Concepts for direct frequency-comb spectroscopy of 229m Th and an internal-conversion-based solid-state nuclear clock
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Concepts for direct frequency-comb spectroscopy of 229mTh and an internal-conversion-based solid-state nuclear clock Lars von der Wense1,2,a and Chuankun Zhang2 1 2
Ludwig-Maximilians-Universit¨ at M¨ unchen, Garching 85748, Germany JILA and Department of Physics, University of Colorado, Boulder, CO 80309-0440, USA Received 20 November 2019 / Received in final form 10 April 2020 Published online 7 July 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. A new concept for narrow-band direct nuclear laser spectroscopy of 229m Th is proposed, using a single comb mode of a vacuum ultraviolet frequency comb generated from the 7th harmonic of an Yb-doped fiber laser system. In this concept more than 1013 229 Th atoms on a surface are irradiated in parallel and a successful nuclear excitation is probed via the internal-conversion (IC) decay channel. A net scanning time of 15 min for the most recent 1σ energy uncertainty interval of 0.34 eV appears to be achievable when searching for the nuclear transition. In case of successful observation, the isomer’s energy value would be constrained to an uncertainty of about 100 MHz, which is a factor of 106 of improvement compared to today’s knowledge. Further, the comb mode could be stabilized to the nuclear transition using the same detection method, allowing for the development of an IC-based solid-state nuclear clock, which is shown to achieve the same performance as a crystal-lattice nuclear clock, however, with the advantage of a drastically simpler detection scheme. Finally, it is shown that the same laser system could be used to narrow down the isomer’s transition energy by further six orders of magnitude during laser excitation of 229 Th3+ ions in a Paul trap and to drive nuclear Rabi oscillations, as required for the development of a nuclear clock based on a single 229 Th3+ ion.
1 Introduction The accuracy of time measurements has considerably evolved within the past decades, starting with the development of the first atomic clock by Essen and Parry [1], followed by the legal definition of the second by means of the Cesium standard in 1967 [2] and the invention of the fountain clock in the late 1980s [3]. With the invention of the optical frequency comb [4–6] a new technological leap has occurred, allowing for the development of optical atomic clocks [7], which by today pose the most precise timekeepers. The achieved accuracies of these clocks vary around 10−18 , corresponding to an error of 1 s in 30 billion years, significantly longer than the age of the universe [8–11]. Such accuracy in frequency measurement opens up a plethora of applications, e.g., in satellite-based navigation [12], geodesy [13] and the search for temporal variation of fundamental constants [14,15]. As an alternative to the existing optical atomic clocks, the idea of a nuclear optical clock was developed [16–19]. Compared to an optical atomic clock, the operational principle rem
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