Interaction-Free Energy Transfer

The interaction-free measurement scheme of Elitzur and Vaidman enables a probe particle to detect the presence of an object blocking one arm of a Mach-Zender (MZ) interferometer without the probe ever locally interacting with that object. THE MZ is tuned so that without the block, the dark port detector never fires. The presence of the block changes the interference pattern in the MZ, allowing the dark port to fire, in which case the block is detected while the probe traveled the unblocked arm. We consider a quantum block in the ground state of a confining potential, a superposition of inside and outside one arm of the MZ. When the dark port detector fires, the quantum block is localized inside the arm, which increases its energy. This energy is delivered by the probe even though it traveled the unblocked arm to reach the dark port, and we thus obtain interaction-free energy transfer. This effect obtains even though the coupling Hamiltonian is local.