Abstract
The proposal for the development of a nuclear optical clock has triggered a multitude of experimental and theoretical studies. In particular the prediction of an unprecedented systematic frequency uncertainty of about 10^{-19} has rendered a nuclear clock an interesting tool for many applications, potentially even for a re-definition of the second. The focus of the corresponding research is a nuclear transition of the ^{229}Th nucleus, which possesses a uniquely low nuclear excitation energy of only 8.12pm 0.11 eV (152.7pm 2.1 nm). This energy is sufficiently low to allow for nuclear laser spectroscopy, an inherent requirement for a nuclear clock. Recently, some significant progress toward the development of a nuclear frequency standard has been made and by today there is no doubt that a nuclear clock will become reality, most likely not even in the too far future. Here we present a comprehensive review of the current status of nuclear clock development with the objective of providing a rather complete list of literature related to the topic, which could serve as a reference for future investigations.
Highlights
Since ancient human history it has been important to subdivide the continuous flow of time into certain repeating intervals or cycles [218]
This consideration requires a critical discussion, which goes beyond the scope of this review and will only be touched briefly: Even in the case that a future nuclear optical clock will be the frequency standard of smallest systematic frequency uncertainty, the practical use of a 10−19 frequency uncertainty on the surface of the earth is unclear, as solid earth tides will lead to frequency changes on a significantly larger scale due to gravitational time dilation
The development of 229Thdoped crystals is driven by two groups, located at the University of California (UCLA), where LiSrAlF6 is investigated as a host material, and at the Technical University (TU) Vienna, where CaF2 is considered
Summary
Since ancient human history it has been important to subdivide the continuous flow of time into certain repeating intervals or cycles [218]. As the frequency of the atomic transition significantly affects the accuracy of time measurement, the possibility to count the oscillations of laser light had an immediate impact on clock technology, leading to the development of optical atomic clocks [209,267]. While an imprecise knowledge of the transition energy has so far hindered the development of a nuclear clock, recently, three new measurements have led to a significant increase in confidence about the isomer’s excitation energy [321,328,412] This new knowledge is likely to lead to a phase transition in the 229mTh-related research, away from previous “high-energy” nuclear-physics dominated research and more towards “low-energy” precision laser spectroscopy. The reader who prefers a shorter discussion is referred to [261,350,402]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
