Quantum communication entanglement

However, in quantum communication, entanglement is much better understood and clearly sets apart quantum protocols as a distinct class. 

In this equation, C andT refer to control and target qubits, respectively. The resulting state (output of the qugate) is said to be an entangled state of the two qubits, that is, a state that cannot be written as a product of states for each qubit [30]. The occurrence of such entangled states is another characteristic trait of QC, at the basis of secure quantum communication or cryptography. It also implies that, as opposed to what happens with a classical bit, an arbitrary quantum bit cannot be copied (the COPY classical operation is, in fact, based on the application of a succession of classical CNOT gates) [4]. 

Besides quantum computations, entanglement has also been at the core of other active research such as quantum teleportation [32, 33], dense coding [34, 35], quantum communication [36], and quantum cryptography [37]. It is believed that the conceptual puzzles posed by entanglement have now become a physical source of novel ideas that might result in applications. 

Entanglement is the main resource of quantum information processing, without which quantum computation will not be faster than its classical counterpart [8] and quantum communication protocols will not work [113-115]. Moreover, as shown... 

Entanglement is a vital information resource employed in quantum teleportation, dense coding and quantum computation [Nielsen 2000], The fundamental role played by the entanglement in quantum information science was discussed in part I this part of the book is devoted to the generation and characterization of the entanglement of photons and their usage in quantum communication and computation protocols. 

Greenberger 1989 Greenberger 1990], Distributed entanglement thus allows to establish non-classical correlations between distant parties and can therefore be considered as a quantum analogue of the classical communication channel, a quantum communication channel. 

Quantum Communication wifii Entangled Photons, Hamid Weinfurter... 

A very active field of current research is the exploration of possible applications of entangled photons to communication, cryptography and quantum computation. 

Finally, I would like to say a few words about entanglement in communication, as the last caveat to the Jozsa-Linden theorem. I will just use the example of quantum teleportation. 

Laboratoire Kastler Brossel is a laboratory of Universite Pierre et Marie Curie and ENS, associated to CNRS (UMR 8552). We acknowledge support of the European Community, of the Japan Science and Technology corporation (International Cooperative Research Project Quantum Entanglement). 

There is an interesting connection between the energy needed to destroy entanglement, as indicated by this experiment, and the entropy production when quantum information is erased [30], Further experiments with femtosecond time resolution will probably help to clarify this connection and its possible influence on future quantum computer and communication systems. 

In microscopic systems, it is not always possible (and generally it is not possible) to observe a system without disturbing it. The phenomenon of entanglement also occurs, in which separated bodies could be correlated in a way that cannot be explained by traditional classical communication. The notion of quantum information can be abstracted, in much the same way as the notions of classical information. There are actually more things that can be done with information, if it is regarded in this quantum fashion. 

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