Exploring Gravity with Optical Clocks



What is an optical clock?

Mission proposals


EU-FP7 project "SOC2"




Project "Space Optical Clocks"
in the ELIPS-3 program of ESA

In 2004, in response to an announcement of opportunity by ESA in the microgravity programme, a team of researchers from French, Italian and German research institutions proposed to operate lattice optical clocks on the ISS, as a natural succession of the mission “ACES” based on microwave clocks (2012). The lattice optical clocks´ frequencies are to be compared with those of ground clocks. The enhanced performance of 10-17 inaccuracy space optical clocks will lead to significantly improved science results in the fields of fundamental physics, time and frequency metrology and geodesy in and from space. The proposal was evaluated and selected in 2005.
Since 2007 a pre-phase-A project is being funded within the ELIPS-3 program of ESA, with co-funding by the German space agency DLR. This project project “Space Optical Clocks” (2007-2010) is aimed at the first step towards the high-accuracy clocks indicated above, namely stationary developing lattice optical clocks with inaccuracies at the 10-16 level and transportable clock subsystems.

Project teams and team leaders:
Team HHUD-I,II: Universität Düsseldorf (S. Schiller (coordinator), A. Görlitz)
Team PTB: Physikalisch-technische Bundesanstalt Braunschweig (U. Sterr)
Team SYRTE: Observatoire de Paris - Systemes de Reference Temps-Espace (P. Lemonde)
Team LENS: Universita di Firenze and European laboratory for Nonlinear Spectroscoy (LENS) (G. Tino)
Team ENS: Ecole Normale Superieure - Laboratoire Kastler Brossel (C. Salomon)

Figure 1: Principle of a lattice optical clock, based on laser-cooled atoms trapped in an optical lattice formed by interfering laser waves. (Figure courtesy of PTB)

Transportable Clocks and Subsystems (Status November 2009)

Figure 2: The transportable Yb clock system (2 m2), developed in the SOC project [Abou-Jaoudeh et al, Nevsky et al.]. Middle: the transportable compact Yb clock laser system (90 x 60 cm) with 2 Hz linewidth. The silvery box contains the reference cavity of the clock laser. Right: Yb atoms trapped in the 1st stage MOT (399 nm). In the apparatus, stable trapping of Yb in the 2nd stage has been obtained.

Figure 3: The cold Sr source breadboard (1.2 m x 0.9 m) developed within project SOC [Poli et al.]. Top: overall view; the two boxes in the foreground contain the 461 nm cooling laser, the black box the frequency distribution system. Bottom left: schematic of compact Sr oven and transverse cooling cell (10 cm long), right: Sr atomic beam in operation with atomic fluorescence.

Figure 4: Transportable Sr clock laser system with 10 Hz linewidth and 330 l volume developed in the project SOC [Legero et al.], to be integrated with the Sr system of shown in Fig. 2. Right: the clock transition of ultracold Sr atoms at 698 nm, obtained using the clock laser shown on the left. The line has an extremely large quality factor of 2 x 1013.

Current results

Results of the project as of October 2009
Results of team PTB
Results of team SYRTE
Results of team LENS
Results of team HHUD

Publications as of October 2009
Lisdat et al., “Collisional Losses, Decoherence, and Frequency Shifts in Optical Lattice Clocks with Bosons”, Phys. Rev. Lett. 103, 90801 (2009),
Lodewyck et al. “Non-destructive measurement of the transition probability in a Sr optical lattice clock”, Phys. Rev. A 79, 061401 (2009),
Nevsky et al., “A narrow-line-width external cavity quantum dot laser for high-resolution spectroscopy in the near-infrared and yellow spectral ranges”, Appl. Phys. 92, 501 (2008),
Westergaard et al, “Optimization of the Dick effect in an optical lattice clock”, Proc. EFTF - IFCS, p. 1187 (2009),
Poli et al, “An optical lattice clock based on bosonic Sr”, Proc. EFTF - IFCS, p. 347 (2009),
Poli et al, “A simplified optical lattice clock”, Appl Phys B 97, 27 (2009),
Legero, T., Lisdat, C., Winfred, J. S. R. V., Schnatz, H., Grosche, G., Riehle, F. & Sterr, U.,''Interrogation laser for a strontium lattice clock '', IEEE Trans. Instrum. Meas. 58, 1252-1257 (2009),
Vellore Winfred et al., “Determining the clock frequency shift due to collisions in a 1-D optical lattice clock with 88Sr”, Proc. EFTF - IFCS, p. 146 (2009),
Abou-Jaoudeh et al. “A Compact Source of Ultracold Ytterbium for an Optical Lattice Clock”, Proc. EFTF - IFCS, p. 756 (2009)
Millo et al. “Ultrastable lasers based on vibration insensitive cavities” Phys. Rev. A, 79, 053829 (2009).

Results of the project as of September 2008
Midterm Project Report (September 2008)