Most precise atomic clock won't lose a second in 15 bln years

A record-setting strontium atomic clock has gotten so precise and stable that it will neither gain nor lose a second in some 15 billion years - roughly the age of the universe, scientists say.
The experimental strontium lattice clock at JILA, a joint institute of National Institute of Standards and Technology (NIST) in the US and the University of Colorado Boulder, is now more than three times as precise as it was last year, when it set the previous world record.
Precision refers to how closely the clock approaches the true resonant frequency at which the strontium atoms oscillate between two electronic energy levels.

The clock's stability - how closely each tick matches every other tick - also has been improved by almost 50 per cent, another world record.
The JILA clock is now good enough to measure tiny changes in the passage of time and the force of gravity at slightly different heights.
Einstein predicted these effects in his theories of relativity, which mean, among other things, that clocks tick faster at higher elevations.

"Our performance means that we can measure the gravitational shift when you raise the clock just 2 centimetres on the Earth's surface," said JILA/NIST Fellow Jun Ye.
"I think we are getting really close to being useful for relativistic geodesy," Ye said.

Relativistic geodesy is the idea of using a network of clocks as gravity sensors to make 3D precision measurements of the shape of the Earth.
Ye agrees with other experts that, when clocks can detect a gravitational shift at 1 centimetre differences in height - just a tad better than current performance - they could be used to achieve more frequent geodetic updates than are possible with conventional technologies such as tidal gauges and gravimeters.
The JILA group made the latest improvements with the help of researchers at NIST's Maryland headquarters and the Joint Quantum Institute (JQI).
Those researchers contributed improved measurements and calculations to reduce clock errors related to heat from the surrounding environment, called blackbody radiation.

The electric field associated with the blackbody radiation alters the atoms' response to laser light, adding uncertainty to the measurement if not controlled.
Researchers also built a radiation shield to surround the atom chamber, which allowed clock operation at room temperature rather than much colder, cryogenic temperatures.
"The clock operates at normal room temperature," Ye said.
"This is actually one of the strongest points of our approach, in that we can operate the clock in a simple and normal configuration while keeping the blackbody radiation shift uncertainty at a minimum," Ye added.