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Updated: Nov 28, 2025

Generation and Coherent Control of Pulsed Quantum Frequency Combs
Published on: June 8, 2018
Two-photon frequency comb spectroscopy of atomic hydrogen
Alexey Grinin1, Arthur Matveev2, Dylan C Yost2
1Laser Spectroscopy Division Max-Planck-Institut für Quantenoptik, Garching, Germany. alexey.grinin@mpq.mpg.de.
Abstract:
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 [f 1S-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 [r p = 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.
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