What is the Directivity of a Quantum Antenna System? Fundamental Considerations and Examples

Quantum antenna theory is an emerging interdisciplinary field that has gained prominence in recent years. It seeks to explore applications in quantum electromagnetics, particularly in areas such as information processing and sensing using nonclassical resources. Given its foundation in quantum electrodynamics, in contrast to the classical paradigm of Maxwell-Hertz-Heaviside theory, a comprehensive understanding of what constitutes a radiating source system is crucial. Consequently, this subject necessitates a thorough and conceptual reexamination of its fundamental principles, developed rigorously and with a fresh perspective.