Stability of the proton-to-electron mass ratio tested with molecular spectroscopy using an optical link to frequency reference

Time and frequency metrology has experienced a lot of developments since ten years leading to the possibility of many fundamental tests of physics, as, for example, the search for a temporal variation of fundamental constants. However these tests are limited to macroscopic resonators or atomic systems while molecular systems are still difficult to probe with a high sensitivity, since experiments on molecules lacks of absolute frequency measurements set-ups. In that context, we have developed an optical link between our lab and the LNE-SYRTE, which allows us to benefit from their frequency references. Using this link, we performed the first experimental comparison of a molecular clock to an atomic clock, which gives a direct line to the proton-to-electron mass ratio stability. Recently, we extended the frequency dissemination technique to non-dedicated fibers of the telecommunication network simultaneously carrying digital data from the Internet traffic. This is very challenging for the development of transcontinental atomic and molecular clocks comparisons.