Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Terahertz excitation of a coherent three-level {\Lambda}-type
  exciton-polariton microcavity mode   Interactions of few-cycle terahertz pulses with the induced optical
polarization in a quantum-well microcavity reveal that the lower and higher
exciton-polariton modes together with the optically forbidden 2p-exciton state
form a unique {\Lambda}-type three-level system. Pronounced nonlinearities are
observed via time-resolved strong-terahertz and weak-optical excitation
spectroscopy and explained with a fully microscopic theory. The results show
that the terahertz pulses strongly couple the exciton-polariton states to the
2p-exciton state while no resonant transition between the two polariton levels
is observed.

10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
9
The categories of this paper are: nlin
5
The categories of this paper are: gr-qc
18
The categories of this paper are: econ
2
The categories of this paper are: math
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th