1. 1S-2S transition frequency measurements in atomic hydrogen N. Kolachevsky MPQ

2. Hydrogen Theory Frequency comb Mobile fountain clock Optical fiber link Christian Parthey Arthur Matveev Janis Alnis Axel Beyer Nikolai Kolachevsky Randolf Pohl Thomas Udem Theodor Häncsh Tobias Wilken Birgitta Benhardt Ulrich Jents Brett Altschul Michel Abgrall Daniele Rovera Christophe Salomon Philippe Laurent Katharina Predehl Stefan Droste Ronald Holzwarth Harald Schnatz Gesine Grosche Thomas Legero Stefan Weyers The Team

4. Hydrogen Levels (n = 1, 2) Bohr DiracQED Hyperfine structure

5. Hydrogen Levels (n = 1, 2) Bohr DiracQED Hyperfine structure

6. Energy levels Schrödinger: Schrödinger in atomic units: Dirac in atomic units: QED: recoil: finite nuclear size:

7. Talk by Randolf Pohl, Monday

10. N. Kolachevsky et al., Opt. Lett. 36, 4299 (2011)

11. 972 nm diode laser with a 20 cm long external resonator and intra-cavity EOM Beat note diode - dye laser Master oscillator 8-photon process => at 972 nm

12. FP at zero expansion temperature Typical drift @ T c is of 50 mHz/s Janis Alnis

13. FP1-FP2 Allan deviation Thermal noise limit

14. Fiber Laser I(  )  Hydrogen maser Stabilized optical fiber FP5 Distribution amplifier Wenzel Chain  4  5  5 Wenzel Chain  4  5  5 PLL I(  )  temperature stabilized 1GHz Comb-comb comparison setup 250 MHz system 100 MHz system 1542 nm

15. Comb-comb comparison: result

23. In zero magnetic field B: known precisely to be measured 1420 405.751 768(1) Hz Optical measurement of the 2S HFS

24. Frequency [Hz] Uncertainty [Hz] Averaged interval frequency 177 556 835.36.2 Line shape / temperature 02 AC Stark shift 01.2 DC Stark shift 1 Magnetic fields 00.5 Total177 556 834.36.7 2s HFS result - 2009 N. Kolachevsky et al., PRL 102, 213002 (2009) FFK‘2009

31. C.G. Parthey et al., PRL 107, 203001 (2011)

34. 34 LNM-SYRTE, Observatoire de Paris Mobile fountain clock

43. Thank you for attention! C.G. Parthey et al., PRL 107, 203001 (2011)