Physikalisch-Technische Bundesanstalt (PTB)

PTB is the national institute for science and technology and the highest technical authority of the Federal Republic of Germany for the field of metrology and certain sectors of safety engineering. PTB comes under the auspices of the Federal Ministry of Economics and Technology. A fundamental task of PTB is to realize and maintain the legal units in compliance with the International System of Units (SI) and to disseminate them, above all within the framework of legal and industrial metrology.

The realization of time and frequency is among the most prominent activities of PTB. For nearly 50 years PTB has developed and operated primary cesium clocks and has contributed to the realisation of international atomic time TAI. PTB has long-standing experience in operating an Yb+ single-ion clock. PTB’s Time and Frequency Department presently operates two primary Cs fountain clocks and femtosecond frequency combs for absolute frequency and frequency ratio measurements.

At PTB in Brauschweig an ion trapping experiment for Th+ has been set up, including several tunable laser sources for resonance lines of Th+ and for two-photon excitation of the isomeric state. The laboratory is integrated into the infrastructure of the time and frequency department, including optical and microwave frequency standards. Staff includes experienced technicians and workshops for electronics, optics, mechanical and vacuum systems.



Division “Time and Frequency”


Publications of the PTB group

Experimental search for the low-energy nuclear transition in Th-229 with undulator radiation

A. Yamaguchi, M. Kolbe, H. Kaser, T. Reichel, A. Gottwald, and E. Peik
New J. Phys. 17, 053053 (2015)

Observation of an unexpected negative isotope shift in 229Th+ and its theoretical explanation

M.V. Okhapkin, D.M. Meier, E. Peik, M.S. Safronova, M.G. Kozlov, and S.G. Porsev
arXiv:1505.05818 and Phys. Rev. A 92, 020503 (2015)

Nuclear clocks based on resonant excitation of gamma-transitions

Ekkehard Peik and Maxim Okhapkin
arXiv:1502.07322 and Comptes Rendus Physique 16, 5 (2015)

Energy levels of Th+ between 7.3 and 8.3 eV

O. A. Herrera-Sancho, N. Nemitz, M. V. Okhapkin, and E. Peik
Phys. Rev. A 88, 012512 (2013)

Laser ablation loading of a radiofrequency ion trap, K. Zimmermann, M. V. Okhapkin

M. V. Okhapkin, O. A. Herrera Sancho, and E. Peik
Appl. Phys. B 107, 883 (2012)

Two-photon laser excitation of trapped 232Th+ ions via the 402-nm resonance line

O. A. Herrera-Sancho, M. V. Okhapkin, K. Zimmermann, Chr. Tamm, E. Peik, A. V. Taichenachev, V. I. Yudin, and P. Głowacki
Phys. Rev. A 85, 033402 (2012)

Excitation of the isomeric 229mTh nuclear state via an electronic bridge process in 229Th+

S. G. Porsev, V. V. Flambaum, E. Peik, and Chr. Tamm
Phys. Rev. Lett. 105, 182501 (2010)

Nuclear laser spectroscopy of the 3.5 eV transition in Th-229

E. Peik and Chr. Tamm
Europhys. Lett. 61, 181 (2003)

Contact persons

Ekkehard Peik


  • since 2007 Head of Department Time and Frequency at PTB
  • since 2003 Head of Working Group Optical Clocks at PTB
  • 2001           Scientist in the Time Unit Laboratory at PTB
  • 1994 – 1996 Marie-Curie-Fellow at Ecole normale supérieure, Paris
  • 1993              PhD, Ludwig-Maximilians-Universität München
  • 1982-1988   Study of physics at the universities of Göttingen and München


  • Nuclear laser spectroscopy of the 3.5 eV transition in Th-229
    E. Peik, Chr. Tamm, Europhys. Lett. 61, 181-186 (2003)
  • Sub-hertz optical frequency comparisons between two trapped 171Yb+ ions
    T. Schneider, E. Peik, Chr. Tamm, Phys. Rev. Lett. 94, 230801 (2005)
  • Limit on the present temporal variation of the fine structure constant
    E. Peik, B. Lipphardt, H. Schnatz, T. Schneider, Chr. Tamm, S. G. Karshenboim,
    Phys. Rev. Lett. 93, 170801 (2004)
  • High-accuracy optical clock based on the octupole transition in 171Yb+
    N. Huntemann, M. V. Okhapkin, B. Lipphardt, Chr. Tamm, E. Peik
    Phys. Rev. Lett. 108, 090801 (2012)
  • Optical atomic clocks
    A. D. Ludlow, M. M. Boyd, Jun Ye, E. Peik, P. O. Schmidt
    Rev. Mod. Phys. 87, 637 (2015)

Maksim Okhapkin


  • 1991 – 2008    Researcher, Senior Researcher in Institute of laser physics (ILP SB RAS), Novosibirsk
  • 1995          Ph.D. in Laser Physics
  • 2001 – 2002    Visiting Scientist in Max-Plank Institut für Quantenoptik
  • 2003 – 2008   Visiting Scientist in Institut of Experimentalphysik Universität Düsseldorf
  • since 2008     Researcher in PTB, Braunschweig
  • 2012       Habilitation in Laser Physics
  • Publications

  • Test of constancy of speed ol light with rotating cryogenic optical resonators. Phys. Rev. A, 2005, 71, 050101 (2005)
  • Atomic Clocks with Suppressed Blackbody Radiation Shift. Phys. Rev. Lett., 107, 030801 (2011)
  • High-Accuracy Optical Clock Based on the Octupole Transition in 171Yb+. Phys. Rev. Lett. 108, 090801 (2012)
  • Two-photon laser excitation of trapped 232Th+ ions via the 402-nm resonance line. Phys. Rev. A 85, 033402 (2012)
  • Generalized Ramsey Excitation Scheme with Suppressed Light Shift. Phys. Rev. Lett. 109, 213002 (2012)
  • Energy levels of Th+ between 7.3 and 8.3 eV. Phys. Rev. A 88, 012512 (2013)