Applications of quantum coherence in fundamental and applied physics

Summary form only given, as follows. Much (indeed most!) of quantum mechanics is concerned with determining the eigenvalues and eigenstates of the system of interest and scattering rates between these states. But in many cases (e.g. in superconductors and lasers) coherent superpositions of states are required to understand the physics. Furthermore some of the deepest issues of physics arise from correlations and coherences between subsystems (e.g. the EPR paradox and the Bell inequalities). Quantum optics is at the heart of such such considerations. On the one hand, we find that the application of atomic coherence concepts yields lasers that operate without inversion, light pulses that propagate at a few meters/sec, and new tools for the detection of Bell states applied to quantum dense coding and teleportation. On the other hand, quantum optics yields experimental and conceptual insights into many of the counterintuitive and puzzling aspects of quantum mechanics.