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Combination of an Optical Clock and Hydrogen Masers for Accurate time Scale Calculation

Chinese Astronomy and Astrophysics 2024年第4期48卷 763-780页

作者： Shu-hong, Zhao Shao-wu, Dong Shan-shan, Bai Li-li, Qu Ji-hai, Zhang Yu, Zhang National Time Service Center Chinese Academy of Sciences Xi'an 710600 China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi'an 710600 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing 100049 China

The frequency stability and uncertainty of the optical clock have reached a magnitude of 10−18, making it a promising candidate for the next generation of time and frequency standards, and it may be used to redefine t... 详细信息

The frequency stability and uncertainty of the optical clock have reached a magnitude of 10⁻¹⁸, making it a promising candidate for the next generation of time and frequency standards, and it may be used to redefine the international unit “second”. The time scale serves as a benchmark for accurately and continuously marking the passage of time, being the foundation of high-precision time generation. The production of a time scale relies on the continuous and stable operation of atomic clocks;however, optical clocks, as laboratory prototype devices, generally cannot operate continuously, thus involving optical clocks in time scale calculation presents a challenging issue. The proposed application of the Vondrak-Cepek combined filtering algorithm for joint time scale calculations with an optical clock and hydrogen masers aims to address the challenges posed by the intermittent operation of an optical clock. Initially, the ALGOS algorithm is used on the time difference data of the hydrogen masers to calculate and obtain a continuous and stable hydrogen maser clock time scale. Subsequently, the Vondrak-Cepek combined filtering algorithm is used to integrate the hydrogen maser time scale with the optical clock data to acquire a combined time scale that involves optical clocks in the calculation. Finally, the experimental results prove that the Vondrak-Cepek combined filtering algorithm effectively improves the performance of the combined time scale of optical clocks and hydrogen masers, with the time deviation of this time scale reaching the sub-nanosecond magnitude when compared with Coordinated Universal time (UTC). © 2024

关键词： methods: data analysis—Vondrak-Cepek combined filtering algorithm techniques: hydrogen maser—optical clock time: time scale—frequency stability

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Atom Fountains at NTSC 9

Atom Fountains at NTSC

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9th Symposium on Frequency Standards and Metrology, FSM 2023

作者： Ruan, Jun Wang, Xinliang Zhang, Hui Liu, Dandan Guan, Yong Shi, Junru Bai, Yang Fan, Sichen Hao, Qiang Nie, Shuai Lei, Pengyue Zhu, Ziyi Zhang, Shougang National Time Service Center Chinese Academy of Sciences Xi'an710600 China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi'an710600 China University of Chinese Academy of Sciences Beijing100049 China

Atom fountains as primary frequency standard (PFS) and continuously operated clocks have been developed to improve the local time scale at the National time Service Center (NTSC), Chinese Academy of Sciences. Cesium fountain NTSC-CsF2 as PFS showed that the type B uncertainty was evaluated at 4.3 × 10-16. Frequency comparisons were completed between NTSC-CsF2 and the SI second through a GNSS link for 14 months, the results of which were consistent with those of the other fountains within the uncertainty. A cryogenic Cs fountain is being developed to reduce the blackbody radiation shift (BBR) and verify the BBR theory. An Rb fountain clock NTSC-RbF1 was operated to generate local and EAL time scale. The frequency drift was reduced by maintaining a stable vapor pressure. NTSC-RbF2 features a more robust optical system consisting of all fiber-optical components and an ultra-stable OCXO as a local oscillator. An instability time scale below 100 ps is expected based on the Rb atom fountain clocks. © Published under licence by IOP Publishing Ltd.

关键词： Atoms

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Research on Space-Ground Two-Way time Comparison Method Based on Carrier Phase Smoothing Pseudo-Range 3

Research on Space-Ground Two-Way Time Comparison Method Base...

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3rd International Symposium on Aerospace Engineering and Systems, ISAES 2024

作者： Li, Hongjun Liu, Yinhua Zhang, Yingbo Liu, Ya National Time Service Center Chinese Academy of Sciences Shaanxi Xi'an China University of Chinese Academy of Sciences Shaanxi Xi'an China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Shaanxi Xi'an China

ISBN: (纸本)9798350350418

The high-precision time-frequency system has been sent to the China Space Station(CSS), which improves the accuracy of the time-frequency reference in space and puts forward the higher requirements on the matching time comparison technology. Aiming at this demand, the carrier phase smoothing pseudo-range method is proposed to improve the accuracy of the two-way time comparison based on the pseudo-range. Aiming at the problem of cycle slip in high dynamic, this paper proposes a combination of ionospheric residual method and carrier phase difference fitting method, and analyzes its error correction method. It can detect and repair all cycle slip combinations that affect two-way time comparison. The experimental result using the observation data of the CSS shows that this method improves the accuracy of the two-way time comparison from hundreds of picoseconds to picoseconds. © 2024 IEEE.

关键词： carrier phase smoothing pseudo-range cycle slip detection and repair space station two-way time comparison

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Analysis of detailed errors affecting the calibration of Space Station common-view geometric distance 1

Analysis of detailed errors affecting the calibration of Spa...

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1st Aerospace Frontiers Conference, AFC 2024

作者： Liu, Yinhua Liu, Ya Li, Xiaohui Yanming, Guo National Time Service Center Chinese Academy of Sciences Xi’an710600 China University of Chinese Academy of Science Beijing100049 China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi’an710600 China

ISBN: (纸本)9781510681613

Making good use of Space Station and maximizing its value is the important work in the manned spaceflight field currently. The time and frequency resources in Chinese Space Station are better than that loaded in the navigation satellite. Thus the accuracy of Space Station CV(common-view) time comparison can be better than GNSS(Global Navigation Satellite System) CV that realizes the highest CV accuracy now. But the low orbit characteristic of Space Station magnifies the effect of geometric distance error on CV time comparison, and the geometric distance error is one kind of main errors that need to be researched detailed in order to improve Space Station CV performance. In the paper, the magnifying phenomenon of geometric distance error on CV time comparison is analyzed in theory. Then the factors affecting geometric distance calibration are studied, including orbit error, attitude error, calibration error of antenna phase center, Space Station movement, and so on. Based on simulation experiments, the quantitative effect of these errors on CV time comparison are analyzed. The simulation results show that the Space Station geometric distance error affects the CV accuracy most greatly, and its root mean square error is about 150 pico-seconds. The simulation also shows that the attitude error causes about 20 picoseconds CV errors and the CV error caused by calibration error of antenna phase center or Space Station movement factor is in the magnitude of several pico-seconds. In order to realize the Space Station CV accuracy of several hundred or ten pico-seconds magnitude, the effect of orbit error, attitude error, calibration error of antenna phase center and Space Station movement can’t be ignored. Reducing Space Station’s orbit error is the most efficient way for CV accuracy improvement. © 2024 SPIE.

关键词： Manned space flight

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Real-time GNSS satellite SISRE and its integrity for LEO satellite Precise Orbit Determination

Real-Time GNSS satellite SISRE and its integrity for LEO sat...

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2024 International Technical Meeting of The Institute of Navigation, ITM 2024

作者： Chen, Beixi Wang, Kan El-Mowafy, Ahmed Yang, Xuhai National Time Service Center Chinese Academy of Sciences Xi’an China University of Chinese Academy of Sciences Beijing China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences China School of Earth and Planetary Sciences Curtin University Perth Australia

ISBN: (纸本)9780936406367

The real-time Global Navigation Satellite System (GNSS) precise orbital and clock products are essential prerequisites for the Positioning, Navigation, and Timing (PNT) services and have been assessed in various studies. Compared to the precision of the orbital and clock products, their combined effect expressed in Signal-In-Space Ranging Error (SISRE) is of higher concern for positioning users. As a special user of the GNSS, the Low Earth Orbit (LEO) satellites need high-precision real-time GNSS products for their Precise Orbit Determination (POD) and clock determination in real time, which enables the future LEO-augmented GNSS PNT service. This study performs a comprehensive analysis of the real-time GNSS products from five different analysis centers, including analysis of their continuity, accuracy of their orbits, precision of their clocks, and their SISREs for LEO satellites at different altitudes. Using the tested products, the LEO POD was also performed to verify the correlation between the quality of the GNSS products and the accuracy of the LEO POD. Furthermore, to assess the integrity of real-time GNSS products, the overbounding standard deviations and mean values of the combined clock and orbital errors were computed and compared for different institutions. It was found that the GPS and Galileo SISRE range from a few centimeters to around 8 cm, while the SISRE of the Beidou Satellite Navigation System (BDS) Medium Earth Orbit (MEO) is a bit worse, i.e., around 1-2 dm. It has been demonstrated that there exists a positive correlation between the SISRE and user altitude, which implies a higher bias introduced to LEO satellites than ground users. The overbounding standard deviations and mean values of the GPS and Galileo products are all within 1 dm, whereas for BDS they are about 1-2 dm. Among the tested products, the smallest SISRE and overbounding values were delivered by the National Centre for Space Studies (CNES) in France for GPS and Galileo, while th

关键词： Clocks

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Spatial transparency in atomic vapor: effects of transverse magnetic field on cylindrical vector beams 15

Spatial transparency in atomic vapor: effects of transverse ...

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15th International Conference on Information Optics and Photonics, CIOP 2024

作者： Ma, Yan Chang, Hong Bai, Xi-Xi Cao, Ming-Tao Dong, Rui-Fang Zhang, Shou-Gang Key Laboratory of Time Reference and Applications National Time Service Center Chinese Academy of Sciences Xi’an710600 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China School of Science Xi’an Polytechnic University Xi’an710048 China

ISBN: (数字)9781510686175

ISBN: (纸本)9781510686168

The interaction between cylindrical vector beams and atoms under a weak magnetic field induces spatially dependent electromagnetically induced transparency (EIT). Based on this coherence effect, we investigated the relationship between the magnitude and orientation of the transverse magnetic field (TMF) and the spatial intensity distribution of cylindrical vector beams passing through a thermal atom ensemble, which is intuitively manifested in polarization selection absorption. The radially polarized beam exhibits a spatial axisymmetric polarization structure. When a TMF is applied, transparent regions in the transmitted beam strongly correlate with the beam’s polarization distribution. Variations in the TMF magnitude alter the absorption of specific polarization components by the atomic system, thereby affecting the local transmittance. This enables the TMF magnitude to be inferred from the single transmittance of the intensity pattern. The alignment of the TMF orientation is reflected in the rotation of the petal-shaped transmission patterns aligned with the mirror axis. Theoretical solutions using optical Bloch equations reveal this specific spatially dependent EIT is closely related to the transverse relaxation rate between the ground state energy levels. Experimental data align perfectly with the theoretical results, suggesting potential applications in light field manipulation and magnetic field measurement. © 2024 SPIE.

关键词： Ground state

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基于最先进的光钟直接演示自旋压缩引起的计量增强

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Science Bulletin 2024年第10期69卷 1359-1361页

作者：陈景标于得水 State Key Laboratory of Advanced Optical Communication System and NetworkSchool of ElectronicsPeking UniversityBeijing 100871China National Time Service Center Chinese Academy of SciencesXi’an 710600China Key Laboratory of Time Reference and Applications Chinese Academy of SciencesXi’an 710600China

Benefiting from the recent progress in precise engineering of quantum states and sub-10 mHz linewidth lasers,the stability and accuracy of optical atomic clocks have reached and even exceeded the 1018 level,surpassing their microwave counterparts by over two orders of magnitude[1,2].These advances lead to an anticipated redefinition of the international system of units(SI)second in terms of an optical reference transition as early as 2026.

关键词： optical 光钟自旋压缩

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A novel scheme for acoustic sensing based on a Floquet optical lattice clock

A novel scheme for acoustic sensing based on a Floquet optic...

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2023 Advanced Fiber Laser Conference, AFL 2023

作者： Yin, Mojuan Wang, Tao Chang, Hong Key Laboratory of Time Reference and Applications National Time Service Center Chinese Academy of Sciences Xi an710600 China School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing100049 China Department of Physics and Center of Quantum Materials and Devices Chongqing University Chongqing401331 China Chongqing Key Laboratory for Strongly Coupled Physics Chongqing University Chongqing401331 China

ISBN: (纸本)9781510677661

The optical lattice clocks were proved to be a powerful tool for precision measurement, like measuring the gravitational redshift at tiny gravity potential difference and monitoring the crustal deformations with ultrahigh accuracy. The Floquet optical lattice clock utilizes a time periodical acoustic wave acting on the optical lattice potential. Those atoms trapped in the lattice site will be compelled to move slightly with the modulated potential. These micromotions generate a series of Floquet quasi-energies which the atomic spectra would present for us. In virtue of Floquet engineering optical lattice theoretical model, the periodic acoustic wave signal acting on the lattice potential could be extracted. In this paper, we propose a novel way for acoustic sensing based on a 87Sr Floquet optical lattice clock. It may assist the traditional acoustic sensing technology based on fiber in achieving higher signal-noise ratio and accuracy. From the clockmaker's point of view, it may help us monitoring the environmental acoustic noise caused by vibrations and calibrate in time, especially when the optical clock operating in a movable carrier both on earth and space, what is even more important. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

关键词： Optical lattices

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Combined Separated Oscillatory Fields Technique

Combined Separated Oscillatory Fields Technique

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European Frequency and time Forum (EFTF)

作者： Fuyu Sun Chao Li Xuwen Hu Shougang Zhang National Time Service Center Chinese Academy of Sciences Xi'an China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi'an China

ISBN: (数字)9798350354270

ISBN: (纸本)9798350354287

Ramsey's method of separated oscillatory fields (SOFs) has been originally used in beam magnetic resonance apparatuses, which leads to the establishment of atomic definition of time interval and frequency. Since then, various versions of the SOFs technique have been widely used for precise measurement of different physical quantities. Here, we present an alternative method to generate atomic beam magnetic resonance signals by combining two Ramsey cavities with phase differences of 0 and 1t. It is found that the strength of the resonance signals generated using this combined SOFs technique is approximately twice that of the resonance signals produced by the conventional SOFs techniques. In addition to generating stronger resonance, the combined Ramsey method eliminates the Rabi background superimposed on the Ramsey interference pattern without increasing the Ramsey signal linewidth. Thus, this technique serves a promising tool for high-precision measurements.

关键词： Atomic measurements time-frequency analysis Magnetic field measurement Atomic beams Magnetic resonance Europe Interference

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Leveraging Future LEO Constellations for the Precise Orbit Determination of Lower Small Satellites

Leveraging Future LEO Constellations for the Precise Orbit D...

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2024 International Technical Meeting of The Institute of Navigation, ITM 2024

作者： Allahvirdi-Zadeh, Amir El-Mowafy, Ahmed Wang, Kan School of Earth and Planetary Sciences Curtin University GPO Box U1987 PerthWA6845 Australia National Time Service Center Chinese Academy of Sciences Xi'an China University of Chinese Academy of Sciences Beijing China Key Laboratory of Time Reference and Applications Chinese Academy of Sciences Xi'an China

ISBN: (纸本)9780936406367

Low earth orbit (LEO) constellations offer possible significant augmentation to the Global Navigation Satellite Systems (GNSS) for positioning, navigation, and timing (PNT) applications. This study explores a new application of forthcoming LEO-PNT constellations;the utilization of signals from higher LEO satellites for precise orbit determination (POD) of lower satellites, such as CubeSats. The integration of LEO-based orbit determination with existing GNSS-based LEO POD methods introduces redundancy and resilience, critical for monitoring the increasingly crowded LEO region in the future. To explore this approach, a simulation is conducted using a constellation of 240 LEO satellites at 1000 km altitude, designed to provide global coverage for the POD of lower satellites. Actual onboard GNSS observations of a 3U CubeSat and its attitude information are employed in a reduced-dynamic POD, generating a true trajectory for the CubeSat. Simulated orbits for the entire constellation and the true trajectory of the CubeSat are used to simulate the navigation signals from the LEO constellation to the CubeSat. Various errors and biases are considered in the simulated observations. To mimic the constraints of limited onboard processing resources, a LEO-PNT module is developed within the new Geoscience Australia's GNSS processing software, Ginan, to process the simulated onboard observations in a Raspberry Pi. The integration of data from higher LEO satellites into the extended Kalman filter model, developed for LEO POD in Ginan, is elucidated and validated through various processing scenarios, including LEO-only case and data fusion with GPS observations. The overall 3D accuracy for the onboard POD is achieved at around 22 cm in the solely LEO-PNT case and improved to about 15 cm with a lower level of observation residuals when combining LEO and GPS observations. This approach holds immense potential for enhancing onboard LEO orbit determination accuracy, robustness, and effic

关键词： Global positioning system

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