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arXiv:1709.02170 · Physical Review A

Comment on “Null weak values and the past of a quantum particle”

D. Sokolovski

Published Apr 13, 2018• 20 citations
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Abstract

In a recent paper [Phys. Rev. A 95, 032110 (2017)], Duprey and Matzkin investigated the meaning of vanishing weak values and their role in the retrodiction of the past of a preselected and postselected quantum system in the presence of interference. Here we argue that any proposition regarding the weak values should be understood as a statement about the probability amplitudes. With this in mind, we revisit some of the conclusions reached in Duprey and Matzkin's work.

DOI
10.1103/physreva.97.046102

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Comment on "Does the weak trace show the past of a quantum particle?"

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In the paper "Does the weak trace show the past of a quantum particle?" [arXiv:2109.14060v2], it is argued that null weak values of the spatial projectors are inadequate to infer the presence of a quantum particle at an intermediate time between preparation and detection. This conclusion relies on two arguments - (i) the role of the disturbance induced by a weak measurement, and (ii) classical-like features like continuous paths that must purportedly be associated with a quantum particle presence. Here we first show that (i) arises from a misunderstanding of null weak values by putting forward a simple counter-example that highlights that the relevant quantities to examine are the vanishing amplitudes, not the wavefunction. Then we briefly argue that enforcing classical pre-conditions in order to account for quantum properties during unitary evolution is unlikely to lead to a consistent understanding of quantum phenomena.

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Reply to “Comment on ‘Null weak values and the past of a quantum particle”’

Quentin Duprey, A. Matzkin

We discuss the preceding Comment [D. Sokolovski, preceding Comment, Phys. Rev. A 97, 046102 (2018)] and conclude that the arguments given there against the relevance of null weak values as representing the absence of a system property are not compelling. We give an example in which the transition matrix elements that make the projector weak values vanish are the same ones that suppress detector clicks in strong measurements. Whether weak values are taken to account for the past of a quantum system or not depend on general interpretational commitments of the quantum formalism itself rather than on peculiarities of the weak measurements framework.

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Comment on “Weak values and the past of a quantum particle”

Lev Vaidman A

In a recent paper, Hance et al. [Phys. Rev. Res. 5, 023048 (2023)] criticized recent proposals connecting weak values and the past of a quantum particle. I argue that their conclusion follows from a conceptual error in understanding the approach to the past of the particle they discuss.

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Reply to “Comment on ‘Weak values and the past of a quantum particle' ”

Jonte R. Hance, John Rarity, James Ladyman

We here reply to a recent comment by Vaidman [Phys. Rev. Res. 5, 048001 (2023)] on our paper [Phys. Rev. Res. 5, 023048 (2023)]. In his Comment, Vaidman first admits that he is just defining (assuming) the weak trace gives the presence of a particle---however, in this case, he should use a term other than presence, as this already has a separate, intuitive meaning other than ``where a weak trace is.'' Despite this admission, Vaidman then goes on to argue for this definition by appeal to ideas around an objectively existing idea of presence. We show these appeals rely on their own conclusion---that there is always a matter of fact about the location of a quantum particle.

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Reply to “Comment on ‘Weak values and the past of a quantum particle' ”

Jonte R. Hance, JG Rarity, J Ladyman

We here reply to a recent comment by Vaidman [Phys. Rev. Res. 5, 048001 (2023)] on our paper [Phys. Rev. Res. 5, 023048 (2023)]. In his Comment, Vaidman first admits that he is just defining (assuming) the weak trace gives the presence of a particle—however, in this case, he should use a term other than presence, as this already has a separate, intuitive meaning other than “where a weak trace is.” Despite this admission, Vaidman then goes on to argue for this definition by appeal to ideas around an objectively existing idea of presence. We show these appeals rely on their own conclusion—that there is always a matter of fact about the location of a quantum particle.

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Comment on “Past of a quantum particle”

Zheng-Hong Li, M. Al-Amri, Muhammad Suhail Zubairy

We present an analysis of a nested Mach-Zehnder interferometer in which an ensemble of identical pre- and postselected particles leaves a weak trace. A knowledge of the weak value partially destroys the quantum interference. The results, contrary to some recent claims [Vaidman, Phys. Rev. A 87, 052104 (2013)], are in accordance with the usual quantum-mechanical expectations.

Physical Review A•Oct 29, 2013•65 citations
In a recent paper [Phys. Rev. A 95, 032110 (2017)], Duprey and Matzkin investigated the meaning of vanishing weak values and their role in the retrodiction of the past of a preselected and postselected quantum system in the presence of interference. Here we argue that any proposition regarding the weak values should be understood as a statement about the probability amplitudes. With this in mind, we revisit some of the conclusions reached in Duprey and Matzkin's work.
In the paper "Does the weak trace show the past of a quantum particle?" [arXiv:2109.14060v2], it is argued that null weak values of the spatial projectors are inadequate to infer the presence of a quantum particle at an intermediate time between preparation and detection. This conclusion relies on two arguments - (i) the role of the disturbance induced by a weak measurement, and (ii) classical-like features like continuous paths that must purportedly be associated with a quantum particle presence. Here we first show that (i) arises from a misunderstanding of null weak values by putting forward a simple counter-example that highlights that the relevant quantities to examine are the vanishing amplitudes, not the wavefunction. Then we briefly argue that enforcing classical pre-conditions in order to account for quantum properties during unitary evolution is unlikely to lead to a consistent understanding of quantum phenomena.
We discuss the preceding Comment [D. Sokolovski, preceding Comment, Phys. Rev. A 97, 046102 (2018)] and conclude that the arguments given there against the relevance of null weak values as representing the absence of a system property are not compelling. We give an example in which the transition matrix elements that make the projector weak values vanish are the same ones that suppress detector clicks in strong measurements. Whether weak values are taken to account for the past of a quantum system or not depend on general interpretational commitments of the quantum formalism itself rather than on peculiarities of the weak measurements framework.
We here reply to a recent comment by Vaidman [Phys. Rev. Res. 5, 048001 (2023)] on our paper [Phys. Rev. Res. 5, 023048 (2023)]. In his Comment, Vaidman first admits that he is just defining (assuming) the weak trace gives the presence of a particle---however, in this case, he should use a term other than presence, as this already has a separate, intuitive meaning other than ``where a weak trace is.'' Despite this admission, Vaidman then goes on to argue for this definition by appeal to ideas around an objectively existing idea of presence. We show these appeals rely on their own conclusion---that there is always a matter of fact about the location of a quantum particle.
We here reply to a recent comment by Vaidman [Phys. Rev. Res. 5, 048001 (2023)] on our paper [Phys. Rev. Res. 5, 023048 (2023)]. In his Comment, Vaidman first admits that he is just defining (assuming) the weak trace gives the presence of a particle—however, in this case, he should use a term other than presence, as this already has a separate, intuitive meaning other than “where a weak trace is.” Despite this admission, Vaidman then goes on to argue for this definition by appeal to ideas around an objectively existing idea of presence. We show these appeals rely on their own conclusion—that there is always a matter of fact about the location of a quantum particle.