Thorium Transition Through Laser Excitation of Nucleus Could Pave Way for Developing Nuclear Clock, Experts Suggest

Over the years, experts have been looking for a very specific state of thorium atomic nuclei since they are known to have promising applications in physics. This discovery could be the key in creating a nuclear clock that measures time more precisely than the current atomic clocks.

Shifting Quantum States

Modern science has allowed the manipulation of atoms or molecules where they can be switched from one state to another using a laser of right wavelength. This enables precise measurement of energies of atoms or molecules.

A lot of precision measurement strategies, like current atomic clocks, are based on this mechanism in combination with chemical analysis methods. In most cases, lasers are also used in quantum computers to store information in atoms or molecules. For a long time, however, these techniques seemed impossible to apply to atomic nuclei.

Atomic nuclei can shift between various quantum states, although it takes much more energy to alter an atomic nucleus from one state to another. With insufficient energy of photons, it would be impossible for lasers to manipulate normal atomic nuclei.

This limitation is unfortunate because atomic nuclei are the ideal quantum objects for precision measurements. Since they are much smaller than atoms and molecules, they are less susceptible to external disturbances like electromagnetic fields. In principle, they can enable measurements with unprecedented accuracy.

Long-Sought Thorium Transition

Since the 1970s, it was believed that there could be a special atomic nucleus which can be manipulated with a laser. The target nucleus, thorium-229, has two energy states so closely adjacent that a laser can be enough to change its state.

Still, there has been no direct evidence of the existence of this transition. Previous research groups have attempted studying thorium nuclei by holding them individually in place in electromagnetic traps.

This hope has finally come true as scientists have found the long-sought thorium transition with known energy. For the first time, experts have demonstrated the possibility of using a laser to transfer atomic nuclei into a higher energy state and return them precisely to their original state.

Led by Professor Thorsten Schumm from Vienna University of Technology, the research team made it possible to combine classical quantum physics and nuclear physics. A vital prerequisite for this breakthrough was the creation of special thorium-containing crystals. The details of their study were discussed in the paper "Laser Excitation of the Th-229 Nucleus."

On November 21, 2023, the research team got successful in exactly hitting the correct energy of the thorium transition. For the first time, the thorium nuclei delivered a clear signal as a laser beam switched the state.

This breakthrough marks a new exciting technology which can be used for precision measurements, especially in building an atomic clock. Just like how a pendulum clock relies on swinging pendulum as a timer, the oscillation of the light that excites thorium transition can be utilized as a timer for a new type of clock. Additionally, thorium transition can be useful in precisely analyzing the gravitational field of the Earth to provide information about mineral resources or earthquakes.