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Optical Fiber Communication Conference

On a classical analog of quantum entanglement

Sandu Popescu

Published Jan 1, 2001• 0 citations
Publisher

Abstract

Entanglement is considered to be a quintessential quantum effect. We show however that, surprisingly, there exists a very close classical analog of quantum entanglement. We explicitly show how many results of entanglement manipulations give interesting new results in the classical setting. We also show how the classical results shed light upon the nature of the quantum ones, and lead to more intuitive proofs of some entanglement results.

DOI
10.1364/icqi.2001.qcb2

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Entanglement is considered to be a quintessential quantum effect. We show however that, surprisingly, there exists a very close classical analog of quantum entanglement. We explicitly show how many results of entanglement manipulations give interesting new results in the classical setting. We also show how the classical results shed light upon the nature of the quantum ones, and lead to more intuitive proofs of some entanglement results.
We show that quantum entanglement has a very close classical analog, namely, secret classical correlations. The fundamental analogy stems from the behavior of quantum entanglement under local operations and classical communication and the behavior of secret correlations under local operations and public communication. A large number of derived analogies follow. In particular, teleportation is analogous to the one time pad, the concept of ``pure state'' exists in the classical domain, entanglement concentration and dilution are essentially classical secrecy protocols, and single-copy-entanglement manipulations have such a close classical analog that the majorization results are reproduced in the classical setting. This analogy allows one to import questions from the quantum domain into the classical one, and vice versa, helping to get a better understanding of both. Also, by identifying classical aspects of quantum entanglement, it allows one to identify those aspects of entanglement that are uniquely quantum mechanical.
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Summary form only given. The interference between two paths of a single photon at a double slit is widely considered to be the most paradoxical result of quantum theory. Here is a new interesting question to the phenomenon: Can a single shutter simultaneously close two slits by effectively being in a superposition of different locations? Aharonov and Vaidman have shown that it is indeed possible to construct a quantum shutter that can close two slits and reflect a probe photon perfectly when its initial and final states are appropriately selected [1]. Here we report the experimental demonstration of their proposal overcoming the difficulty to realize a quantum shutter' by employing photonic quantum routers [2]. The reflectance ratio of 0.61 ± 0.027 surpasses the classical limit with 4.1 standard deviation, shedding new light on the unusual physical properties of quantum operations. This experimental demonstration, where the strong measurement and non-local superposition seem co-existing, provides an alternative to weak measurements as a way to explore the nature of quantum physics.