title: Precision measurement of the hydrogen-deuterium 1S-2S isotope shift.
abstract: Measuring the hydrogen-deuterium isotope shift via two-photon spectroscopy of the 1S-2S transition, we obtain 670,994,334,606(15) Hz. This is a 10-times improvement over the previous best measurement [A. Huber, Phys. Rev. Lett. 80, 468 (1998)] confirming its frequency value. A calculation of the difference of the mean square charge radii of deuterium and hydrogen results in <r2>d - <r2>p =3.82007(65)  fm2, a more than twofold improvement compared to the former value.
authors.affiliation: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.
authors.forename: Christian G
authors.initials: CG
authors.lastname: Parthey
authors.forename: Arthur
authors.initials: A
authors.lastname: Matveev
authors.forename: Janis
authors.initials: J
authors.lastname: Alnis
authors.forename: Randolf
authors.initials: R
authors.lastname: Pohl
authors.forename: Thomas
authors.initials: T
authors.lastname: Udem
authors.forename: Ulrich D
authors.initials: UD
authors.lastname: Jentschura
authors.forename: Nikolai
authors.initials: N
authors.lastname: Kolachevsky
authors.forename: Theodor W
authors.initials: TW
authors.lastname: Hänsch