  We employ a viable $f(R)$ gravity model capable of giving an inflationary
phase in order to study the subsequent reheating phase due to particle creation
at the expense of energy in the scalaron field. Since quantum mechanics is
expected to play a dominant role in particle creation, we formulate a plausible
scenario of reheating obeying Heisenberg's uncertainty principle that imposes
constraints on the particles that can be created in the configuration space. We
show that, so long as the energy available in the scalaron field is sufficient
to populate the entire configuration space, the energy density of the particles
grows, attaining a maximum value giving an efficient reheating. Beyond this
maximum, the available energy becomes insufficient to populate the entire
configuration space leading to a declining energy density.
  We further find that there is a negligible growth of energy density in the
inflationary phase that lasts for $\sim 10^2 \, t_{\rm P}$, although particles
are constantly created in this phase. The subsequent reheating phase spans for
$\sim10^{11} \, t_{\rm P}$ and it begins with a well-defined preheating stage
lasting for $\sim 10^{5} \, t_{\rm P}$, making a cross-over to a thermilization
regime. The temperature at the cross-over is found to be $T_{\rm x}\sim
10^{12}$ GeV corresponding to a temperature of $T_{r}\sim10^{13}$ GeV at the
end of reheating.
