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Title: Applications and detection of entanglement
Author: Bauml, Stefan
ISNI:       0000 0004 5915 4303
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Entanglement is an effect at the heart of quantum mechanics, which is both useful as a resource for information theoretic tasks and important in the fundamental understanding of physics. While bipartite maximal entangled states are well understood, applications as well as detection of other forms of entanglement - multipartite, mixed, bound - still provide many open questions. The fact that some bound entangled states can be used as a resource for quantum key distribution motivates the question of how such states can be distributed between distant parties. One way would be a conventional quantum repeater starting with distillable entanglement between the nodes and performing subsequent steps of distillation and entanglement swapping. It is, however, an intriguing question whether key can be obtained between distant parties if only bound entanglement is available between the nodes of the repeater. In this work, we provide upper bounds on the key obtainable from a quantum repeater that can be severely limited for bound entangled input states. Understanding the role of entanglement in macroscopic systems is an important task. A particular interesting question is whether there are connections between the entanglement in a given system and its thermodynamic variables. It has previously been shown that for some Hamiltonians all states below a certain internal energy are entangled. We extend this result to higher internal energies by also considering the entropy of the system. This allows us to theoretically certify entanglement of thermal states at higher temperatures than previous results. Another application of entanglement is as an additional resource for classical communication via a quantum channel. While the classical capacity of a channel assisted by maximal entanglement is known, it is an open question whether for any entangled state, there always exists a channel the classical capacity of which can be enhanced by using the state as an additional resource. We show that this is the case for one-way undistillable Werner states in small dimensions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available