  We propose a recipe for demonstrating an autonomous quantum heat engine where
the working fluid consists of a harmonic oscillator, the frequency of which is
tuned by a driving mode. The working fluid is coupled two heat reservoirs each
exhibiting a peaked power spectrum, a hot reservoir peaked at a higher
frequency than the cold reservoir. Provided that the driving mode is
initialized in a coherent state with a high enough amplitude and the parameters
of the utilized optomechanical Hamiltonian and the reservoirs are appropriate,
the driving mode induces an approximate Otto cycle for the working fluid and
consequently its oscillation amplitude begins to increase in time. We build
both an analytical and a non-Markovian quasiclassical model for this quantum
heat engine and show that reasonably powerful coherent fields can be generated
as the output of the quantum heat engine. This general theoretical proposal
heralds the in-depth studies of quantum heat engines in the non-Markovian
regime. Further, it paves the way for specific physical realizations, such as
those in optomechanical systems, and for the subsequent experimental
realization of an autonomous quantum heat engine.
