Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Atomic clock comparison via data highways

27.04.2012
In future, optical fibers could connect all optical atomic clocks within Europe – a milestone for various users of optical frequencies in research and industry
(Joint press release of Physikalisch-Technische Bundesanstalt, PTB, and the Max Planck Institute of Quantum Optics)

Optical atomic clocks measure time with unprecedented accuracy. However, it is the ability to compare clocks with one another that makes them applicable for high-precision tests in fundamental theory, from cosmology all the way to quantum physics. A clock comparison, i.e. a comparison of their optical frequencies, proved to be challenging so far as the few existing optical clocks around the world are not readily portable due to their complex nature.

Atomic clock comparison via data highways (artwork)
(Credit: MPQ + woogie-works Wien)

A team of researchers from the Physikalisch-TechnischeBundesanstalt (PTB) in Braunschweig and from the Laser Spectroscopy Division at the Max Planck Institute of Quantum Optics (MPQ) in Garching have now demonstrated an optical frequency transfer with high stability through a standard telecommunication optical fiber network (Science, April 27, 2012). The optical fiber connecting the two institutes was installed below ground and had a total length of 920 kilometres.

This demonstration enables the ability to compare optical clocks located far apart from each other and to transmit their stability to distant laboratories where the signals can be used for high precision experiments. At first, fundamental research will benefit from this, e.g. in the precise determination of natural constants, tests of the validity of Einstein’s theory of General Relativity or for predictions in quantum electrodynamics.

In an atomic clock the frequency that an atom emits when changing from one energy level to another defines the unit of time. The unit “second” is the interval occupied by 9,192,631,770 cycles of the microwave radiation corresponding to a transition of the cesium-133 isotope. The generation and dissemination of the second is statutory and in Germany the duty of the PTB. Optical atomic clocks use a frequency that is about 100,000 times higher compared to microwave clocks and thus slice time into much finer intervals. The latest generation of optical atomic clocks differs only in the 18th decimal place – that corresponds to one second in a time period of the age of the universe.

The researchers asked themselves the question of how well one can transfer optical frequencies over long distances. Well established techniques with the help of satellites reach a stability of 15 decimal places. While this is sufficient for microwave signals it is inadequate to exploit the full potential of optical atomic clocks. During the last years the MPQ/PTB researchers therefore investigated how to transmit an optical frequency through optical fibers. They were supported by the Cluster of Excellence QUEST at Leibniz Universität Hannover, the European Space Agency (ESA), the Deutsches Forschungsnetzwerk DFN as well as GasLine, a German consortium of gas distribution companies.

In the project described here the researchers feed light from a highly stable laser with a wavelength around 1.5 micrometers (near infrared) in the optical fiber connecting the laboratories at MPQ and PTB. The optical fiber is commonly used in telecommunication and has an attenuation minimum for light in the near infrared. However, to transmit a signal over a distance of almost 1,000 kilometers it has to be refreshed periodically. For this, novel optical amplifier units have been developed and installed along the entire path of the optical fiber.

Another problem to overcome is the falsification of the sent laser frequency due to mechanical, acoustic or thermal disturbances that originate from temperature fluctuations, traffic or construction work close to the optical fiber. New techniques allow for detection and compensation of these disturbances in such a way, that the entire 920 kilometers of optical fiber between Garching and Braunschweig is changing its optical length by less than one atomic diameter in one second. Hence, the delivered frequency of 194,353 Gigahertz at the remote laboratory differs by less than one ten thousandth from the fed frequency. To put the frequency transfer to the test, the researchers of the laser spectroscopy division used the signal from PTB’s primary cesium fountain clock for the spectroscopy of hydrogen at MPQ. By means of a frequency comb, this signal is compared to the optical phase of the transfer laser. They achieved a significantly higher accuracy as would have been possible with satellite-based frequency transfer.

Optical frequencies can now be disseminated with a quality that was only available locally at metrology institutes so far. The use of optical fiber infrastructure that the national research networks provide already today will in future allow for the connection of optical atomic clocks pan-European. In the same way as it is state-of-the-art that conventional alarm or station clocks receive the “correct time” from the PTB via the long-wave transmitter DCF77, the dissemination of an optical reference via optical fibers for the determination of wavelengths or frequencies of optical radiation will find wide application in research and industry.

Original publication:
K. Predehl, G. Grosche, S.M.F. Raupach, S. Droste, O. Terra, J. Alnis, Th. Legero, T.W. Hänsch, Th. Udem, R. Holzwarth, and H. Schnatz: A 920 km Optical Fiber Link for Frequency Metrology at the 19th Decimal Place. Science, April 27, 2012

Contact:
Dr. Harald Schnatz, Department 4.3 Quantum Optics and Unit of Length, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany, Phone: +49 531 592-4300, E-mail: harald.schnatz@ptb.de

Dr. Gesine Grosche, Department 4.3 Quantum Optics and Unit of Length, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany, Phone: +49 531 592 -4318, E-Mail: Gesine.Grosche@ptb.de

Katharina Predehl, Max Planck Institute of Quantum Optics, Hans-Kopfermann-Straße 1,85748 Garching, Germany, Phone: +49 89 32905-295, E-mail: katharina.predehl@mpq.mpg.de

Dr. Ronald Holzwarth, Max Planck Institute of Quantum Optics, Hans-Kopfermann-Straße 1, 85748 Garching, Germany, Phone: +49 89 32905-262, E-mail: ronald.holzwarth@mpq.mpg.de

Erika Schow | PTB
Further information:
http://www.ptb.de

More articles from Physics and Astronomy:

nachricht Breaking the optical bandwidth record of stable pulsed lasers
24.01.2017 | Institut national de la recherche scientifique - INRS

nachricht European XFEL prepares for user operation: Researchers can hand in first proposals for experiments
24.01.2017 | European XFEL GmbH

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: Scientists spin artificial silk from whey protein

X-ray study throws light on key process for production

A Swedish-German team of researchers has cleared up a key process for the artificial production of silk. With the help of the intense X-rays from DESY's...

Im Focus: Quantum optical sensor for the first time tested in space – with a laser system from Berlin

For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.

According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Breaking the optical bandwidth record of stable pulsed lasers

24.01.2017 | Physics and Astronomy

Choreographing the microRNA-target dance

24.01.2017 | Life Sciences

Spanish scientists create a 3-D bioprinter to print human skin

24.01.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>