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Displaying 1 - 23 of 23

A Resilient Architecture for the Realization and Distribution of Coordinated Universal Time to Critical Infrastructure Systems in the United States: Methodologies and Recommendations from the National Institute of Standards and Technology (NIST)

November 3, 2021
Author(s)
Jeffrey Sherman, Ladan Arissian, Roger Brown, Matthew J. Deutch, Elizabeth Donley, Vladislav Gerginov, Judah Levine, Glenn Nelson, Andrew Novick, Bijunath Patla, Tom Parker, Benjamin Stuhl, Jian Yao, William Yates, Michael A. Lombardi, Victor Zhang, Douglas Sutton
The Time and Frequency Division of the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce (DOC), was tasked with fulfilling Section 4, Part (i) of the Position, Navigation and Timing (PNT) Executive

Frequency Ratio Measurements with 18-Digit Accuracy Using a Network of Optical Clocks

March 24, 2021
Author(s)
Kyle Beloy, Martha I. Bodine, Tobias B. Bothwell, Samuel M. Brewer, Sarah L. Bromley, Jwo-Sy Chen, Jean-Daniel Deschenes, Scott Diddams, Robert J. Fasano, Tara Fortier, Youssef Hassan, David Hume, Dhruv Kedar, Colin J. Kennedy, Isaac Kader, Amanda Koepke, David Leibrandt, Holly Leopardi, Andrew Ludlow, Will McGrew, William Milner, Daniele Nicolodi, Eric Oelker, Tom Parker, John M. Robinson, Stefania Romisch, Stefan A. Schaeffer, Jeffrey Sherman, Laura Sinclair, Lindsay I. Sonderhouse, William C. Swann, Jian Yao, Jun Ye, Xiaogang Zhang
Atomic clocks occupy a unique position in measurement science, exhibiting higher accuracy than any other measurement standard and underpinning six out of seven base units in the SI system. By exploiting higher resonance frequencies, optical atomic clocks

Measurement of the 27Al+ and 87Sr absolute optical frequencies

January 21, 2021
Author(s)
Holly Leopardi, Kyle Beloy, Tobias B. Bothwell, Samuel M. Brewer, Sarah L. Bromley, Jwo-Sy Chen, Scott Diddams, Robert J. Fasano, Youssef S. Hassan, David B. Hume, Dhruv Kedar, Colin J. Kennedy, Isaac H. Khader, David R. Leibrandt, Andrew D. Ludlow, William F. McGrew, William R. Milner, Daniele Nicolodi, Eric Oelker, Thomas E. Parker, John M. Robinson, Stefania Romisch, Jeffrey A. Sherman, Lindsay I. Sonderhouse, William C. Swann, Jian Yao, Jun Ye, Xiaogang Zhang, Tara M. Fortier
We perform absolute measurement of the 27Al+ single-ion and 87Sr neutral lattice clock frequencies at the National Institute of Standards and Technology and JILA at the University of Colorado against a global ensemble of primary frequency standards. Over

Optical-Clock-Based Time Scale

October 30, 2019
Author(s)
Jian Yao, Jeffrey A. Sherman, Tara M. Fortier, Andrew D. Ludlow, Holly Leopardi, Thomas E. Parker, William F. McGrew, Scott A. Diddams, Judah Levine
A time scale is a procedure for accurately and continuously marking the passage of time. It is exemplified by coordinated universal time (UTC), and provides the backbone for critical navigation tools such as the global positioning system (GPS). Present

Towards the optical second: verifying optical clocks at the SI limit

April 11, 2019
Author(s)
William F. McGrew, Xiaogang Zhang, Robert J. Fasano, Holly Leopardi, Daniele Nicolodi, Kyle P. Beloy, Jian Yao, Jeffrey A. Sherman, Stefan A. Schaeffer, Joshua J. Savory, Stefania Romisch, Christopher W. Oates, Thomas E. Parker, Tara M. Fortier, Andrew D. Ludlow
The pursuit of ever more precise measures of time and frequency motivates redefinition of the second in terms of an optical atomic transition. To ensure continuity with the current definition, based on the microwave hyperfine transition in 133 Cs, it is

Progress on Optical-clock-based Time Scale at NIST: Simulations and Preliminary Real-Data Analysis

April 20, 2018
Author(s)
Jian Yao, Jeffrey A. Sherman, Tara M. Fortier, Thomas E. Parker, Judah Levine, Joshua J. Savory, Stefania Romisch, William F. McGrew, Robert J. Fasano, Stefan A. Schaeffer, Kyle P. Beloy, Andrew D. Ludlow
This paper shows the recent NIST work on incorporating an optical clock into a time scale. We simulate a time scale composed of continuously-operating commercial hydrogen masers and an optical frequency standard that does not operate continuously as a

Incorporating an Optical Clock into a Time Scale at NIST: Simulations and Preliminary Real-Data Analysis

March 29, 2018
Author(s)
Jian Yao, Jeffrey A. Sherman, Tara M. Fortier, Thomas E. Parker, Judah Levine, Joshua J. Savory, Stefania Romisch, William F. McGrew, Robert J. Fasano, Stefan A. Schaeffer, Kyle P. Beloy, Andrew D. Ludlow
This paper shows the recent NIST work on incorporating an optical clock into a time scale. We simulate a time scale composed of continuously-operating commercial hydrogen masers and an optical frequency standard that does not operate continuously as a

Incorporating an Optical Clock into a Time Scale

January 1, 2018
Author(s)
Jian Yao, Thomas E. Parker, Neil Ashby, Judah Levine
This paper discusses how to build a time scale with an intermittently-operated optical clock. In particular, it gives suggestions on how long and how often to run an optical clock. It also explores the benefits of having an optical clock in a time scale

JY1 Time Scale: a New Kalman-Filter Time Scale Designed at NIST

October 17, 2017
Author(s)
Jian Yao, Thomas E. Parker, Judah Levine
We report on a new Kalman-filter Hydrogen-maser time scale (i.e., JY1 time scale) designed at NIST. The JY1 time scale is composed of a few Hydrogen masers and a Cs clock. The Cs clock is used as a reference clock, to ease operations with existing data

Accurate TWSTFT time transfer with indirect links

January 31, 2017
Author(s)
Victor S. Zhang, Zhiheng Jiang, Thomas E. Parker, Jian Yao, Yi-Jiun Huang, Shinn-Yan Lin
The conventional wisdom suggests a direct Two-Way Satellite Time and Frequency Transfer (TWSTFT or TW) time link should result in a smaller uncertainty than that of an indirect TW link over the same baseline [12]. This is why all Coordinated Universal Time

The development of a new Kalman-filter time scale at NIST

January 31, 2017
Author(s)
Jian Yao, Thomas E. Parker, Judah Levine
We report on a preliminary design of a new Kalman-filter Hydrogen-maser time scale at NIST. The time scale is composed of a few Hydrogen masers and a Cs clock. The Cs clock is used as a reference clock, just for easy operations with the existing data. All

The effects of the January 2016 UTC offset anomaly on GPS clocks monitored at NIST

January 31, 2017
Author(s)
Jian Yao, Michael A. Lombardi, Andrew N. Novick, Bijunath Patla, Jeffrey A. Sherman, Victor S. Zhang
Errors in the Coordinated Universal Time (UTC) offset parameters broadcast by Global Positioning System (GPS) satellites caused many thousands of GPS clocks to be in error by approximately -13 µs on January 25-26, 2016. The erroneous UTC offset information

GPS Jamming and GPS Carrier-Phase Time Transfer

January 25, 2016
Author(s)
Jian Yao, Marc A. Weiss, Charles Curry, Judah Levine
This paper studies the impact of GPS jamming on GPS carrier-phase time transfer. To study this issue, at NIST, we have installed a commercial GPS jamming detector since 2014 April. During 2014 April – 2015 April, the detector detected more than 100 jamming

A detailed comparison of two continuous GPS carrier-phase time transfer techniques

September 8, 2015
Author(s)
Jian Yao, Judah Levine, Skakun Ivan, Zhiheng Jiang
The wide application of GPS carrier-phase (CP) time transfer is limited by the problem of boundary discontinuity (BD). The discontinuity has two categories. One is "day boundary discontinuity," which has been studied extensively and can be solved by a few

Long-Term Uncertainty in Time Transfer Using GPS and TWTFT Techniques

April 13, 2015
Author(s)
Victor S. Zhang, Thomas E. Parker, Jian Yao
The techniques of GPS time and frequency transfer (code based and carrier phase) and two-way satellite time and frequency transfer (TWSTFT) are widely used in remote clock comparison and in the computation of International Atomic Time (TAI). Many timing

Comparison of Two Continuous GPS Carrier-Phase Time Transfer Techniques

April 12, 2015
Author(s)
Jian Yao, Skakun Ivan, Zhiheng Jiang, Judah Levine
Global Positioning System (GPS) carrier-phase (CP) time transfer, as a widely accepted high-precision time transfer method, frequently shows a data-batch boundary discontinuity of up to 1 ns, because of the inconsistency of the phase ambiguities between

GPS Measurements Anomaly and Continuous GPS Carrier-Phase Time Transfer

December 4, 2014
Author(s)
Jian Yao, Judah Levine
The wide application of GPS carrier-phase (CP) time transfer is limited by the problem of boundary discontinuity (BD). The discontinuity has two categories. One is "day boundary discontinuity", which has been studied a lot and can be solved by a few

GPS Carrier-Phase Time Transfer Boundary Discontinuity Investigation

November 26, 2012
Author(s)
Jian Yao, Judah Levine
We report on a study of the carrier-phase time transfer boundary discontinuity by the use of the precise point positioning (PPP) technique. Carrier-phase time transfer is first compared with two-way satellite time and frequency transfer (TWSTFT) between