Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The cooperative Lamb shift in an atomic nanolayer   We present an experimental measurement of the cooperative Lamb shift and the
Lorentz shift using an atomic nanolayer with tunable thickness and atomic
density. The cooperative Lamb shift arises due to the exchange of virtual
photons between identical atoms. The interference between the forward and
backward propagating virtual fields is confirmed by the thickness dependence of
the shift which has a spatial frequency equal to $2k$, i.e. twice that of the
optical field. The demonstration of cooperative interactions in an easily
scalable system opens the door to a new domain for non-linear optics.

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The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
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The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
7
The categories of this paper are: hep-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: solv-int
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
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The categories of this paper are: adap-org
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an