Bogeyman
FULL MEMBER
- Joined
- Nov 21, 2019
- Messages
- 534
- Reaction score
- 0
- Country
- Location
NIST Atomic Clocks Now Keep Time Well Enough to Improve Models of Earth November 28, 2018
Experimental atomic clocks at the National Institute of Standards and Technology (NIST) have achieved three new performance records, now ticking precisely enough to not only improve timekeeping and navigation, but also detect faint signals from gravity, the early universe and perhaps even dark matter.
The clocks each trap a thousand ytterbium atoms in optical lattices, grids made of laser beams. The atoms tick by vibrating or switching between two energy levels. By comparing two independent clocks, NIST physicists achieved record performance in three important measures: systematic uncertainty, stability and reproducibility.
Published online today in the journal Nature, the new NIST clock records are:
“This is especially true because the demonstrated reproducibility shows that the clocks’ total error drops below our general ability to account for gravity’s effect on time here on Earth. Hence, as we envision clocks like these being used around the country or world, their relative performance would be, for the first time, limited by Earth's gravitational effects.”
Einstein’s theory of relativity predicts that an atomic clock’s ticking, that is, the frequency of the atoms’ vibrations, is reduced—shifted toward the red end of the electromagnetic spectrum—when observed in stronger gravity. That is, time passes more slowly at lower elevations.
While these so-called redshifts degrade a clock’s timekeeping, this same sensitivity can be turned on its head to exquisitely measure gravity. Super-sensitive clocks can map the gravitational distortion of space-time more precisely than ever. Applications include relativistic geodesy, which measures the Earth’s gravitational shape, and detecting signals from the early universe such as gravitational waves and perhaps even as-yet-unexplained dark matter.
NIST’s ytterbium clocks now exceed the conventional capability to measure the geoid, or the shape of the Earth based on tidal gauge surveys of sea level. Comparisons of such clocks located far apart such as on different continents could resolve geodetic measurements to within 1 centimeter, better than the current state of the art of several centimeters.
In the past decade of new clock performance records announced by NIST and other labs around the world, this latest paper showcases reproducibility at a high level, the researchers say. Furthermore, the comparison of two clocks is the traditional method of evaluating performance.
Among the improvements in NIST’s latest ytterbium clocks was the inclusion of thermal and electric shielding, which surround the atoms to protect them from stray electric fields and enable researchers to better characterize and correct for frequency shifts caused by heat radiation.
The ytterbium atom is among potential candidates for the future redefinition of the second—the international unit of time—in terms of optical frequencies. NIST’s new clock records meet one of the international redefinition roadmap's requirements, a 100-fold improvement in validated accuracy over the best clocks based on the current standard, the cesium atom, which vibrates at lower microwave frequencies.
NIST is building a portable ytterbium lattice clock with state-of-the-art performance that could be transported to other labs around the world for clock comparisons and to other locations to explore relativistic geodesy techniques.
The work is supported by NIST, the National Aeronautics and Space Administration and the Defense Advanced Research Projects Agency.
https://www.nist.gov/news-events/ne...ow-keep-time-well-enough-improve-models-earth
Atomic clock performance enabling geodesy below the centimetre level
https://sci-hub.tw/10.1038/s41586-018-0738-2
NIST Researchers Boost Microwave Signal Stability a Hundredfold May 21, 2020
Researchers at the National Institute of Standards and Technology (NIST) have used state-of-the-art atomic clocks, advanced light detectors, and a measurement tool called a frequency comb to boost the stability of microwave signals a hundredfold. This marks a giant step toward better electronics to enable more accurate time dissemination, improved navigation, more reliable communications and higher-resolution imaging for radar and astronomy. Improving the microwave signal’s consistency over a specific time period helps ensure reliable operation of a device or system.
The work transfers the already superb stability of the cutting-edge laboratory atomic clocks operating at optical frequencies to microwave frequencies, which are currently used to calibrate electronics. Electronic systems are unable to directly count optical signals, so the NIST technology and techniques indirectly transfer the signal stability of optical clocks to the microwave domain. The demonstration is described in the May 22, 2020, issue of Science.
In their setup, the researchers used the “ticking” of two of NIST’s ytterbium lattice clocks to generate light pulses, as well as frequency combs serving as gears to translate the higher-frequency optical pulses accurately into lower-frequency microwave signals. Advanced photodiodes converted light pulses into electrical currents, which in turn generated a 10 gigahertz (GHz, or a billion cycles per second) microwave signal that tracked the clocks’ ticking exactly, with an error of just one part in a quintillion (1 followed by 18 zeros). This performance level is on par with that of both optical clocks and 100 times more stable than the best microwave sources.
“Years of research, including important contributions from NIST, have resulted in high-speed photodetectors that can now transfer optical clock stability to the microwave domain,” lead researcher Frank Quinlan said. “The second major technical improvement was in the direct tracking of the microwaves with high precision, combined with lots of know-how in signal amplification.”
Optical waves have shorter, faster cycles than microwaves do, so they have different shapes. In converting stable optical waves to microwaves, the researchers tracked the phase — the exact timing of the waves — to ensure they were identical, and not shifted relative to one another. The experiment tracked phase changes with a resolution corresponding to just one millionth of a cycle.
“This is a field where just doubling microwave stability can take years or decades to achieve,” group leader Chris Oates said. “A hundred times better is almost unfathomable.”
Some components of the NIST system, such as the frequency combs and detectors, are ready to be used in field applications now, Quinlan said. But NIST researchers are still working on transferring state-of-the-art optical clocks to mobile platforms. The ytterbium clocks, which operate at frequencies of 518 terahertz (trillion cycles per second), currently occupy large tables in highly controlled laboratory settings.
Ultra-stable electronic signals could support widespread applications, including future calibration of electronic clocks, such as electric devices powered by oscillating quartz crystals. This is an important consideration for the redefinition of the international time standard, the SI second, now based on the microwave frequencies absorbed by the cesium atoms in conventional clocks. In the coming years, the international scientific community is expected to select a new time standard based on optical frequencies that other atoms, such as ytterbium, absorb. Super-stable signals could also make wireless communications systems more reliable.
Optically derived electronic signals could make imaging systems more sensitive. Radar sensitivity, particularly for slow-moving objects, is now limited by microwave noise and could be greatly enhanced. New photodiodes, produced in a collaboration between NIST and the University of Virginia, convert the optical signals to microwave signals more predictably and with lower noise than earlier designs. In addition, microwaves could carry signals from distant optical clocks for applications in navigation and fundamental physics research.
Astronomical imaging and relativistic geodesy, which measures the Earth’s gravitational shape, are now based on detecting microwave signals at receivers around the world and combining them to form images of objects. Remote calibration of these receivers could make it possible to move the network from Earth into space, which would enhance image resolution and avoid atmospheric distortions that limit observation time. With hours of observing time instead of seconds, researchers could image many more objects.
The research was supported in part by the Defense Advanced Research Projects Agency.
https://www.nist.gov/news-events/news/2020/05/nist-researchers-boost-microwave-signal-stability-hundredfold
Coherent optical clock down-conversion for microwave frequencies with 10−18 instability
https://sci-hub.tw/10.1126/science.abb2473
I shared this thread topic to justify ascending order.
Experimental atomic clocks at the National Institute of Standards and Technology (NIST) have achieved three new performance records, now ticking precisely enough to not only improve timekeeping and navigation, but also detect faint signals from gravity, the early universe and perhaps even dark matter.
The clocks each trap a thousand ytterbium atoms in optical lattices, grids made of laser beams. The atoms tick by vibrating or switching between two energy levels. By comparing two independent clocks, NIST physicists achieved record performance in three important measures: systematic uncertainty, stability and reproducibility.
Published online today in the journal Nature, the new NIST clock records are:
- Systematic uncertainty: How well the clock represents the natural vibrations, or frequency, of the atoms. NIST researchers found that each clock ticked at a rate matching the natural frequency to within a possible error of just 1.4 parts in 1018—about one billionth of a billionth.
- Stability: How much the clock’s frequency changes over a specified time interval, measured to a level of 3.2 parts in 1019 (or 0.00000000000000000032) over a day.
- Reproducibility: How closely the two clocks tick at the same frequency, shown by 10 comparisons of the clock pair, yielding a frequency difference below the 10-18 level (again, less than one billionth of a billionth).
“This is especially true because the demonstrated reproducibility shows that the clocks’ total error drops below our general ability to account for gravity’s effect on time here on Earth. Hence, as we envision clocks like these being used around the country or world, their relative performance would be, for the first time, limited by Earth's gravitational effects.”
Einstein’s theory of relativity predicts that an atomic clock’s ticking, that is, the frequency of the atoms’ vibrations, is reduced—shifted toward the red end of the electromagnetic spectrum—when observed in stronger gravity. That is, time passes more slowly at lower elevations.
While these so-called redshifts degrade a clock’s timekeeping, this same sensitivity can be turned on its head to exquisitely measure gravity. Super-sensitive clocks can map the gravitational distortion of space-time more precisely than ever. Applications include relativistic geodesy, which measures the Earth’s gravitational shape, and detecting signals from the early universe such as gravitational waves and perhaps even as-yet-unexplained dark matter.
NIST’s ytterbium clocks now exceed the conventional capability to measure the geoid, or the shape of the Earth based on tidal gauge surveys of sea level. Comparisons of such clocks located far apart such as on different continents could resolve geodetic measurements to within 1 centimeter, better than the current state of the art of several centimeters.
In the past decade of new clock performance records announced by NIST and other labs around the world, this latest paper showcases reproducibility at a high level, the researchers say. Furthermore, the comparison of two clocks is the traditional method of evaluating performance.
Among the improvements in NIST’s latest ytterbium clocks was the inclusion of thermal and electric shielding, which surround the atoms to protect them from stray electric fields and enable researchers to better characterize and correct for frequency shifts caused by heat radiation.
The ytterbium atom is among potential candidates for the future redefinition of the second—the international unit of time—in terms of optical frequencies. NIST’s new clock records meet one of the international redefinition roadmap's requirements, a 100-fold improvement in validated accuracy over the best clocks based on the current standard, the cesium atom, which vibrates at lower microwave frequencies.
NIST is building a portable ytterbium lattice clock with state-of-the-art performance that could be transported to other labs around the world for clock comparisons and to other locations to explore relativistic geodesy techniques.
The work is supported by NIST, the National Aeronautics and Space Administration and the Defense Advanced Research Projects Agency.
https://www.nist.gov/news-events/ne...ow-keep-time-well-enough-improve-models-earth
Atomic clock performance enabling geodesy below the centimetre level
https://sci-hub.tw/10.1038/s41586-018-0738-2
NIST Researchers Boost Microwave Signal Stability a Hundredfold May 21, 2020
Researchers at the National Institute of Standards and Technology (NIST) have used state-of-the-art atomic clocks, advanced light detectors, and a measurement tool called a frequency comb to boost the stability of microwave signals a hundredfold. This marks a giant step toward better electronics to enable more accurate time dissemination, improved navigation, more reliable communications and higher-resolution imaging for radar and astronomy. Improving the microwave signal’s consistency over a specific time period helps ensure reliable operation of a device or system.
The work transfers the already superb stability of the cutting-edge laboratory atomic clocks operating at optical frequencies to microwave frequencies, which are currently used to calibrate electronics. Electronic systems are unable to directly count optical signals, so the NIST technology and techniques indirectly transfer the signal stability of optical clocks to the microwave domain. The demonstration is described in the May 22, 2020, issue of Science.
In their setup, the researchers used the “ticking” of two of NIST’s ytterbium lattice clocks to generate light pulses, as well as frequency combs serving as gears to translate the higher-frequency optical pulses accurately into lower-frequency microwave signals. Advanced photodiodes converted light pulses into electrical currents, which in turn generated a 10 gigahertz (GHz, or a billion cycles per second) microwave signal that tracked the clocks’ ticking exactly, with an error of just one part in a quintillion (1 followed by 18 zeros). This performance level is on par with that of both optical clocks and 100 times more stable than the best microwave sources.
“Years of research, including important contributions from NIST, have resulted in high-speed photodetectors that can now transfer optical clock stability to the microwave domain,” lead researcher Frank Quinlan said. “The second major technical improvement was in the direct tracking of the microwaves with high precision, combined with lots of know-how in signal amplification.”
Optical waves have shorter, faster cycles than microwaves do, so they have different shapes. In converting stable optical waves to microwaves, the researchers tracked the phase — the exact timing of the waves — to ensure they were identical, and not shifted relative to one another. The experiment tracked phase changes with a resolution corresponding to just one millionth of a cycle.
“This is a field where just doubling microwave stability can take years or decades to achieve,” group leader Chris Oates said. “A hundred times better is almost unfathomable.”
Some components of the NIST system, such as the frequency combs and detectors, are ready to be used in field applications now, Quinlan said. But NIST researchers are still working on transferring state-of-the-art optical clocks to mobile platforms. The ytterbium clocks, which operate at frequencies of 518 terahertz (trillion cycles per second), currently occupy large tables in highly controlled laboratory settings.
Ultra-stable electronic signals could support widespread applications, including future calibration of electronic clocks, such as electric devices powered by oscillating quartz crystals. This is an important consideration for the redefinition of the international time standard, the SI second, now based on the microwave frequencies absorbed by the cesium atoms in conventional clocks. In the coming years, the international scientific community is expected to select a new time standard based on optical frequencies that other atoms, such as ytterbium, absorb. Super-stable signals could also make wireless communications systems more reliable.
Optically derived electronic signals could make imaging systems more sensitive. Radar sensitivity, particularly for slow-moving objects, is now limited by microwave noise and could be greatly enhanced. New photodiodes, produced in a collaboration between NIST and the University of Virginia, convert the optical signals to microwave signals more predictably and with lower noise than earlier designs. In addition, microwaves could carry signals from distant optical clocks for applications in navigation and fundamental physics research.
Astronomical imaging and relativistic geodesy, which measures the Earth’s gravitational shape, are now based on detecting microwave signals at receivers around the world and combining them to form images of objects. Remote calibration of these receivers could make it possible to move the network from Earth into space, which would enhance image resolution and avoid atmospheric distortions that limit observation time. With hours of observing time instead of seconds, researchers could image many more objects.
The research was supported in part by the Defense Advanced Research Projects Agency.
https://www.nist.gov/news-events/news/2020/05/nist-researchers-boost-microwave-signal-stability-hundredfold
Coherent optical clock down-conversion for microwave frequencies with 10−18 instability
https://sci-hub.tw/10.1126/science.abb2473
I shared this thread topic to justify ascending order.
