S. Bize

UPMC, Pittsburgh, Pennsylvania, United States

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Publications (138)217.17 Total impact

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    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 LNE-SYRTE FO2-Rb fountain frequency standard using the $^{87}$Rb ground state hyperfine transition. We describe FO2-Rb 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 FO2-Rb 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.
    01/2014; 51(1).
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    ABSTRACT: We present a comprehensive set of high resolution comparisons between strontium optical lattice clocks in agreement at the 10-16 level and three microwave cesium fountains. The microwave to optical comparison reaches a total uncertainty of 3.1×10-16.
    Laser Science; 10/2013
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    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 state-of-the-art 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 microwave-defined second, at the level of 3.1 × 10−16.
    Nature Communications 07/2013; 4. · 10.74 Impact Factor
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    ABSTRACT: The frequencies of three separate Cs fountain clocks and one Rb fountain clock have been compared to various hydrogen masers to search for periodic changes correlated with the changing solar gravitational potential at the Earth and boost with respect to the cosmic microwave background rest frame. The data sets span over more than 8 yr. The main sources of long-term noise in such experiments are the offsets and linear drifts associated with the various H-masers. The drift can vary from nearly immeasurable to as high as 1.3×10-15 per day. To circumvent these effects, we apply a numerical derivative to the data, which significantly reduces the standard error when searching for periodic signals. We determine a standard error for the putative local position invariance coefficient with respect to gravity for a Cs-fountain H-maser comparison of |βH−βCs|≤4.8×10-6 and |βH−βRb|≤10-5 for a Rb-Fountain H-maser comparison. From the same data, the putative boost local position invariance coefficients were measured to a precision of up to parts in 1011 with respect to the cosmic microwave background rest frame. By combining these boost invariance experiments to a cryogenic sapphire oscillator vs H-maser comparison, independent limits on all nine coefficients of the boost-violation vector with respect to fundamental constant invariance, Bα, Be, and Bq (fine structure constant, electron mass, and quark mass, respectively), were determined to a precision of parts up to 1010.
    Physical review D: Particles and fields 06/2013; 87(12).
  • International Quantum Electronics Conference; 05/2013
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    ABSTRACT: We report the operation of a dual Rb/Cs atomic fountain clock. 133Cs and 87Rb atoms are cooled, launched, and detected simultaneously in LNE-SYRTE's FO2 double fountain. The dual clock operation occurs with no degradation of either the stability or the accuracy. We describe the key features for achieving such a simultaneous operation. We also report on the results of the first Rb/Cs frequency measurement campaign performed with FO2 in this dual atom clock configuration, including a new determination of the absolute 87Rb hyperfine frequency.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 01/2013; 57(3). · 1.80 Impact Factor
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    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 proof-of-principle 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.
    European Frequency and Time Forum & International Frequency Control Symposium (EFTF/IFC), 2013 Joint; 01/2013
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    ABSTRACT: In this paper, we review several characteristics of optical lattice clocks as candidates for a future redefinition of the International System of Units (SI) second using an atomic transition in the optical domain, focusing on experiments performed at SYRTE using one mercury (Hg) and two strontium (Sr) optical lattice clocks. Beyond the technical aspects such as the stability and systematic frequency-shift assessments of the clocks, practical aspects have to be considered, such as the careful determination of the optical frequency with respect to the cesium primary standard and the worldwide reproducibility of the clock frequency by local and remote clock comparisons.
    IEEE Transactions on Instrumentation and Measurement 01/2013; 62(6):1568-1573. · 1.71 Impact Factor
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    ABSTRACT: The new realization of UTC(OP) is described. The steering algorithm and the prediction of UTC(OP) are presented in details. The results of the first semester of operation are reported.
    European Frequency and Time Forum & International Frequency Control Symposium (EFTF/IFC), 2013 Joint; 01/2013
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    ABSTRACT: We report the main features and performances of a prototype of an ultra-stable cavity designed and realized by industry for space applications with the aim of space missions. The cavity is a 100 mm long cylinder rigidly held at its midplane by a engineered mechanical interface providing an efficient decoupling from thermal and vibration perturbations. Intensive finite element modeling was performed in order to optimize thermal and vibration sensitivities while getting a high fundamental resonance frequency. The system was designed to be transportable, acceleration tolerant (up to several g) and temperature range compliant [-33°C ; 73°C]. Thermal isolation is ensured by gold coated Aluminum shields inside a stainless steel enclosure for vacuum. The axial vibration sensitivity was evaluated at (4 ± 0.5) × 10<sup>-11</sup>/(m.s<sup>-2</sup>), while the transverse one is < 1 × 10<sup>-11</sup>/(m.s<sup>-2</sup>). The fractional frequency instability is ≲ 1×10<sup>-15</sup> from 0.1 to a few seconds and reaches 5-6×10<sup>-16</sup> at 1s.
    Optics Express 11/2012; 20(23):25409-20. · 3.55 Impact Factor
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    ABSTRACT: We have observed Feshbach resonances for 133 Cs atoms in two different hyperfine states at static magnetic fields of a few milligauss. These resonances are unusual for two main reasons. First, they are the lowest static-field resonances investigated up to now, and we explain their multipeak structure in these ultralow fields. Second, they are robust with respect to temperature effects. We have measured them using an atomic fountain clock and reproduced them using coupled-channels calculations, which are in excellent agreement with our measurements. We show that these are s-wave resonances due to a very weakly bound state of the triplet molecular Hamiltonian. We also describe a model explaining their asymmetric shape in the regime where the kinetic energy dominates over the coupling strength.
    Physical Review A 10/2012; 86:040701(R). · 3.04 Impact Factor
  • Sébastien Bize
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    ABSTRACT: An ultrastable optical laser based on a single-crystal silicon Fabry-Pérot cavity offers a fractional frequency instability of 1 × 10-16 on short timescales and supports a laser linewidth of less than 40 mHz at a wavelength of 1.5 μm.
    Nature Photonics 10/2012; 6(10):638-639. · 27.25 Impact Factor
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    ABSTRACT: With Hg199 atoms confined in an optical lattice trap in the Lamb–Dicke regime, we obtain a spectral line at 265.6 nm for which the FWHM is ∼15 Hz. Here we lock an ultrastable laser to this ultranarrow S01−P03 clock transition and achieve a fractional frequency instability of 5.4×10−15/τ for τ≤400 s. The highly stable laser light used for the atom probing is derived from a 1062.6 nm fiber laser locked to an ultrastable optical cavity that exhibits a mean drift rate of −6.0×10−17 s−1 (−16.9 mHz s−1 at 282 THz) over a six month period. A comparison between two such lasers locked to independent optical cavities shows a flicker noise limited fractional frequency instability of 4×10−16 per cavity.
    Optics Letters 09/2012; 37(17). · 3.39 Impact Factor
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    ABSTRACT: With 199Hg atoms confined in an optical lattice trap in the Lamb-Dicke regime, we obtain a spectral line at 265.6 nm for which the FWHM is ~15 Hz. Here we lock an ultrastable laser to this ultranarrow 1S0-3P0 clock transition and achieve a fractional frequency instability of 5.4×10(-15)/✓τ for τ ≤ 400 s. The highly stable laser light used for the atom probing is derived from a 1062.6 nm fiber laser locked to an ultrastable optical cavity that exhibits a mean drift rate of -6.0×10(-17) s(-1) (-16.9 mHz s(-1) at 282 THz) over a six month period. A comparison between two such lasers locked to independent optical cavities shows a flicker noise limited fractional frequency instability of 4×10(-16) per cavity.
    Optics Letters 09/2012; 37(17):3477-9. · 3.39 Impact Factor
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    ABSTRACT: 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.
    06/2012;
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    ABSTRACT: With Hg atoms confined in an optical lattice trap in the Lamb-Dicke regime, we obtain a spectral line at 265.6 nm in which the full-width at half-maximum is <15Hz. Here we lock an ultrastable laser to this ultranarrow clock transition and achieve a fractional frequency stability of 5.4x10^(-15)/sqrt(tau) for tau<=400s. The highly stable laser light used for the atom probing is derived from a 1062.6 nm fiber laser locked to an ultrastable optical cavity that exhibits a mean drift rate of -6.0x10^(-17) s^(-1) (or -16.9 mHz.s^(-1) at 282 THz) over a five month period. A comparison between two such lasers locked to independent optical cavities shows a flicker noise limited fractional frequency instability of 4x10^(-16) per cavity.
    05/2012;
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    ABSTRACT: We report tests of local position invariance based on measurements of the ratio of the ground state hyperfine frequencies of 133Cs and 87Rb in laser-cooled atomic fountain clocks. Measurements extending over 14 years set a stringent limit to a possible variation with time of this ratio: d ln(nu_Rb/nu_Cs)/dt=(-1.39 +/- 0.91)x 10-16 yr-1. This improves by a factor of 7.7 over our previous report (H. Marion et al., Phys. Rev. Lett. 90, 150801 (2003)). Our measurements also set the first limit to a fractional variation of the Rb/Cs ratio with gravitational potential at the level of c^2 d ln(nu_Rb/nu_Cs)/dU=(0.11 +/- 1.04)x 10^-6, providing a new stringent differential redshift test. The above limits equivalently apply to the fractional variation of the quantity alpha^{-0.49}x(g_Rb/g_Cs), which involves the fine structure constant alpha and the ratio of the nuclear g-factors of the two alkalis. The link with variations of the light quark mass is also presented together with a global analysis combining with other available highly accurate clock comparisons.
    Physical Review Letters 05/2012; 109(8). · 7.73 Impact Factor
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    ABSTRACT: We have observed Feshbach resonances for 133Cs atoms in two different hyperfine states at ultra-low static magnetic fields by using an atomic fountain clock. The extreme sensitivity of our setup allows for high signal-to-noise-ratio observations at densities of only 2*10^7 cm^{-3}. We have reproduced these resonances using coupled-channels calculations which are in excellent agreement with our measurements. We justify that these are s-wave resonances involving weakly-bound states of the triplet molecular Hamiltonian, identify the resonant closed channels, and explain the observed multi-peak structure. We also describe a model which precisely accounts for the collisional processes in the fountain and which explains the asymmetric shape of the observed Feshbach resonances in the regime where the kinetic energy dominates over the coupling strength.
    05/2012;
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    ABSTRACT: We present an assessment of the (6s2) (1)S0 ↔ (6s6p)(3)P0 clock transition frequency in 199Hg with an uncertainty reduction of nearly 3 orders of magnitude and demonstrate an atomic quality factor Q of ∼10(14). The 199Hg atoms are confined in a vertical lattice trap with light at the newly determined magic wavelength of 362.5697±0.0011  nm and at a lattice depth of 20E(R). The atoms are loaded from a single-stage magneto-optical trap with cooling light at 253.7 nm. The high Q factor is obtained with an 80 ms Rabi pulse at 265.6 nm. We find the frequency of the clock transition to be 1,128,575,290,808,162.0±6.4(syst)±0.3(stat)  Hz (i.e., with fractional uncertainty=5.7×10(-15)). Neither an atom number nor second order Zeeman dependence has yet been detected. Only three laser wavelengths are used for the cooling, lattice trapping, probing, and detection.
    Physical Review Letters 05/2012; 108(18):183004. · 7.73 Impact Factor
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    ABSTRACT: We give an overview of the work done with the Laboratoire National de Métrologie et d'Essais-Systèmes de Référence Temps-Espace (LNE-SYRTE) fountain ensemble during the last five years. After a description of the clock ensemble, comprising three fountains, FO1, FO2, and FOM, and the newest developments, we review recent studies of several systematic frequency shifts. This includes the distributed cavity phase shift, which we evaluate for the FO1 and FOM fountains, applying the techniques of our recent work on FO2. We also report calculations of the microwave lensing frequency shift for the three fountains, review the status of the blackbody radiation shift, and summarize recent experimental work to control microwave leakage and spurious phase perturbations. We give current accuracy budgets. We also describe several applications in time and frequency metrology: fountain comparisons, calibrations of the international atomic time, secondary representation of the SI second based on the (87)Rb hyperfine frequency, absolute measurements of optical frequencies, tests of the T2L2 satellite laser link, and review fundamental physics applications of the LNE-SYRTE fountain ensemble. Finally, we give a summary of the tests of the PHARAO cold atom space clock performed using the FOM transportable fountain.
    IEEE transactions on ultrasonics, ferroelectrics, and frequency control 03/2012; 59(3):391-410. · 1.80 Impact Factor

Publication Stats

2k Citations
217.17 Total Impact Points

Institutions

  • 2009–2014
    • UPMC
      Pittsburgh, Pennsylvania, United States
    • Polytech Paris-UPMC
      Lutetia Parisorum, Île-de-France, France
  • 2003–2013
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
    • National Institute of Standards and Technology
      • Time and Frequency Division
      Gaithersburg, MD, United States
  • 2010
    • Pennsylvania State University
      University Park, Maryland, United States
  • 2005
    • Laboratoire National de Métrologie et d'Essais
      Lutetia Parisorum, Île-de-France, France
    • University of Western Australia
      • School of Physics
      Perth, Western Australia, Australia