Publications (158)264.33 Total impact
 [Show abstract] [Hide abstract] ABSTRACT: UTC(OP), the French national realization of the international coordinated universal time, was redesigned and rebuilt. The first step was the implementation in October 2012 of a new algorithm based on a Hmaser and on atomic fountain data. Thanks to the new implementation, the stability of UTC(OP) was dramatically improved and UTC(OP) competes with the best time scales available today. Then the hardware generation and distribution of the UTC(OP) physical signals were replaced. Part of the new hardware is composed of commercial devices, but the key elements were specifically developed. One of them is a special switch that allows the UTC(OP) signals to be derived from one of two time scales, based on two different Hmasers, which are generated simultaneously. This insures the continuity of the UTC(OP) signal even when a change of the reference Hmaser is required. With the new hardware implementation, UTC(OP) is made available through three coherent signals: 100 MHz, 10 MHz and 1 PPS. For more than 3 years, UTC(OP) remained well below 10 ns close to UTC, with a difference even less than 5 ns if we except a short period around MJD 56650.

 [Show abstract] [Hide abstract] ABSTRACT: We use six years of accurate hyperfine frequency comparison data of the dual Rubidium and Caesium cold atom fountain FO2 at LNESYRTE to search for a massive scalar dark matter candidate. Such a scalar field can induce harmonic variations of the fine structure constant, of the mass of fermions and of the quantum chromodynamic mass scale, which will directly impact the Rubidium/Caesium hyperfine transition frequency ratio. We find no signal consistent with a scalar dark matter candidate but provide improved constraints on the coupling of the putative scalar field to standard matter. Our limits are complementary to previous results that were only sensitive to the finestructure constant, and improve them by more than an order of magnitude when only a coupling to electromagnetism is assumed.
 [Show abstract] [Hide abstract] ABSTRACT: The ESA mission "Space Optical Clock" project aims at operating an optical lattice clock on the ISS in approximately 2023. The scientific goals of the mission are to perform tests of fundamental physics, to enable spaceassisted relativistic geodesy and to intercompare optical clocks on the ground using microwave and optical links. The performance goal of the space clock is less than $1 \times 10^{17}$ uncertainty and $1 \times 10^{15} {\tau}^{1/2}$ instability. Within an EUFP7funded project, a strontium optical lattice clock demonstrator has been developed. Goal performances are instability below $1 \times 10^{15} {\tau}^{1/2}$ and fractional inaccuracy $5 \times 10^{17}$. For the design of the clock, techniques and approaches suitable for later space application are used, such as modular design, diode lasers, low power consumption subunits, and compact dimensions. The Sr clock apparatus is fully operational, and the clock transition in $^{88}$Sr was observed with linewidth as small as 9 Hz.
 [Show abstract] [Hide abstract] ABSTRACT: In this paper we report the evaluation of an optical lattice clock based on neutral mercury down to a relative uncertainty of $1.7\times 10^{16}$. Comparing this characterized frequency standard to a Cs atomic fountain we determine the absolute frequency of the $^1S_0 \rightarrow \phantom{}^3P_0$ transition of $^{199}$Hg as $\nu_{\mathrm{Hg}} = 1 128\,575\,290\,808\,154.62\,$Hz $\pm\,0.19\,$Hz (statistical) $\pm\,0.38\,$Hz (systematic), limited solely by the realization of the SI second. Furthermore, by comparing the mercury optical lattice clock to a Rb atomic fountain, we determine for the first time to our knowledge the ratio between the $^{199}$Hg clock transition and the $^{87}$Rb ground state hyperfine transition. Finally we present a direct optical to optical measurement of the $^{199}$Hg/$^{87}$Sr frequency ratio. The obtained value of $\nu_{\mathrm{Hg}}/\nu_{\mathrm{Sr}}=2.629\,314\,209\,898\,909\,15$ with a fractional uncertainty of $1.8\times10^{16}$ is in excellent agreement with the same measurement obtained by Yamanaka et al. (arXiv:1503.07941). This makes this frequency ratio one of the few physical quantities agreed upon by different laboratories to this level of uncertainty. Frequency ratio measurements of the kind of those reported in this paper have a strong impact for frequency metrology but also for fundamental physics as they can be used to monitor putative variations of fundamental constants.

 [Show abstract] [Hide abstract] ABSTRACT: This corrects the article DOI: 10.1103/PhysRevLett.108.183004.
 [Show abstract] [Hide abstract] ABSTRACT: This paper presents the current results obtained with the new version of the French timescale UTC(OP) in operation since more than two years now. The time scale is based on an hydrogen maser steered by one of the SYRTE atomic fountains. Thanks to this technique, UTC(OP) is one of the best real time realization of UTC. A statistical analysis of different UTC  UTC(k) comparisons is presented.

Conference Paper: Towards a High Resolution Geopotential Model Using Chronometric Geodesy
[Show abstract] [Hide abstract] ABSTRACT: In the framework of recent technological advances in atomic clocks, new perspectives in the determination of the geopotential are opened. Thanks to the relation of the relativistic gravitational redshift, determinations of geopotential differences at a centimetric level of accuracy can be considered in the future. This work aims at evaluating the contribution of optical clocks for the determination of the geopotential at high spatial resolution. We have chosen to study mainly a test area from the French Alps to the Mediterranean Sea. Located at the limit between different countries, this region is very interesting because, the gravitational field varies greatly from place to place at high resolution due to the mountains and the bathymetry. Here we describe our approach and the synthetic tests methodology: generation of synthetic gravity and potential data, then estimation of the potential from these data using least squares collocation, and assessment of the clocks contribution.  [Show abstract] [Hide abstract] ABSTRACT: In this article, we report on the work done with the LNESYRTE atomic clock ensemble during the last 10 years. We cover progress made in atomic fountains and in their application to timekeeping. We also cover the development of optical lattice clocks based on strontium and on mercury. We report on tests of fundamental physical laws made with these highly accurate atomic clocks. We also report on work relevant to a future possible redefinition of the SI second.
 [Show abstract] [Hide abstract] ABSTRACT: Ultraprecise optical clocks in space will allow new studies in fundamental physics and astronomy. Within an European Space Agency (ESA) program, the Space Optical Clocks (SOC) project aims to install and to operate an optical lattice clock on the International Space Station (ISS) towards the end of this decade. It would be a natural followon 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. Within the EUFP7SPACE20101 project no. 263500, during the years 20112015 a compact, modular and robust strontium lattice optical clock demonstrator has been developed. Goal performance is a fractional frequency instability below 1x10^{15}, tau^{1/2} and a fractional inaccuracy below 5x10^{17}. Here we describe the current status of the apparatus' development, including the laser subsystems. Robust preparation of cold {88}^Sr atoms in a second stage magnetooptical trap (MOT) is achieved.
 [Show abstract] [Hide abstract] ABSTRACT: We present the current realization of UTC(OP) generated at LNESYRTE, Observatoire de Paris (OP), Paris, France, which is also the source of French legal time. UTC(OP) is based on a HMaser standard steered on the atomic fountains developed by LNESYRTE. The steering algorithm and the prediction of UTC(OP) departure from UTC are described, together with the results of the first year of operation. Since October 2012, the departure of UTC(OP) from UTC stayed well below 10 ns.

Conference Paper: Strontium optical lattice clocks at LNESYRTE
[Show abstract] [Hide abstract] ABSTRACT: In optical lattice clocks, a large number of neutral atoms confined in an optical lattice are probed by a narrow linewidth laser. These clocks combine an excellent control of the systematic effects, while offering a record stability thanks to the large number of interrogated atoms. Here, we report on recent results obtained with two strontium optical lattice clocks at LNESYRTE, Observatoire de Paris.  [Show abstract] [Hide abstract] ABSTRACT: Highresolution spectroscopy has been carried out on the ${}^{199}Hg$ ${}^{1}{S}_{0}$${}{\phantom{\rule{0.16em}{0ex}}}^{3}{P}_{0}$ spin and dipole forbidden transition, where the atoms are confined in a vertical onedimensional optical lattice trap using light at the magic wavelength. We describe various characteristics of the resulting line spectra and assess the strength of the LambDicke confinement. Through a series of absolute frequency measurements of the ${}^{199}Hg$ clock transition with respect to the LNESYRTE primary frequency standard, recorded over a 3month period, we demonstrate a statistical fractional uncertainty of $2.5\ifmmode\times\else\texttimes\fi{}{10}^{$${}16}$. We include details relating to the generation of ultraviolet light at three wavelengths necessary for the experiment: 253.7 nm for cooling and detection, 265.6 nm for clock transition probing, and 362.570 nm for lattice trapping, along with further aspects related to the magic wavelength evaluation.

 [Show abstract] [Hide abstract] ABSTRACT: We report the first contribution to the international atomic time (TAI) based on a secondary representation of the SI second. This work is done with the LNESYRTE FO2Rb fountain frequency standard using the $^{87}$Rb ground state hyperfine transition. We describe FO2Rb and how it is connected to local and international time scales. We report on local measurements of this frequency standard in the SI system, i.e. against primary frequency standards, down to a fractional uncertainty of $4.4\times 10^{16}$, and on the establishment of the recommended value for the $^{87}$Rb hyperfine transition by the CIPM. We also report on the process that led to the participation of the FO2Rb frequency standard to $Circular~T$ and to the elaboration of TAI. This participation enables us to demonstrate absolute frequency measurement directly in terms of the SI second realized by the TAI ensemble with a statistical uncertainty of $1.1\times 10^{16}$, therefore at the limit allowed by the accuracy of primary frequency standards. This work constitutes a demonstration of how other secondary representations, based on optical transitions, could also be used for TAI, and an investigation of a number of issues relevant to a future redefinition of the SI second.

Article: Relativistic geodesy using balloons
[Show abstract] [Hide abstract] ABSTRACT: Relativistic geodesy is gaining impetus due to the relentless improvement of atomic clocks. In conjunction to them, stratospheric balloons are very adequate tools. We present a concept under study at CNES, where an optical clock is carried to an altitude of 40 km where its signal is compared to the one of a sister clock on the ground. The experiment is aimed at checking the redshift predicted by General Relativity to an unprecedented accuracy with an improvement factor between 100 and 300 over current knowledge, and 3 to 10 over space missions planned in the meantime. The challenges of the experiment are presented, namely 1) the ability of the balloon platform to accommodate the clock in terms of mass, power requirements, mechanical and thermal constraints, as well as to offer proper flight duration, safety and a positioning in elevation to better than one cm by postprocessing, 2) the availability of a device capable of time transfer in the range of 108 relative accuracy over the mission duration, 3) the difficulty of relating elevation values with actual gravitational potential, which places a constraint on the location where to operate the flight and 4) the need to use optical clocks with the required reliability (at least 12 h continuous operation), mass constraint (less than one metric ton) and performance (better the 5.1016 stability at one second). The first flight may take place in 2018/2019 time frame. Beyond this experiment, more possibilities of comparison of the potential in two places a few hundreds kilometers apart are allowed by balloon flights, possibly with lighter, pressurized balloons. For instance tethered balloons flying at lower altitudes (e.g. 4km) would allow a direct comparison of optical clocks resting on the ground, while their signals are transmitted to the balloon by fiber optics and exchanged by a dedicated time transfer tool. Copyright © 2014 by the International Astronautical Federation. All rights reserved. 
Conference Paper: Comparison of Sr Optical Lattice Clocks at the 1016 Level
[Show abstract] [Hide abstract] ABSTRACT: We present a comprehensive set of high resolution comparisons between strontium optical lattice clocks in agreement at the 1016 level and three microwave cesium fountains. The microwave to optical comparison reaches a total uncertainty of 3.1×1016. 
Conference Paper: International timescales with optical clocks (ITOC)
[Show abstract] [Hide abstract] ABSTRACT: A new collaborative European project “International timescales with optical clocks” (ITOC) aims to tackle the key challenges that must be addressed prior to a redefinition of the SI second. A coordinated programme of comparisons will be carried out between European optical clocks developed in five different laboratories, enabling their performance levels to be validated at an unprecedented level of accuracy. Supporting work will be carried out to evaluate relativistic effects that influence the comparisons, including the gravitational redshift of the clock transition frequencies. A proofofprinciple experiment will also be performed to demonstrate that optical clocks could be used to make direct measurements of the Earth's gravity potential with high temporal resolution.  [Show abstract] [Hide abstract] ABSTRACT: Progress in realizing the SI second had multiple technological impacts and enabled further constraint of theoretical models in fundamental physics. Caesium microwave fountains, realizing best the second according to its current definition with a relative uncertainty of 2–4 × 10−16, have already been overtaken by atomic clocks referenced to an optical transition, which are both more stable and more accurate. Here we present an important step in the direction of a possible new definition of the second. Our system of five clocks connects with an unprecedented consistency the optical and the microwave worlds. For the first time, two stateoftheart strontium optical lattice clocks are proven to agree within their accuracy budget, with a total uncertainty of 1.5 × 10−16. Their comparison with three independent caesium fountains shows a degree of accuracy now only limited by the best realizations of the microwavedefined second, at the level of 3.1 × 10−16.
Publication Stats
4k  Citations  
264.33  Total Impact Points  
Top Journals
Institutions

2014

French National Centre for Scientific Research
Lutetia Parisorum, ÎledeFrance, France


20042013

Observatoire de Paris
 Systèmes de Référence TempsEspace (SYRTE)
Lutetia Parisorum, ÎledeFrance, France


2012

Pierre and Marie Curie University  Paris 6
Lutetia Parisorum, ÎledeFrance, France


2009

Polytech ParisUPMC
Lutetia Parisorum, ÎledeFrance, France


2005

Laboratoire National de Métrologie et d'Essais
Lutetia Parisorum, ÎledeFrance, France
