Realization of a timescale with an accurate optical lattice clock

Abstract

Optical clocks are not only powerful tools for prime fundamental research, but are also deemed for the re-definition of the SI base unit second as they now surpass the performance of caesium atomic clocks in both accuracy and stability by more than an order of magnitude. However, an important obstacle in this transition has so far been the limited reliability of the optical clocks that made a continuous realization of a timescale impractical. In this paper, we demonstrate how this situation can be resolved and that a timescale based on an optical clock can be established that is superior to one based on even the best caesium fountain clocks. The paper also gives further proof of the international consistency of strontium lattice clocks on the 10 −16 accuracy level, which is another prerequisite for a change in the definition of the second.

Transportable Optical Lattice Clock with7×10−17Uncertainty

“…The 40 Ca + -ion clock reported in [29] reaches an uncertainty of 7.7 × 10 −17 and an instability of 2.3 × 10 −14 / √ τ , but has not left the laboratory yet. Here we present a transportable OLC that is characterized and compared to an established, stationary optical frequency standard [5,10,18,31] and tested outside the laboratory in a transportable car-trailer (Fig. 1).…”

“…This has triggered a discussion about a redefinition of the SI second [7,8], pushes the frontiers of precision spectroscopy and tests fundamental physics [9][10][11][12][13][14], and enables chronometric leveling [15][16][17][18][19], where gravitational redshifts are exploited to measure height differences.…”

“…Furthermore, transportability is a first step towards applications of optical clocks in space. Developments in these directions are ongoing for optical lattice clocks (OLCs) with strontium [27,28]; however, to our knowledge the single-ion clock reported recently [29] is the only other transportable clock with uncertainty below 10 −16 .The requirements on such a TOC are challenging indeed: To enable comparisons of other optical clocks it has to achieve uncertainties similar to those of the clocks to be tested or at least considerably better than what can be reached by comparing to primary cesium clocks [10,11,30,31]. Further, for geodetic applications, i.e., chronometric leveling, a resolution of below ten centimeters is required to compete with established methods that connect sites separated by a few hundreds of kilometers.…”

Horloges à réseau optique au strontium

“…Ces mesures, qui constituent la meilleure détermination d'une fréquence absolue à ce jour, sont reproductibles sur plusieurs années avec un écart inférieur à l'incertitude systématique, ce qui indique une excellente maîtrise des effets systé-matiques sur les deux horloges. De plus, elles sont en très bon accord avec des mesures similaires effectuées à la PTB [29,30] (voir également paragraphe 5.6). Plus récemment, nous avons mesuré pour la première fois le rapport de fréquence entre les horloges au strontium et au rubidium, avec une incertitude comparable ( fig.…”

“…9). Enfin, les premières comparaisons tout optique entre les horloges à réseau optique au strontium et au mercure LNE-SYRTE [26,35], le JILA (Colorado, États-unis) [36,37], la PTB (Allemagne) [29,30,38], l'Université de Tokyo (Japon) en 2006 et 2008 [39], le NICT (Japon) [40][41][42], le NMIJ (Japon) [43,44] et le NIM en 2015 (Chine) [45]. Un ajustement de ces mesures par une dérive linéaire dans le temps superposée à une variation sinusoïdale d'amplitude a calée sur la rotation de la Terre autour du soleil permet de contraindre la dérive du rapport de fréquence par d ln(ν Sr /ν Cs )/dt = −(1, 7 ± 0, 7) × 10 conduites au LNE-SYRTE permettent de s'affranchir des étalons micro-onde, et ainsi de démontrer une stabilité de fréquence dix fois meilleure, à quelques 10 −15 / √ τ.…”