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A new record in atomic clock performance

TitleA new record in atomic clock performance
Publication TypeThesis
Year of Publication2015
AuthorsNicholson, TL
Academic DepartmentPhysics
Number of Pages220
Date Published05-29-2015
UniversityUniversity of Colorado
CityBoulder, CO

The pursuit of better atomic clocks has advanced many fields of research, providing better quantum state control, new insights in quantum science, tighter limits on fundamental constant variation, and improved tests of relativity. This thesis describes the construction and characterization of an 87Sr optical lattice clock with a state-of-the-art stable laser. The performance of an atomic clock is typically gauged by two figures of merit: stability and total systematic uncertainty. Stability is the statistical precision of a clock or frequency standard, and the total systematic uncertainty is the combined uncertainty of all known systematic measurement biases. Several demonstrations of clock stability are presented in this work, one of which was the first to significantly outperform ion clocks. The most recent of these measurements resulted in fractional stability of 2.2 x 10−16 at 1 s, which is the best reported to date. These stability improvements are used for two systematic evaluations of our clock. The first full evaluation at 6.4 x 10−18 total uncertainty took the record for best clock performance. The second evaluation used improved strategies for systematic measurements, achieving a new best total systematic uncertainty of 2.1 x 10−18. With a combination of accurate radiation thermometry and temperature stabilization of the measurement environment, we demonstrate the first lattice clock to achieve the longstanding goal of 10−18 level uncertainty in the formidable blackbody radiation shift. Improvements in the density, lattice ac Stark, and dc Stark shifts were also a result of innovations that are described in this thesis. Due to the low total uncertainty of the Sr clock, timekeeping based on this system would not lose a second in 15 billion years (longer than the age of the Universe), and it is sensitive to a gravitational redshift corresponding to a height change of 2 cm above the Earth’s surface.

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