  We study the quantum energy teleportation in a four-spin one-dimensional
Heisenberg model. A local magnetic field is applied at the edge sites to
control the degree of the ground-state entanglement. In the teleportation
protocol, an energy sender performs a projective measurement at one edge site,
while an energy receiver performs a feedback control at the other edge site
dependent on the measurement result to extract energy. We find that the energy
extracted by the receiver takes a maximum at intermediate value of the local
magnetic field. We also find that this magnetic-field behavior is almost
proportional to entropy changes due to the feedback control. The role of a
feedback control in an entropy change is discussed in terms of entanglement
thermodynamics.
