Photonic Crystal Waveguides for Integration into an Atomic Physics Experiment

Strongly interacting systems of atoms and photons are an important resource in many active areas of research, including quantum information science, quantum simulation, and metrology. Frequently, the strength of these interactions is enhanced by using an optical resonator to confine light to a small volume. In recent years, there have been efforts to replace traditional Fabry–Pérot resonators, formed from macroscopic mirrors, with micro- and nano-fabricated systems, leveraging techniques and infrastructure from semiconductor manufacture to scalably produce high-quality, small mode volume waveguides and resonators. Of particular interest are nano-fabricated photonic crystals, in which very fine control over modal and dispersion properties is possible. Here I describe our efforts to reliably produce photonic crystal waveguides with guided modes designed to trap and interrogate an array of ultracold cesium atoms. Specifically, I present models capturing band placement, modal structure, finite photonic crystal effects, and waveguide input and output coupling; I discuss the techniques we use to fabricate our photonic crystal waveguides; and I describe our characterization capabilities and the packaging and installation of the waveguides into the atomic physics system.</p

Multifunctional 25D metastructures enabled by adjoint optimization

Optical metasurfaces are two-dimensional arrays of meta-atoms that modify different characteristics of light such as phase, amplitude, and polarization. One intriguing feature that distinguishes them from conventional optical components is their multifunctional capability. However, multifunctional metasurfaces with efficiencies approaching those of their single-functional counterparts require more degrees of freedom. Here we show that 2.5D metastructures, which are stacked layers of interacting metasurface layers, provide sufficient degrees of freedom to implement efficient multifunctional devices. The large number of design parameters and their intricate intercoupling make the design of multifunctional 2.5D metastructures a complex task, and unit-cell approaches to metasurface design produce suboptimal devices. We address this issue by designing 2.5D metastructures using the adjoint optimization technique. Instead of designing unit cells individually, our technique considers the structure as a whole, accurately accounting for inter-post and inter-layer coupling. As proof of concept, we experimentally demonstrate a double-wavelength metastructure, designed using adjoint optimization, that has significantly higher efficiencies than a similar device designed with a simplified approach conventionally used in metasurface design. The 2.5D metastructure architecture empowered by the optimization-based design technique is a general platform for realizing high-performance multifunctional components and systems

Band flipping and bandgap closing in a photonic crystal ring and its applications

The size of the bandgap in a photonic crystal ring is typically intuitively considered to monotonically grow as the modulation amplitude of the grating increases, causing increasingly large frequency splittings between the 'dielectric' and 'air' bands. In contrast, here we report that as the modulation amplitude in a photonic crystal ring increases, the bandgap does not simply increase monotonically. Instead, after the initial increase, the bandgap closes and then reopens again with the dielectric band and the air bands flipped in energy. The air and dielectric band edges are degenerate at the bandgap closing point. We demonstrate this behavior experimentally in silicon nitride photonic crystal microrings, where we show that the bandgap is closed to within the linewidth of the optical cavity mode, whose quality factor remains unperturbed with a value $\approx$ 1$\times$10$^6$ (i.e., linewidth of 2 pm). Moreover, through finite-element simulations, we show that such bandgap closing and band flipping phenomena exist in a variety of photonic crystal rings with varying units cell geometries and cladding layers. At the bandgap closing point, the two standing wave modes with a degenerate frequency are particularly promising for single-frequency lasing applications. Along this line, we propose a compact self-injection locking scheme that integrates many core functionalities in one photonic crystal ring. Additionally, the single-frequency lasing might be applicable to DFB lasers to increase their manufacturing yield.Comment: 7 pages, 4 figure

The placebo and nocebo effects on peak minute power during incremental arm crank ergometry

This is an Accepted Manuscript of an article published by Taylor & Francis Group in European Journal of Sport Science on 19 May 2014, available online: http://www.tandfonline.com/doi/abs/10.1080/17461391.2013.822564.This investigation aimed to explore the effects of inert sugar-free drinks described as either 'performance enhancing' (placebo) or 'fatigue inducing' (nocebo) on peak minute power (PMP;W) during incremental arm crank ergometry (ACE). Twelve healthy, non-specifically trained individuals volunteered to take part. A single-blind randomised controlled trial with repeated measures was used to assess for differences in PMP;W, oxygen uptake, heart rate (HR), minute ventilation, respiratory exchange ratio (RER) and subjective reports of local ratings of perceived exertion (LRPE) and central ratings of perceived exertion (CRPE), between three separate, but identical ACE tests. Participants were required to drink either 500 ml of a 'sports performance' drink (placebo), a 'fatigue-inducing' drink (nocebo) or water prior to exercise. The placebo caused a significant increase in PMP;W, and a significant decrease in LRPE compared to the nocebo (p=0.01; p=0.001) and water trials (p=0.01). No significant differences in PMP;W between the nocebo and water were found. However, the nocebo drink did cause a significant increase in LRPE (p=0.01). These results suggest that the time has come to broaden our understanding of the placebo and nocebo effects and their potential to impact sports performance.Peer reviewe

Cloning of the rice Xo1 resistance gene and interaction of the Xo1 protein with the defense-suppressing Xanthomonas effector Tal2h

The Xo1 locus in the heirloom rice variety Carolina Gold Select confers resistance to bacterial leaf streak and bacterial blight, caused by Xanthomonas oryzae pv. oryzicola and X. oryzae pv. oryzae, respectively. Resistance is triggered by pathogen-delivered transcription activator-like effectors (TALEs) independent of their ability to activate transcription and is suppressed by truncated variants called truncTALEs, common among Asian strains. By transformation of the susceptible variety Nipponbare, we show that one of 14 nucleotide-binding, leucine-rich repeat (NLR) protein genes at the locus, with a zinc finger BED domain, is the Xo1 gene. Analyses of published transcriptomes revealed that the Xo1-mediated response is more similar to those mediated by two other NLR resistance genes than it is to the response associated with TALE-specific transcriptional activation of the executor resistance gene Xa23 and that a truncTALE dampens or abolishes activation of defense-associated genes by Xo1. In Nicotiana benthamiana leaves, fluorescently tagged Xo1 protein, like TALEs and truncTALEs, localized to the nucleus. And endogenous Xo1 specifically coimmunoprecipitated from rice leaves with a pathogen-delivered, epitope-tagged truncTALE. These observations suggest that suppression of Xo1-function by truncTALEs occurs through direct or indirect physical interaction. They further suggest that effector coimmunoprecipitation may be effective for identifying or characterizing other resistance genes

Denosumab rapidly increases cortical bone in key locations of the femur: a 3D bone mapping study in women with osteoporosis.

Women with osteoporosis treated for 36 months with twice-yearly injections of denosumab sustained fewer hip fractures compared with placebo. Treatment might improve femoral bone at locations where fractures typically occur. To test this hypothesis, we used 3D cortical bone mapping of postmenopausal women with osteoporosis to investigate the timing and precise location of denosumab versus placebo effects in the hips. We analyzed clinical computed tomography scans from 80 female participants in FREEDOM, a randomized trial, wherein half of the study participants received subcutaneous denosumab 60 mg twice yearly and the others received placebo. Cortical 3D bone thickness maps of both hips were created from scans at baseline, 12, 24, and 36 months. Cortical mass surface density maps were also created for each visit. After registration of each bone to an average femur shape model followed by statistical parametric mapping, we visualized and quantified statistically significant treatment effects. The technique allowed us to pinpoint systematic differences between denosumab and control and to display the results on a 3D average femur model. Denosumab treatment led to an increase in femoral cortical mass surface density and thickness, already evident by the third injection (12 months). Overall, treatment with denosumab increased femoral cortical mass surface density by 5.4% over 3 years. One-third of the increase came from increasing cortical density, and two-thirds from increasing cortical thickness, relative to placebo. After 36 months, cortical mass surface density and thickness had increased by up to 12% at key locations such as the lateral femoral trochanter versus placebo. Most of the femoral cortex displayed a statistically significant relative difference by 36 months. Osteoporotic cortical bone responds rapidly to denosumab therapy, particularly in the hip trochanteric region. This mechanism may be involved in the robust decrease in hip fractures observed in denosumab-treated women at increased risk of fracture.This study was funded by Amgen Inc., Thousand Oaks, CA, USA. Cambridge Bone Group is supported by Arthritis Research UK, The Evelyn Trust, and Cambridge NIHR Biomedical Research Centre.This is the final version of the article. It first appeared from Wiley via http://dx.doi.org/10.1002/jbmr.232

Vitamin D status in female military personnel during combat training

Vitamin D is an essential nutrient for maintaining bone health. Recent data suggest that vitamin D and calcium supplementation might affect stress fracture incidence in military personnel. Although stress fracture is a health risk for military personnel during training, no study has investigated changes in vitamin D status in Soldiers during United States (US) Army basic combat training (BCT). This longitudinal study aimed to determine the effects of BCT on 25-hydroxyvitamin D (25(OH)D) and parathyroid hormone (PTH) levels in female Soldiers. Serum 25(OH)D and PTH were assessed in 74 fasted Soldier volunteers before and after an 8-week BCT course conducted between August and October in Columbia, South Carolina. In the total study population, 25(OH)D levels decreased (mean ± SD) from 72.9 ± 30.0 to 63.3 ± 19.8 nmol/L (P < 0.05) and PTH levels increased from 36.2 ± 15.8 to 47.5 ± 21.2 pg/mL (P < 0.05) during BCT. Ethnicity affected changes in vitamin D status (ethnicity-by-time interaction, P < 0.05); 25(OH)D decreased (P < 0.05) in both Hispanic and non-Hispanic whites, but did not change in non-Hispanic blacks. Ethnicity did not affect BCT-induced changes in PTH. These data indicate that vitamin D status in female Soldiers may decline during military training in the late summer and early autumn months in the Southeastern US. Future studies should strive to determine the impact of military clothing and seasonality on vitamin D status, as well as the functional impact of declining vitamin D status on bone health