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Introduction to Quantum Information Science$
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Vlatko Vedral

Print publication date: 2006

Print ISBN-13: 9780199215706

Published to Oxford Scholarship Online: January 2010

DOI: 10.1093/acprof:oso/9780199215706.001.0001

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Quantum entanglement in practice

Quantum entanglement in practice

(p.102) 9 Quantum entanglement in practice
Introduction to Quantum Information Science

Vlatko Vedral

Oxford University Press

This chapter explains how entanglement witnesses can be measured in practice. The main idea behind the Mach–Zehnder interferometer experiment described earlier is to test for and even measure quantum entanglement. The key idea is discussed along with its exact application. Partial transposition is not a physical operation because it is a positive map rather than a CP-map. Therefore, it cannot be implemented directly within the quantum formalism. However, an entanglement witness is the average of some Hermitian operator, and this average is a physically measurable quantity. Thus, it is possible to measure the effects of the partial transposition in some indirect way. This chapter discusses the implementation of the Peres Horodecki criterion using an interferometer. The important message is that a simple apparatus that measures quantum superpositions, such as a Mach–Zehnder interferometer, can also be used for much more complicated measurements.

Keywords:   quantum entanglement, entanglement witnesses, Mach–Zehnder interferometer, partial transposition, Peres Horodecki criterion, quantum superpositions

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