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).
The measurement of the time difference between two heterogeneous electrical sources is a necessary task in several branches of metrology. In particular the dissemination of Coordinated Universal Time ...(UTC) around the world requires one to quantify the synchronization between two or more co-located time scales. The task is usually carried out using a time interval counter, by directly measuring the time difference between signals at its inputs. We found that special care must be taken when a total uncertainty significantly smaller than 1 ns is desired. The goal of this paper is to present a complete analysis of the total uncertainty for the measurement of time differences between co-located time scales, with considerations for improvement.
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.
We present a direct comparison between two satellite time transfer techniques on independently calibrated links: Time Transfer by Laser Link (T2L2) and Common-Views (CV) of satellites from the Global ...Positioning System (GPS) constellation. The GPS CV and T2L2 links between three European laboratories where independently calibrated against the same reference point of the local timescales. For all the links the mean values of the differences between GPS CV and T2L2 are equal or below 240 ps, with standard deviations below 500 ps, mostly due to GPS CV. Almost all deviations from 0 ns are within the combined uncertainty estimates. Despite the weak number of common points obtained, due to the fact that T2L2 is weather dependent, these results are providing an unprecedented sub-ns consistency between two independently calibrated microwave and optical satellite time transfer techniques.
Accurate spectroscopy of Sr atoms COURTILLOT, I; QUESSADA-VIAL, A; BRUSCH, A ...
The European physical journal. D, Atomic, molecular, and optical physics,
05/2005, Letnik:
33, Številka:
2
Journal Article
Recenzirano
We report the frequency measurement with an accuracy in the 100 kHz range of several optical transitions of atomic Sr : $^1S_0- ^3P_1$ at 689 nm, $^3P_1- ^3S_1$ at 688 nm and $^3P_0- ^3S_1$ at 679 ...nm. Measurements are performed with a frequency chain based on a femtosecond laser referenced to primary frequency standards. They allowed the indirect determination with a 70 kHz uncertainty of the frequency of the doubly forbidden $5s^2^1S_0- 5s5p^3P_0$ transition of $^{87}$Sr at 698 nm and in a second step its direct observation. Frequency measurements are performed for $^{88}$Sr and $^{87}$Sr, allowing the determination of $^3P_0$, $^3P_1$ and $^3S_1$ isotope shifts, as well as the $^3S_1$ hyperfine constants.
We present the current realization of UTC(OP) generated at LNE-SYRTE, Observatoire de Paris (OP), Paris, France, which is also the source of French legal time. UTC(OP) is based on a H-Maser standard ...steered on the atomic fountains developed by LNE-SYRTE. 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.
This paper presents a direct comparison of two time transfer techniques on independently calibrated links: Time Transfer by Laser Link (T2L2) and Global Positioning System (GPS) satellite ...common-views (CV). The two different techniques are described, along with the independent link calibrations. The results achieved during one measurement campaign involving three European laboratories are presented, the differences between the two techniques remaining in average below 300 ps, with a standard-deviation below 500 ps mostly due to GPS CV.
In the legend to Fig. 4c in this Article, references 47 and 48 were incorrectly included in a list of sources for 87 Sr clock frequency measurements. The correct sources are Hong et al. 49 and ...Yamaguchi et al. 50 , as follows.
We describe the operation and the performances of the French time scale UTC(OP) since the change of its design in October 2012. The new UTC(OP) is based on an active H-maser steered using LNE-SYRTE ...atomic fountains frequency calibrations. Later on, the generation and distribution systems were entirely rebuilt to improve the short term stability and the robustness of the time scale and to provide redundancy. With the new design, UTC(OP) remains close to UTC within a few ns. This paper is focussed on the performances of the time scale and on the major events encountered.
The frequency noise of the local oscillator may degrade the long-term stability of high-stability frequency standard; a simple evaluation of this effect is performed to optimize the design of a ...synthesizer to be used in Cs atomic primary frequency standard. A description of the microwave synthesis chain realized, which is suitable as a local oscillator for Cs atomic primary frequency standard, is reported. Phase noise spectra in the key points of the chain are also reported. The measured fractional frequency stability of the chain is better than 10/sup -17/ at one day.
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