I just listened to a lecture on this, and I'm not sure I quite get the point. What the lecturer did was examine coherent states in the simple harmonic oscillator then linked excitations of an oscillator to the number of field quanta. The goal of the lecture was to show how Maxwell's equations naturally fall out of attempting to link quantum mechanics with special relativity. We were not trying to go through second quantization. Does this ring a bell to anyone? Maybe I'm not explaining it exactly right, but I'm looking for a resource (link or book) where I can read about this in detail to get a better grip on it. He was going quite fast and my lecture notes aren't that good because I was trying to pay attention to understand.