The original 3-paths interferometer with a nested Mach-Zehnder, introduced in [2] and discussed in [4]. We have pictured here the weakly coupled pointers (the pointers in orange shift after post-selection, while those pictured in black remain unshifted as the weak value vanishes). The interferometer is balanced so that destructive interference is obtained along arm E in the absence of weak interactions.

Contexts in source publication

Context 1

... us now examine a quantum particle propagating inside the interferometer depicted in Fig. 1 in a pre and post-selected situation. Weak couplings can be implemented jointly on the different arms. Typically, the corresponding weak values are generally non-zero and all the coupled quantum pointers will shift. Vaidman [2] proposed that the weak values of the spatial projector, ˆ O = Π x ≡ |x x| could be used as a "weak trace ...

Context 2

... case, but this observation is irrelevant to having a vanishing weak value. Put differently Eq. (4) may hold irrespective of whether ψ E (x) vanishes or not 1 . A vanishing weak value requires the numerator of Eq. (1), a transition amplitude, to vanish, not the wavefunctions. This can be seen by slightly modifying the interferometer pictured in Fig. 1 in the following way (see Fig. 2). We now include the polarization of the photon and choose 1 Note this is the case here for arm D, since Π w D = 0 but ψ D (x) is not zero. The post-selected state evolved backward in time does vanish on arm D, but this backward evolved state does not seem to be taken as physically real in Ref. ...