Synopsis: Cross-Country Time Keeping

A new distance record is set in the fiber transmission of stable frequency signals capable of synchronizing atomic clocks.
Synopsis figure
MPQ (WoogieWorks, Vienna)

Next-generation atomic clocks are so precise they can’t be synchronized remotely with traditional communication pathways. Researchers are therefore investigating novel synchronization methods. A new milestone in this development is presented in Physical Review Letters, with the longest distance transmission of a highly stable optical frequency. The signal was sent back and forth across Germany on optical fibers, while keeping a fixed frequency to within a few parts in 1019.

Several applications, such as navigation and fundamental physics, require the comparison of clocks at large physical separation. In geodesy, for example, the time difference between two distant clocks can provide relative elevation measurements with centimeter precision. Currently, clock signals are relayed by satellite communication, but the frequency of these radio signals drifts over time by as much as a few parts per 1016. Higher stability is needed to compare recently developed optical atomic clocks that have precisions on the order of one part in 1017.

Several past experiments have shown that optical fibers can faithfully transmit a clock-synchronizing frequency signal over hundreds of kilometers. Stefan Droste of Max Planck Institute of Quantum Optics, Germany, and his colleagues have now sent a highly stable 194 terahertz (1542 nanometer) frequency over a distance of 1840 kilometers, doubling their previous record. The team achieved this result by equipping the dedicated optical fiber connecting two German research institutions with active stabilization to overcome frequency shifts from thermal noise and acoustic noise. The method might one day link together optical clocks around the world. – Michael Schirber


Features

More Features »

Subject Areas

Atomic and Molecular PhysicsOptics

Previous Synopsis

Particles and Fields

Neutron Bursts in Lab Lightning

Read More »

Next Synopsis

Atomic and Molecular Physics

Photonic Matchmaking

Read More »

Related Articles

Synopsis: A Dark Side for Qubits
Quantum Information

Synopsis: A Dark Side for Qubits

Dark solitons in a Bose-Einstein condensate could, according to calculations, function as qubits with long lifetimes. Read More »

Synopsis: Blocking out Starlight
Astrophysics

Synopsis: Blocking out Starlight

A proposed telescope update could enable incoming light from multiple stars to be simultaneously blocked, making it easier to image exoplanets orbiting two or more stars. Read More »

Viewpoint: Measuring the Tidal Force on a Particle’s Matter Wave
Gravitation

Viewpoint: Measuring the Tidal Force on a Particle’s Matter Wave

The effect of the tidal force, which is directly related to the curvature of spacetime, on an individual particle’s wave function has been measured with an atom interferometer. Read More »

More Articles