  In their work [J. Phys. A: Math. Gen. 33, 4427 (2000)], Bender, Brody, and
Meister have shown by employing a two-state model of a particle confined in the
one-dimensional infinite potential well that it is possible to construct a
quantum-mechanical analog of the Carnot engine through the changes of both the
width of the well and the quantum state in a specific manner. Here, a
discussion is developed about realizing the maximum power of such an engine,
where the width of the well moves at low but finite speed. The efficiency of
the engine at the maximum power output is found to be universal independently
of any of the parameters contained in the model.
