In this chapter, the quantum communication system is described. The concept of fidelity quantifying the faithfulness of quantum state transfer is discussed. For detailed exposure on this topic, [ 71 , 86 , 113 ] is helpful references.
This chapter contains concepts from quantum physics which are essential for the understanding of the teleportation protocols. Qubit system is discussed separately along with the laws of its evolution. Quantum gates and quantum circuits are described. The description is limited to the technical and conceptual requirements for understanding the materials in the book. For an extensive appraisal of the topics included in this chapter, [ 6 , 12 , 15 , 32 , 35 , 55 , 77 , 81 , 107 , 113 , 117 , 134 , 139 , 140 , 149 , 163 , 171 ] are helpful references.
Abstract This chapter gives an overview of the theory of optical absorption and emission in atoms at the level appropriate to introductory quantum and atomic-physics texts. The aim is to provide an introduction to the more advanced treatment of these topics given later in the book, especially in Chapters 9 and 10. It is assumed that the reader is reasonably familiar with the concepts, and so the material is only developed in summary form. Readers who are less well acquainted with these topics may find it helpful to refer to the bibliography for further details.
This article provides a quick overview of quantum communication, bringing together several innovative aspects of quantum enabled transmission. We first take a neutral look at the role of quantum communication, presenting its importance for the forthcoming wireless. Then, we summarise the principles and basic mechanisms involved in quantum communication, including quantum entanglement, quantum superposition, and quantum teleportation. Further, we highlight its groundbreaking features, opportunities, challenges and future prospects.
This chapter describes the principle of compression in quantum communication channels. The underlying concept is that it is possible to convey “faithfully” a quantum message with a large number of qubits, while transmitting a compressed version of this message with a reduced number of qubits through the channel. Beyond the mere notion of fidelity , which characterizes the quality of quantum message transmission, the description brings the new concept of typicality in the space defined by all possible “quantum codewords.” The theorem of Schumacher's quantum compression states that for a qubit source with von Neumann entropy S , the message compression factor R has S − ε for the lower bound, where ε is any nonnegative parameter that can be made arbitrarily small for sufficiently long messages (hence, R ≈ S is the best possible compression factor). An original graphical and numerical illustration of the effect of Schumacher's quantum compression and the evolution of the typical quantum-codeword subspace with increasing message length is provided. Quantum data compression and fidelity In this chapter, we have reached the stage where it is possible to start addressing the issues that are central to information theory, namely, “How efficiently can we code information in a quantum communication channel?” both in terms of economy of means – the concept of data compression – and accuracy of transmission – the concept of message integrity or minimal data error , referred to here as fidelity .