Detailed Schedule

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Optical clocks exhibit better performances in terms of frequency stability and accuracy compared with microwave Cs fountain clocks, and are considered as promising candidates for a redefinition of the SI second. However, the robustness of optical clocks has not generally reached to a level of Cs fountain clocks that are running nearly continuously for a long period. At National Metrology Institute of Japan (NMIJ), we have developed an Yb optical lattice clock NMIJ-Yb1 which can be operated for many months with an uptime of > 80 %. Our best operation records include uptimes of 80.3 % for half a year from October 2019 to March 2020, 94.5 % for 30 days in August 2021, and 97.0 % for 20 days in March 2022. We here present some technical details about the robustness of NMIJ-Yb1 and its applications to (i) the frequency calibration of International Atomic Time (TAI) with reduced link uncertainties, (ii) generation of a stable local time scale by steering a hydrogen maser with NMIJ-Yb1, and (iii) search for ultralight dark matter candidates by high uptime comparisons between NMIJ-Yb1 and our Cs fountain clock NMIJ-F2.

This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number JP17H01151, JP17K14367, JP18K04989, JP22H01241, JST-Mirai Program Grant Number JPMJMI18A1, and JST Moonshot R&D Program Grant Number JPMJMS2268, Japan.

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The long-lived noble-gas isotope ⁸¹Kr is the ideal tracer for old water and ice with ages of 0.1 – 1 million years, a range beyond the reach of ¹⁴C.  ⁸¹Kr-dating, a concept pursued over the past six decades, is now available to the earth science community at large.  This is made possible by the development of the Atom Trap Trace Analysis (ATTA) method, in which individual atoms of the desired isotope are captured and detected.  ATTA possesses superior selectivity, and is thus far used to analyze the environmental radioactive isotopes ⁸⁵Kr, ³⁹Ar, ⁴¹Ca, and ⁸¹Kr,  These isotopes have extremely low isotopic abundances in the range of 10^-17 to 10^-11, and cover a wide range of ages and applications.  In collaboration with earth scientists, we are dating groundwater and mapping its flow in major aquifers around the world, and dating old ice from the deep ice cores of Antarctica, Greenland, and the Tibetan Plateau. For an update on this worldwide effort, please google “ATTA Primer”.

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Trapped and laser-cooled ions allow for a high degree of control of atomic quantum systems. They are the basis for modern atomic clocks, quantum computers and quantum simulators. In our research we use ion Coulomb crystals, i.e. many-body systems with complex dynamics, for precision spectroscopy. Multi-ion clocks will not only improve the stability by exploiting the higher signal to noise of multiple ions or their uncertainty by allowing for sympathetic cooling of clock ions using a separate ion species but will be the basis for future entangled clocks and cascaded clocks.

This paves the way to novel optical frequency standards with ultra-high stability reaching 10^-19 relative accuracy and stability, and for applications such as relativistic geodesy and quantum simulators in which complex dynamics becomes accessible with atomic resolution. We will report on the first multi-ion clock operation and frequency comparisons.

Last but not least, I will briefly discuss new world-record limits we obtained in our work on an improved test of local Lorentz invariance using ¹⁷²Yb⁺ ions and the search for new bosons using clock spectroscopy on even Yb⁺ isotopes.

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The extraordinary advances in quantum control of matter and light have been transformative for atomic and molecular precision measurements enabling probes of the most basic laws of Nature to gain a fundamental understanding of the physical Universe. Exceptional versatility, inventiveness, and rapid development of precision experiments supported by continuous technological advances and improved atomic and molecular theory led to rapid development of many avenues to explore new physics. The development of high-precision optical atomic clocks enables searches for the variation of fundamental constants, dark matter, violations of Lorentz invariance, and tests of gravity. Deployment of high-precision clocks in space will open the door to new applications, including precision tests of gravity and relativity, searches for a dark-matter halo bound to the Sun, and gravitational wave detection in wavelength ranges inaccessible on Earth, and others.

I will give a broad overview of atomic clock applications on Earth and in space, focusing on searches for physics beyond the standard model of elementary particles. Several examples will be highlighted, including dark matter searches with atomic and nuclear clocks and new ideas for searches of physics beyond the standard model with quantum sensors in space. New ideas for detection of transient signals will be presented.

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The extreme electronic properties of highly charged ions (HCI) render them highly sensitive probes for testing fundamental physical theories. The same properties reduce systematic frequency shifts, making HCI excellent optical clock candidates [1]. The technical challenges that hindered the development of such clocks have now been overcome, starting with their extraction from a hot plasma and sympathetic cooling in a Paul trap [2], readout of their internal state via quantum logic spectroscopy [3], and finally the preparation of the HCI in the motional ground state of the trap [4]. Here, we present the first optical clock based on an HCI (Ar¹³⁺ in our case) and a full evaluation of systematic frequency shifts [5]. The achieved uncertainty is almost eight orders of magnitude lower than any previous frequency measurements using HCI and comparable to other optical clocks. By measuring the isotope shift between ³⁶Ar¹³⁺ and ⁴⁰Ar¹³⁺ the theoretically predicted QED nuclear recoil effect could be confirmed. Finally, first results on the search for a 5^th force based on isotope shift spectroscopy of Ca⁺/Ca¹⁴⁺ isotopes will be presented. This demonstrates the suitability of HCI as references for high-accuracy optical clocks and to probe for physics beyond the standard model.

References

1. Kozlov, M. G. et al., Rev. Mod. Phys. 90, 045005 (2018).
2. Schmöger, L. et al., Science 347, 1233 (2015).
3. Micke, P. et al., Nature 578, 60 (2020).
4. King, S. A. et al., Phys. Rev. X 11, 041049 (2021).
5. King, S. A. et al., Nature 611, 43 (2022).

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Precise atomic spectroscopy has played a pivotal role in advancing our knowledge of physics.  With the emergence of laser cooling and trapping techniques alongside stable light sources, an exceedingly high level of spectroscopic precision has been attained.  More recent developments have extended this ultrahigh precision, including atomic clock technologies, to more intricate quantum systems such as diatomic molecules.  This extension enables the characterization of molecular degrees of freedom, such as vibrational motion, with a level of resolution approaching that of atomic clocks.  Illuminating previously unknown molecular properties, this capability also suggests interesting avenues for exploring fundamental aspects of physical interactions, including the refinement of laboratory based tests probing Newtonian gravity at the nanometer scale.

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