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 performed two-photon ultraviolet direct frequency comb spectroscopy on the 1S-3S transition in atomic hydrogen to illuminate the so-called proton radius puzzle and to demonstrate the potential of this method. The proton radius puzzle is a significant discrepancy between data obtained with muonic hydrogen and regular atomic hydrogen that could not be explained within the framework of quantum electrodynamics. By combining our result [f1S-3S = 2,922,743,278,665.79(72) kilohertz] with a previous measurement of the 1S-2S transition frequency, we obtained new values for the Rydberg constant [R∞ = 10,973,731.568226(38) per meter] and the proton charge radius [rp = 0.8482(38) femtometers]. This result favors the muonic value over the world-average data as presented by the most recent published CODATA 2014 adjustment.

We give a pedagogical description of the method to extract the charge radii and Rydberg constant from laser spectroscopy in regular hydrogen (H) and deuterium (D) atoms, that is part of the CODATA least-squares adjustment (LSA) of the fundamental physical constants. We give a deuteron charge radius r d from D spectroscopy alone of 2.1415(45) fm. This value is independent of the measurements that lead to the proton charge radius, and five times more accurate than the value found in the CODATA Adjustment 10. The improvement is due to the use of a value for the 1S → 2S transition in atomic deuterium which can be inferred from published data or found in a PhD thesis.One could thus argue that the CODATA deuteron charge radius is larger than the muonic deuterium value only because the correlated, and very accurately determined, proton charge radius is larger than the muonic hydrogen value.Here we use the available data on spectroscopy of atomic deuterium to deduce a precise value of r d which does not depend on r p through Eq. (5). In our analysis we use a value of the 1S → 2S transition in atomic deuterium (see Tab. VI) that has not been used by CODATA. Its value can either be inferred from published data or found in a PhD thesis [10]. This 1S → 2S value helps improve the accuracy of the deuteron charge radius by a factor of five, compared to the CODATA Partial Adjustment 10 [3]. A. CODATA Partial AdjustmentsThe final CODATA-2010 recommended values of the fundamental constants are deduced in the so-called "Adjustment 3". As detailed in Sec. XIII.B.2 on page 1577 ff. of the CODATA-2010 report [3], there are additional adjustments that use only a subset of the available input data. "Adjustments 6-12" are the ones relevant for r p , r d and the Rydberg constant R ∞ , and the results are summarized in Tab. XXXVIII of Ref. [3].These auxiliary Partial Adjustments serve two purposes: On the one hand, they verify the internal consistency of the CODATA LSA, as results from different subsets of the data are in good agreement with each other. On the other hand,

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