Photonic Quantum Information Processing

This book provides a structured, self-contained path from the quantum theory of light to the photonic quantum technologies built on it. Starting from canonical quantization, coherent states, and phase-space representations, it develops the full Gaussian-state and covariance-matrix formalism, then builds the information-theoretic layer — state discrimination, quantum channels, and parameter estimation — before culminating in quantum key distribution, bosonic error correction, and photonic quantum computing. Every result is derived from first principles, with physical intuition leading and supporting appendices supplying the mathematical machinery. Develops coherent, squeezed, cat, and thermal states alongside Wigner functions, quasiprobability distributions, and the covariance-matrix formalism, giving a unified phase-space framework for states, dynamics, and measurement. Treats beam splitters, interferometers, and Reck/Clements linear-optical networks as both mathematical objects and programmable hardware, together with photodetection, homodyne, and heterodyne measurement. Presents two-mode squeezing and continuous-variable entanglement as the resource layer for teleportation and cluster-state architectures. Builds the information-theoretic core — quantum state discrimination, quantum channels and the Holevo bound, and quantum parameter estimation via Fisher information and Cramer-Rao bounds — with squeezed-light-enhanced interferometry as the flagship application. Covers quantum key distribution end to end, from BB84 through continuous-variable protocols, including security analysis and privacy amplification. Concludes with bosonic quantum error correction (GKP and cat codes) and photonic quantum computing, including the KLM protocol, boson sampling, and measurement-based computation with cluster states. With complete derivations, worked examples, and exercises in every chapter, this text is ideal for graduate students and researchers seeking a rigorous, intuition-first foundation in photonic quantum information.