Scientists create an atomic clock of ytterbium that can detect dark matter

Physicists have created a very precise and very complex atomic clock based on ytterbium, which can test the limits of the Standard Model and even search for invisible dark matter.

Led by Taiki Ishiyama, PhD, a physicist at Kyoto University’s School of Science in Japan, the project used the unusual orbital change of atoms, which for a long time was considered promising but very difficult to measure with high precision.

The team believes their method could lead to the most powerful experiments predicted by the Standard Mode, which describes three of the four fundamental forces that govern the universe: electromagnetism, the strong force and the weak force.

“These results pave the way for a variety of new physics research experiments and a wide range of applications in quantum science with this clock revolution,” the researchers said.

A rare change in the atom

Atomic clocks keep time by measuring how electrons bounce between two specific energy levels in atoms, usually cesium-133, which acts as a very stable, natural pendulum.

These changes occur at very stable frequencies, making atomic clocks the most accurate timekeepers ever created. The most accurate atomic clocks trap atoms in an optical beam, a pattern of light and dark created by colliding lasers.

They operate with optical waves and oscillations of hundreds of billions per second. Some, such as the strontium optical lattice clock, are so precise that they would drift in less than a second over a period of about 30 billion years.

But researchers have long suspected that they could achieve even greater sensitivity using a rare type of orbital change in ytterbium atoms. It occurs between configurations involving an electron in the innermost shell of an atom.

However, according to the group, it can still be measured and controlled with the same precision as a regular clock shift. It also exhibits high sensitivity, allowing it to pick up subtle physical phenomena, such as dark matter particles or other unknown particles.

Although theoretically, the change is suitable for error checking in the Standard Model, achieving the required accuracy remains difficult in practice. “When our group first observed this change in 2023 and other groups followed, the measurement decisions were much worse than those of modern clocks,” said Ishiyama.

Chasing a dark matter

The team’s first experiments had problems with accurate measurements, mainly due to interference from the lasers used to trap the atoms. To solve this challenge they used a technique called ‘magic wavelength,’ which trapped ytterbium atoms in the lenses of three eyes.

In this way, they were able to eliminate the unwanted changes in the energy levels of the atoms caused by the trapping light. “By combining this with a highly stable excitation laser, we achieved a narrow spectral range of 80 Hz, which is about a two-order improvement over previous results,” Ishiyama continued.

The team brought the system closer to the accuracy of modern optical clocks. This level of control allowed them to make a series of very precise measurements, including observing the coordinated motion between atomic states and detecting interorbital Feshbach resonances.