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nuClock Report Summary

Project ID: 664732
Funded under: H2020-EU.1.2.1.

Periodic Reporting for period 1 - nuClock (Towards a nuclear clock with Thorium-229)

Reporting period: 2015-06-01 to 2016-05-31

Summary of the context and overall objectives of the project

"The quest for a more precise way of measuring time is a theme that prevails through the history of mankind. In turn, clocks have always reflected humanities state of knowledge. As we briefly recall the evolution of man-made clocks, we find that most of them did not measure time directly, but the frequency of oscillations. With every generation of newly developed cocks, the oscillating objects used for reference gradually reduced in size, spanning from the largest structures in the universe to the smallest ones. Early researchers went from observing the (apparent) annual motion of the Sun or the night sky (e.g. observatories such as Stonehenge) and the motion of Earth around Sun (e.g. sundials) to the fabrication of mechanic pendulums and, later, to the development of quartz crystals in electronic watches. Today's best clocks employ single atoms or ions in atom clocks, which loose or gain less than a fraction of a second over the age of the univere. Within the nuClock project, we are advancing one step further: Employing the nucleus of an atom (1000-times smaller than the atom itself) might allow us to improve the performance of today's clocks even further.

Only very few types of atomic nuclei (referred to as isotopes) are suitable for such a "nuclear clock": Candidate nuclei need to possess a certain well-defined, long-lived excited state of low energy (a so-called isomer); this is true for only very few isotopes. Taking into account the range of currently available lasers (used for manipulation of the nuclei), there is only one single isotope suitable for such a nuclear clock: Thorium-229.

A clock based on Th-229 would "tick" faster compared to today's atomic clocks, it would be less sensitive to external perturbations, and it might prove to be smaller and more robust by design. It might therefore supersede atomic clocks in a number of applications. The most prominent application of highly precise clocks is the generation of timing signals that are used by navigation systems, such as GPS. Apart from these navigation systems, which are built into billion cars and cell phones, modern society heavily relies on precise synchronization and timekeeping in power grids, telecommunication networks, and financial markets.

While the operation of a nuclear clock cannot anticipated for the near future, work within the nuClock project will lay the foundations for such a device. Three major challenges are tackled within the consortium: (1) A thorough characterization of the Th-229 isotope, (2) Designing the hardware components of the future clock, and (3) development of suitable laser sources. To advance at the maximum possible speed, these three strands of research are persued in parallel."

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The first reporting period stretches over 12 months, the project started 1. July 2015.
A few months after the start of the project, the LMU Munich group was able to present the first-ever direct observation of the isomeric state in Th-229. This discovery marks an important step towards the development of a nuclear clock and was published in the highly reputated journal Nature. This work included the introduction of a new detection method, which will be used to measure important properties of the isomeric state.

While the LMU experiment measures electrons to obtain information about the nucleus, other groups performed or prepared experiments using optical methods. The PTB group in Braunschweig studies thorium ions trapped in an ion trap, while the TU Wien group investigates thorium nuclei doped into crystals. In Jyväskylä (Finland), Th-229 will be freshly produced in a particle accelerator, and probed right after production. Yet another approach is taken in Heidelberg: here, detectors with supreme resolution will detect gamma rays that are emitted by Th-229 following radiodactive alpha decay. Anticipating a precise measurement of the isomer's energy in the near future, two experimental groups already started to develop suitable laser systems that are necessary to operate a future nuclear clock. All of these activities are supported by three theoreticians that are experts in calculating the interaction between electrons and nuclei. This group is based in Heidelberg.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The nuClock project is the first and only consortium with a clear mission to develop a nuclear clock. While previous experiments were carried out by single isolated groups from various disciplines of physics, the nuClock consortium presents the only aggregation of researcher from all relevant fields of physics (atomic and nuclear physics, quantum optics, laser development, theory support) that is required to tackle the problem in a broad and well-thought-out fashion. The success of this strategy is evidenced by the vivid teamwork between the eight partners of the consortium. The scientific work already led to a number of publications and earned world-wide reputation.

Within the realms of basic research, precision laser spectroscopy of atomic nuclei would open an entirely new field of research, merging the otherwise quite distinct fields of atomic and nuclear physics. Spectroscopy of the clock transition allows to search for drifts in fundamental constants, a hot topic in astrophysics and cosmology. A future nuclear clock might have the potantial to outperform today's best optical clocks and could contribute to international timekeeping. When cast into a rigid design, nuclear clocks could be operated on naviagtion satellites to improve the precision of navigation (GPS and the like). Improved and highly reliable synchronization of networks is a prerequisite for today's industry and society.

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