Non-locality and quantum nanostructures

Hegerfeldt has shown that quantum systems with positive energy initially localized in a finite region, immediately develop infinite tails. We analyze Hegerfeldt’s theorem using quantum and classical wave packets and investigate the applicability of Hegerfeldts arguments on quantum non-locality in quantum electrodynamics. We demonstrate the appearance of non-local effects at the level of quantum states. We show, however that the expectation values of some observables spread causally. Therefore the measurement of the non-locality is questionable. We show that the classical measurement cannot detect the “acausal” effects of the non-locality. The possibility that quantum detectors may measure the effect should be investigated in the future.