Laser Entropy

Abstract

The entropy of an ordinary (photon) laser and an atom laser (Bose condensate) is calculated. In particular, the nonzero entropy of a single mode laser or maser operating near threshold is obtained. This result is to be compared with the statement frequently made in the study of the maser heat engine to the effect that: "because maser radiation is in a pure state, its entropy is zero." Similarly, the entropy of the ground state of a Bose-Einstein condensate (a.k.a. the atom laser) is also calculated for the first time. This is to be compared with the textbook wisdom which holds that: "The condensed particles ... are condensed in momentum space, a set of stationary particles ... having zero energy and zero entropy."