LASER: A REVERSIBLE QUANTUM DYNAMICAL SYSTEM WITH IRREVERSIBLE CLASSICAL MACROSCOPIC MOTION.

The authors describe a mathematical machine which behaves like a laser but is much simpler than any laser found in the laboratory. The machine will consist of two main parts. The first part which is the laser proper, consists of atoms and photons which are the quantized proper vibrations of a resonant cavity. It is essential that the number, N, of atoms be allowed to become very large, but the number of different photon modes can be infinite or finite. The second part consists of reservoirs. They are dynamical systems which in some sense are infinitely large compared to N, and they are so constructed that they can both pump energy into and drain energy out of the laser. However, although the energy flux from reservoir to laser is thoroughly chaotic, the laser can take this energy and structure it. In other words, the laser, when suitably coupled to the reservoir, will go into a cooperative oscillatory state in which all the N atoms and the photons vibrate coherently and periodically.