Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

1400 km of optical fiber connect optical clocks in France and Germany

09.08.2016

Best comparison worldwide between distant optical clocks confirms excellent quality of the connection

In the past few years, optical atomic clocks have made spectacular progress, becoming 100 times more precise than the best caesium clocks. So far, their precision has been available only locally, since frequency transfer via satellite cannot provide sufficient resolution.


This image shows the metrological optical fiber link between LNE-SYRTE in Paris, France and PTB in Braunschweig, Germany, connected in Strasbourg. The overall link length is 1400 km.

(Graphic: PTB)

This has recently changed thanks to a new direct optical connection between France and Germany, established by joint work of Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Systèmes de Référence Temps-Espace (LNE-SYRTE) in Paris, and Laboratoire de Physique des Lasers (LPL) in Villetaneuse. High-precision optical frequencies can now "travel" through a 1400 km optical fibre link between LNE-SYRTE and PTB, where the most precise optical clocks in Europe are operated.

The first comparison between the French and German optical strontium clocks confirms the high expectations placed in the connection. It represents the first frequency comparison of its kind across national borders: the fully independent clocks agree with an unrivalled fractional uncertainty of 5 × 10e-17.

The scientists report their results in the current issue of Nature Communications. Their successful collaboration is a first step towards a European network of optical clocks providing ultrastable high-precision optical reference signals to diverse users. This will benefit various research areas, with applications in fundamental physics, astrophysics and geoscience.

Comparisons of clocks at the highest resolution allow a wide range of very sensitive physical experiments, for instance, the search for time-dependent changes of fundamental constants. Also, the apparent rate of a clock depends on the local gravitational potential: comparing two clocks measures the gravitational redshift between them, and thus yields their height difference.

Such measurements provide data points for the geodetic reference surface, the so-called "geoid". This research approach is pursued jointly by physicists and geodesists in the Collaborative Research Centre 1128 ("geo-Q") of the German Science Foundation (DFG).

Today's most precise atomic clocks are based on optical transitions. Such optical clocks can provide a stable frequency with a fractional uncertainty of only a few 10e-18. This is approximately 100 times more precise than the best caesium fountain clocks, which realize the unit of time, the SI second. However, clock comparisons using frequency transfer via satellites are limited to a frequency resolution near 10e-16.

For this reason, scientists from PTB and from two French institutes in Paris (Systèmes de Référence Temps-Espace, LNE-SYRTE and Laboratoire de Physique des Lasers, LPL) have been working for several years on an optical fibre connection between the German and the French national metrology institutes, PTB and LNE-SYRTE. The 1400 km long link is now completed: it is based on standard telecom optical fibres and optical power losses of 200 dB (10e20) are compensated by means of specially developed amplifiers. Furthermore, frequency fluctuations added during the propagation along the fibre are actively suppressed by up to 6 orders of magnitude. This allows the transmission of optical signals with very high stability.

The German part of the link uses commercially rented optical fibres and facilities of the German National Research and Education Network (DFN). The French part of the link uses the network for Education and Research RENATER, operated by the GIP RENATER. Approximately midway, signals from LNE-SYRTE and PTB meet at the IT Centre of the University of Strasbourg, so that the clocks of the two institutes can be compared there. The partners involved are: Physikalisch-Technische Bundesanstalt (PTB), Institut für Erdmessung (IfE) der Leibniz-Universität Hannover, Laboratoire de Physique des Lasers (Université Paris 13/Sorbonne Paris Cité/CNRS), LNE-SYRTE (Observatoire de Paris/PSL Research University/CNRS/Sorbonne Université/UPMC Univ. Paris 6/Laboratoire National de Métrologie et d'Essais), and the GIP RENATER (CNRS, CPU, CEA, INRIA, CNES, INRA, INSERM, ONERA, CIRAD, IRSTEA, IRD, BRGM, and the MESR).

In a first comparison using the most stable optical clocks of PTB and LNE-SYRTE, the link lived up to the high expectations. Frequency fluctuations between the two strontium optical lattice clocks of less than 2×10e-17 were observed after only 2000 s of averaging time, and the link itself supports fast clock comparisons with an uncertainty below 10e-18. As both clocks are based on the same atomic transition they should theoretically supply exactly the same frequency - except for the gravitational redshift due to the 25 m difference in height between the two institutes. This was indeed confirmed within the clocks' combined uncertainty of 5×10e-17, corresponding to a height uncertainty of only 0.5 m.

The partners consider this successful collaboration the first important step towards a European network of optical clocks connected by optical fibre links which could successively be joined by the optical clocks of further European metrology institutes. This should place them in a leading role for the dissemination of optical reference frequencies. As a long-term perspective, such a network may provide ultrastable high-precision optical reference signals (like those currently available from metrology institutes) to a broad range of users. Various research areas will benefit from this, including fundamental research (to test the fundamental laws of physics), geoscience and, last but not least, metrology. This work also clears the path towards a redefinition of the unit of time, the SI second, through regular international comparisons of optical clocks.

###

Contacts for the strontium clocks:

Dr. Christian Lisdat, PTB Working Group 4.32 Optical Lattice Clocks,
phone: +49 (0)531 592-4320,
e-mail: christian.lisdat@ptb.de

Dr. Jérôme Lodewyck, LNE-SYRTE, CNRS
phone: +33 (0) 1 40 51 22 24,
e-mail: jerome.lodewyck@obspm.fr

Contacts for the optical fibre link:

Dr. Gesine Grosche, PTB Working Group 4.34 Frequency Dissemination with Fibres,
phone: +49 (0)531 592-4340,
e-mail: gesine.grosche@ptb.de

Dr. Paul-Eric Pottie, LNE-SYRTE
phone: + 33 (0) 1 40 51 22 22,
e-mail: paul-eric.pottie@obspm.fr

Scientific publication

C. Lisdat et al.: A clock network for geodesy and fundamental science. Nature Comms. 7:12443 (2016), DOI 10.1038/NCOMMS12443

Dr. Christian Lisdat | EurekAlert!

Further reports about: CNRS PTB gravitational optical clocks optical fiber optical fibre

More articles from Physics and Astronomy:

nachricht Breakthrough with a chain of gold atoms
17.02.2017 | Universität Konstanz

nachricht New functional principle to generate the „third harmonic“
16.02.2017 | Laser Zentrum Hannover e.V.

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Biocompatible 3-D tracking system has potential to improve robot-assisted surgery

17.02.2017 | Medical Engineering

Real-time MRI analysis powered by supercomputers

17.02.2017 | Medical Engineering

Antibiotic effective against drug-resistant bacteria in pediatric skin infections

17.02.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>