Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coherent Population Trapping of Electron Spins in a Semiconductor   In high-purity n-type GaAs under strong magnetic field, we are able to
isolate a lambda system composed of two Zeeman states of neutral-donor bound
electrons and the lowest Zeeman state of bound excitons. When the two-photon
detuning of this system is zero, we observe a pronounced dip in the
excited-state photoluminescence indicating the creation of the coherent
population-trapped state. Our data are consistent with a steady-state
three-level density-matrix model. The observation of coherent population
trapping in GaAs indicates that this and similar semiconductor systems could be
used for various EIT-type experiments.

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The categories of this paper are: hep-ph
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The categories of this paper are: stat
24
The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys
2
The categories of this paper are: math
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The categories of this paper are: econ
30
The categories of this paper are: q-alg
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The categories of this paper are: adap-org
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The categories of this paper are: nucl-ex
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The categories of this paper are: nlin
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The categories of this paper are: ao-sci
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The categories of this paper are: patt-sol
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The categories of this paper are: solv-int
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat