Atomic fountains and optical clocks at SYRTE: Status and perspectives

Abstract

In this article, we report on the work done with the LNE-SYRTE 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. IntroductionResearch on highly accurate atomic frequency standards and their applications is making fast and steady progress. The quest for ever increased accuracy is advancing hand in hand with advances in quantum physics, with better understanding and manipulation of atomic systems, with exploration of fundamental laws of nature and with the development of important services and infrastructures for science and society. The quest for increased accuracy is also a powerful incentive to innovation in such areas as lasers, laser stabilization, low noise electronics, stable oscillators, low noise detection of optical signals, fiber devices and cold-atom based instrumentation for ground or space applications. Finally, in addition to enhancing existing applications, improved accuracy leads to new applications.This article focuses on key achievements and trends of the last 10 years. Over this period of time, the first generation of laser-cooled standards, using the atomic fountain geometry, reached maturity and had large impact on international timekeeping. The typical accuracy of these frequency standards, 2 parts in 10 16 , is now permanently accessible both locally and globally. At the same time, a new generation of optical clocks showed tremendous and steady improvement, gaining more than two orders of magnitude in a decade. To date, an accuracy of 6.4 × 10 −18 [1] was reported. Similarly, major improvements occurred in many other aspects of optical frequency metrology, notably in optical frequency combs and optical fiber links.In this article, we will report on developments of the LNE-SYRTE atomic clock ensemble since our 2004 report in the Special Issue of the Comptes Rendus de l'Académie des sciences on Fundamental Metrology [2]. This work exemplifies many of the above mentioned features of research on highly accurate atomic frequency standards. We will focus on frequency standards and their impact on timescales and timekeeping, on clock comparisons, including optical-to-microwave comparisons with combs, and their applications. Several

The ACES/PHARAO space mission

“…Microwave clocks operating with laser-cooled cesium atoms in atomic fountains are today used to realize the unit of time, the second, with the best accuracy [25,26,30]. About ten of these devices are operating continuously and report their accuracy to BIPM for the realization of the International Atomic Time and UTC, the Universal Coordinate Time [34].…”

“…These mission objectives were previously detailed in [12][13][14][15] and are also discussed in [37] and [30]. Here we only summarize the main aspects and present the current status of development of the ACES mission elements.…”

Horloges à réseau optique au strontium

“…Ces deux effets sont le déplacement de fréquence dû à la présence de charges statiques (paragraphe 4.3) et le déplacement lumineux in- . Les horloges impliquées dans cette mesure sont la fontaine atomique au césium FO1 et la fontaine mixte au rubidium et au cé-sium FO2 [2,27]. Pour les comparaisons entre les horloges au strontium et au césium, l'échelle de droite indique la fréquence absolue correspondante pour la fréquence de l'horloge au strontium dans le SI.…”

“…Le LNE-SYRTE dispose d'un ensemble d'horloges atomiques micro-onde [27] et une horloge optique au mercure [2], qui peuvent être comparées aux horloges au strontium via un peigne de fréquences généré par un laser femto-seconde fibré [28]. Cet ensemble d'horloges nous a permis de réaliser des mesures répétées du rapport de fréquence entre l'horloge au strontium et les étalons primaires au césium.…”

“…Ces horloges, actuellement au stade opérationnel, sont utilisées couramment pour calibrer les échelles de temps internationales (le temps universel coordonné UTC et le temps atomique international TAI) via des comparaisons satellitaires, ainsi que pour réaliser la définition de la seconde du Système international d'unités (SI). L'exactitude de ces étalons primaires de fréquence, au niveau de quelques 10 −16 [1,2], résulte notamment de l'utilisation d'atomes ultra-froids en chute libre pour lesquels le dé-placement de fréquence Doppler dû au mouvement des atomes est fortement réduit et le temps d'interrogation de la transition d'horloge est de l'ordre de la seconde.…”