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Entanglement, Complementarity, and Vacuum Fields in Spontaneous Parametric Down-Conversion

1
Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht Straße 24-25, D-14476 Potsdam, Germany
2
Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
3
Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627, USA
*
Author to whom correspondence should be addressed.
Atoms 2019, 7(1), 27; https://doi.org/10.3390/atoms7010027
Received: 16 January 2019 / Revised: 9 February 2019 / Accepted: 12 February 2019 / Published: 19 February 2019
(This article belongs to the Special Issue Stochastic Electrodynamics)
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Abstract

Using two crystals for spontaneous parametric down-conversion in a parallel setup, we observe two-photon interference with high visibility. The high visibility is consistent with complementarity and the absence of which-path information. The observations are explained as the effects of entanglement or equivalently in terms of interfering probability amplitudes and also by the calculation of a second-order field correlation function in the Heisenberg picture. The latter approach brings out explicitly the role of the vacuum fields in the down-conversion at the crystals and in the photon coincidence counting. For comparison, we show that the Hong–Ou–Mandel dip can be explained by the same approach in which the role of the vacuum signal and idler fields, as opposed to entanglement involving vacuum states, is emphasized. We discuss the fundamental limitations of a theory in which these vacuum fields are treated as classical, stochastic fields. View Full-Text
Keywords: complementarity; vacuum fields; entanglement; Hong-Ou-Mandel effect; spontaneous parametric down-conversion complementarity; vacuum fields; entanglement; Hong-Ou-Mandel effect; spontaneous parametric down-conversion
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Menzel, R.; Heuer, A.; Milonni, P.W. Entanglement, Complementarity, and Vacuum Fields in Spontaneous Parametric Down-Conversion. Atoms 2019, 7, 27.

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