Laboratory demonstration of geopotential measurement using transportable optical clocks
Open accessAbstract
We report an experimental demonstration of geopotential difference measurement using a pair of transportable 40 Ca+ optical clocks (TOC-729-1 and TOC-729-3) in the laboratory, each of them has an uncertainty of 1.3 × 10−17 and an instability of 4.8 × 10 − 15 / τ . Referenced to a stationary clock of TOC-729-1, the geopotential difference measurements are realized by moving TOC-729-3 to three different locations and the relevant altitude differences are measured with uncertainties at the level of 20 cm. After correcting the systematic shifts (including gravitational red shift), the two-clock frequency difference is measured to be –0.7(2.2) × 10−17, considering both the statistic (1.0 × 10−17) and the systematic (1.9 × 10−17) uncertainties. The frequency difference between these two clocks is within their respective uncertainties, verifying the reliability of transportable 40 Ca+ optical clocks at the low level of 10−17.
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Clock 2 could only be operated in the laboratory with larger volume, but its measurement systematic error reached 3 × 10^-18.
“The latter could only be operated in the laboratory with larger volume, but the measurement systematic error reached 3 × 10 -18 .”
From Performance Evaluation and Requirement Analysis for Chronometric Leveling with High-Accuracy Optical Clocks (2022) · cites this paper as [36]
The Introduction (page unavailable) says TOC-729-2 was transported 1200 km from Wuhan to Beijing and resumed operation, contrary to the claim that it could only operate in a laboratory. It reports a systematic uncertainty of 1.1 × 10^-17, not 3 × 10^-18. (LLM, conf=0.88)
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Experimental — accuracy not yet measuredThe differences from the true value measured by the classical geodetic method are 0.015 m, 0.038 m, and 0.052 m, respectively, indicating that the difference between observed results and true value could be reduced to cm level after multiple observations.
“The difference from the true value measured by the classical geodetic method is 0.015 m, 0.038 m, and 0.052 m, respectively, indicating that the difference between the observed results and the true value could be reduced to cm level after multiple observations.[36].”
From Performance Evaluation and Requirement Analysis for Chronometric Leveling with High-Accuracy Optical Clocks (2022) · cites this paper as [36]
Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.
Experimental — accuracy not yet measuredThe measurement systematic error of the optical clock mainly includes eleven items, including blackbody radiation (BBR), second-order Doppler shift, and so on, which should be evaluated before application.
“The measurement systematic error of the optical clock mainly includes eleven items, including blackbody radiation (BBR), second-order Doppler shift, and so on, which should be evaluated before application [16,18,36].”
From Performance Evaluation and Requirement Analysis for Chronometric Leveling with High-Accuracy Optical Clocks (2022) · cites this paper as [36]
Section 3.2 says systematic frequency-shift uncertainties must be evaluated, and Table 2 lists both blackbody-radiation and second-order Doppler effects. But Table 2 lists 15 individual effects, not eleven, so the claimed count is not supported. (LLM, conf=0.89)
Experimental — accuracy not yet measuredClock 1 and 2 are 40Ca+ optical clocks developed by APM.
“Both Clock 1 and 2 are 40 Ca + optical clocks developed by APM [18,36].”
From Performance Evaluation and Requirement Analysis for Chronometric Leveling with High-Accuracy Optical Clocks (2022) · cites this paper as [36]
The Introduction (page unavailable) says that TOC-729-1, TOC-729-2, and TOC-729-3 are transportable ⁴⁰Ca⁺ optical clocks developed in Wuhan, supporting the clock type for 1 and 2. Our copy does not identify APM as their developer; the Experimental details also clarify that this paper's measurement used clocks 1 and 3, not 1 and 2. (LLM, conf=0.82)
Experimental — accuracy not yet measuredIn the 2022 laboratory experiment, two transportable 40Ca+ optical clocks were connected by a 10 m long optical fiber, one fixed and the other at three different heights, and the height measurement uncertainty was about 21 cm.
“In 2022, the experiment has been completed in the laboratory [36].Two transportable 40 Ca + optical clocks were connected by a 10 m long optical fiber.One of the optical clocks was fixed, and the other optical clock was located at three different heights for the experiments.The uncertainty of the height measurement was about 21 cm.”
From Performance Evaluation and Requirement Analysis for Chronometric Leveling with High-Accuracy Optical Clocks (2022) · cites this paper as [36]
The Introduction and Experimental details describe two transportable ⁴⁰Ca⁺ clocks, with one stationary and the other moved to three altitudes. Section 3.1 reports height uncertainties of 20, 21, and 22 cm, so “about 21 cm” is supported. Our copy does not establish that the clocks were connected by a 10 m optical fiber or that the experiment took place in 2022. (LLM, conf=0.88)
Experimental — accuracy not yet measured
Several groups today operate transportable optical clocks.
“Today, several groups operate transportable optical clocks [16, 17, 25-31].”
From Long-distance chronometric leveling with a portable optical clock (2024) · cites this paper as [17]
Experimental — accuracy not yet measuredClock 1 is a miniaturized transportable optical clock with systematic error 1.3 × 10^-17.
“The former is a miniaturized transportable optical clock, and the systematic error reaches 1.3 × 10 -17 .”
From Performance Evaluation and Requirement Analysis for Chronometric Leveling with High-Accuracy Optical Clocks (2022) · cites this paper as [36]
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Long-distance chronometric leveling with a portable optical clock
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“Previously, extremely small redshifts have been resolved with optical clocks [12, 13] by differential observations in a single apparatus.”
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Self-citation
- Authors
- Liu, D.-X., Cao, J., Yuan, J.-B., Cui, K.-F., Yuan, Y., Zhang, P., Chao, S.-J., Shu, H.-L., & Huang, X.-R.
- Affiliations
- Innovation Academy for Precision Measurement Science and Technology, CAS (CN)
- Chinese Academy of Sciences (CN)
- Venue
- Chinese Physics B
- Publisher
- IOP Publishing
- Published
- 2023-01-01
- Volume
- 32
- Issue
- 1
- Pages
- 010601
- ISSN
- 1674-1056 (ISSN-L)
- OpenAlex
- W4220948699
- Cited by
- 10
- References
- 40
- Citations by year
- 2026: 2 · 2025: 4 · 2024: 3 · 2022: 1
- FWCI
- 0.81
- Type
- journal article
- Language
- lv
- Open access
- bronze
- doi.org
- Licence
- Locations
- Chinese Physics B (publishedVersion)
- Funders
- National Natural Science Foundation of China (ZDBS-LY-DQC028, 11674357)
- Chinese Academy of Sciences (ZDBS-LY-DQC028)
- National Key Research and Development Program of China (2017YFA0304404)
- Topics
- Physical Sciences › Physics and Astronomy › Atomic and Molecular Physics, and Optics › Advanced Frequency and Time Standards
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Relativity and Gravitational Theory
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Scientific Measurement and Uncertainty Evaluation
- Keywords
- frequency comparison, gravitational redshift, altitude measurement, frequency stability
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