{1/2} to 6S1/26\mathit{S}_{1/2} transition using one-color two-photon excitation

We experimentally demonstrate a one-color two-photon transition from the $5\mathit{S}_{1/2}$ ground state to the $6\mathit{S}_{1/2}$ excited state in rubidium (Rb) vapor using a continuous wave laser at 993 nm. The Rb vapor contains both isotopes ($^{85}$Rb and $^{87}$Rb) in their natural abundances. The electric dipole allowed transitions are characterized by varying the power and polarization of the excitation laser. Since the optical setup is relatively simple, and the energies of the allowed levels are impervious to stray magnetic fields, this is an attractive choice for a frequency reference at 993 nm, with possible applications in precision measurements and quantum information processing.Comment: 8 pages, 4 figures, research articl

A Three Dimensional Lattice of Ion Traps

We propose an ion trap configuration such that individual traps can be stacked together in a three dimensional simple cubic arrangement. The isolated trap as well as the extended array of ion traps are characterized for different locations in the lattice, illustrating the robustness of the lattice of traps concept. Ease in the addressing of ions at each lattice site, individually or simultaneously, makes this system naturally suitable for a number of experiments. Application of this trap to precision spectroscopy, quantum information processing and the study of few particle interacting system are discussed.Comment: 4 pages, 4 Figures. Fig 1 appears as a composite of 1a, 1b, 1c and 1d. Fig 2 appears as a composite of 2a, 2b and 2

Generation of cold Rydberg atoms at submicron distances from an optical nanofiber

We report on a controllable, hybrid quantum system consisting of cold Rydberg atoms and an optical nanofiber interface. Using a two-photon ladder-type excitation in 87Rb, we demonstrate both coherent and incoherent Rydberg excitation at submicron distances from the nanofiber surface. The 780-nm photon, near resonant to the 5S→5P transition, is mediated by the cooling laser, while the 482-nm light, near resonant to the 5P→29D transition, is mediated by the guided mode of the nanofiber. The population loss rate of the cold atom ensemble is used to measure the Rydberg population rate. A theoretical model is developed to interpret the results and link the population loss rate to the experimentally measured, effective Rabi frequency of the process. This work makes headway in the study of Rydberg atom-surface interactions at submicron distances and the use of cold Rydberg atoms for all-fibered quantum networks

Optical control of resonant light transmission for an atom-cavity system

We demonstrate the manipulation of transmitted light through an optical Fabry-Pérot cavity, built around a spectroscopy cell containing enriched rubidium vapor. Light resonant with the 87RbD2 (F=2,F=1) ↔F′ manifold is controlled by the transverse intersection of the cavity mode by another resonant light beam. The cavity transmission can be suppressed or enhanced depending on the coupling of atomic states due to the intersecting beams. The extreme manifestation of the cavity-mode control is the precipitous destruction (negative logic switching) or buildup (positive logic switching) of the transmitted light intensity on intersection of the transverse control beam with the cavity mode. Both the steady-state and transient responses are experimentally investigated. The mechanism behind the change in cavity transmission is discussed in brief

1.6 GHz Frequency Scanning of a 482 nm Laser Stabilized Using Electromagnetically Induced Transparency

We propose a method to continuously frequency shift a target laser that is frequency stabilized by a reference laser, which is several hundreds of nanometers detuned. We demonstrate the technique using the 5S1/2→5P3/2→29D5/2 Rydberg transition in ⁸⁷ Rb vapor and lock the 482 nm target laser to the 780 nm reference laser using the cascaded electromagnetically induced transparency signal. The stabilized frequency of the target laser can be shifted by about 1.6 GHz by phase modulating the reference laser using a waveguide-type electro-optical modulator. This simple method for stable frequency shifting can be used in atomic or molecular physics experiments that require a laser frequency scanning range on the order of several GHz

Spin selection rule for {\it S} level transitions in atomic rubidium under paraxial and nonparaxial two-photon excitation

We report on an experimental test of the spin selection rule for two-photon transitions in atoms. In particular, we demonstrate that the $5S_{1/2}\to 6S_{1/2}$ transition rate in a rubidium gas follows a quadratic dependency on the helicity parameter linked to the polarization of the excitation light. For excitation via a single Gaussian beam or two counterpropagating beams in a hot vapor cell, the transition rate scales as the squared degree of linear polarization. The rate reaches zero when the light is circularly polarized. In contrast, when the excitation is realized via an evanescent field near an optical nanofiber, the two-photon transition cannot be completely extinguished (theoretically, not lower than 13\% of the maximum rate, under our experimental conditions) by only varying the polarization of the fiber-guided light. Our findings lead to a deeper understanding of the physics of multiphoton processes in atoms in strongly nonparaxial light

Observation of the 87Rb 5S1/2 to 4D3/2 electric quadrupole transition at 516.6 nm mediated via an optical nanofibre

Light guided by an optical nanofibre has a very steep evanescent field gradient extending from the fibre surface. This gradient can be exploited to drive electric quadrupole transitions in nearby quantum emitters. In this paper, we report on the observation of the 5S 1/2 →4D 3/2 electric quadrupole transition at 516.6 nm (in vacuum) in laser-cooled 87Rb atoms using only a few μW of laser power propagating through an optical nanofibre embedded in the atom cloud. This work extends the rangeof applications for optical nanofibres in atomic physics to include more fundamental tests such as high-precision measurements of parity non-conservation