Comment on Backow in relativistic wave equations Maximilien Barbier1 Christopher J. Fewster2 Arseni Goussev3 Gregory Morozov1 and Shashi C. L. Srivastava45

2025-04-27 0 0 122.55KB 2 页 10玖币
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Comment on “Backflow in relativistic wave equations”
Maximilien Barbier1, Christopher J. Fewster2, Arseni Goussev3, Gregory Morozov1, and
Shashi C. L. Srivastava4,5
1Scottish Universities Physics Alliance, Institute of Thin Films, Sensors and Imaging, University of the
West of Scotland, Paisley PA1 2BE, Scotland, UK
2Department of Mathematics, University of York, York YO10 5DD, UK
3School of Mathematics and Physics, University of Portsmouth, Portsmouth PO1 3HF, UK
4Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata 700064, India
5Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai - 400094, India
The stated goal of Ref. [1] is to argue that “the phenomenon of backflow is a common feature
of various physical system[s], quantum and classical, described by the linear wave equations”.
The authors challenge a perceived view that “backflow is inseparably connected with quantum
theory”. In particular, the authors strongly oppose statements in the literature that backflow is
a “peculiar quantum effect”, an “intriguing quantum-mechanical phenomenon”, a “surprising
and clearly nonclassical effect”, a “classically impossible phenomenon”, and a “generic purely
quantum phenomenon”.
It appears that the authors of [1] have misunderstood the purpose of the statements to which
they object. To explain, we must distinguish two mathematically inseparable, but physically
distinct phenomena: backflow (B) and quantum backflow (QB). In more detail:
(B) Backflow. This is a general wave phenomenon, which may be defined, quoting [1], as “the
counterintuitive behavior of the flow of some quantity (energy, probability, etc). Namely,
in some regions of space the direction of the flow is opposite with respect to the direction
of all its constituent elementary waves.” As the authors correctly state, B is “a common
feature of various physical system[s], quantum and classical, described by the linear wave
equations” [1]. This statement is not subject to doubt and, to our knowledge, has never
been challenged.
(QB) Quantum backflow [2, 3]. This is the phenomenon of backflow specific to quantum
particles such as electrons, which concerns the following question: Can the position prob-
ability density of a particle flow to the left if the particle’s momentum points to the right?
Consider a free quantum particle moving in one dimension and suppose that, in the initial
state, the measured value of momentum would be positive with probability 1. Is it possible
that the probability of finding the particle in the left-hand half-line is higher at a later time
than it is initially? In classical particle mechanics, the answer to this question is negative.
In quantum mechanics, it is positive. This is why numerous authors have referred to QB
as a “peculiar quantum effect”, “intriguing quantum-mechanical phenomenon”, “surpris-
ing and clearly nonclassical effect”, “classically impossible phenomenon”, and “generic
purely quantum phenomenon”. Such phrases concern the contrast between the classical
and quantum dynamics of particles.
QB arises, of course, because quantum mechanics describes particle mechanics using a wave
equation. For exactly the same reason, quantum particles exhibit diffraction and interference
1
arXiv:2210.05368v1 [quant-ph] 11 Oct 2022
摘要:

CommentonBackowinrelativisticwaveequations"MaximilienBarbier1,ChristopherJ.Fewster2,ArseniGoussev3,GregoryMorozov1,andShashiC.L.Srivastava4,51ScottishUniversitiesPhysicsAlliance,InstituteofThinFilms,SensorsandImaging,UniversityoftheWestofScotland,PaisleyPA12BE,Scotland,UK2DepartmentofMathematics,Un...

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