Power, Puzzles and Properties of Entanglement

Abstract

Quantum entanglement is behind various puzzling/mysterious or paradoxical phenomena of quantum mechanics in general and of quantum information processing and communication (QIPC) in particular. Or, using less strong terms, quantum entanglement leads to highly nonintuitive or even counterintuitive effects. Some of them have been known for long time. New are being discovered almost daily. At the same time quantum entanglement is considered to be a very powerful resource for QIPC and, together quantum superposition, quantum parallelism and quantum measurement, to be the main resource of the (provable) exponentially larger power of QIPC respect to the classical information processing and communication. It is increasingly realized that quantum entanglement is at the heart of quantum physics and as such it may be of very broad importance for modern science and future technologies. It has also been to a large extent quantum entanglement that has led in quantum mechanics to asking fundamentally new questions and has brought a chance to see in a more profound way various features of the quantum world (and this way it can contribute to a new understanding of the foundations of quantum mechanics). There is therefore a large need to understand, analyze and utilize this resource. The aim of the paper is, on one side, to illustrate and analyze various puzzling phenomena that are due to the quantum entanglement and related nonlocality of quantum mechanics, as well as computational and, especially, communicational power of quantum entanglement. On the other side, the aim of the paper is to discuss main basic concepts, methods and results of the already very rich body of knowledge obtained recently at the attempts to understand, qualitatively and quantitatively, entanglement, laws and limitations of its distribution as well as its properties, structures and potentials for applications. In order to demonstrate special power of quantum entanglement two puzzles with science fiction overtones are dealt first. They look like exhibiting a telepathy.