Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Synchronization of Distant Optical Clocks at the Femtosecond Level   The use of optical clocks/oscillators in future ultra-precise navigation,
gravitational sensing, coherent arrays, and relativity experiments will require
time comparison and synchronization over terrestrial or satellite free-space
links. Here we demonstrate full unambiguous synchronization of two optical
timescales across a free-space link. The time deviation between synchronized
timescales is below 1 fs over durations from 0.1 s to 6500 s, despite
atmospheric turbulence and kilometer-scale path length variations. Over several
days, the time wander is 40 fs peak-to-peak. Our approach relies on the two-way
reciprocity of a single-spatial-mode optical link, valid to below 225
attoseconds across a turbulent 4-km path. This femtosecond level of
time-frequency transfer should enable optical networks using state-of-the-art
optical clocks/oscillators.

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The categories of this paper are: bayes-an
0
The categories of this paper are: hep-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: patt-sol
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The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: alg-geom
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The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat
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The categories of this paper are: nucl-ex
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The categories of this paper are: econ
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The categories of this paper are: cmp-lg