Hyperpolarizability and operational magic wavelength in an optical lattice clock

Optical clocks benefit from tight atomic confinement enabling extended interrogation times as well as Doppler- and recoil-free operation. However, these benefits come at the cost of frequency shifts that, if not properly controlled, may degrade clock accuracy. Numerous theoretical studies have predicted optical lattice clock frequency shifts that scale nonlinearly with trap depth. To experimentally observe and constrain these shifts in an $^{171}$Yb optical lattice clock, we construct a lattice enhancement cavity that exaggerates the light shifts. We observe an atomic temperature that is proportional to the optical trap depth, fundamentally altering the scaling of trap-induced light shifts and simplifying their parametrization. We identify an "operational" magic wavelength where frequency shifts are insensitive to changes in trap depth. These measurements and scaling analysis constitute an essential systematic characterization for clock operation at the $10^{-18}$ level and beyond.Comment: 5 + 2 pages, 3 figures, added supplementa

Demonstration of a Transportable 1 Hz-Linewidth Laser

We present the setup and test of a transportable clock laser at 698 nm for a strontium lattice clock. A master-slave diode laser system is stabilized to a rigidly mounted optical reference cavity. The setup was transported by truck over 400 km from Braunschweig to D\"usseldorf, where the cavity-stabilized laser was compared to a stationary clock laser for the interrogation of ytterbium (578 nm). Only minor realignments were necessary after the transport. The lasers were compared by a Ti:Sapphire frequency comb used as a transfer oscillator. The thus generated virtual beat showed a combined linewidth below 1 Hz (at 1156 nm). The transport back to Braunschweig did not degrade the laser performance, as was shown by interrogating the strontium clock transition.Comment: 3 pages, 4 figure

Health-related quality of life burden in scleroderma patients treated with two different intravenous iloprost regimens

Systemic sclerosis (SSc)-related Raynaud's phenomenon (RP) and digital ulcers (DU) can impair health-related quality of life (HRQoL). The aim of our study was to estimate HRQoL in SSc patients treated with two different intravenous (IV) iloprost (ILO) regimens and in patients not treated with IV ILO. 96 consecutive SSc patients were enrolled in a pragmatic, prospective and non-randomized study, and divided into 3 groups: not requiring therapy with IV ILO (N=52), IV ILO once monthly (N=24) or IV ILO for 5 consecutive days every 3 months (N=20). Patients were followed up for three months. We assessed HRQoL using the generic preference-based questionnaire EQ-5D-5L. We conducted multiple regression analyses to estimate, in each treatment group, the mean general health (GH) and the mean utility index of the EQ-5D-5L, adjusting for possible confounders. The mean adjusted utility index and GH score, after three months' follow-up, were not different in the three groups: IV ILO was able to make patients requiring IV ILO similar to those not requiring it. Moreover, there was no difference in this model between the two ILO regimens (1 day monthly vs 5 consecutive days every 3 months). The two different IV ILO regimens (the most appropriate regimen was decided according to patients' characteristics and needs) were able to stabilize HRQoL in RP secondary to SSc non-adequately controlled by oral therapy

Translation and cross-cultural adaptation into italian of the self-administered FLARE-RA questionnaire for rheumatoid arthritis

The aim was to provide a translation into Italian with cross-cultural adaptation of the French FLARE-Rheumatoid Arthritis (RA) questionnaire, and to test its acceptability, feasibility, reliability and construct validity in a single-centre cohort study. The French version of the FLARE-RA questionnaire was cross-culturally adapted and translated into Italian following an established forward\u2013backward translation procedure, with independent translations and backtranslations. To validate the Italian version we tested the internal validity with Cronbach\u2019s alpha, test-retest reliability with the intraclass correlation coefficient, agreement between assessments with Bland-Altman plots and construct validity with Spearman\u2019s correlation coefficients. The questionnaire was tested on 283 consecutive RA outpatients (mean age 56.1\ub1}13.9 years, 226/283 females, median disease duration 12.6 years ranging from 0.2 to 70.6). For the global score (11 items) the Cronbach\u2019s alpha coefficient was 0.94. The intraclass correlation coefficient was 0.87 (95% CI, 0.76-0.96). The correlation of FLARE-RA global score was 0.59 (95% CI, 0.50-0.66) with the Disease Activity Score on 28 joints, 0.63 (95% CI, 0.55-0.71) with the Simplified Disease Activity Index, 0.77 (95% CI, 0.71-0.83) with the RA Impact of Disease and 0.67 (95% CI, 0.59-0.73) with the Health Assessment Questionnaire. The Italian version of the FLARE-RA is feasible, brief and easy to administer. The translated and cross-cultural adapted showed accordingly to be valid and reliable. This questionnaire has some practical advantages, such as clarity, comprehensiveness, simplicity, and a minimum filling time. The development of cross-cultural adapted questionnaires in different languages is of pivotal importance to obtain standardized and comparable data across countries

A posteriori dietary patterns and rheumatoid arthritis disease activity: A beneficial role of vegetable and animal unsaturated fatty acids

To our knowledge, no studies have investigated the relationship between a posteriori dietary patterns (DPs)\u2014representing current dietary behavior\u2014and disease activity in patients with rheumatoid arthritis (RA). We analyzed data from a recent Italian cross-sectional study including 365 RA patients (median age: 58.46 years, 78.63% females). Prevalent DPs were identified through principal component factor analysis on 33 nutrients. RA activity was measured according to the Disease Activity Score on 28 joints (DAS28) and the Simplified Disease Activity Index (SDAI). Single DPs were related to disease activity through linear and logistic regression models, adjusted for the remaining DPs and confounders. We identified five DPs (~80% variance explained). Among them, Vegetable unsaturated fatty acids (VUFA) and Animal unsaturated fatty acids (AUFA) DPs were inversely related to DAS28 in the overall analysis, and in the more severe or long-standing RA subgroups; the highest score reductions (VUFA: 0.81, AUFA: 0.71) were reached for the long-standing RA. The SDAI was inversely related with these DPs in subgroups only. This Italian study shows that scoring high on DPs based on unsaturated fats from either source provides independent beneficial effects of clinical relevance on RA disease activity, thus strengthening evidence on the topic

The Space Optical Clocks Project: Development of high-performance transportable and breadboard optical clocks and advanced subsystems

The use of ultra-precise optical clocks in space ("master clocks") will allow for a range of new applications in the fields of fundamental physics (tests of Einstein's theory of General Relativity, time and frequency metrology by means of the comparison of distant terrestrial clocks), geophysics (mapping of the gravitational potential of Earth), and astronomy (providing local oscillators for radio ranging and interferometry in space). Within the ELIPS-3 program of ESA, the "Space Optical Clocks" (SOC) project aims to install and to operate an optical lattice clock on the ISS towards the end of this decade, as a natural follow-on to the ACES mission, improving its performance by at least one order of magnitude. The payload is planned to include an optical lattice clock, as well as a frequency comb, a microwave link, and an optical link for comparisons of the ISS clock with ground clocks located in several countries and continents. Undertaking a necessary step towards optical clocks in space, the EU-FP7-SPACE-2010-1 project no. 263500 (SOC2) (2011-2015) aims at two "engineering confidence", accurate transportable lattice optical clock demonstrators having relative frequency instability below 1\times10^-15 at 1 s integration time and relative inaccuracy below 5\times10^-17. This goal performance is about 2 and 1 orders better in instability and inaccuracy, respectively, than today's best transportable clocks. The devices will be based on trapped neutral ytterbium and strontium atoms. One device will be a breadboard. The two systems will be validated in laboratory environments and their performance will be established by comparison with laboratory optical clocks and primary frequency standards. In this paper we present the project and the results achieved during the first year.Comment: Contribution to European Frequency and Time Forum 2012, Gothenburg, Swede

A high stability semiconductor laser system for a 88^{88}Sr-based optical lattice clock

We describe a frequency stabilized diode laser at 698 nm used for high resolution spectroscopy of the 1S0-3P0 strontium clock transition. For the laser stabilization we use state-of-the-art symmetrically suspended optical cavities optimized for very low thermal noise at room temperature. Two-stage frequency stabilization to high finesse optical cavities results in measured laser frequency noise about a factor of three above the cavity thermal noise between 2 Hz and 11 Hz. With this system, we demonstrate high resolution remote spectroscopy on the 88Sr clock transition by transferring the laser output over a phase-noise-compensated 200 m-long fiber link between two separated laboratories. Our dedicated fiber link ensures a transfer of the optical carrier with frequency stability of 7 \cdot 10^{-18} after 100 s integration time, which could enable the observation of the strontium clock transition with an atomic Q of 10^{14}. Furthermore, with an eye towards the development of transportable optical clocks, we investigate how the complete laser system (laser+optics+cavity) can be influenced by environmental disturbances in terms of both short- and long-term frequency stability.Comment: 9 pages, 9 figures, submitted to Appl. Phys.

Comparing ultrastable lasers at 7 × 10−17 fractional frequency instability through a 2220 km optical fibre network

Ultrastable lasers are essential tools in optical frequency metrology enabling unprecedented measurement precision that impacts on fields such as atomic timekeeping, tests of fundamental physics, and geodesy. To characterise an ultrastable laser it needs to be compared with a laser of similar performance, but a suitable system may not be available locally. Here, we report a comparison of two geographically separated lasers, over the longest ever reported metrological optical fibre link network, measuring 2220 km in length, at a state-of-the-art fractional-frequency instability of 7 × 10−17 for averaging times between 30 s and 200 s. The measurements also allow the short-term instability of the complete optical fibre link network to be directly observed without using a loop-back fibre. Based on the characterisation of the noise in the lasers and optical fibre link network over different timescales, we investigate the potential for disseminating ultrastable light to improve the performance of remote optical clocks

Ultra-stable optical clock with two cold-atom ensembles

Atomic clocks based on optical transitions are the most stable, and therefore precise, timekeepers available. These clocks operate by alternating intervals of atomic interrogation with dead time required for quantum state preparation and readout. This non-continuous interrogation of the atom system results in the Dick effect, an aliasing of frequency noise of the laser interrogating the atomic transition. Despite recent advances in optical clock stability achieved by improving laser coherence, the Dick effect has continually limited optical clock performance. Here we implement a robust solution to overcome this limitation: a zero-dead-time optical clock based on the interleaved interrogation of two cold-atom ensembles. This clock exhibits vanishingly small Dick noise, thereby achieving an unprecedented fractional frequency instability of $6 \times 10^{-17} / \sqrt{\tau}$ for an averaging time $\tau$ in seconds. We also consider alternate dual-atom-ensemble schemes to extend laser coherence and reduce the standard quantum limit of clock stability, achieving a spectroscopy line quality factor $Q> 4 \times 10^{15}$