The book provides the definitive treatment of first-order and second-order coherence. Loudon’s notation for correlation functions (g¹ and g²) has become the global standard. For anyone working in quantum communication or computing, understanding these chapters is mandatory.
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While Loudon is a masterpiece, it is not for beginners. If you find the PDF (legally) and struggle, consider these companion texts:
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Loudon masterfully interweaves theoretical derivations with experimental results. You do not just learn the density matrix; you learn how to measure it via quantum homodyne tomography. You do not just learn about photon antibunching; you read the actual experimental data from the 1970s that proved it.
Rodney Loudon was a British theoretical physicist at the University of Essex and later a visiting professor at Imperial College. Beyond his textbook, he made fundamental contributions to the theory of phonons, Raman scattering, and quantum noise. His writing style—terse, precise, and economical—reflects a deep respect for the reader’s intelligence. The Quantum Theory of Light has been cited over 25,000 times (Google Scholar) and remains the standard reference for the canonical quantization of the EM field.
