ABSTRACT
Quantum principles are exploited to study the peculiar nature of light, including a phenomenon referred to as entanglement, to which Einstein objected, calling it "spooky" action at a distance. For nearly a century, researchers have confronted the foundation of quantum mechanics, questioning the lack of determinism and the violation of causality inherent in the Copenhagen interpretation of the wave function collapse when a system is measured. This chapter develops quantum mechanics from the point of view of the Heisenberg picture. It discusses the essential elements of quantum mechanics with an emphasis on quantum aspects of nonlinear optics. The Heisenberg uncertainty principle forms a cornerstone of quantum theory with implications on the accuracy with which observable quantities can be measured. The chapter demonstrates the effects of the bath reservoir vacuum modes on a central system using a quantum-based model approach. It also introduces the concept of balanced homodyne detection to eliminate the dominant local oscillator (LO) contribution.
