This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The Korea Research Institute of Standards and Science (KRISS) has remeasured a key transition frequency of the strontium (Sr) atom for the first time in 88 years, since 1938, using a photonic grating chip. It has established a new absolute frequency value with a measurement uncertainty reduced by more than 50 times.
By providing an accurate reference value for next-generation quantum technologies, this achievement is expected to contribute to the precise control and miniaturization of quantum devices, including atomic clocks and neutral-atom quantum computers. The work is published in the journal Metrologia. Strontium is an atom widely used in precision quantum technologies such as optical lattice clocks and quantum sensors.
To use strontium in these technologies, fast-moving atoms must be slowed down and trapped with precisely tuned lasers. This requires knowing the exact resonant frequency of the laser light for the atomic transition. However, the previous frequency value was obtained in 1938 by comparing the solar spectrum with the arc light of strontium, and its uncertainty was too large for today's precise laser frequency settings.
As a result, researchers have had to observe the atoms' response directly and adjust the laser frequency as needed, much like turning the dial of an analog radio to tune in to a station. As frequency control and measurement technology for light has advanced and the miniaturization of quantum devices has been pursued, the need for an accurate absolute frequency value has grown. In response, the research team measured the absolute frequency of the 461-nanometer (nm) optical transition of strontium atoms.
After a yearlong campaign of precision measurements, the uncertainty was reduced to about 5 megahertz (MHz), an improvement of more than 50 times over the previous value. This measurement established traceability to the national time and frequency standard of Korea Standard Time, which KRISS establishes and maintains. Because this standard is linked to the International System of Units (SI), measurements can be reliably compared against the same reference anywhere in the world, regardless of differences in laboratory or equipment environments.
The key device that enhanced measurement stability is the "photonic grating chip," jointly developed by KRISS with the Korea Advanced Institute of Science and Technology and the National NanoFab Center. The fine grating structure on the surface of the chip, installed inside a vacuum, diffracts and reflects light in set directions, reducing measurement errors caused by mechanical vibrations compared with conventional methods that require aligning multiple external mirrors. In addition, a single chip can generate laser beams in multiple directions, simplifying the optical setup.
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