Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Four Atomic Optical Energy Levels as a Two Qubit Quantum Computer
  Register   It is proposed to use four atomic optical energy levels as a two qubit
quantum register. A single Pr3+ atom in a monocrystal LaF3 subjected to
resonant laser irradiation is used as an example to illustrate the
implementation of the universal set of quantum gates. The equilibrium state of
this physical system is a desirable input state for quantum computation and
therefore there is no need for its special preparation procedure.

19
The categories of this paper are: eess
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
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The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
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The categories of this paper are: q-fin
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex