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 »

Announcements

More Announcements »

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

Viewpoint: Sensing Magnetic Fields with a Giant Quantum Wave
Strongly Correlated Materials

Viewpoint: Sensing Magnetic Fields with a Giant Quantum Wave

A refined version of a Bose-Einstein-condensate microscope detects static magnetic fields near the surface of a chip with unprecedented sensitivity and over a wide temperature range. Read More »

Synopsis: A Neat Way to Slow Down Light
Optics

Synopsis: A Neat Way to Slow Down Light

A new technique slows down light in a crystal by simply shining a laser on it and varying an applied voltage. Read More »

Focus: Reversing Light Scattering with a Handful of Photons
Optics

Focus: Reversing Light Scattering with a Handful of Photons

When a beam of light is sent through a nearly opaque material, the scattered light that emerges can be unscrambled even with relatively few photons detected. Read More »

More Articles