  Established heat engines in quantum regime can be modeled with various
quantum systems as working substances. For example, in the non-relativistic
case, we can model the heat engine using infinite potential well as a working
substance to evaluate the efficiency and work done of the engine. Here, we
propose quantum heat engine with a relativistic particle confined in the
one-dimensional potential well as working substance. The cycle comprises of two
isothermal processes and two potential well processes of equal width, which
forms the quantum counterpart of the known isochoric process in classical
nature. For a concrete interpretation about the relation between the quantum
observables with the physically measurable parameters (like the efficiency and
work done), we develop a link between the thermodynamic variables and the
uncertainty relation. We have used this model to explore the work extraction
and the efficiency of the heat engine for a relativistic case from the
standpoint of uncertainty relation, where the incompatible observables are the
position and the momentum operators. We are able to determine the bounds (the
upper and the lower bounds) of the efficiency of the heat engine through the
thermal uncertainty relation.
