‘Quantum logic clock’ now rivals the world’s most accurate

An atomic clock that uses an aluminum atom to apply the logic of computers to the peculiarities of the quantum world now rivals the world’s most accurate clock, which is based on a single mercury atom.

The measurements were made in a yearlong comparison of the two next-generation clocks, both designed and built at the Commerce Department’s National Institute of Standards and Technology (NIST) in the US.

“The aluminum clock is very accurate because it is insensitive to background magnetic and electric fields, and also to temperature,” said Till Rosenband, the NIST physicist who built the clock. “It has the lowest known sensitivity of any atomic clock to temperature, which is one of the most difficult uncertainties to calibrate,” he added.

The new atomic clock is referred to as the quantum logic clock, because it is based on the logical reasoning process used in quantum computers. The clock is a spin-off of NIST research on quantum computers, which grew out of earlier atomic clock research.

The atomic and mercury clocks were compared with record precision, allowing scientists to measure the relative frequencies of the two clocks to 17 digits - the most accurate measurement of this type ever made.

The comparison produced the most precise results yet in the worldwide quest to determine whether some of the fundamental constants that describe the universe are changing slightly over time, a hot research question that may alter basic models of the cosmos.

The aluminum and mercury clocks are both based on natural vibrations in ions (electrically charged atoms) and would neither gain nor lose one second in over 1 billion years - if they could run for such a long time - compared to about 80 million years for NIST-F1, the U.S. time standard based on neutral cesium atoms.

The mercury clock was first demonstrated in 2000 and is now four times better than its last published evaluation in 2006, thanks to ongoing improvements in the clock design and operation.

The mercury clock continues its reign as the world’s most accurate for now, by a margin of 20 percent over the aluminum clock.

But the quantum logic clocks tandem ion approach is unique among the world’s atomic clocks and has a key advantage over the mercury clock.

“You can pick from a bigger selection of atoms,” explains NIST physicist Jim Bergquist, who built the mercury clock. “And aluminum has a lot of good qualities - better than mercury’s,” he added.

Source: http://www.thaindian.com

Suicidal man barricades himself in house

Allen Police surrounded a house on Monroe Court in response to a suicidal call to 911 operators.

According to Sgt. Jon Felty, Allen Police public information officer, a man called emergency dispatch about 3 p.m. today, saying he wanted to kill himself.

“Basically this is a barricaded suicidal person. The person is in the house by themselves,” Felty said. “The only person they are threatening is themselves. We are in contact with him.”

Felty said police thought the man was alone and did not want to harm anyone else.

Police responded and surrounded the house and blocked off some nearby streets.

Allen ISD Public Information Director Tim Carroll said he received a call from police who advised Ford Middle School be put on precautionary lockdown with children not allowed to walk home. Buses continued to run normally and parents were allowed to pick up their children.

Source: http://www.courier-gazette.com/articles/2008/02/28/breaking_news/57.txt