Optical Clock Networks

Optical Clock Networks

Establish fiber-based optical clock networks, improve optical clocks and frequency transfer techniques, exploit chronometric levelling for geodesy.


  • Optical clocks:
    • Bring the inaccuracy and instability stationary optical clocks below the level of 1 part in 1018
    • Bring today’s optical clocks from prototype status to more reliable, rugged, transportable and miniaturized devices
    • Investigate compound clocks
    • Improve transportable Sr clock
    • Test new Al+ logic clock
  • Frequency Transfer:
    • Consolidate inaccuracy and instability of interferometric fibre links in the 10-19to 10-20 regime
    • Investigate link non-reciprocality and relativistic effects
    • Investigate coherent free-space frequency transfer
  • CRC 1464 TerraQ:
    • Establish chronometric levelling with cm resolution as routine tool for geodesy
    • Transfer lab-based link performance to robust in-field systems
    • Identify locations and applications for chronometric levelling
  • Other:
    • Coordinate measurement campaigns and results
    • Investigate new network schemes


  • Grosche: Frequency transfer techniques
  • Lisdat: Stationary and transportable Sr optical lattice clocks
  • Schmidt: Transportable Al+ clocks
  • Müller: Relativistic geodesy
  • Lämmerzahl: Relativistic geodesy

Scientific Output

  • Publications

    Filzinger M, Dörscher S, Lange R, Klose J, Steinel M, Benkler E et al. Improved limits on the coupling of ultralight bosonic dark matter to photons from optical atomic clock comparisons. 2023 Jan 9.


    Bondza S, Lisdat C, Kroker S, Leopold T. Two-Color Grating Magneto-Optical Trap for Narrow-Line Laser Cooling. Physical review applied. 2022 Apr 1;17(4). 044002.


    Herbers S, Häfner S, Dörscher S, Lücke T, Sterr U, Lisdat C. Transportable clock laser system with an instability of 1.6 × 10-16. Optics letters. 2022 Okt 15;47(20):5441-5444.


    Schioppo M, Kronjäger J, Silva A, Ilieva R, Paterson JW, Baynham CFA et al. Comparing ultrastable lasers at 7 × 10−17 fractional frequency instability through a 2220 km optical fibre network. Nature Communications. 2022 Jan 11;13(1). 212.


    Dörscher S, Huntemann N, Schwarz R, Lange R, Benkler E, Lipphardt B et al. Optical frequency ratio of a 171Yb+ single-ion clock and a 87Sr lattice clock. METROLOGIA. 2021 Feb;58(1). 015005.


    Pelzer L, Dietze K, Kramer J, Dawel F, Krinner L, Spethmann N et al. Tailored optical clock transition in 40Ca+. Measurement: Sensors. 2021 Dez;18. 100326.


    Micke P, Leopold T, King SA, Benkler E, Spieß LJ, Schmöger L et al. Coherent laser spectroscopy of highly charged ions using quantum logic. NATURE. 2020 Feb 6;578:60-65.




    Porsev SG, Safronova UI, Safronova MS, Schmidt PO, Bondarev AI, Kozlov MG et al. Optical clocks based on the Cf15+ and Cf17+ ions. Physical Review A. 2020 Jul 6;102(1). 012802.




    Schulte M, Lisdat C, Schmidt PO, Sterr U, Hammerer K. Prospects and challenges for squeezing-enhanced optical atomic clocks. Nature Communications. 2020 Nov 24;11(1). 5955.


    Wu H, Müller J, Lämmerzahl C. Clock networks for height system unification: A simulation study. Geophysical journal international. 2018 Nov 28;216(3):1594-1607.


TG Members

  • Involved Members and their Relevant Expertise
    Members Institution Relevant Expertise
    Christian Lisdat, Leader PTB Sr Optical Lattice Clock
    Gesine Grosche PTB Free-Space Frequency Transfer; Frequency Transfer Techniques
    Alexander Kuhl PTB Free-Space Frequency Transfer
    Chetan Vishwakarma PTB Sr Optical Lattice Clock
    Jürgen Müller LUH Relativistic Geodesy; LLR Relativity Test; Application of Quantum Gravimetry
    Piet O. Schmidt PTB / LUH Quantum Logic Spectroscopy of Highly Charged Ions; Al+ Clock
    Stephan Hannig PTB Transportable Al+ Clock
    Claus Lämmerzahl ZARM Quantum Sensors in Free Fall; Relativistic Geodesy; Quantum Objects in Gravity
    Steffen Sauer TUBS Ultra-stable cavities for optical clocks
    Tara Liebisch PTB Clock Network Schemes
    Ernst M. Rasel LUH Quantum Gravimeters; Atom-Chip Based Gravimeters and Inertial Sensors
    Stefanie Kroker PTB / Complex Coupled High Index Waveguide Arrays; Photonic Nanomaterials in the Strong Optomechanical Coupling Regime
    Dennis Philipp ZARM General Relativity, relativistic geodesy
    Eva Hackmann ZARM General Relativity, relativistic geodesy
    Steffen Schön IfE GNSS Frequency Transfer
    Sebastian Koke PTB Frequency Transfer Techniques
    Jingxian Ji PTB Free-Space Frequency Transfer
    Jaffar Kadum PTB Frequency Transfer, Fibre Brillouin Amplifiers
    Akbar Shabanloui LUH Gravity field modelling, clock networks, height systems, precise satellite orbit determination