Final Report Summary - HYDROGEN 1S-2S (Precision Spectroscopy of the 1S-2S Optical Clock Transition in Atomic Hydrogen) During the MC-ERG grant Dr. Alnis continued to work at the Max-Planck Institute of Quantum Optics (MPQ) on the long-lasting project of precision optical spectroscopy of hydrogen atoms. Hydrogen, the simples atom, is a corner stone of Quantum Mechanics, that can be calculated and measured with ever increasing precision to understand how the Nature works. The ERG grant project was proceeding as planned and all the proposed tasks were completed. Hydrogen - Deuterium isotopic shift frequency was measured 10 times more precisely compared to the previous best published value. A new improved measurement of the 1S-2S optical transition frequency with the precision of 4 parts in 10 to power 15 was made with a help of the invited mobile Cs fountain clock from Paris. Optical fiber link to German metrology institute PTB in Braunschweig was established allowing to send frequency stabilized laser light from the MPQ to PTB via a 900 km long link with record-breaking 19 digits of precision. This impressive result is possible to achieve only using the Nobel-prize-winning optical frequency comb technique pioneered by Prof. Thodor Hänsch. For comparison, microwave links allow to send frequencies only with 16 digits of precision. Fiber link project is of global importance as it allows to improve timekeeping between metrology laboratories with a potential to have faster telecommunications and better GPS navigation. Scientific results obtained during the ERG grant period resulted in 6 peer-reviewed journal papers. Financial resources were used for attending conferences, buying consumables for experiment and to finance the stay of short-time visiting scientists who participated in the project. MPQ Laser Spectroscopy Division website: http://www.mpq.mpg.de/~haensch/Hydrogen 1S-2S precision spectroscopy project website:http://www.mpq.mpg.de/~abeyer/hydrogen/
