  Landauer's principle has seen a boom of interest in the last few years due to
the growing interest in quantum information sciences. However, its relevance
and validity in the contexts of quantum field theory (QFT) remain surprisingly
unexplored. In the present paper, we consider Landauer's principle in
qubit-cavity QFT interaction perturbatively, in which the initial state of the
cavity QFT is chosen to be a vacuum or thermal state. In the vacuum case, the
QFT always absorbs heat and jumps to excited states. For the qubit at rest, its
entropy decreases, whereas if the qubit accelerates, it may also gain energy
and it increases its entropy due to the Unruh effect. For the thermal state,
the QFT can both absorb and release heat, depending on its temperature and the
initial state of the qubit, and the higher-order perturbations can excite or
deexcite the initial state to a higher or lower state. Landauer's principle is
valid in all the cases we consider. We hope that this paper will pave the way
for future explorations of Landauer's principle in QFT and gravity theories.
