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Mercury atomic clock keeps time with record accuracy
July 17, 2006An experimental atomic clock based on a single mercury atom is now at least five times more precise than the national standard clock based on a "fountain" of cesium atoms, according to a paper by physicists at the Commerce Department's National Institute of Standards and Technology (NIST) in the July 14 issue of Physical Review Letters.
The experimental clock, which measures the oscillations of a mercury ion (an electrically charged atom) held in an ultra-cold electromagnetic trap, produces "ticks" at optical frequencies. Optical frequencies are much higher than the microwave frequencies measured in cesium atoms in NIST-F1, the national standard and one of the world's most accurate clocks. Higher frequencies allow time to be divided into smaller units, which increases precision.
A prototype mercury optical clock was originally demonstrated at NIST in 2000. Over the last five years its absolute frequency has been measured repeatedly with respect to NIST-F1. The improved version of the mercury clock is the most accurate to date of any atomic clock, including a variety of experimental optical clocks using different atoms and designs.
The current version of NIST-F1-if it were operated continuously-would neither gain nor lose a second in about 70 million years. The latest version of the mercury clock would neither gain nor lose a second in about 400 million years.
"We finally have addressed the issue of systemic perturbations in the mercury clock. They can be controlled, and we know their uncertainties," says NIST physicist Jim Bergquist, the principal investigator. "By measuring its frequency with respect to the primary standard, NIST-F1, we have been able to realize the most accurate absolute measurement of an optical frequency to date. And in the latest measurement, we have also established that the accuracy of the mercury-ion system is at a level superior to that of the best cesium clocks."
Improved time and frequency standards have many applications. For instance, ultra-precise clocks can be used to improve synchronization in navigation and positioning systems, telecommunications networks, and wireless and deep-space communications. Better frequency standards can be used to improve probes of magnetic and gravitational fields for security and medical applications, and to measure whether "fundamental constants" used in scientific research might be varying over time-a question that has enormous implications for understanding the origins and ultimate fate of the universe.
Scientists have long recognized that optical atomic clocks could be more stable and accurate than cesium microwave clocks, which have kept world time for more than 50 years. Even with the latest results at NIST, however, optical clocks based on mercury, strontium or other atoms remain a long way from being accepted as standards. Research groups around the world would first need to agree on an atom and clock design to be used internationally.
In addition, a system of additional optical clocks would be needed to continuously keep time, because primary standard clocks-such as the mercury ion or other future optical standard-are generally operated only periodically for calibrations. NIST-F1, for instance, is operated several times a year for periods of about one month to calibrate the frequencies of several NIST microwave atomic clocks that continuously track current time. These clocks contribute to an international group of atomic clocks that define the official world time.
National Institute of Standards and Technology (NIST)
The current version of NIST-F1-if it were operated continuously-would neither gain nor lose a second in about 70 million years. The latest version of the mercury clock would neither gain nor lose a second in about 400 million years.
"We finally have addressed the issue of systemic perturbations in the mercury clock. They can be controlled, and we know their uncertainties," says NIST physicist Jim Bergquist, the principal investigator. "By measuring its frequency with respect to the primary standard, NIST-F1, we have been able to realize the most accurate absolute measurement of an optical frequency to date. And in the latest measurement, we have also established that the accuracy of the mercury-ion system is at a level superior to that of the best cesium clocks."
Improved time and frequency standards have many applications. For instance, ultra-precise clocks can be used to improve synchronization in navigation and positioning systems, telecommunications networks, and wireless and deep-space communications. Better frequency standards can be used to improve probes of magnetic and gravitational fields for security and medical applications, and to measure whether "fundamental constants" used in scientific research might be varying over time-a question that has enormous implications for understanding the origins and ultimate fate of the universe.
Scientists have long recognized that optical atomic clocks could be more stable and accurate than cesium microwave clocks, which have kept world time for more than 50 years. Even with the latest results at NIST, however, optical clocks based on mercury, strontium or other atoms remain a long way from being accepted as standards. Research groups around the world would first need to agree on an atom and clock design to be used internationally.
In addition, a system of additional optical clocks would be needed to continuously keep time, because primary standard clocks-such as the mercury ion or other future optical standard-are generally operated only periodically for calibrations. NIST-F1, for instance, is operated several times a year for periods of about one month to calibrate the frequencies of several NIST microwave atomic clocks that continuously track current time. These clocks contribute to an international group of atomic clocks that define the official world time.
National Institute of Standards and Technology (NIST)
Atomic Clock Current Events and Atomic Clock News RSSOptical atomic clock becomes portable
You imagine a clock to be different - yet the optical table with its many complicated set-ups really is one. Optical clocks like the strontium clock in the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig could be the atomic clocks of the future; some of them though are already ten times more precise and stable than the best primary caesium atomic clocks.
Ytterbium gains ground in quest for next-generation atomic clocks
An experimental atomic clock based on ytterbium atoms is about four times more accurate than it was several years ago, giving it a precision comparable to that of the NIST-F1 cesium fountain clock, the nation's civilian time standard, scientists at the National Institute of Standards and Technology (NIST) report in Physical Review Letters.
New JILA technique reveals hidden properties of ultracold atomic gases
Physicists at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder, have demonstrated a powerful new technique that reveals hidden properties of ultracold atomic gases.
New method to directly probe the quantum collisions of individual atoms
The first demonstration of a fundamentally new method for measuring a particular quantum property of individual atoms will be described in a research paper to be published in the 19 April 2007 edition of the journal Nature.
Atomic clock signals may be best shared by fiber-optics
Time and frequency information can be transferred between laboratories or to other users in several ways, often using the Global Positioning System (GPS). But today's best atomic clocks are so accurate—neither gaining nor losing one second in as long as 400 million years—that more stable methods are needed.
Biologists find biological clock for smell in mice
Biologists at Washington University in St. Louis have discovered a large biological clock in the smelling center of mice brains and have revealed that the sense of smell for mice is stronger at night, peaking in evening hours and waning during day light hours.
Physicists make atomic clock breakthrough
Andrei Derevianko, Kyle Beloy, and Ulyana Safronova sat down six months ago and began work on a calculation that will help the world keep better time. In competition with scientists at the University of New South Wales, the University team led by associate professor Derevianko conducted research that increased the accuracy of atomic clocks, and they did it without running a single experiment.
New technologies enhance quantum cryptography
A team of Los Alamos National Laboratory scientists, in collaboration with researchers from the National Institute of Standards and Technology in Boulder, Colo., and Albion College, in Albion, Mich., have achieved quantum key distribution (QKD) at telecommunications industry wavelengths in a 50-kilometer (31 mile) optical fiber.
Tandem ions may lead the way to better atomic clocks
Physicists at the Commerce Department's National Institute of Standards and Technology (NIST) have used the natural oscillations of two different types of charged atoms, or ions, confined together in a single trap, to produce the "ticks" that may power a future atomic clock.
Physicists lead the field in solving matter mystery of the Big Bang
A University of Sussex-led team of scientists is ahead in the race to solve one of the biggest mysteries of our physical world: why the Universe contains matter. With the help of a new £2.3 million grant, the team is working on a project to make one of the most sensitive measurements ever of sub-atomic particles. The results, expected within six years, could finally help to explain the creation of matter in the aftermath of the Big Bang. Physicist Dr Philip Harris, the leader of the Sussex group, says: "Although there are a couple of other teams in the world working in this same area, we're managing to stay ahead of them, and we are constantly striving to beat our own world record.
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