Washington, Feb 9 : Physicists at the National Institute of Standards and Technology (NIST) have built an enhanced version of an experimental atomic clock based on a single aluminum atom, which is now the world's most precise clock would neither gain nor lose one second in about 3.7 billion years.

The new aluminum clock is more than twice as precise as the previous pacesetter based on a mercury atom.

The new clock is the second version of NIST's "quantum logic clock," so called because it borrows the logical processing used for atoms storing data in experimental quantum computing, another major focus of the same NIST research group.

The second version of the logic clock offers more than twice the precision of the original.

"This paper is a milestone for atomic clocks" for a number of reasons, said NIST postdoctoral researcher James Chou, who developed most of the improvements.

NIST's construction of a second, independent version of the logic clock proves it can be replicated, making it one of the first optical clocks to achieve that distinction.

NIST scientists evaluated the new logic clock by probing the aluminum ion with a laser to measure the exact "resonant" frequency at which the ion jumps to a higher-energy state, carefully accounting for all possible deviations such as those caused by ion motions.

No measurement is perfect, so the clock's precision is determined based on how closely repeated measurements can approach the atom's exact resonant frequency.

The smaller the deviations from the true value of the resonant frequency, the higher the precision of the clock.

Physicists also evaluate the performance of new optical clocks by comparing them to older optical clocks.

In this case, NIST scientists compared their two logic clocks by using the resonant laser frequency from one clock to probe the ion in the other clock.

Fifty-six separate comparisons were made, each lasting between 15 minutes and 3 hours.

The two logic clocks exhibit virtually identical "tick" rates. Differences don't show up until measurements are extended to 17 decimal places.

The agreement between the two aluminum clocks is more than 10 times closer than any previous two-clock comparison, with the lowest measurement uncertainty ever achieved in such an evaluation.