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Physikalisch-Technische Bundesanstalt

StructureDiv. 4 Optics > 4.4 Time and Frequency
Time and Frequency
Department 4.4


The main task of the department time and frequency is the realization and dissemination of the base unit time (second) and the dissemination of the legal time in the Federal Republic of Germany.

The second is defined as the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

For the realization and dissemination of the unit of time, the department develops and operates caesium atomic clocks as primary standards of time and frequency. In the past decades, these, as the worldwide most accurate atomic clocks, have contributed to the international atomic time scale (TAI) and represent the basis for the legal time in Germany. Dissemination of the legal time to the various users in industry, society, and research is performed via satellite, via a low frequency transmitter DCF77 and via an internet- and telephone service.

The department participates in the tests for the future European satellite navigation system „Galileo“.

Presently the primary clocks realizing the time unit are augmented by Cs clocks with laser cooled atoms („Cs-fountain clocks“) whose accuracy presently exceeds the clocks with thermal beams by a factor of 10 (frequency uncertainty of 1 . 10-15). 

Future atomic clocks will most likely be based on atomic transitions in the optical range of single stored ions. Such standards are presently being developed along with the means to relate their optical frequencies without errors to radio-frequencies or 1 second pulsed. The department coordinates as well the project "High-accuracy optical clocks with trapped ions", which is financed by the EU in the frame of EMRP.

As one may expect transitions in nuclei of atoms to be better shielded from environmental perturbations than electron-shell transitions which have been used so far as atomic clock references, the department attempts to use an optical transition in the nucleus of 229Th for a future generation of atomic clocks.

The work of the department is complemented by research precision time transfer techniques, funded in the frame of several European projects and by national funding by Deutsche Forschungsgemeinschaft.


Head of Department Dr. Ekkehard Peik
Phone: +49-531 592-4400
E-Mail: ekkehard.peik@ptb.de

Secretariat Eva-Maria Berber
Phone: +49-531 592-4401
Fax: +49-531 592-4479
E-Mail: eva-maria.berber@ptb.de 

Address Physikalisch-Technische Bundesanstalt
Fachbereich 4.4
Bundesallee 100
38116 Braunschweig

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