Synopsis: A Distant Second

By measuring hydrogen line emission with an atomic clock hundreds of kilometers away, researchers place strict limits on possible corrections to relativity.
Synopsis figure
APS/Don Monroe

Light emission from hydrogen atoms allows spectacularly precise confirmation of quantum-mechanical laws. But theorists have yet to fully reconcile those laws with relativity, the other major foundation of modern physics. In Physical Review Letters, a multilaboratory collaboration reports improved hydrogen measurements that place limits on how big one possible correction to relativity could be.

Researchers at the Max Planck Institute for Quantum Optics in Garching, Germany, have pioneered methods that connect optical emission frequencies to the much lower radio frequencies of atomic clocks. But the best atomic clocks, based on a fountain of cesium atoms, are in distant labs such as the Federal Physical-Technical Institute (PTB) in Braunschweig, and can’t be easily moved. So the two labs synchronized their setups by sending light signals back and forth over a 920-km-long optical fiber. The connection allowed them to express the 1S-2S transition frequency in terms of the international standard definition of the second as 2,466,061,413,187,018 hertz, with an uncertainty of just 11 hertz.

The researchers exploited the unprecedented precision to look for variations of the frequency over a year. Such variations would show that the frequency depends on the motion of the Earth around the Sun, which is forbidden by relativity. But the team estimates that parameters that quantify that dependence can be no larger than a few parts in 1011. One of the parameters is slightly different from zero, but even more precise measurements will be needed to determine if this difference is truly significant. – Don Monroe


Announcements

More Announcements »

Subject Areas

Atomic and Molecular Physics

Previous Synopsis

Quantum Information

Solving for X and Y

Read More »

Next Synopsis

Biological Physics

How Plants Do Their Math

Read More »

Related Articles

Synopsis: Deep Freezing Molecules
Atomic and Molecular Physics

Synopsis: Deep Freezing Molecules

Researchers cooled trapped molecules well below 1mK—a record temperature for molecules that have not been assembled from pre-cooled atoms. Read More »

Viewpoint: Journey from Classical to Quantum in Two Dimensions
Atomic and Molecular Physics

Viewpoint: Journey from Classical to Quantum in Two Dimensions

Two separate groups have extracted the thermodynamic equation of state for a two-dimensional gas of fermionic atoms, revealing its peculiar quantum features. Read More »

Synopsis: A Short but Strong Encounter
Photonics

Synopsis: A Short but Strong Encounter

Broadband single-photon pulses can have a strong, if transient, interaction with an atomic medium. Read More »

More Articles