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

TL;DR

This paper critiques a previous argument by clarifying misconceptions about null weak values and emphasizing the importance of quantum amplitudes over wavefunctions in inferring a particle’s past, challenging classical assumptions in quantum analysis.

Contribution

It provides a counter-example to clarify the interpretation of null weak values and argues against classical pre-conditions for understanding quantum phenomena.

Findings

Null weak values do not necessarily indicate the absence of a particle.

The relevant quantities are the vanishing amplitudes, not the wavefunction.

Classical pre-conditions are unlikely to yield a consistent quantum interpretation.

Abstract

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.