G. D. Rovera

Absolute frequency measurement of the 40Ca+ 4s(2)S_(1/2)-3d(2)D_(5/2) clock transition.

We report on the first absolute transition frequency measurement at the 10 -15 level with a single, laser-cooled 40 Ca + ion in a linear Paul trap. For this measurement, a frequency comb is referenced to the transportable Cs atomic fountain clock of LNE-SYRTE and is used to measure the 40 Ca + 4s 2 S 1/2 -3d 2 D 5/2 electric-quadrupole transition frequency. After the correction of systematic shifts, the clock transition frequency v Ca + = 411 042 129 776 393.2 (1.0) Hz is obtained, which corresponds to a fractional uncertainty within a factor of 3 of the Cs standard. In addition, we determine the Lande g factor of the 3d 2 D 5/2 level to be g 5/2 = 1.2003340(3).

UTC(OP) based on LNE-SYRTE atomic fountain primary frequency standards

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 H-maser 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 H-masers, which are generated simultaneously. This insures the continuity of the UTC(OP) signal even when a change of the reference H-maser 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.

Absolute Frequency Measurement of the 40Ca+ 4s 2S1/2 -3d2D5/2 Clock Transition

We report on the first absolute transition frequency measurement at the 10 -15 level with a single, laser-cooled 40 Ca + ion in a linear Paul trap. For this measurement, a frequency comb is referenced to the transportable Cs atomic fountain clock of LNE-SYRTE and is used to measure the 40 Ca + 4s 2 S 1/2 -3d 2 D 5/2 electric-quadrupole transition frequency. After the correction of systematic shifts, the clock transition frequency v Ca + = 411 042 129 776 393.2 (1.0) Hz is obtained, which corresponds to a fractional uncertainty within a factor of 3 of the Cs standard. In addition, we determine the Lande g factor of the 3d 2 D 5/2 level to be g 5/2 = 1.2003340(3).

The new UTC(OP) based on LNE-SYRTE atomic fountains

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.

Construction and evaluation of the first Brazilian atomic clock

For the past two years we have been implementing a program for the establishment of scientific time and frequency metrology in Brazil. The main objective of this program is to construct an atomic fountain and use it as a primary standard. As a first step toward this goal, we have constructed a /sup 133/Cs beam optically pumped conventional clock. In this paper we describe the system and the results of its evaluation. The possible limitations of our short-term stability are discussed.

Progress in the link calibration for UTC time transfer

The dominant part of the total uncertainty budget in the [UTC-UTC(k)] is from the type B uncertainty (uB) in time link calibration. In fact, 60% of the type A uncertainty (ua) in UTC time links are <; 1 ns while the 93% of uB ≥ 5ns. In 2011, the BIPM launched a pilot experiment to reduce the uB from 5 ns at present to ≤ 2 ns and has developed a standard calibration scheme, namely METODE, associated with an integrated portable GNSS calibrator together with the reference receivers stationary at BIPM. Similar setups are made in TL. Using these systems, we performed a series experiments at BIPM, OP and TL to study the attainable uncertainty of METODE. The results are compared to that of the traditional differential receiver calibrations.

ABSOLUTE FREQUENCY MEASUREMENT OF THE 40Ca+ 4s 2S1/2 - 3d 2D5/2 CLOCK TRANSITION

We report on the first absolute transition frequency measurement at the 10;{-15} level with a single, laser-cooled 40Ca+ ion in a linear Paul trap. For this measurement, a frequency comb is referenced to the transportable Cs atomic fountain clock of LNE-SYRTE and is used to measure the 40Ca+ 4s ;{2}S_{1/2}-3d ;{2}D_{5/2} electric-quadrupole transition frequency. After the correction of systematic shifts, the clock transition frequency nu_{Ca;{+}}=411 042 129 776 393.2(1.0) Hz is obtained, which corresponds to a fractional uncertainty within a factor of 3 of the Cs standard. In addition, we determine the Landé g factor of the 3d;{2}D_{5/2} level to be g_{5/2}=1.200 334 0(3).

A sub-ns comparison between GPS common view and T2L2

T2L2 (Time Transfer by Laser Link) permits the synchronization of remote ultra stable clocks over intercontinental distances. The principle is based upon laser telemetry technology with a network of laser stations on ground and dedicated space equipment designed to record arrival time of laser pulses at the satellite. T2L2 allows realization of some links between distant clocks with time stability of a few picoseconds and accuracy better than 100 ps. The instrumental metrology associated with such performance needs to be designed with utmost care. This requirement concerns all the instrumentation directly linked with the specific T2L2 equipment as well as the instrumentation doing the link between the laboratory reference and the T2L2 ground segment. Several campaigns were done to demonstrate both the ultimate time accuracy and time stability capabilities of T2L2. The paper is focused on the current high accuracy equipment that has been designed for the picosecond metrology and on some recent campaigns involving global calibrations of both laser stations and GNSS equipment. Results obtained during two months of comparisons between GPS in common view and T2L2 at three European laboratories show some differences below 300 ps with a standard deviation better than 500 ps. This is the first time that two different techniques of time transfer independently calibrated are in agreement at sub-ns level over continental distances.

Evaluation of the first Brazilian atomic clock

For the past two years we have been implementing a program for the establishment of scientific time and frequency metrology in Brazil. The main objective of this program is to construct an atomic fountain and use that as a primary standard. As a first step toward this goal we have constructed a traditional /sup 133/Cs beam clock and here we describe the results of its evaluation as well as the first steps towards the atomic fountain.

A simple computation technique for improving the short term stability and the robustness of GPS TAIP3 common-views

We propose a new simple technique to improve the short term stability and the robustness of Common-Views (CV) of Global Positioning System (GPS) satellites. We use the ionosphere free linear combination of P-code data broadcast on both GPS carriers, called TAIP3, the data files being built according to the Common GNSS Time Transfer Standard (CGTTS) format. Instead of averaging the outliers out by using a given filter around a mean value computed for each CGTTS sampling epoch, we average the outliers out from a linear fit on daily CV files. We analyze the results over more than 200 d of data. Over a short baseline between remote stations, we see that the average number of satellites left by the daily filtering for the CV computation is almost twice as large as the number obtained from the epoch filtering, increasing that way the robustness of the time transfer. On the short term stability of the time transfer, the white phase noise modulation is improved by a factor larger than the square root of 2, above what was expected. Over a long baseline, the improved short term stability is about twice smaller between 10 000 s and 1 d, together with an average increase of more than 20 per cent on the number of satellites left after filtering for the CV computation. We study the singular event which causes the discrepancy between these two criteria, and conclude that the daily approach is providing the best results in all cases. This automated filtering technique might be useful for any GNSS time transfer based on code data.