Asian Journal of Physics Vol. 35, Nos 1 – 3 (2026) 123-139

Measuring space-time with optical lattice clocks

A M Guzmán1,2
1Universidad Nacional de Colombia, Departamento de Física, Bogotá. Colombia

2Universidad del Atlántico, Barranquilla, Colombia

In memory of Professor Gallieno Denardo, ICTP Italy

Time measurement has reached the accuracy required to observe the relativistic redshift that causes clocks to run slower in stronger gravitational fields, within terrestrial height differences of the order of centimeters. With this accuracy we are indeed measuring the four-dimensional spacetime continuum rather than performing separate measurements of distance and time. The best cesium microwave clocks measure the SI second to within one second in 100 million years, using the time-of-flight technique of a “cloud” of cold atoms. In 2001, Hidetoshi Katori of the University of Tokyo proposed the first clock of strontium atoms trapped in a horizontal optical lattice, with a transition at 430 THz in the red range of visible light. By the 2010s, this clock held the record for accuracy of one second in 15 billion years, exceeding the estimated age of the universe. In July 2024, Jun Ye’s group at JILA, NIST, presented a vertically oriented one-dimensional optical lattice clock of strontium atoms with a total systematic uncertainty of 8.1 × 10−19 in fractional frequency units, representing the lowest uncertainty of any clock to date. We provide a timeline of key scientific advancements, challenges, and progress in verifying the global consistency of optical clocks, a critical step toward the redefinition of the second by the International Committee on Weights and Measures, anticipated in 2030. Additionally, we highlight recent contributions of optical lattice clocks to quantum metrology, precision quantum sensing, fundamental physics invariance, and the exploration of the relationship between quantum physics and general relativity. © Anita Publications. All rights reserved.
Doi: xxx
Keywords: Optical lattice clocks, atomic clocks, Time standard

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