Abstract
Despite their important applications in metrology and in spite of numerous experimental demonstrations, weak measurements are still confusing for part of the community. This sometimes leads to unjustified criticism. Recent papers have experimentally clarified the meaning and practical significance of weak measurements, yet in Kastner (Found Phys 47:697–707, 2017), Kastner seems to take us many years backwards in the the debate, casting doubt on the very term “weak value” and the meaning of weak measurements. Kastner appears to ignore both the basics and frontiers of weak measurements and misinterprets the weak measurement process and its outcomes. In addition, she accuses the authors of Aharonov et al. (Ann Phys 355:258–268, 2015) in statements completely opposite to the ones they have actually made. There are many points of disagreement between Kastner and us, but in this short reply I will leave aside the ontology (which is indeed interpretational and far more complex than that described by Kastner) and focus mainly on the injustice in her criticism. I shall add some general comments regarding the broader theory of weak measurements and the two-state-vector formalism, as well as supporting experimental results. Finally, I will point out some recent promising results, which can be proven by (strong) projective measurements, without the need of employing weak measurements.
Highlights
Found Phys (2017) 47:1261–1266 nature of weak values [14] and their physical meaning, which goes far beyond a conditional average [15]
I examine and disprove several of Kastner’s claims [16], but first I shall correct some injustice made to the authors of [17], which Kastner denotes by ACE. She asserts that “It should be clarified that taking post-selection into account does not indicate any departure from standard one-vector quantum theory, as ACE suggest”
This claim of Kastner stands in stark contrast with the statements that Aharonov, Elitzur and I have made in [17]: “As TSVF and traditional quantum theory are equivalent, obliging one- and two-vector explanations to be valid, this contradiction can be resolved in two ways” and “TSVF is unique among the above models in that it has derived several predictions that, fully consistent with the standard formalism, seem surprising and more acutely opposed to classical laws”
Summary
Found Phys (2017) 47:1261–1266 nature of weak values [14] and their physical meaning, which goes far beyond a conditional average [15]. Kastner’s repetitive claims that weak measurements and weak values are part of standard quantum mechanics, are obvious and well-known. When using weak values, and both pre- and postselection at the same time, all outcomes can be found (up to minor corrections which scale like the square of coupling strength).
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