Quantum cryptography

Recently, quantum mechanics and information science have been combined to create a new field, namely, quantum information processing, which has been growing up rapidly in these years. The so-called quantum computing and quantum cryptography are included in this field. Although quantum information processing is quite attractive for its amazing possibility, it is also considered to be hard to realize any of such new ideas into practical use. The author develops a theory on quantum key distribution (QKD) with coherent states and a theory on two-state QKD with noisy light sources.