Thorium-229 nuclear clock

In 2024, the realisation of the thorium-229 nuclear clock was ranked as the number one achievement in one of the global selections of the 10 best scientific results of the year. Three international experimental groups measured the transition frequency of the thorium-229 isomer using laser spectroscopy. The race is now on to design and build a nuclear clock that may be more accurate than all atomic clocks in existence and be a unique test bed for ‘new physics’ effects, such as sensitive detection of well-motivated dark matter candidates such as axions.Researchers at UNSW made key theoretical contributions that underpinned this breakthrough. The thorium-229 nucleus features a uniquely low-energy transition, enabling the development of a nuclear clock that could potentially surpass the precision and stability of current atomic clocks. UNSW researchers demonstrated how this nuclear transition could be used to detect potential variations in fundamental constants of nature, such as the fine-structure constant and the strength of the strong nuclear force.

UNSW scientists also conducted calculations on the electron bridge process, wherein the electron cloud in thorium atoms acts as an antenna, transferring laser energy to the nucleus. This mechanism enhances the rate of nuclear clock transitions by several orders of magnitude, which could significantly improve the clock’s performance.

This achievement underscores the critical role of UNSW research in leadership in fundamental nuclear physics and how the Centre is advancing technologies with profound implications for science and society.