Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An exact effective two-qubit gate in a chain of three spins   We show that an effective two-qubit gate can be obtained from the free
evolution of three spins in a chain with nearest neighbor XY coupling, without
local manipulations. This gate acts on the two remote spins and leaves the
mediating spin unchanged. It can be used to perfectly transfer an arbitrary
quantum state from the first spin to the last spin or to simultaneously
communicate one classical bit in each direction. One ebit can be generated in
half of the time for state transfer.
  For longer spin chains, we present methods to create or transfer entanglement
between the two end spins in half of the time required for quantum state
transfer, given tunable coupling strength and local magnetic field. We also
examine imperfect state transfer through a homogeneous XY chain.

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The categories of this paper are: gr-qc
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The categories of this paper are: plasm-ph
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The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
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The categories of this paper are: nlin
6
The categories of this paper are: astro-ph
2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
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The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
14
The categories of this paper are: math-ph
29
The categories of this paper are: funct-an
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The categories of this paper are: stat
10
The categories of this paper are: q-bio