Commentary: “Asking photons where they have been” - without telling them what to say

Abstract

We argue that, in the recent letter by A. Danan et al. [PRL 111, 240402 (2013), arXiv:1304.7469], if weak measurements are performed such that complete destructive interference is not disturbed, claims such as "some photons have been inside the inner interferometer but they never entered and never left" should not arise. Standard quantum mechanics not only explains the physics better than the two-state vector formulation the authors advocate, but it can tell a very different story.