Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Time resolved multi-photon effects in the fluorescence spectra of
  two-level systems at rest and in motion   We study the time-resolved fluorescence spectrum in two-level systems
interacting with an incident coherent field, both in the weak and intermediate
coupling regimes. For a single two-level system in the intermediate coupling
case, as time flows, the spectrum develops distinct features, that are not
captured by a semi-classical treatment of the incident field. Specifically, for
a field on resonance with the atomic transition energy, the usual Mollow
spectrum is replaced by a four peak structure, and for a frequency that is half
of the atomic transition energy, the time-dependent spectrum develops a second
harmonic peak with a superimposed Mollow triplet. In the long-time limit, our
description recovers results previously found in the literature. After
analyzing why a different behavior is observed in the quantum and classical
dynamics, the reason for the occurrence of a second harmonic signal in a
two-level system is explained via a symmetry analysis of the total (electron
and photon) system, and in terms of a three level system operating in limiting
regimes. We find an increased second harmonic signal in an array of two-level
systems, suggesting a superradiance-like enhancement for multiple two-level
systems in cavity setups. Finally, initial explorative results are presented
for two-level model atoms entering and exiting a cavity, which hint at an
interesting interplay between cavity-photon screening and atomic dynamics
effects.

25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
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The categories of this paper are: eess
11
The categories of this paper are: hep-lat
1
The categories of this paper are: cs
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org