Fundamental units, such as the meter, the Ampere or the second, allow for the measurement of any physical quantity. The precision with which they are defined stimulates many scientific works, and has led to an important technological progress. Clocks onboard satellites of the positioning systems, such as the GPS or the European equivalent Galileo, allow for the localization of a point on earth with a resolution of a few centimeters.
Since 1967, the second is defined according to the resonance frequency of a very stable microwave energy transition of the caesium, at 9.2 GHz. A new research field developed in the last 10 years consists in confining neutral atoms in a so-called "optical lattice" - a trap formed by the light itself - and in studying the atomic transitions occurring at a much higher frequency, in the optical domain (1015 Hz). The team of Jérôme Lodewyck and Rodolphe Le Targat, at the laboratoire des Systèmes de référence Temps et Espace - SYRTE (Observatoire de Paris/CNRS/LNE /UPMC) has built two optical lattice clocks based on strontium atoms. They showed that not only these clocks have a very reliable connection to the three caesium primary frequency standards of the laboratory, but also that they are in agreement with 16 significant digits, i.e. at a level surpassing the precision of the current definition of the second.
This is the first time that two optical lattice clocks are proved to agree beyond the uncertainty of the second, it is a very important step in the direction of a possible redefinition of the second. These results were obtained in a very competitive context worldwide, since several optical clocks, operated with neutral atoms or with ions, have progressed very rapidly these last few years and are considered as possible contenders for a new second. The constantly improved precision of these devices raises extraordinary prospects, especially in fundamental Physics (tests of general relativity) and Earth Sciences (relativistic geodesy). The SYRTE optical lattice clocks will soon be compared with those of other European laboratories via a network of optical fibers. They will also be central to the comparisons with a clock operated from March 2016 in the International Space Station in the framework of the space mission PHARAO-ACES. This mission, supervised by CNES and ESA, is expected to have a major impact both in terms of scientific results and of promotion of the SYRTE activities to the public.
Financial supports :
LNE, CNES, IFRAF, DGA, projet EMRP T1 J2.1 OCS, projet ESA SOC1, projet FP7 SOC2.
Last update on 21 December 2021