ForschungTopical Groups
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


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.


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 Dez 1;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 Jan 29;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;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.


Involved QF Members
Members Institution Relevant Expertise
Christian Lisdat, LeaderPTBSr Optical Lattice Clock
Gesine GroschePTBFree-Space Frequency Transfer; Frequency Transfer Techniques
Alexander KuhlPTBFree-Space Frequency Transfer
Thomas WaterholterPTBFrequency Transfer Techniques
Chetan VishwakarmaPTBSr Optical Lattice Clock
Jürgen MüllerLUHRelativistic Geodesy; LLR Relativity Test; Application of Quantum Gravimetry
Piet O. SchmidtPTB / LUHQuantum Logic Spectroscopy of Highly Charged Ions; Transportable Al+ Clock
Stephan HannigPTBTransportable Al+ Clock
Claus LämmerzahlZARMQuantum Sensors in Free Fall; Relativistic Geodesy; Quantum Objects in Gravity
Steffen SauerTUBSUltra-stable cavities for optical clocks
Tara LiebischPTBClock Network Schemes
Ernst M. RaselLUHQuantum Gravimeters; Atom-Chip Based Gravimeters and Inertial Sensors
Stefanie KrokerPTB / LUHComplex Coupled High Index Waveguide Arrays; Photonic Nanomaterials in the Strong Optomechanical Coupling Regime
Dennis PhilippZARMGeneral Relativity, relativistic geodesy
Eva HackmannZARMGeneral Relativity, relativistic geodesy
Steffen SchönIfEGNSS Frequency Transfer
Sebastian KokePTBFrequency Transfer Techniques
Jingxian JiPTBFree-Space Frequency Transfer
Jaffar KadumPTBFrequency Transfer, Fibre Brillouin Amplifiers
Dominika FimLUHMg Optical Lattice clock
Akbar ShabanlouiLUHGravity field modelling, clock networks, height systems, precise satellite orbit determination