Nuclear clocks, which are predicted to be even more precise than atomic clocks, could open new doors for scientists to explore the fundamental forces of the universe. A team of researchers from LMU, as part of an international collaboration, has made significant progress in characterizing the excitation energy of thorium-229, the element expected to be the timekeeping element in nuclear clocks.
Atomic clocks are already extremely accurate, gaining or losing less than one second every 30 billion years. However, nuclear clocks have the potential to measure time even more precisely, offering a deeper understanding of fundamental physical phenomena. While atomic clocks register forces outside the atomic nucleus, nuclear clocks would register forces inside the nucleus, providing researchers with a whole new range of research fields to investigate.
LMU physicist Professor Peter Thirolf, who has been researching nuclear clocks for many years, explained that nuclear clocks could offer insights into the forces that hold the world together at its core. His colleague Dr. Sandro Kraemer added that nuclear clocks could open up research fields that could never be investigated with atomic clocks.
The team of researchers at LMU has made a significant breakthrough by accurately characterizing the excitation energy of thorium-229, the nucleus that could be used as the timekeeping component in nuclear clocks. Thorium-229 is unique because it can be put into an excited state using a relatively low light frequency, which is achievable with UV lasers. However, confirming the excited state of thorium-229 was a challenge for scientists for many years.
In 2016, the research group at LMU confirmed the excited state of thorium-229, which initiated the race for the development of the first nuclear clock. Since then, many research groups worldwide have joined the race. To develop a nuclear clock, researchers need to precisely determine the exact frequency at which the atomic nucleus of thorium-229 oscillates, so lasers can be developed to excite that frequency.
The team took a unique approach to narrow down the range of oscillation frequency. Instead of trying out all possible frequencies with different lasers, they used the decay of radioactive nuclei to produce a thorium-229 nucleus in an excited state. By embedding the actinium-229, the parent nucleus of thorium-229, into special crystals, they were able to accurately determine the energy of the state transition and demonstrate the feasibility of a nuclear clock based on thorium embedded in a crystal.
Next, the researchers will continue their experiments to study the thorium-229 nucleus, using more precise lasers to home in on the exact oscillation frequency. The team is confident that their new method will lead to the development of a nuclear clock. While challenges remain, such as understanding the thorium isomer better and developing the necessary lasers, the researchers are optimistic about the future of nuclear clocks and the insights they could provide into the fundamental forces of the universe.