Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Secrecy content of two-qubit states   We analyze the set of two-qubit states from which a secret key can be
extracted by single-copy measurements plus classical processing of the
outcomes. We introduce a key distillation protocol and give the corresponding
necessary and sufficient condition for positive key extraction. Our results
imply that the critical error rate derived by Chau, Phys. Rev. A {\bf 66},
060302 (2002), for a secure key distribution using the six-state scheme is
tight. Remarkably, an optimal eavesdropping attack against this protocol does
not require any coherent quantum operation.

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The categories of this paper are: chem-ph
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The categories of this paper are: q-alg
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The categories of this paper are: alg-geom
11
The categories of this paper are: hep-lat
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The categories of this paper are: ao-sci
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ
6
The categories of this paper are: astro-ph
20
The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
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The categories of this paper are: comp-gas
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The categories of this paper are: chao-dyn
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The categories of this paper are: mtrl-th
2
The categories of this paper are: math
16
The categories of this paper are: stat