Researchers at the Korea Research Institute of Standards and Science have redetermined strontium’s 461-nanometer optical transition frequency for the first time since 1938, slashing measurement uncertainty by over fifty times to roughly five megahertz using a photonic grating chip.
The Korea Research Institute of Standards and Science (KRISS, President Dr. Ho Seong Lee) has re-measured a key transition frequency of the strontium atom for the first time in 88 years. That marks an improvement of more than 50 times over the previous benchmark, which dated back to 1938 when scientists relied on comparing the solar spectrum with strontium arc light.
Tracing the Resonant Frequency of Strontium Atoms
Quantum sensors and optical lattice clocks are examples of precision quantum technologies that frequently employ strontium atoms. Applying strontium in these applications requires slowing and capturing rapidly moving atoms with meticulously adjusted lasers, rendering knowledge of the precise resonant frequency for the atomic transition crucial. Modern precise laser frequency configurations could not directly utilize the prior frequency value established in 1938 because its uncertainty was excessive. Korea Standard Time, which is created and maintained by KRISS, served as the national time and frequency standard to which this measurement was linked.
Deployment of Photonic Grating Chips
The breakthrough relies heavily on a photonic grating chip, using a single chip that can generate laser beams in multiple directions to simplify the optical setup. Having reduced measurement errors on the equipment side, the researchers determined the transition frequency independently using two methods based on different principles to verify the reliability of the results.
Dual Methods and Independent Verification
While one technique evaluates atomic reactions to light across varying laser frequencies, the alternative approach derives the transition frequency by examining the velocity distribution of laser-decelerated atomic beams. International standards were followed to compute the final figure by incorporating the uncertainty of each outcome, and the figures derived from both techniques matched within their respective error limits.
Advancing Next-Generation Quantum Devices
Pairing this with optical frequency synthesis systems currently under development liberates advanced quantum equipment from dependence on large, external atomic frequency standards.
I believe the main significance of this research is not simply that we remeasured a single frequency value, but that we proactively delivered an accurate measurement reference point for next-generation quantum technologies.
Dr. Jae Hoon Lee, principal research scientist in the Atomic Quantum Sensing Group at KRISS
Publication and National Metrology Standards
The results were published in July in Metrologia, with Jaewhan Lee and colleagues listed as authors. KRISS, functioning as the national metrology institute, remains committed to leading the development of measurement standards required for emerging fields in quantum science and technology.