Nuclear relaxation of the Thorium-229 isomer in a crystal

Modern optical atomic clocks are the most precise measurement devices ever build by mankind; two high-performance clocks deviate from each other only in the 18th decimal digit, they would need billions of years to accumulate a time discrepancy of 1 s. Several research groups worldwide have demonstrated this incredible precision in the last few years. These optical clocks however fill entire laboratories; extreme shielding is required to protect them from external electric or magnetic field perturbations, vibrations, and temperature fluctuations. Therefore, these optical clocks are currently not compatible with field applications such as satellite-based navigation (GPS, Galileo) earth- surveying/geodesy, or to coordinate the global Internet traffic. Much less performing systems, essentially dating from the 70s, are hence still used in most practical applications. We propose to replace the electronic transition within an atom, commonly used in optical atomic clocks as time references, by a very specific nuclear transition in the Thorium-229 isotope. Nuclear transitions are many orders of magnitudes less sensitive to external perturbations, may that be fields, temperature, or mechanical influences. Due to this intrinsic robustness, it becomes possible to fuse Thorium nuclei into optically transparent crystals of only a few millimetres in size and build a solid-state nuclear clock. This Thorium-229 nuclear transition is the only one that is accessible to optical manipulation, but its exact transition frequency is currently not known. It is the aim of this project to precisely determine this transition frequency, which is key to the construction of the nuclear clock. Furthermore, we want to investigate interactions between the Thorium nucleus with the crystal environment.