In another advance at the far frontiers of timekeeping by National Institute of Standards and Technology (NIST) researchers, the latest modification of a record-setting strontium atomic clock has achieved precision and stability levels that now mean the clock would neither gain nor lose one second in some 15 billion years*--roughly the age of the universe.
Precision timekeeping has broad potential impacts on advanced communications, positioning technologies (such as GPS) and many other technologies. Besides keeping future technologies on schedule, the clock has potential applications that go well beyond simply marking time. Examples include a sensitive altimeter based on changes in gravity and experiments that explore quantum correlations between atoms.
JILA's strontium lattice atomic clock now performs better than ever because scientists literally "take the temperature" of the atoms' environment. Two specialized thermometers, calibrated by NIST researchers and visible in the center of the photo, are inserted into the vacuum chamber containing a cloud of ultracold strontium atoms confined by lasers.
As described in Nature Communications,** the experimental strontium lattice clock at JILA, a joint institute of NIST 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 percent, 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. Many scientists have demonstrated this, but with less sensitive techniques.****
"Our performance means that we can measure the gravitational shift when you raise the clock just 2 centimeters on the Earth's surface," JILA/NIST Fellow Jun Ye says. "I think we are getting really close to being useful for relativistic geodesy."
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 centimeter 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.
In the JILA/NIST clock, a few thousand atoms of strontium are held in a 30-by-30 micrometer column of about 400 pancake-shaped regions formed by intense laser light called an optical lattice. JILA and NIST scientists detect strontium's "ticks" (430 trillion per second) by bathing the atoms in very stable red laser light at the exact frequency that prompts the switch between energy levels.
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.
To help measure and maintain the atoms' thermal environment, NIST's Wes Tew and Greg Strouse calibrated two platinum resistance thermometers, which were then installed in the clock's vacuum chamber in Colorado. 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 notes. "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."
In addition, JQI theorist Marianna Safronova used the quantum theory of atomic structure to calculate the frequency shift due to blackbody radiation, enabling the JILA team to better correct for the error.
Overall, the clock's improved performance tracks NIST scientists' expectations for this area of research, as described in "A New Era in Atomic Clocks" at http://www.
The JILA research is supported by NIST, the Defense Advanced Research Projects Agency and the National Science Foundation.
* For the general public, NIST converts an atomic clock's systematic or fractional total uncertainty to an error expressed as 1 second accumulated over a certain minimum length of time. That is calculated by dividing 1 by the clock's systematic uncertainty, and then dividing that result by the number of seconds in a year (31.5 million) to find the approximate minimum number of years it would take to accumulate 1 full second of error. The JILA clock has reached a higher level of precision (smaller uncertainty) than any other clock.
** T.L. Nicholson, S.L. Campbell, R.B. Hutson, G.E. Marti, B.J. Bloom, R.L. McNally, W. Zhang, M.D. Barrett, M.S. Safronova, G.F. Strouse, W.L. Tew and J. Ye. 2015. Nature Communications. Systematic evaluation of an atomic clock at 2 × 10-18 total uncertainty. April 21.
*** See 2014 NIST Tech Beat article, "JILA Strontium Atomic Clock Sets New Records in Both Precision and Stability," at http://www.
**** Another NIST group demonstrated this effect by raising the quantum logic clock, based on a single aluminum ion, about 1 foot. See 2010 NIST news release, "NIST Pair of Aluminum Atomic Clocks Reveal Einstein's Relativity at a Personal Scale," at http://www.
Laura Ost | EurekAlert!
UNH scientists help provide first-ever views of elusive energy explosion
16.11.2018 | University of New Hampshire
NASA keeps watch over space explosions
16.11.2018 | NASA/Goddard Space Flight Center
Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.
Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
09.11.2018 | Event News
06.11.2018 | Event News
23.10.2018 | Event News
16.11.2018 | Health and Medicine
16.11.2018 | Life Sciences
16.11.2018 | Life Sciences