Comment on “Past of a quantum particle revisited”

The recent criticism of Vaidman's proposal for the analysis of the past of a particle in the nested interferometer is refuted. It is shown that the definition of the past of the particle adopted by Englert et al. [B. G. Englert et al., Phys. Rev. A 96, 022126 (2017)] is applicable only to a tiny fraction of photons in the interferometer which indeed exhibit different behavior. Their proof that all pre- and postselected particles behave this way, i.e., follow a continuous trajectory, does not hold, because it relies on the assumption that it is intended to prove.

Figure 1

Vaidman's nested interferometer in the Englert et al. notation. The inner interferometer is tuned to destructive interference towards F.