Atomic clock comparison could impact multiple scientific fields

The results of the ICOF project, in combination with the NEAT-FT Joint Research Project of the European Metrology Research Program, will pave the way for improved clock comparisons within Europe and the dissemination of highly accurate, stable frequency and timing signals to academia and industry.

ICOF will substantially impact the time and frequency metrology fields, geodesy and other areas of science, as well as change the way we conduct fundamental physics experiments. The high precision of atomic clocks, now reaching relative uncertainties at the level of 10^-17 can help us find answers to fundamental questions by putting stringent limits on variations of fundamental constants.

Because the tick rate (frequency) of any clock is affected by gravity, potential also exists for geodetic applications, such as those used in surveying and mapping.

The bridge pictured above in Laufenburg, a town straddling Germany and Switzerland, was accidently built using two versions of sea level to calculate its height. As the two halves grew closer, one side was found to be 54cm higher than the other. Sea levels in continental Europe differ by some 10cm due to different gauges in northern and southern Europe. The comparison of a portable optical clock, connected through a high-accuracy fibre link to a reference clock at a fixed location and height, would allow an unambiguous determination of these height differences.

The unprecedented stability of optical clocks will also allow tides caused by the orbiting moon around the earth to be measured using clocks at remote locations.

“Optical fibre links will allow for time and frequency comparisons to be performed at a much higher level of accuracy and stability than that currently achievable by more conventional satellite links,” said Harald Schnatz, Project Manager, ICOF. “The GÉANT Open Call project has given us access to the GÉANT long haul dark fibre link between NPL (London) and OBSPARIS (Paris). Currently, there is nothing else available that allows us to connect NPL with OBSPARIS with the required performance.”

“What’s different about ICOF to other Open Call projects is that there is no digital data being carried across this particular GÉANT fibre, which is a very strange concept to the average network operator! ICOF is sending a very precise single optical frequency (with a spectral bandwidth less than 10Hz) that allows the comparison, with unprecedented levels of precision, of very accurate optical clocks operated in widely distributed locations,” added Michael Enrico, Technical Coordinator, GÉANT project. “This is a great example of how the GÉANT network can support novel research with potentially huge implications to the wider scientific and engineering landscape, and the results of ICOF are likely to keep the metrology institutes busy for many years to come. We are really excited by this project and are watching closely to see how it develops.”