Posts Tagged ‘atomic clocks’
New Strides Toward Better Clocks, Accurate to One Second in 32 Billion Years
Hyper-sensitive atomic clocks are used for GPS navigation, communications between space probes and Earth, and quantum computing studies, among other uses. Timekeepers keep building clocks that are , meaning it takes them longer and longer to “lose” a second through small uncertainties.
Right now, the most accurate atomic clock is an aluminum quantum-logic clock, which is based on atomic energy levels in a positively charged aluminum ion. Its uncertainty rate is such that it will be off by one second 3.7 billion years from now.
Atomic clocks define seconds based on the oscillations between the nucleus of an atom and its orbiting electrons. If anything affects those electrons, their oscillation rates could change, making the clock less accurate. Researchers at the Joint Quantum Institute found that heat radiation can do just this — even when atoms are completely isolated and protected, as is the case in atomic clocks.
Any object at any temperature releases some warmth, whether it’s the sun, yourself or a perfectly radiant object called a “black body.” Temperature is tied to the speed and distance at which electrons orbit the nuclei of atoms — in very general terms, colder objects move more slowly and warmer objects move faster. Black body radiation enlarges the size of the electron clouds of an atom, which affects their oscillations. This BBR effect is one part in a hundred trillion, but when you want something to stay the same for 32 billion years, that adds up to a lot.
Now that scientists have figured this out, they can calculate how much the aluminum ions’ energy levels will change because of black-body radiation.
Current clocks are actually more inaccurate than the changes induced by BBR effect, according to a news release from NIST. But the next generation of atomic clocks will have lower uncertainties, so knowledge of the BBR shift will make them even better.
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In Test of Relativity Theory, Superaccurate Atomic Clocks Prove Your Head Ages Nanoseconds Faster than Your Feet
Relativity experiment is the most accurate yet
Now, scientists have shown this time difference in action on — clocks move at different speeds on a staircase.
In a study published today in the journal Science, researchers at the National Institute of Standards and Technology explain that a one-foot difference in altitude between two clocks caused them to tick at slightly different rates. The optical clocks can even measure caused by a 20-mile-per-hour speed difference.
The clocks are based on the oscillations of a single aluminum ion that vibrates between two energy levels a million billion times per second. One clock is accurate to within one second in about 3.7 billion years, and the other is almost as accurate, NIST says.
In one experiment, James Chin-Wen Chou and his colleagues placed one clock about 13 inches higher than its counterpart. The higher clock felt less gravity, because it was a teeny bit farther from Earth’s gravitational field. It ticked more slowly — albeit a tiny, tiny bit more slowly. The time difference adds up to about 90 billionths of a second over a 79-year lifetime, according to NIST.
Still, this means that the people who conducted this study, in Boulder, Colo., are apparently aging faster than those of you reading this at sea level.
In another experiment, the NIST scientists also observed that time passes more slowly when you move more quickly — a key tenet of relativity — even at very small speed variations. Clocks ticked more slowly at a difference of just 20 miles per hour, they say.
Before these experiments, the most accurate relativity tests involved rockets and jet aircraft. Though the differences are imperceptible to humans, they might be useful for geophysics and other fields, such as measuring the Earth’s gravitational field, NIST says. To improve those measurements, NIST’s next step is to make clocks that can differentiate time at a distance of just one centimeter.
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DARPA Wants Portable Atomic Clocks for Better Synchronicity
DARPA’s Quantum Assisted Sensing and Readout () program aims to take high-performance atomic clocks like the National Institute of Standards and Technology’s NIST-F1, the massive room-sized clock housed in a lab in Boulder, Colo. Doing so won’t be any easier than many other challenges DARPA brings to the table, but the agency thinks advances in nanoelectromechanical systems (NEMS) resonators and nitrogen-vacancy (NV) centers in diamonds that exhibit single-atom-like properties could create a close analog to an atomic clock in a miniature, portable package.
Atomic clocks don’t lose seconds or even fractions of seconds over time (well, that’s not entirely true, but time lost is negligible; NIST-F1 will neither gain nor lose a second in 60 million years), and that opens up major possibilities for syncronisity. Such portable clocks would allow for communications systems that are far more secure less susceptible to jamming and GPS positioning that is unrivaled. DARPA also thinks they might lead to precision sensors unrivaled in resolution and sensitivity.
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The ISS’s New Atomic Clock Will be the Most Accurate Clock in Space, Possibly the Universe
Cesium clocks, like the one the National Institute of Standards and Technology uses to keep the official time in the U.S., generally rely on the microwave signals that electrons emit when they change energy levels to keep highly precise, consistent measurements of time (it's estimated that the NIST's current clock won't gain or lose a second for more than 60 million years).
The cesium atoms are laser-cooled, then launched upward into a sensor cavity where instruments can tap into that microwave frequency that gives us our standard concept of the second, minute, hour, etc. A microgravity environment the atoms spend longer in the microwave chamber, and that should allow for better measurements of the microwaves emitted, making the Atomic Clock Ensemble in Space (ACES) 100 times more accurate as the clocks ticking away on satellites.
As a bonus, a single frame of reference in space could help atomic clocks back on the ground synchronize better, and it might even reveal if certain physical constants are as constant as physics says they are.
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