Related papers: A clock network for geodesy and fundamental scienc…
We demonstrate a fully optical, long-distance remote comparison of independent ultrastable optical frequencies reaching a short term stability that is superior to any reported remote comparison of optical frequencies. We use two ultrastable…
We performed a two-way remote optical phase comparison on optical fiber. Two optical frequency signals were launched in opposite directions in an optical fiber and their phases were simultaneously measured at the other end. In this…
We demonstrate combined high-fidelity long-haul transfer of a linearly chirped, optical frequency and time transfer. In a proof-of-principle experiment we transfer an optical frequency with a linear chirp of around 238 kHz/s via a…
Some 50~years ago, physicists, and after them the entire world, started to found their time reference on atomic properties instead of motions of the Earth that have been in use since the origin. Far from being an arrival point, this…
We describe a fiber-optic solution for simultaneous distribution of all signals generated at todays most advanced time and frequency laboratories, i.e. an ultrastable optical reference frequency derived from an optical atomic clock, a radio…
Fiber-delay measurement is one of the key fundamental technologies in numerous fields. Here we propose and experimentally demonstrate a high-precision and concise optical time delay measurement system based on the technique of linear…
We transferred the frequency of an ultra-stable laser over a 108 km urban fiber link comprising 22 km of optical communications network fiber simultaneously carrying Internet data traffic. The metrological signal and the digital data signal…
We report the first direct frequency comparison between two multi-ion optical clocks based on the S$_{1/2}$ to D$_{5/2}$ transition in \Ca and \Sr ions. Using linear chains of up to nine \Ca ions and six \Sr ions, we demonstrate improved…
Questioning the presumably most basic assumptions about the structure of space and time has revolutionized our understanding of Nature. State-of-the-art atomic clocks make it possible to precisely test fundamental symmetry properties of…
We present our work on realizing two-branch fiber links enabling multiple-partner clock comparisons in Europe. We report in detail on the setup connecting two long haul links, and report for the relative frequency stability and accuracy. We…
We used Precise Point Positioning, a well-established GPS carrier-phase frequency transfer method to perform a direct remote comparison of two optical frequency standards based on single laser-cooled $^{171}$Yb$^+$ ions operated at NPL, UK…
The two-way quantum clock synchronization has been shown not only providing femtosecond-level synchronization capability but also security against symmetric delay attacks, thus becoming a prospective method to compare and synchronize…
We report a stability below $7\times 10{}^{-17}$ of two independent optical lattice clocks operating with bosonic ${}^{88}$Sr isotope. The value (429228066418008.3(1.9)${}_{syst}$(0.9)${}_{stat}$~Hz) of the absolute frequency of the…
The frequency comb created by a femtosecond mode-locked laser and a microstructured fiber is used to phase coherently measure the frequencies of both the Hg^+ and Ca optical standards with respect to the SI second as realized at NIST. We…
Recently invented and demonstrated, optical lattice clocks hold great promise for improving the precision of modern timekeeping. These clocks aim at the 10^-18 fractional accuracy, which translates into a clock that would neither lose or…
We report on a fully bi-directional 680~km fiber link connecting two cities for which the equipment, the set up and the characterization are managed for the first time by an industrial consortium. The link uses an active telecommunication…
Today's most precise optical instruments -- gravitational-wave interferometers and optical atomic clocks -- rely on long storage times for photons to realize their exquisite sensitivity. Optical fiber technology is the most widely deployed…
A time scale is a procedure for accurately and continuously marking the passage of time. It is exemplified by Coordinated Universal Time (UTC), and provides the backbone for critical navigation tools such as the Global Positioning System…
We report a comprehensive evaluation of all known sources of systematic uncertainty for two independent $^{176}$Lu$^+$ single-ion optical references, finding total systematic uncertainty of $1.1\times10^{-19}$ and $1.4\times10^{-19}$ for…
We have explored the performance of two "dark fibers" of a commercial telecommunication fiber link for a remote comparison of optical clocks. The two fibers, linking the Leibniz University of Hanover (LUH) with the Physi-kalisch-Technische…