Fiber-optical switch controlled by a single atom

We demonstrate highly efficient switching of optical signals between two optical fibers controlled by a single atom. The key element of our experiment is a whispering-gallery mode bottle microresonator, which is coupled to a single atom and interfaced by two tapered fiber couplers. Even in the presence of the coupling fibers, the atom--resonator system reaches the strong coupling regime of cavity quantum electrodynamics (CQED), leading to a vacuum Rabi splitting in the excitation spectrum. We systematically investigate the switching efficiency of our system, i.e., the probability that the CQED fiber-optical switch redirects the light into the desired output. We obtain a large redirection efficiency reaching a raw fidelity of more than 60% without post-selection.Comment: 5 pages, 4 figure

All-optical coherent population trapping with defect spin ensembles in silicon carbide

Divacancy defects in silicon carbide have long-lived electronic spin states and sharp optical transitions, with properties that are similar to the nitrogen-vacancy defect in diamond. We report experiments on 4H-SiC that investigate all-optical addressing of spin states with the zero-phonon-line transitions. Our magneto-spectroscopy results identify the spin $S=1$ structure of the ground and excited state, and a role for decay via intersystem crossing. We use these results for demonstrating coherent population trapping of spin states with divacancy ensembles that have particular orientations in the SiC crystal.Comment: 28 page document: Pages 1-14 main text (with 3 figures); pages 15-28 supplementary information (with 5 figues). v2 has minor correction

Upconversion channels in Er3+:ZBLALiP fluoride glass microspheres

We present results on the realization of a multicolour microspherical glass light source fabricated from the erbium doped fluoride glass ZBLALiP. Whispering gallery mode lasing and upconversion processes give rise to laser and fluorescent emissions at multiple wavelengths from the ultraviolet to the infrared. Thirteen discrete emissions ranging from 320 to 849 nm have been observed in the upconversion spectrum. A Judd-Ofelt analysis was performed to calculate the radiative properties of Er3+:ZBLALiP microspheres, including the radiative transition probabilities, the electric dipole strengths, the branching ratios and the radiative lifetimes of the transitions involved. We have also identified the primary processes responsible for the generation of the observed wavelengths and have shown that this material has an improved range of emissions over other erbium doped fluoride glasses

Prebiotics and Dietary Fibers from Food Processing By-Products

The abundance of agricultural wastes or by-products from industrial and domesti- Q1 cated food processing is the main cause of environment problems. These by-products are generally managed by disposal or even sold at a cheaper price. Disposal of these underutilized by-products are commonly done in inappropriate ways, i.e. discharge effluent into rivers or by burning in the open, which may cause air and water pollutions. Presently, scientific investigation on the benefits or functional properties of waste and by-products from industrial food processing, which produces a large amount of by-products, is necessary in the search for possible ways for their utilization (Vanesa et al., 2011). Three main groups of by-product from food processing, classified according to their main chemical compositions, are carbohydrate and dietary fibers, protein and lipids. The most common by-products are generated by the food industry, in particular the beverage, starch and flour industries. These items are classified under carbohydrate and dietary fiber groups. They are further divided into four sub-groups: monosaccharides, disaccharides, oligosaccharides and polysaccharides. Dietary fibers are a class of non-starch polysaccharides (i.e. cellulose, dextrins, chitins, pectins, β-glucans and waxes) and lignin, which are able to modulate the transit time through the gut. Thus, it provides similar beneficial effects to those of inulin-type fructans. These compounds are commonly found in many foods such as cereal, nuts etc. They are also partially susceptible to bacterial fermentation and may induce changes in bacterial populations, particularly in the numerous bifidobacteria and lactobacilli. These soluble dietary fibers have been shown to exert additional beneficial effects, for instance by improving gut barrier function in vitro and in vivo, which could be partially a consequence of their effect on the microflora composition (Laparra and Sanz, 2010)

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Cavity QED experiments with a whispering-gallery-mode bottle resonator

The interaction of a two-level atom with a single mode of the quantized electromagnetic field constitutes one of the most fundamental systems investigated in quantum optics. We have pursued such an investigation where rubidium atoms are strongly coupled to the modes of a whispering-gallery-mode (WGM) resonator that is itself interfaced with an optical fiber. In order to facilitate studies of this atom-light interaction, an experimental apparatus was constructed around a novel type of WGM resonator developed in our group. The spectral and spatial mode structure of this resonator yield an intriguing atom-light response arising principally from the existence of two frequency-degenerate modes.This thesis reports on high resolution experiments studying the transmission and reflection spectra of modes with a high quality factor (Q=10^7-10^8) in our WGM resonator. Light is coupled into and out of WGMs by frustrated total internal reflection using an optical nanofiber.The atom-light interaction is facilitated by an atomic fountain that delivers a cloud of atoms to the location of the resonator. At random moments, single-atoms are clearly observed transiting the evanescent field of the resonator modes with a transit time of a few microseconds. A high-speed experimental control system was developed to firstly detect the coupling of individual atoms to the resonator and secondly to perform time-resolved spectroscopy on the strongly coupled atom-resonator system.Spectral measurements clearly resolve an atom-induced change in the resonant transmission of the coupled system (65% absolute change) that is much larger than predicted in the standard Jaynes-Cummings model (25% absolute change) and that has thus far not been observed. To gain further insight, we experimentally explored the properties of the interaction and performed supporting simulations.Spectroscopy was performed on the atom-resonator system using two nanofibers to in- and out-couple light for probing/observing the system.Using this setup, we find an asymmetric response in the fraction of reflected light from the empty resonator mode. The coupling of atoms to a mode similarly produces asymmetric transmission and reflection spectra that critically depend on the direction of light propagation in the mode. Possible explanations for the spectral properties are identified and possible routes to verifying the exact nature of the atom-light interaction are suggested.The observation of directional asymmetries and large atom-induced changes in the transmission and reflection spectra provide important new perspectives on the fundamental dynamics of atom-light coupling with WGM resonators. Moreover, our novel resonator design features four-port functionality using two optical fibers as well as very low intrinsic losses, which altogether makes the system a versatile platform for fundamental studies of open quantum systems. Within the architecture of an optical fiber-based quantum network, for example, our resonator can in principle serve as a platform for the deterministic generation of light-matter entanglement while simultaneously operating as a four-port optical switch, i.e., a quantum-mechanical switch for light.17

Strong Coupling between Single Atoms and Nontransversal Photons

Light is often described as a fully transverse-polarized wave, i.e., with an electric field vector that is orthogonal to the direction of propagation. However, light confined in dielectric structures such as optical waveguides or whispering-gallery-mode microresonators can have a strong longitudinal polarization component. Here, using single Rb-85 atoms strongly coupled to a whispering-gallery-mode microresonator, we experimentally and theoretically demonstrate that the presence of this longitudinal polarization fundamentally alters the interaction between light and matter