Quantum interference: from microscopic measurements to macroscopic reality

According to Feynman, the double slit experiment, which is the archetype of interference experiments, constitutes the only mystery in quantum mechanics. The sensitive dependence of the interference fringes on small differences in path length traversed by a single particle travelling in superposition are a key signature of wave-particle duality. I will give an overview of some experimental schemes that try to use interference to increase the precision of sensors, and also tell a little of the more modern experiments that can be used to learn about the fundamental nature of quantum systems, both micro and macro.