  Similarity between quantum mechanics and thermodynamics is discussed. It is
found that if the Clausius equality is imposed on the Shannon entropy and the
analogue of the heat quantity, then the value of the Shannon entropy comes to
formally coincide with that of the von Neumann entropy of the canonical density
matrix, and pure-state quantum mechanics apparently transmutes into quantum
thermodynamics. The corresponding quantum Carnot cycle of a simple two-state
model of a particle confined in a one-dimensional infinite potential well is
studied, and its efficiency is shown to be identical to the classical one.
