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NTT technical review

Optical-lattice-clock-network Technology for Gravitational Potential Sensing

Katsuya Oguri, Tomoya Akatsuka, Hiromitsu Imai, Toshikazu Hashimoto, Tetsuomi Sogawa

Published Jun 1, 2023• 3 citations
Publisher

Abstract

Optical lattice clocks have an ultrahigh frequency accuracy that exceeds that of cesium atomic clocks by a few orders of magnitude, enabling quantum sensing of gravitational potential equivalent to an altitude difference of only 1 cm on the Earth's surface.An optical-lattice-clock network, in which multiple optical lattice clocks are interconnected by optical fibers, is expected to become a new infrastructure, such as for a real-time sensing network of crustal movements with 1-cm-level accuracy.In this article, we introduce the elemental technologies comprising an optical-lattice-clock network.We also report on the construction of the ultrahigh-precision optical frequency transmission fiber link in the Tokyo metropolitan area and the experiment to evaluate its transmission stability.

DOI
10.53829/ntr202306fa4

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Optical lattice clocks have an ultrahigh frequency accuracy that exceeds that of cesium atomic clocks by a few orders of magnitude, enabling quantum sensing of gravitational potential equivalent to an altitude difference of only 1 cm on the Earth's surface.An optical-lattice-clock network, in which multiple optical lattice clocks are interconnected by optical fibers, is expected to become a new infrastructure, such as for a real-time sensing network of crustal movements with 1-cm-level accuracy.In this article, we introduce the elemental technologies comprising an optical-lattice-clock network.We also report on the construction of the ultrahigh-precision optical frequency transmission fiber link in the Tokyo metropolitan area and the experiment to evaluate its transmission stability.
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Differential comparisons of distant optical clocks with uncertainties in the 10-18level linked by phase-stabilized optical fibers can be used to probe the Geoid potential at the centimeter sensitivity. Here, we present the realization and characterization of a coherent optical link that will enable gravitational potential measurements on a baseline of 90km and at 1000m of difference in altitude. This is a proof-of-principle experiment that aims at exploring extensive interconnections between geodesy and frequency metrology.
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Laboratory optical atomic clocks based on quantum-logic spectroscopy of the1S0↔3P0transition in27Al+have reached a systematic uncertainty of 8.6×1018[1], enabling table-top tests of fundamental physics [2] as well as measurements of gravitational potential differences [3]. New applications in geodesy and hydrology will require that such clocks be ruggedized and packaged so that they can be deployed to and operated at sites of interest outside the laboratory. Before a high-precision global optical-frequency transfer network is realized, a portable optical clock with high accuracy could also facilitate comparison between high-accuracy clocks developed around the globe.