New strontium atomic clock built by American researchers is 50 per cent more precise than the previous record-holding device.
The clock, built by a joint research group of the US National Institute of Standards and Technology (NIST) and the Joint Institute for Laboratory Astrophysics (JILA), has been introduced in a recent issue of the journal Nature.
The new strontium clock is so precise it won’t lose a second in about five billion years, which is more than the current age of the Earth. The previous record holder – NIST’s quantum logic clock was only 50 per cent that precise. The only competitor that can match the strontium precision is the NIST’s ytterbium clock, unveiled in August 2013.
Besides being incredibly precise, the clock also offers an unprecedented level of stability. Stability determines in part how long an atomic clock must run to achieve its best performance through continual averaging. The strontium and ytterbium lattice clocks are so stable that in just a few seconds of averaging they outperform other types of atomic clocks that have been averaged for hours or days.
“We already have plans to push the performance even more,” said NIST/JILA Fellow and group leader Jun Ye. “So in this sense, even this new Nature paper represents only a ‘mid-term’ report. You can expect more new breakthroughs in our clocks in the next five to ten years.”
The current international definition of units of time requires the use of caesium-based atomic clocks, such as the current US civilian time standard clock, the NIST-F1 caesium fountain clock. However, the strontium clock offers even better precision and the NIST and JILA researchers hope that one day their devices could replace the current standard-setting caesium clock.
The new strontium clock is the first to hold world records for both precision and stability since the 1990s, when caesium fountain atomic clocks were introduced. In the past decade, the rapid advances in experimental atomic clocks have surprised even some of the scientists leading the research.
NIST, which operates the NIST-F1 time standard, pursues multiple clock technologies because scientific research can take unpredictable turns, and because different types of atomic clocks are better suited for different practical applications.
In JILA’s world-leading clock, a few thousand atoms of strontium are held in a column of about 100 pancake-shaped traps called an optical lattice formed by intense laser light. JILA 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.
To check the performance, the JILA team compared two versions of the strontium clock, one built in 2005 and the other just last year. Both clocks have set previous records of various types. In the latest work, the two clocks fully agreed with each other within their reported precision, demonstrating the ability to make a duplicate copy and maintain the performance level.
This is an advantage for clock comparisons to lay the groundwork for the eventual selection of a next-generation time standard. Recent technical advances enabling the strontium clock's record performance include the development of ultra-stable lasers and precise measurements of key effects – atom collisions and environmental heating – that cause tiny changes in the clock’s ticking rate.
Next-generation atomic clocks have already contributed to scientific research and are expected to lead to the development of novel technologies such as super-sensors for quantities including gravity and temperature.