Optical clocks show unprecedented accuracy, surpassing that of previously available clock systems by more than one order of magnitude. Precise intercomparisons will enable a variety of experiments, including tests of fundamental quantum physics and cosmology and applications in geodesy and navigation. Well-established, satellite-based techniques for… (More)
We investigated the transfer of a 194 THz optical frequency along a 1840 km fiber link. The fractional frequency instability expressed as the modified Allan deviation is 2.7 × 10<sup>-15</sup> at 1 s with 4 × 10<sup>-19</sup> after 100 s. The transferred frequency shows no systematic offset within an uncertainty of 3 × 10<sup>-19</sup>.… (More)
We report on the status of the optical link project between PTB and MPQ and present the to our knowledge first frequency transfer using urban fiber networks over a distance of about 500 km length.