Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Broadband coupling of fast electrons to high-Q whispering-gallery mode
  resonators   Transmission electron microscopy is an excellent experimental tool to study
the interaction of free electrons with nanoscale light fields. However, up to
now, applying electron microscopy to quantum optical investigations was
hampered by the lack of experimental platforms which allow a strong coupling
between fast electrons and high-quality resonators. Here, as a first step, we
demonstrate the broad-band excitation of optical whispering-gallery modes in
silica microresonators by fast electrons. In the emitted coherent
cathodoluminescence spectrum, a comb of equidistant peaks is observed,
resulting in cavity quality factors larger than 700. These results enable the
study of quantum optical phenomena in electron microscopy with potential
applications in quantum electron-light metrology.

26
The categories of this paper are: bayes-an
29
The categories of this paper are: funct-an
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
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The categories of this paper are: patt-sol
6
The categories of this paper are: astro-ph
17
The categories of this paper are: q-fin
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The categories of this paper are: alg-geom
36
The categories of this paper are: cmp-lg
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The categories of this paper are: acc-phys
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The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
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The categories of this paper are: atom-ph
16
The categories of this paper are: stat