If I understand things correctly, the coherent state of a laser beam implies that the photon quantum field is a superposition of states with different particle numbers. This also implies that a laser beam is not in an energy eigenstate. To get energy conservation, I assume that this corresponds to the laser medium that creates the laser beam to exist in an overlap of different states with different numbers of atoms excited, so there is entanglement between the state in the laser beam and the state in the laser medium. If, for example, I start with 100 atoms in the excited state (and I measured that very precisely so that there is no initial uncertainty of energy), the part of the laser wave function that contains one photon would be entangled with the state of the laser medium where 99 atoms are excited (one photon emitted) and so on. Is this a correct picture? If so, what would happen to the laser beam if I later on measure the energy content of the laser medium (for example using a very precise weighing apparatus)? Would the state of the laser beam collapse to a state of well-defined photons? And, if so, to spin the idea further, would this mean that it is impossible to create a laser beam if I were to weigh the laser medium continuously? Not that any of this seems impossible, but it does seem weird to me and is not something that I ever read anywhere. So, is it all rubbish? If so, why?