Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Can single photon excitation of two spatially separated modes lead to a
  violation of Bell inequality via homodyne measurements?   We reconsider the all-optical homodyne-measurement based experimental schemes
that aim to reveal Bell nonclassicality of a single photon, often termed
`nonlocality'. We focus on the schemes put forward by Tan, Walls and Collett
(TWC, 1991) and Hardy (1994). In the light of our previous work the Tan, Walls
and Collett setup can be described by a precise local hidden variable model,
hence the claimed nonclassicality of this proposal is apparent, whereas the
nonclassicality proof proposed by Hardy is impeccable. In this work we resolve
the following problem: which feature of the Hardy's approach is crucial for its
successful confirmation of nonclassicality. The scheme of Hardy differs from
the Tan, Walls and Collett setup in two aspects. (i) It introduces a
superposition of a single photon excitation with vacuum as the initial state of
one of the input modes of a 50-50 beamsplitter, which creates the superposition
state of two separable (exit) modes under investigation. (ii) In the final
measurements Hardy's proposal utilises a varying strengths of the local
oscillator fields, whereas in the TWC case they are constant. In fact the local
oscillators in Hardy's scheme are either on or off (the local setting is
specified by the presence or absence of the local auxiliary field). We show
that it is the varying strength of the local oscillators, from setting to
setting, which is the crucial feature enabling violation of local realism in
the Hardy setup, whereas it is not necessary to use initial superposition of a
single photon excitation with vacuum as the initial state of the input mode.
Neither one needs to operate in the fully on/off detection scheme. Despite the
failure of the Tan, Walls and Collett scheme in proving Bell nonclassicality,
we show that their scheme can serve as an entanglement indicator.

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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: math
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The categories of this paper are: hep-ex
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The categories of this paper are: atom-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: astro-ph
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The categories of this paper are: math-ph
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The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: supr-con
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: adap-org
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The categories of this paper are: eess
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The categories of this paper are: q-bio