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AGPhil: Arbeitsgruppe Philosophie der Physik

AGPhil 9: Quantum Mechanics I

AGPhil 9.4: Talk

Thursday, March 24, 2022, 12:30–13:00, AGPhil-H14

Does the weak trace show the past of a quantum particle in an unperturbed system? — •Jonte R Hance1, John Rarity1, and James Ladyman21Quantum Engineering Technology Laboratories, Department of Electrical and Electronic Engineering, University of Bristol, Woodland Road, Bristol, BS8 1US, UK — 2Department of Philosophy, University of Bristol, Cotham House, Bristol, BS6 6JL, UK

We investigate the weak trace method for determining the path of a quantum particle in an unperturbed system. Specifically, looking at nested interferometer experiments, when internal interferometers are tuned to destructive interference, we show that the weak trace method gives misleading results. This is because the methods used experimentally to obtain the weak value of the position operator necessarily perturb the system, hence, in some cases the assumption that weak coupling being equivalent to no coupling is incorrect. Further, even if we assume there is no disturbance, there is no reason to associate the weak value of the spatial projection operator with the classical idea of `particle presence', especially if it has features which go against the classical ideas associated with a particle being present (i.e. a particle having a single, continuous path). Experiments performed that are claimed to support the interpretation simply show the effects of this coupling acting as measurement, rather than tapping into the underlying reality of what happens in a quantum system when no-one is looking.

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