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RESEARCH PRODUCT

Direct detection of the 229Th nuclear clock transition

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Today’s most precise time and frequency measurements are performed with optical atomic clocks. However, it has been proposed that they could potentially be outperformed by a nuclear clock, which employs a nuclear transition instead of an atomic shell transition. There is only one known nuclear state that could serve as a nuclear clock using currently available technology, namely, the isomeric first excited state of 229Th (denoted 229mTh). Here we report the direct detection of this nuclear state, which is further confirmation of the existence of the isomer and lays the foundation for precise studies of its decay parameters. On the basis of this direct detection, the isomeric energy is constrained to between 6.3 and 18.3 electronvolts, and the half-life is found to be longer than 60 seconds for 229mTh2+. More precise determinations appear to be within reach, and would pave the way to the development of a nuclear frequency standard. Direct detection of the 229Th nuclear clock transition has been achieved, placing direct constraints on transition energy and half-life; these results are a step towards a nuclear clock, nuclear quantum optics and a nuclear laser. The accuracy of atomic clocks, which measure time based on atomic transitions, is central to the function of systems as diverse as GPS navigation and radio astronomy. In theory, a nuclear clock based on an optical excitation of a nuclear transition, could be even better than atomic clocks in terms of stability and compactness. However, the only nuclear state with an excitation energy sufficiently low for this application is the first excited state of thorium-229. But this is arguably most exotic transition in the whole nuclear landscape, and has proven to be extremely hard to detect. Only some indirect evidence could be obtained previously. Here, based on low-energy microchannel plate detection, Lars von der Wense and colleagues achieve direct detection of the thorium-229 nuclear-clock transition, placing new limits on the transition energy and measuring the state's half-life. As well as being a step towards a nuclear clock, these results also suggest that nuclear quantum optics and nuclear lasers based on this transition may be plausible possibilities.