"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."
