Since the development of the laser in 1960, laser spectroscopy of the atomic shell has led to significant technological advances, including, but not limited to, various quantum technologies. In contrast, almost all nuclear transition energies lie in the keV to MeV range. This is far beyond what a conventional laser can reach. However, thorium-229 has an excited metastable state with an excitation energy of only 8.3 eV. This energy corresponds to a wavelength of 148 nm, in the vacuum-ultraviolet (VUV) region. Nuclear laser spectroscopy of thorium is the basis for the development of a nuclear optical clock, which could surpass the accuracy of existing optical atomic clocks and has potential applications in metrology, geodesy, satellite-based navigation and data transmission, as well as the development of a nucleus-based qubit for quantum computing.

Until a few years ago, laser spectroscopy of a nuclear transition seemed to be a technology of the distant future. However, in 2016, the first excited nuclear state of thorium was directly detected for the first time. This was followed by the direct laser excitation with VUV pulses in 2024, which narrowed down the transition frequency considerably.

Based on these new findings, NuQuant aims to excite the thorium-229 nucleus by a continuous wave laser source. For this purpose, a novel continuous-wave (cw) laser system at a wavelength of 148 nm is to be developed, which will then be used for spectroscopy. After successful excitation, the experiment will be further developed into a nuclear clock. This will transfer existing quantum technological tools to the atomic nucleus domain to open up the exciting new field of nuclear quantum optics.