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Biercuk M.J.,NIST Time and Frequency Division | Biercuk M.J.,University of Sydney | Uys H.,NIST Time and Frequency Division | Uys H.,South African Council for Scientific and Industrial Research | And 3 more authors.
Nature Nanotechnology | Year: 2010

The ability to detect extremely small forces and nanoscale displacements is vital for disciplines such as precision spin-resonance imaging, microscopy, and tests of fundamental physical phenomena. Current force-detection sensitivity limits have surpassed 1aN Hz -1/2 (refs 6,7) through coupling of nanomechanical resonators to a variety of physical readout systems 1,7-10. Here, we demonstrate that crystals of trapped atomic ions11,12 behave as nanoscale mechanical oscillators and may form the core of exquisitely sensitive force and displacement detectors. We report the detection of forces with a sensitivity of 390±150 yN Hz -1/2, which is more than three orders of magnitude better than existing reports using nanofabricated devices 7, and discriminate ion displacements of μ18 nm. Our technique is based on the excitation of tunable normal motional modes in an ion trap and detection through phase-coherent Doppler velocimetry, and should ultimately allow force detection with a sensitivity better than 1 yN Hz -1/2 (ref. 16). Trapped-ion-based sensors could enable scientists to explore new regimes in materials science where augmented force, field and displacement sensitivity may be traded against reduced spatial resolution. © 2010 Macmillan Publishers Limited. All rights reserved.


Weiss M.,NIST Time and Frequency Division | Cosart L.,Microsemi | Hanssen J.,Us Naval Observatory | Hicks S.,CenturyLink | And 6 more authors.
Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI | Year: 2014

There is a need to back up critical timing infrastructure at the national level. This paper describes a joint project employing commercial equipment to send national timing signals through a telecommunication network. This experiment connects UTC(NIST) in Boulder, Colorado with UTC(USNO) at the Alternate Master Clock at Schriever AFB via a telecommunication provider's optical network using the Precise Time Protocol (PTP) to compare the time standards. The experiment was started in April 2014 and will run through the end of 2014. The paper provides insight into both the planning and validation of the transport path as well as analysis of the experimental data. The focus here is using a US commercial telecom carrier to transfer time between two national real-time standards of UTC. While many researchers have shown that fiber can transfer time and frequency with high accuracy, this experiment addresses the practicality of using the US telecom infrastructure for timing. Our results thus far show a bias of about 40 microseconds between the two one-way directions of PTP signals, with the best method having a variation of under about 50 nanoseconds peak-to-peak. Research is continuing to determine the cause of the bias.


Weiss M.,NIST Time and Frequency Division | Yao J.,NIST Time and Frequency Division | Cosart L.,Microsemi | Hanssen J.,Us Naval Observatory
Proceedings of the Annual Precise Time and Time Interval Systems and Applications Meeting, PTTI | Year: 2016

There is a need to back up critical timing infrastructure at the national level. This paper provides an update on a joint project employing commercial equipment to send national timing signals through a telecommunication network. This experiment connects the UTC(NIST) time scale located in Boulder, Colorado with the UTC(USNO) Alternate Master Clock time scale located at Schriever AFB in Colorado via a telecommunication provider's optical network. Timing signals using the Precision Time Protocol (PTP) were sent in the usual two-way fashion, but each one-way delay was measured, because we had UTC time scales at both ends of the network that were within 10 ns of each other. This part of the experiment is now nearly complete. The experiment was started in April 2014 and extensions of the project will run through the end of 2016. It appears that there is at least one commercial transport mechanism that could serve to back up GPS for time transfer at the 100 ns level. We found that the asymmetry of the PTP time transfer resulted in 10's of microseconds of time transfer error, but that the stability through the entire connection was less than 100 ns, as long as the connection remained complete. This implies that if the time delays of the network could be calibrated, it could maintain under 100 ns accuracy as long as it did not go down. We have established the likely causes of the bias, as well as run simulations of various configurations in a laboratory. Thus, we have some certainty that similar results will apply if this technique were used as a service across the country. While many researchers have shown that fiber can transfer time and frequency with high accuracy, this experiment addresses the practicality of using the US telecom infrastructure for timing. © 2016 The Institute of Navigation, Inc.


PubMed | Polytechnic University of Turin, NIST Time and Frequency Division and INRIM - Istituto Nazionale di Ricerca Metrologica
Type: Journal Article | Journal: Physical review letters | Year: 2014

We report a high-accuracy direct measurement of the blackbody radiation shift of the 133Cs ground-state hyperfine transition. This frequency shift is one of the largest systematic frequency biases encountered in realizing the current definition of the International System of Units (SI) second. Uncertainty in the blackbody radiation frequency shift correction has led to its being the focus of intense theoretical effort by a variety of research groups. Our experimental measurement of the shift used three primary frequency standards operating at different temperatures. We achieved an uncertainty a factor of five smaller than the previous best direct measurement. These results tend to validate the claimed accuracy of the recently calculated values.


Andrade H.A.,National Instruments | Derler P.,National Instruments | Eidson J.C.,University of California at Berkeley | Li-Baboud Y.-S.,NIST Software and Systems Division | And 3 more authors.
2015 International Conference on ReConFigurable Computing and FPGAs, ReConFig 2015 | Year: 2015

Timing and synchronization play a key role in cyber-physical systems (CPS). Precise timing, as often required in safety-critical CPS, depends on hardware support for enforcement of periodic measure, compute, and actuate cycles. For general CPS, designers use a combination of application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs) and conventional microprocessors. Microprocessors as well as commonly used computer languages and operating systems are essentially devoid of any explicit support for precise timing and synchronization. Modern computer science and microprocessor design has effectively removed time from the abstractions used by designers with the result that time is regarded as a performance metric rather than a correctness specification or criterion. There are interesting proposals and avenues of research to correct this situation, but the barrier is quite high for conducting proof of concept studies or collaborative research and development. This paper proposes a conceptual design and use model for a reconfigurable testbed designed specifically to support exploratory research, proof of concept, and collaborative work to introduce explicit support for time and synchronization in microprocessors, reconfigurable fabrics, language and design system architecture for time-sensitive CPS. Reconfigurable computing is used throughout the system in several roles: as part of the prototyping platform infrastructure, the measurement and control system, and the application system under test. © 2015 IEEE.


Weiss M.A.,NIST Time and Frequency Division | Yao J.,University of Colorado at Boulder | Li J.,University of Colorado at Boulder
44th Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting 2012 | Year: 2012

A previous publication [1] showed problems with the current NIST Time and Frequency Division primary GPS receiver when used for Precise Point Positioning (PPP)-based carrier phase time transfer. We confirm that, for this receiver, boundary discontinuities during overlapping data runs tend to be biased away from zero on average and that this bias increases as the a-priori pseudo-range sigma increases. We show that this problem does not occur for other receivers at NIST, even receivers of the same model or make. Next we review results for selecting a new primary receiver from others now at NIST, focusing on two desired properties: an average overlap bias close to zero using PPP, and a low code instability. We want at least one year of good data on a receiver before considering it as a replacement. © (2012) by the Institute of Navigation. All rights reserved.


Liebisch T.C.,NIST Time and Frequency Division | Blanshan E.,NIST Time and Frequency Division | Donley E.A.,NIST Time and Frequency Division | Kitching J.,NIST Time and Frequency Division
Proceedings of the IEEE International Frequency Control Symposium and Exposition | Year: 2011

We demonstrate atom number enhancement in a magneto-optical trap (MOT) by use of bichromatic cooling to slow an atomic beam that is loaded into a MOT. Bichromatic cooling employs stimulated emission to apply strong cooling forces that are not limited by spontaneous emission. We demonstrate a factor of 3.5 increase in atom number captured from the atomic beam for a 1.5 cm cooling length. For a 1.5 cm effective cooling length, our technique yields MOT atom number enhancement that is about three times higher than the enhancement acheived via spontaneous emission. © 2011 IEEE.


Heavner T.P.,NIST Time and Frequency Division | Parker T.E.,NIST Time and Frequency Division | Shirley J.H.,NIST Time and Frequency Division | Kunz P.,NIST Time and Frequency Division | Jefferts S.R.,NIST Time and Frequency Division
42nd Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting 2010 | Year: 2010

The national institute of standards and technology operates a cesium fountain primary frequency standard, NIST-F1, which has been contributing to international atomic time (tai) since 1999. during the intervening 11 years, we have improved NIST-F1 so that the uncertainty is currently, dominated by uncertainty in the blackbody-radiationinduced frequency shift. in order to circumvent the uncertainty associated with the blackbody shift, we have built a new fountain, NIST-F2, in which the microwave interrogation region is cryogenic (80 k), reducing the blackbody shift to negligible levels. we briefly describe here the series of improvements to NIST-F1 that have allowed its uncertainty to reach the low 10-16 level and present early results from NIST-F2. © 2010 by Precise Time and Time Interval (PTTI) - Time Service Department.


Jefferts S.R.,NIST Time and Frequency Division | Heavner T.P.,NIST Time and Frequency Division | Barlow S.E.,NIST Time and Frequency Division | Ashby N.,NIST Time and Frequency Division
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

The theory of a frequency shift in primary frequency standards due to microwave lensing in Gibble [Phys. Rev. A 90, 015601 (2014)10.1103/PhysRevA.90.015601] contains a number of problems that undermine its validity. Furthermore, because the exposition of the theory has multiple errors and because the shift has never been experimentally observed, we believe this possible shift should not be included as a correction to primary frequency standards contributing to international atomic time. Although the theory may describe the basic mechanisms of a possible frequency shift, we argue it is not possible to use this theory to make reliable corrections to a primary frequency standard at the δf/f∼10-16 level. © 2015 us. Published by the American Physical Society.


PubMed | NIST Time and Frequency Division
Type: Journal Article | Journal: Nature nanotechnology | Year: 2010

The ability to detect extremely small forces and nanoscale displacements is vital for disciplines such as precision spin-resonance imaging, microscopy, and tests of fundamental physical phenomena. Current force-detection sensitivity limits have surpassed 1 aN Hz(-1/2) (refs 6,7) through coupling of nanomechanical resonators to a variety of physical readout systems. Here, we demonstrate that crystals of trapped atomic ions behave as nanoscale mechanical oscillators and may form the core of exquisitely sensitive force and displacement detectors. We report the detection of forces with a sensitivity of 390 +/- 150 yN Hz(-1/2), which is more than three orders of magnitude better than existing reports using nanofabricated devices(7), and discriminate ion displacements of approximately 18 nm. Our technique is based on the excitation of tunable normal motional modes in an ion trap and detection through phase-coherent Doppler velocimetry, and should ultimately allow force detection with a sensitivity better than 1 yN Hz(-1/2) (ref. 16). Trapped-ion-based sensors could enable scientists to explore new regimes in materials science where augmented force, field and displacement sensitivity may be traded against reduced spatial resolution.

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