Amsterdam Physicists Achieve Breakthrough in Strontium Measurements

A team of physicists from the University of Amsterdam has achieved a significant breakthrough in measuring the properties of strontium atoms, specifically the isotope 87 Sr. This advancement, published on November 4, 2025, in the journal Physical Review Letters, utilizes nearby rubidium atoms to enhance measurement precision, a development with important implications for atomic clocks and quantum computing.

Strontium, while not widely recognized outside scientific circles, is a member of the alkaline earth metals and is known for its unique properties. The 87 Sr isotope is particularly noteworthy due to its odd number of particles, which transforms it into a fermion. This characteristic endows it with a nonzero nuclear spin, allowing it to function as a tiny bar magnet. The distinction between fermions and bosons is crucial in understanding the behavior of atoms and their applications in technology.

Applications in Atomic Clocks and Quantum Computing

Atomic clocks, which rely on precise transitions between energy states of atoms, are set to benefit significantly from this research. The most accurate optical clocks utilize light frequencies emitted by strontium atoms, specifically at a wavelength of 698 nanometers. However, the bosonic isotopes of strontium do not allow for the necessary transitions due to their zero spin.

The nuclear spin of the fermionic isotope 87 Sr enables these critical transitions, allowing for stable and well-defined frequencies essential for high-precision timekeeping. The research also explores the Zeeman effect, discovered by Dutch Nobel laureate Pieter Zeeman in 1896, which describes how energy levels in atoms split when exposed to a magnetic field. This effect is pivotal in determining the g-factor of 87 Sr, which is vital for enhancing the performance of optical clocks.

The g-factor reflects the strength of the nuclear magnet and is influenced by the magnetic properties of the nucleus as well as the electron cloud surrounding it. The challenge has been to measure this accurately, as previous measurements had remained unchanged for over fifty years.

Innovative Measurement Techniques

The breakthrough in precision measurement came from an unexpected avenue. Premjith Thekkeppatt, the first author and a postdoctoral researcher at the Niels Bohr Institute, explained that the project initially aimed to create rubidium-strontium molecules. The complexity of this task prompted the team to investigate the proximity of both atom types without their overlap, leading to improved methods for measurement.

By employing a technique called optical trapping, the researchers successfully combined the two species in a controlled environment. They then utilized nuclear magnetic resonance to measure the energy splitting related to the g-factor of 87 Sr. The established properties of rubidium served as an accurate reference for calibrating the magnetic field strength, leading to a remarkable one-hundredfold improvement over previous measurements.

The newly achieved precision not only sets a benchmark for future research but also opens avenues for further applications in quantum computing. The ten-fold splitting of 87 Sr energy levels could enable the development of qudits—quantum bits that can exist in multiple states, enhancing computational capabilities beyond traditional binary systems.

Thekkeppatt emphasized the significance of their findings, stating, “Our results form a new challenging benchmark for atomic structure calculations. The demonstrated methods will inspire extensions to further atomic species and states relevant for all sorts of applications.”

This research marks a pivotal moment in the pursuit of more accurate atomic clocks and the advancement of quantum computing technologies. As scientists continue to probe the complexities of atomic behavior, the implications of these findings may resonate across various fields, paving the way for future innovations.