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arXiv · 1308.6346

Mixing nonclassical pure states in a linear-optical network almost always generates modal entanglement

Zhang Jiang·Matthias D. Lang·Carlton M. Caves
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Abstract

In quantum optics a pure state is considered classical, relative to the statistics of photodetection, if and only if it is a coherent state. A different and newer notion of nonclassicality is based on modal entanglement. One example that relates these two notions is the Hong-Ou-Mandel effect, where modal entanglement is generated by a beamsplitter from the nonclassical photon-number state. This suggests that beamsplitters or, more generally, linear-optical networks are mediators of the two notions of nonclassicality. In this Brief Report, we show the following: Given a nonclassical pure-product-state input to an N-port linear-optical network, the output is almost always mode entangled; the only exception is a product of squeezed states, all with the same squeezing strength, input to a network that does not mix the squeezed and anti-squeezed quadratures. Our work thus gives a necessary and sufficient condition for a linear network to generate modal entanglement from pure product inputs, a result that is of immediate relevance to the boson sampling problem.

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Zhang Jiang, Matthias D. Lang, Carlton M. Caves. 2013-10-07. Mixing nonclassical pure states in a linear-optical network almost always generates modal entanglement. https://doi.org/10.1103/physreva.88.044301

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