Nonclassicality

This thesis examines the nonclassicality of quantum theory, including entanglement, and its application to quantum information, with special emphasis on quantum cryptography. The various nonclassical aspects of quantum theory, including their application to quantum cryptographic protocol, are studied in terms of their implementation using quantum optics. We first study the generation of two types of nonclassical quantum state, a coherent-state superposition and the non-Gaussian state obtained through the addition or subtraction of a single photon from a Gaussian field. In the work we examine several nonclassical properties, for example, quantum nonlocality, tested using Bell in-equalities, quantum teleportation, negativity of Wigner function, etc. Secondly, we examine the problem of spring-like coupling between bosons in an open chain configuration. This allows us to include the effects of the counter-rotating terms in the long-haul entanglement distribution. Finally, we provide one example of an application of quantum theory to the area of quantum information, more specifically to the field of quantum cryptography.