The $$^{229}$$Th isomer: prospects for a nuclear optical clock

Abstract

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 $$10^{-19}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mo>-</mml:mo><mml:mn>19</mml:mn></mml:mrow></mml:msup></mml:math> 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 $$^{229}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow/><mml:mn>229</mml:mn></mml:msup></mml:math> Th nucleus, which possesses a uniquely low nuclear excitation energy of only $$8.12\pm 0.11$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>8.12</mml:mn><mml:mo>±</mml:mo><mml:mn>0.11</mml:mn></mml:mrow></mml:math> eV ( $$152.7\pm 2.1$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>152.7</mml:mn><mml:mo>±</mml:mo><mml:mn>2.1</mml:mn></mml:mrow></mml:math> 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.

Topics & Concepts