  A four stroke quantum engine which alternately interacts with a measurement
apparatus and a single heat bath is discussed in detail with respect to the
average work and heat as well as to the fluctuations of work and heat. The
efficiency and the reliability of such an engine with a harmonic oscillator as
working substance are analyzed under different conditions such as different
speeds of the work strokes, different temperatures of the heat bath and various
strengths of the energy supplying measurement. For imperfect thermalization
strokes of finite duration also the power of the engine is analyzed. A
comparison with a two-temperature Otto engine is provided in the particular
case of adiabatic work and ideal thermalization strokes.
