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arXiv:quant-ph/0105080 · Physical Review A

Bell-inequality violation with “thermal” radiation

Radim Filip, Miloslav Dušek, Jaromı́r Fiurášek, Ladislav Mišta

Published Mar 14, 2002• 14 citations
arXivHTMLPDF

Abstract

We demonstrate that radiation field in mixed thermal or phase-randomized coherent state can be entangled in such a way that Bell inequalities are violated. A counterintuitive result is obtained: a specific test reveals that maximal violation can be achieved with mixed states exhibiting large entropy.
DOI
10.1103/physreva.65.043802

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Bell’s inequality plays an important role in quantum mechanics. Many experiments have been made to test the Bell’s inequality by using various bipartite entangled sources. However, the maximal violation of the Bell inequality (i.e., the Cirel’son’s limit) has not been reached yet, due to various practically-existing imperfections (e.g., entangled source is not the pure maximally-entangled state, and the measurement settings used are not the best ones). In this paper, we investigate experimentally an approach to enhance the violation degree of Bell’s inequality with the commercialized entangled photons by optimizing the measurement settings for the experimentally-reconstructed density matrix of the entangled photons. It is shown that the measurement setting related to the pure entangled state can not get maximally violation generally. However, upon the density matrix reconstructed by tomographic technique, optimal measurement settings can be found. With these optimal settings, we consequently found that the violation degree of the Bell’s inequality can be increased. This suggests a possible approach to optimize the test of Bell’s inequality.