Ten to the minus 17th, that is the long term goal outlined in the European Metrology Research Program which can be found at:
The following is a quote from the document:
“The unit of time is considered as the most fundamental base unit. Almost all technological
processes require precise timing or reference frequencies, respectively. Other units such as length are directly linked to the unit of time. In addition, time and frequency are the quantitieswhich can be measured most precisely.
Advantages in the realisation and dissemination of time and frequency are expected to have wide-spread impact on innovation, science and daily life, e.g. GPS.
Europe NMIs provide enormous, however sometimes uncoordinated and fragmented,
capabilities in atomic clocks, time scale generation, time dissemination, space technology,
and network synchronization. Three research focuses have been identified that will capitaliseon the existing potential to the full extent only in a European effort:
· Development of novel atomic clocks with unprecedented accuracy: frequency
standards in the optical regime have to be developed to overcome the limitations of
today’s best primary frequency standards based on laser cooled caesium atoms.
· Establishment of novel ways for time and frequency transfer: Atomic clocks with
lower instabilities and higher accuracies put more stringent requirements on the
performance of time and frequency transfer systems. The existing tools such as Two-
Way Satellite Time and Frequency Transfer (TWSTFT) based on telecom satellites
or techniques exploiting signals from global navigation satellite systems like GPS or
Galileo need to be developed further. In parallel, new techniques shall be
investigated, allowing a link of the major European timing laboratories by optical fibre.
· Atomic clocks for specific space applications: Deep space missions and satellite
navigation impose the most challenging requirements on accuracy and reliability of
clocks. The development of a satellite-borne atomic clock with 10-17 capability is a
long term goal.”