Fundamental Tests of Quantum Mechanics

This chapter discusses experiments aimed at testing three of these concepts: complementarity, or more particularly wave‐particle duality; indistinguishability; and non‐locality. Quantum systems can display both particle‐like and wave‐like properties. A few experiments have been carried out to probe wave‐particle duality in this intermediate domain, both with massive particles and in optics. The chapter expresses that the trajectories evolve from a particle‐like situation as they emerge from the fibres to a wave‐like interference pattern. Another fundamental difference between classical and quantum physics is the indistinguishability of quantum particles. In classical mechanics one can always label different particles in an ensemble by their position and momentum. A unique feature of quantum mechanics is its non‐local character. The effect of entanglement can be observed by measuring continuous quadrature variables of the entangled beams with homodyne detection. The detection of quantum correlation is carried out via the suitable combination of the photocurrents from both beams.