Intercontinental comparison of optical atomic clocks through very long baseline interferometry

Pizzocaro, Marco; Sekido, Mamoru; Takefuji, Kazuhiro; Ujihara, Hideki; Hachisu, Hidekazu; Nemitz, Nils; Tsutsumi, Masahiro; Kondo, Tetsuro; Kawai, Eiji; Ichikawa, Ryuichi; Namba, Kunitaka; Okamoto, Yoshihiro; Takahashi, Rumi; Komuro, J.; Clivati, Cecilia; Bregolin, Filippo; Barbieri, Piero; Mura, Alberto; Cantoni, E.; Cerretto, Giancarlo; Levi, Filippo; Maccaferri, G.; Roma, Mauro; Bortolotti, C.; Negusini, M.; Ricci, R.; Zacchiroli, G.; Roda, J.; Leute, J.; Petit, Gérard; Perini, Federico; Calonico, Davide; Ido, T.

doi:10.1038/s41567-020-01038-6

Cited by 39 publications

(25 citation statements)

References 74 publications

(91 reference statements)

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“…NHS VLBI observations with the 2.4 m antenna pair revealed baseline repeatability at the same level as IVS-R1 and R4 legacy S/X-VLBI observations. The system also enabled longdistance frequency comparisons where the transportable node stations are near the standards to be compared (Pizzocaro et al 2021). Here, we evaluated the absolute delay uncertainty over a 8780 km baseline between the 2.4 m antenna pair to be less than ps, except for a yet-to-becalibrated fixed timing offset.…”

Section: Resultsmentioning

confidence: 99%

“…Performance was initially tested over short baselines in Japan. In the next stage, intercontinental experiments were conducted for the frequency comparison between two optical lattice clocks reported in Pizzocaro et al (2021). ual scans was in the range of 10-40 s, and 33.6 scans/h were recorded on average.…”

Section: Node-hub Vlbi Experimentsmentioning

confidence: 99%

“…Several hydrogen maser frequency references were used as flywheels to bridge interruptions in operation of clocks and links. More details on the frequency link are described in a separate publication (Pizzocaro et al 2021). VLBI sessions were conducted from October 2018 to July 2019 and are listed in Table 4.…”

Section: Observationsmentioning

confidence: 99%

“…A series of sessions during October 2018-February 2019 focused on comparing optical atomic frequency standards to a fractional uncertainty of only a few parts in 10 16 , to which the VLBI link contributed less than 10 −16 (Pizzocaro et al 2021). Since the duration of the individual VLBI sessions was limited by data recording disk capacity, experiments from 30 May to 18 July 2019 explored the feasibility of intermittent operation.…”

Section: Observationsmentioning

confidence: 99%

“…For application to geodesy and clock frequency comparisons, constant delay-offsets as might be introduced by, e.g., signal distribution or electronic propagation delays do not affect the results. The parameters in the following sections represent the clock comparisons between Koganei and Torino (Pizzocaro et al 2021) over the period between 14 October 2018 and 14 February 2019. Table 6 gives an overview of the contributions discussed here, with an overall group delay instability of 27.5 ps under favorable conditions.…”

Section: Uncertainty Of the Group Delay Observablementioning

confidence: 99%

See 4 more Smart Citations

A broadband VLBI system using transportable stations for geodesy and metrology: an alternative approach to the VGOS concept

Sekido

Takefuji

Ujihara

et al. 2021

J Geod

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We have developed a broadband VLBI (very long baseline interferometry) system inspired by the concept of the VLBI Global Observing System (VGOS). The new broadband VLBI system was implemented in the Kashima 34 m antenna and in two transportable stations utilizing 2.4 m diameter antennas. The transportable stations have been developed as a tool for intercontinental frequency comparison but are equally useful for geodesy. To enable practical use of such small VLBI stations in intercontinental VLBI, we have developed the procedure of node-hub style VLBI: In joint observation with a large, high sensitivity ‘hub’ antenna, the closure delay relation provides a virtual delay observable between ‘node’ stations. This overcomes the limited sensitivity of the small diameter node antennas, while error sources associated with large diameter antennas, such as gravitational deformation and delay changes in necessarily long signal cables, are eliminated. We show that this scheme does not result in an increased sensitivity to radio source structure if one side of the baseline triangle is kept short. We have performed VLBI experiments utilizing this approach over both short range and intercontinental distance. This article describes the system components, signal processing procedure, experiment, and results in terms of baseline repeatability. Our measurements reveal signatures of structure effects in the correlation amplitude of several of the observed radio sources. We present a model of the frequency-dependent source size for 1928+738 derived from correlation amplitude data observed in four frequency bands.

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Section: Resultsmentioning

confidence: 99%

Section: Node-hub Vlbi Experimentsmentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%

Section: Uncertainty Of the Group Delay Observablementioning

confidence: 99%

See 3 more Smart Citations

A broadband VLBI system using transportable stations for geodesy and metrology: an alternative approach to the VGOS concept

Sekido

Takefuji

Ujihara

et al. 2021

J Geod

Self Cite

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The Photodetection of Ultrashort Optical Pulse Trains for Low Noise Microwave Signal Generation

Quinlan

2023

Laser & Photonics Reviews

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Electrical signals derived from optical sources have achieved record‐low levels of phase noise, and have demonstrated the highest frequency stability yet achieved in the microwave domain. Attaining such ultrastable phase and frequency performance requires high‐fidelity optical‐to‐electrical conversion, typically performed via a high‐speed photodiode. This paper reviews characteristics of the direct photodetection of optical pulses for the intent of generating high power, low phase noise microwave signals from optical sources. The two most popular types of photodiode detectors used for low noise microwave generation are discussed in terms of electrical pulse characteristics, achievable microwave power, and photodetector nonlinearities. Noise sources inherent to photodetection, such as shot noise, flicker noise, and photocarrier scattering are reviewed, and their impact on microwave phase fidelity is discussed. General guidelines for attaining the lowest noise possible from photodetection that balances power saturation, optical amplification, and amplitude‐to‐phase conversion are also presented.

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Precise Time and Frequency in Geodesy

Defraigne

2022

Encyclopedia of Geodesy

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Intercontinental comparison of optical atomic clocks through very long baseline interferometry

Cited by 39 publications

References 74 publications

A broadband VLBI system using transportable stations for geodesy and metrology: an alternative approach to the VGOS concept

A broadband VLBI system using transportable stations for geodesy and metrology: an alternative approach to the VGOS concept

The Photodetection of Ultrashort Optical Pulse Trains for Low Noise Microwave Signal Generation

Precise Time and Frequency in Geodesy

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