Optical Atomic Clocks for Redefining SI Units of Time and Frequency

Sharma, Lakhi; Rathore, H. K.; Utreja, S.; Neelam, .; Roy, Amit; De, Sun; Panja, Subhasis

doi:10.1007/s12647-020-00397-y

Cited by 12 publications

(5 citation statements)

References 131 publications

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“…This article also discussed the different atomic clocks, optical frequency standards and the recent developments of atomic clocks CSIR-NPL. With the most accuracy, these optical clocks may lead to a possible redefinition of time and frequency SI unit in near future [6].…”

Section: Discussionmentioning

confidence: 99%

Redefinition of SI Units and Its Implications

Schlamminger

Yang

Kumar

2020

MAPAN

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The presented paper discusses the summary of the special issue consisting of 13 peer-reviewed papers regarding Redefinition of SI Units and Its Implications. The papers discuss state-of-the-art reviews and progress made as of now and ongoing progress regarding the redefinition of SI units at different National Metrology Institutes (NMIs) and academic/ research institutes across the globe. Different methodologies adopted while investigating redefinition of SI units have been discussed and summarized by the researchers, which will serve as a pivotal point in guiding the researchers in upcoming time.

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Section: Discussionmentioning

confidence: 99%

Redefinition of SI Units and Its Implications

Schlamminger

Yang

Kumar

2020

MAPAN

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“…So far, the best optical clock has achieved an uncertainty beyond 10 −18 and has been recognised as the most stable and accurate timing solution to date [4,[27][28][29]. Figure 1 shows the continuous development of AFS and OFS with regard to their fractional frequency uncertainties (ultimate), as summarised in [21].…”

Section: Optical Clock Developmentmentioning

confidence: 99%

“…With optical clocks, they do not yet play a formal role in this process. In metrology, however, optical clocks have been recommended as a new way of defining the unit of time [20][21][22][23], second, which was redefined last time in 1967 using the ground state of the caesium 133 atomic clock [24,25]. Additionally, the International Bureau of Weights and Measures (BIPM)-an intergovernmental organisation of more than 63 countries as of 2022 providing the SI standard for a system of measurements throughout the world-has provided the secondary representations of the second based on various OFS with different optical transitions [26].…”

Section: Introductionmentioning

confidence: 99%

Evaluating Optical Clock Performance for GNSS Positioning

Boldbaatar,

Grant,

Choy

et al. 2023

Sensors

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Atomic clocks are highly precise timing devices used in numerous Positioning, Navigation, and Timing (PNT) applications on the ground and in outer space. In recent years, however, more precise timing solutions based on optical technology have been introduced as current technology capabilities advance. State-of-the-art optical clocks—predicted to be the next level of their predecessor atomic clocks—have achieved ultimate uncertainty of 1 × 10−18 and beyond, which exceeds the best atomic clock’s performance by two orders of magnitude. Hence, the successful development of optical clocks has drawn significant attention in academia and industry to exploit many more opportunities. This paper first provides an overview of the emerging optical clock technology, its current development, and characteristics, followed by a clock stability analysis of some of the successfully developed optical clocks against current Global Navigation Satellite System (GNSS) satellite clocks to discuss the optical clock potentiality in GNSS positioning. The overlapping Allan Deviation (ADEV) method is applied to estimate the satellite clock stability from International GNSS Service (IGS) clock products, whereas the optical clock details are sourced from the existing literature. The findings are (a) the optical clocks are more stable than that of atomic clocks onboard GNSS satellites, though they may require further technological maturity to meet spacecraft payload requirements, and (b) in GNSS positioning, optical clocks could potentially offer less than a 1 mm range error (clock-related) in 30 s and at least 10 times better timing performance after 900 s in contrast to the Galileo satellite atomic clocks—which is determined in this study as the most stable GNSS atomic clock type used in satellite positioning.

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“…Thus, via the observation of the frequency change with respect to a clock at a stable location A, the accurate detection of temporal variations of the Earth's gravity field at any clock site B is possible. Clock performances are often characterized by their fractional uncertainty and instabilities (Sharma et al, 2020). The fractional frequency uncertainty determines the sensitivity of the shift detection.…”

Section: Gravitational Redshift and Atomic Clocksmentioning

confidence: 99%

Detection of Time Variable Gravity Signals using Terrestrial Clock Networks

Vincent¹,

Müller²,

Wu³

2022

Preprint

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Local gravity potential variations can be determined from the frequency differences of high-performance optical clocks at different locations. Case studies for three regions affected by different mass change processes - Himalaya, Amazon and Greenland - provide promising results. Time-varying gravity signals can be observed with clocks that achieve fractional frequency uncertainties of 10-18 corresponding to 0.1 m2/s2 in gravity potential variation. As the clocks rest on the deformable earth surface, clock observations do not only include potential variations due to mass changes but also associated variations due to the vertical deformation of the land. For the simulations, vertical displacements were derived from real GNSS measurements, and mass variations were computed from GRACE solutions. In the Himalayan region, seasonal variations with a maximum range of [-0.2 0.2] m2/s2 were obtained. There, early and long-lasting precipitation patterns in North East India and the gradual spreading towards the West can be potentially observed by a dedicated clock network. In the case study for the Amazon region, seasonal variations with a maximum range of [-0.5 0.5] m2/s2 to be observed by clocks also reveals the Amazon&#8217;s seasonal secrets of annual rainfall variability at the north and south of the equator. The rainy season in the north of the equator is during the summer season from June to August, but from November to April in the south of the equator. The long-term trend of the ice mass loss in Greenland between 2004 and 2015 causes signals of potential variations of 1 m2/s2 that again can be observed by clock measurements. Especially, the higher rates of potential mass variations in the west and south parts of Greenland can well be observed. These examples illustrate impressively that terrestrial clock networks can be used as a modern tool for detecting various time-variable gravity signals for understanding the local patterns of the variations and for providing complementary information.&#8239;&#160;&#8239;&#160;Acknowledgment:&#160;This study has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy EXC 2123 Quantum Frontiers - Project-ID 90837967 and the SFB 1464 TerraQ - Project-ID 434617780 within project C02.&#160;

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Optical Atomic Clocks for Redefining SI Units of Time and Frequency

Cited by 12 publications

References 131 publications

Redefinition of SI Units and Its Implications

Redefinition of SI Units and Its Implications

Evaluating Optical Clock Performance for GNSS Positioning

Detection of Time Variable Gravity Signals using Terrestrial Clock Networks

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