July 22, 2026 -- Developing a compact “nuclear clock“ based on thorium-229 and therefore exploring a radically new kind of ultra-precise time and frequency reference: A new European research consortium has been awarded funding for this project through the QuantERA Call 2025. The team led by Pascal Del’Haye at the Max-Planck-Institute for the Science of Light is a key part of the project called ResonaTHOR – Resonator-based nuclear optical frequency reference.

Modern society depends on precise time. Mobile networks, navigation systems, data centers, electrical grids, high-speed trading, and secure communications all rely on synchronized clocks. In many cases, this synchronization is supported by satellite-based timing signals such as GPS or other global navigation satellite systems. These signals can be disrupted by technical failures, interference, jamming, or spoofing. Compact, highly stable local clocks could therefore make critical infrastructure more resilient by maintaining accurate timing when external signals are unavailable or unreliable.

ResonaTHOR aims to take an important step in that direction by using the atomic nucleus of thorium-229. Unlike ordinary atomic clocks, which use transitions in the electrons surrounding an atom, a nuclear clock uses a transition inside the nucleus itself. This nuclear transition is expected to be exceptionally stable and less sensitive to many environmental disturbances. Thorium-229 is unique because its nuclear transition can, in principle, be accessed with laser light, making it a promising basis for a new frequency standard.

The main obstacle is that thorium-229 nuclei interact only very weakly with light. This makes them difficult to excite and read out efficiently. ResonaTHOR will address this challenge by placing thorium-229 into tiny optical resonators known as whispering-gallery-mode resonators. These structures trap light so that it circulates many times around the resonator, much like a whisper traveling around the dome of a cathedral. By forcing the light to interact repeatedly with the thorium nuclei, the project aims to strongly increase the signal while reducing the amount of radioactive material and laser power needed.

The consortium will explore two complementary routes: implanting thorium-229 into high-quality crystalline resonators and fabricating resonators directly from thorium-doped crystals. It will also investigate laser schemes that avoid some of the most complex aspects of today’s vacuum-ultraviolet laser systems, opening a path toward smaller, more robust, and eventually integrated devices.

European scientists are collaborating under the leadership of the Vienna University of Technology

Each partner brings a distinct and essential contribution. The team at TU Wien, led by Thorsten Schumm, coordinates the project and contributes its world-leading expertise in thorium-229 nuclear laser spectroscopy, crystal development, laser infrastructure, and clock integration. The team of Pascal Del’Haye at the Max Planck Institute for the Science of Light is in charge of high-quality resonator design, fabrication, and characterization.

The research consortium also includes the Institute of Science and Technology Austria (ISTA), KU Leuven, Ghent University/imec, and Julius-Maximilians-Universität Würzburg.

Together, the partners aim to move nuclear-clock research from recent proof-of-concept experiments toward a practical compact and deployable photonic platform. If successful, ResonaTHOR could help launch a new class of quantum technologies based on nuclear states of matter: compact, robust, ultra-stable optical references that can operate outside highly specialized laboratories.

Developing this technology in Europe is strategically important. The field of thorium-229 nuclear clocks has been strongly driven by European groups, and the next step is to convert this scientific leadership into technological capability. By combining nuclear physics, materials science, photonics, laser spectroscopy, and quantum theory across several European institutions, ResonaTHOR will strengthen Europe’s position in precision metrology and quantum technology while training the next generation of researchers in a field with high scientific and industrial potential.