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Register a new userAn atomic clock with $10^{-18}$ instability
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Atomic clocks have been transformational in science and technology, leading to innovations such as global positioning, advanced communications, and tests of fundamental constant variation. Next-generation optical atomic clocks can extend the capability of these timekeepers, where researchers have long aspired toward measurement precision at 1 part in $bm{10^{18}}$. This milestone will enable a second revolution of new timing applications such as relativistic geodesy, enhanced Earth- and space-based navigation and telescopy, and new tests on physics beyond the Standard Model. Here, we describe the development and operation of two optical lattice clocks, both utilizing spin-polarized, ultracold atomic ytterbium. A measurement comparing these systems demonstrates an unprecedented atomic clock instability of $bm{1.6times 10^{-18}}$ after only $bm{7}$ hours of averaging.
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The Stark shift due to blackbody radiation (BBR) is the key factor limiting the performance of many atomic frequency standards, with the BBR environment inside the clock apparatus being difficult to characterize at a high level of precision. Here we demonstrate an in-vacuum radiation shield that furnishes a uniform, well-characterized BBR environment for the atoms in an ytterbium optical lattice clock. Operated at room temperature, this shield enables specification of the BBR environment to a corresponding fractional clock uncertainty contribution of $5.5 times 10^{-19}$. Combined with uncertainty in the atomic response, the total uncertainty of the BBR Stark shift is now $1times10^{-18}$. Further operation of the shield at elevated temperatures enables a direct measure of the BBR shift temperature dependence and demonstrates consistency between our evaluated BBR environment and the expected atomic response.
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The passage of time is tracked by counting oscillations of a frequency reference, such as Earths revolutions or swings of a pendulum. By referencing atomic transitions, frequency (and thus time) can be measured more precisely than any other physical quantity, with the current generation of optical atomic clocks reporting fractional performance below the $10^{-17}$ level. However, the theory of relativity prescribes that the passage of time is not absolute, but impacted by an observers reference frame. Consequently, clock measurements exhibit sensitivity to relative velocity, acceleration and gravity potential. Here we demonstrate optical clock measurements surpassing the present-day ability to account for the gravitational distortion of space-time across the surface of Earth. In two independent ytterbium optical lattice clocks, we demonstrate unprecedented levels in three fundamental benchmarks of clock performance. In units of the clock frequency, we report systematic uncertainty of $1.4 times 10^{-18}$, measurement instability of $3.2 times 10^{-19}$ and reproducibility characterised by ten blinded frequency comparisons, yielding a frequency difference of $[-7 pm (5)_{stat} pm (8)_{sys}] times 10^{-19}$. While differential sensitivity to gravity could degrade the performance of these optical clocks as terrestrial standards of time, this same sensitivity can be used as an exquisite probe of geopotential. Near the surface of Earth, clock comparisons at the $1 times 10^{-18}$ level provide 1 cm resolution along gravity, outperforming state-of-the-art geodetic techniques. These optical clocks can further be used to explore geophysical phenomena, detect gravitational waves, test general relativity and search for dark matter.
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