The Race for Nuclear Clocks– Scientists Make Important Advance

Unraveling the Universe’s Fundamental Forces: LMU Researchers Lead the Way

Nuclear clocks represent a potential gateway for scientists to explore the fundamental forces of the universe in future research endeavors. A groundbreaking advancement in this domain has been achieved by an international collaboration, spearheaded by researchers at LMU.

A Leap Towards Precision

Atomic clocks are renowned for their precision, gaining or losing less than one second every 30 billion years. However, the advent of so-called nuclear clocks promises even greater accuracy, affording scientists a deeper understanding of fundamental physical phenomena.

Peering Inside the Atomic Nucleus

The nuclear clock delves into the forces that underpin the core of our world. Unlike conventional atomic clocks, this novel timekeeping device focuses on registering forces within the atomic nucleus itself.

Leading the Race for Nuclear Clocks

LMU physicists Professor Peter Thirolf and Sandro Kraemer have emerged as frontrunners in the quest for nuclear time. Operating from the Chair of Experimental Physics in Garching, these two scientists have achieved a significant breakthrough in the pursuit of the first nuclear clock, collaborating with an international team.

A Key Milestone in Precision

As reported in the journal Nature, the researchers have achieved remarkable precision in characterizing the excitation energy of thorium-229 through an innovative experimental approach. This particular atomic nucleus is slated to serve as the fundamental timekeeping element in nuclear clocks of the future. Acquiring precise knowledge of the frequency required for its excitation is pivotal for making this technology feasible.

The Heart of the Clock

A clock relies on something that oscillates periodically and a mechanism to count those oscillations. In atomic clocks, the atomic shell functions as the timekeeper, with electrons transitioning between high and low energy levels, and the emitted light particles’ frequency acting as the basis for time measurement.

Penetrating the Atomic Nucleus

The nuclear clock operates on a similar principle, but instead penetrates the atomic nucleus, revealing various energy states. If researchers can precisely excite these states with lasers and measure the emitted radiation when the nucleus returns to its ground state, a nuclear clock can be realized. However, among all known atomic nuclei, only one appears suitable for this purpose: thorium-229.

A Nucleus Like No Other

Thorium-229’s uniqueness lies in its ability to be excited by relatively low light frequencies, such as those produced by UV lasers. For four decades, research encountered obstacles as scientists struggled to experimentally confirm the existence of an atomic nucleus with the required characteristics.

A Breakthrough Discovery

In 2016, LMU’s research group, led by Thirolf, achieved a breakthrough by directly confirming the excited state of thorium-229’s nucleus. This marked the commencement of the race for the nuclear clock, attracting numerous research groups worldwide.

Forging New Paths at ISOLDE

Radium-229 and francium-229, referred to as ancestors, are synthesized as they are not readily found in nature. The ISOLDE laboratory at CERN, known for transforming one element into another, has played a crucial role in this synthesis.

The Laborious Path

The research team embedded elaborately manufactured actinium-229 into special crystals, where it decays into thorium-229 in an excited state. Precise localization of the nuclei within the crystal lattice is vital, as any displacement results in the absorption of energy by surrounding electrons, preventing any measurable outcomes.

A Path to Feasibility

The painstaking efforts yielded positive results, as the team precisely determined the energy of the state transition. This demonstrated the viability of a nuclear clock based on thorium embedded in crystals. Such solid-state-based clocks offer an advantage, providing measurement results more rapidly due to their operation with a larger number of atomic nuclei.

Nearing the Finish Line

With the approximate wavelength now known, the researchers will progressively narrow down the exact transition energy. This involves creating an excitation with a laser and homing in on the frequency with increasing accuracy, using a “frequency comb” developed by Professor Theodor Hänsch from LMU.

A World of Possibilities

Despite challenges on the path to nuclear clocks, the potential rewards are immense. Scientists envision detecting minuscule changes in the Earth’s gravitational field, such as those caused by tectonic plate shifts or impending volcanic eruptions. With continued success, prototypes of nuclear clocks may be within reach within a decade or less.

The Future Beckons

The race for nuclear time opens up a myriad of new application possibilities, propelling fundamental physics research and practical applications alike. As scientists approach the finish line, the pursuit of more precise time measurement, including the redefinition of a second in 2030, draws closer to realization – a testament to human ingenuity and perseverance.

 

FAQs (Frequently Asked Questions)

1. What are nuclear clocks, and how do they differ from atomic clocks? Nuclear clocks represent a cutting-edge advancement in precision timekeeping, with the ability to measure time even more accurately than atomic clocks. Unlike atomic clocks that register forces in the atomic shell, nuclear clocks delve into the forces within the atomic nucleus itself, offering a deeper understanding of fundamental physical phenomena.
2. Why is thorium-229 crucial for nuclear clocks? Among all known atomic nuclei, thorium-229 possesses unique characteristics that make it the prime candidate for nuclear clocks. Its nucleus can be excited using relatively low light frequencies, enabling the development of these novel timekeeping devices.
3. How do researchers excite the thorium-229 nucleus for nuclear clocks? Scientists use a sophisticated experimental approach involving actinium-229, the radioactive parent nucleus of thorium-229, embedded in special crystals. The actinium decays into thorium in an excited state, emitting light particles with a specific frequency that is crucial for the development of nuclear clocks.
4. What is the significance of the recent breakthrough by LMU researchers? The researchers at LMU achieved precise characterization of the excitation energy of thorium-229. This milestone brings the world closer to the realization of nuclear clocks and opens up a wealth of new application possibilities in fundamental physics research and practical applications.
5. What advantages do solid-state-based nuclear clocks offer? Solid-state-based clocks, such as those using thorium-229 embedded in crystals, present the advantage of providing measurement results more rapidly due to their operation with a larger number of atomic nuclei. This increased efficiency makes them highly promising for various time measurement applications.

 

Reference: “Observation of the radiative decay of the 229Th nuclear clock isomer” by Sandro Kraemer, Janni Moens, Michail Athanasakis-Kaklamanakis, Silvia Bara, Kjeld Beeks, Premaditya Chhetri, Katerina Chrysalidis, Arno Claessens, Thomas E. Cocolios, João G. M. Correia, Hilde De Witte, Rafael Ferrer, Sarina Geldhof, Reinhard Heinke, Niyusha Hosseini, Mark Huyse, Ulli Köster, Yuri Kudryavtsev, Mustapha Laatiaoui, Razvan Lica, Goele Magchiels, Vladimir Manea, Clement Merckling, Lino M. C. Pereira, Sebastian Raeder, Thorsten Schumm, Simon Sels, Peter G. Thirolf, Shandirai Malven Tunhuma, Paul Van Den Bergh, Piet Van Duppen, André Vantomme, Matthias Verlinde, Renan Villarreal, and Ulrich Wahl, 24 May 2023, Nature. DOI: 10.1038/s41586-023-05894-z.