ZusammenfassungDas Wasserstoffatom (H) stellt ein einzigartiges System für Tests der Quanten-Elektrodynamik dar. Aufgrund seiner einfachen Struktur und genauen theoretischen Beschreibung liefert es außerdem wichtige Daten für die Bestimmung der RydbergKonstante R ∞ und des Proton-Ladungsradius r p im Rahmen der globalen Anpassung fundamentaler Konstanten durch das Committee on Data for Science and Technology (CODATA). Im Jahre 2010 kam das sogenannte "proton size puzzle" auf, eine Diskrepanz von sieben Standardabweichungen zwischen CODATA und dem zehn mal genauer gemessenen Wert von r p in myonischem Wasserstoff (µ -p, [1, 2] AbstractThe hydrogen atom (H) is a unique system for tests of quantum electrodynamics (QED). Due to its simplicity and accurate theoretical description, it also provides key input data for the determination of the Rydberg constant R ∞ and the proton root mean square (r.m.s.) charge radius r p in the global adjustment of fundamental constants [4] by the Committee on Data for Science and Technology (CODATA). In the year 2010, the "proton size puzzle" emerged, which refers to a discrepancy of seven standard deviations between CODATA and a ten times more accurate measurement of r p in muonic hydrogen (µ -p, [1, 2]). Proposed solutions for this puzzle cover a wide range of scenarios, up to physics beyond the standard model [3]. This thesis reports on a novel scheme for high resolution spectroscopy of dipole allowed 2S -nP transitions in H, using a cryogenic beam of H atoms that are prepared in the meta-stable 2S F =0 1/2 state by state selective optical excitation. Such measurements can be used for a new determination of R ∞ and r p from H spectroscopy, shedding new light on the "proton size puzzle". The scheme has been applied to spectroscopy of the 2S-4P transition first, yielding: These values are as accurate as the ones determined from the aggregate world data of precision H spectroscopy (15 measurements) that enter the CODATA adjustment. While a discrepancy of 3.8 combined standard deviations is found to the latter, the presented results agree with the measurements in µ -p. The 2S-4P experiment is essentially unaffected by the systematic effects dominating the uncertainties in the previous most precise determinations of R ∞ using dipole forbidden two photon transitions in H. Instead, the main systematic effects are the first order Doppler effect, canceled by the use of an active fiber-based retroreflector (AFR) developed in this thesis, and line shape distortions due to quantum interference (QI) of neighboring atomic resonances. The latter effect has come to the attention of the precision spectroscopy community only recently [8,9]. Apparent QI line shifts have been studied experimentally, yielding the first direct observation in precision spectroscopy of largely separated atomic resonances. The observed shifts of up to ± 51 kHz are six times larger than the proton size discrepancy for the 2S-4P transition. They are brought under control by a suitable line shape model function, derived and...

We have measured the 1S-2S transition frequency in atomic hydrogen via two-photon spectroscopy on a 5.8 K atomic beam. We obtain f(1S-2S) = 2,466,061,413,187,035 (10)  Hz for the hyperfine centroid, in agreement with, but 3.3 times better than the previous result [M. Fischer et al., Phys. Rev. Lett. 92, 230802 (2004)]. The improvement to a fractional frequency uncertainty of 4.2 × 10(-15) arises mainly from an improved stability of the spectroscopy laser, and a better determination of the main systematic uncertainties, namely, the second order Doppler and ac and dc Stark shifts. The probe laser frequency was phase coherently linked to the mobile cesium fountain clock FOM via a frequency comb.

We have remeasured the absolute 1S-2S transition frequency νH in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of (−29 ± 57) Hz for the drift of νH with respect to the ground state hyperfine splitting νCs in 133 Cs. Combining this result with the recently published optical transition frequency in 199 Hg + against νCs and a microwave 87 Rb and 133 Cs clock comparison, we deduce separate limits onα/α = (−0.9 ± 2.9) × 10 −15 yr −1 and the fractional time variation of the ratio of Rb and Cs nuclear magnetic moments µ Rb /µCs equal to (−0.5 ± 1.7) × 10 −15 yr −1 . The latter provides information on the temporal behavior of the constant of strong interaction. PACS numbers: 06.30.Ft, 06.20.Jr, 32.30.Jc In the era of a rapid development of precision experimental methods, the stability of fundamental constants becomes a question of basic interest. Any drift of non-gravitational constants is forbidden in all metric theories of gravity including general relativity. The basis of these theories is Einstein's Equivalence Principle (EEP) which states that weight is proportional to mass, and that in any local freely falling reference frame, the result of any non-gravitational experiment must be independent of time and space. This hypothesis can be proven only experimentally as no theory predicting the values of fundamental constants exists. In contrast to metric theories, string theory models aiming to unify quantum mechanics and gravitation allow for, or even predict, violations of EEP. Limits on the variation of fundamental constants might therefore provide important constraints on these new theoretical models.A recent analysis of quasar absorption spectra with redshifted UV transition lines indicates a variation of the fine structure constant α = e 2 /4πε 0 c on the level of ∆α/α = (−0.54 ± 0.12) × 10 −5 for a redshift range (0.2 < z < 3.7)[1]. On geological timescales, a limit for the drift of α has been deduced from isotope abundance ratios in the natural fission reactor of Oklo, Gabon, which operated about 2 Gyr ago. Modeling the processes which have changed the isotope ratios of heavy elements gives a limit of ∆α/α = (−0.36 ± 1.44) × 10 −8 [2]. In these measurements, the high sensitivity to the time variation of α is achieved through very long observation times at moderate resolution for ∆α. Therefore, they are vulnerable to systematic effects [3].Laboratory experiments can reach a 10 −15 accuracy within years with better controlled systematics. This type of experiment is typically based on repeated absolute frequency measurements, i.e. comparison of a transition frequency with the reference frequency of the ground state hyperfine transition in Contributions from weak, electromagnetic, and strong interactions can be disentangled by combining several frequency measurements possessing a different sensitivity to the fundamental constants. In this letter, we deduce separate stringent limits for the drifts of the fine structure constant α, µ Cs /µ B and µ Rb /µ Cs ...

We achieved a 0.5 Hz optical beat note linewidth with ϳ0.1 Hz/ s frequency drift at 972 nm between two external cavity diode lasers independently stabilized to two vertically mounted Fabry-Pérot ͑FP͒ reference cavities with a finesse of 400 000. Vertical FP reference cavities are suspended in midplane such that the influence of vertical vibrations to the mirror separation is significantly suppressed. This makes the setup virtually immune for vertical vibrations that are more difficult to isolate than horizontal vibrations. To compensate for thermal drifts the FP spacers are made from ultralow-expansion ͑ULE͒ glass which possesses a zero linear expansion coefficient. A design using Peltier elements in vacuum allows operation at an optimal temperature where the quadratic temperature expansion of ULE could be eliminated as well. The measured linear drift of such ULE FP cavity of 63 mHz/s was due to material aging and the residual frequency fluctuations were less than Ϯ20 Hz during 16 h of measurement. Some part of the temperature-caused drift is attributed to the thermal expansion of the mirror coatings. Thermally induced fluctuations that cause vibrations of the mirror surfaces limit the stability of our cavity. By comparing two similar laser systems we obtain an Allan instability of 2 ϫ 10 −15 between 0.1 and 10 s averaging time, which is close to the theoretical thermal noise limit.