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arXiv:1707.04230 · Journal of Computational and Theoretical Nanoscience

Discrete-Event Simulation Unmasks the Quantum Cheshire Cat

Kristel F. L. Michielsen, Thomas Lippert, Hans A. De Raedt

Published May 1, 2017• 1 citation
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Abstract

It is shown that discrete-event simulation accurately reproduces the experimental data of a single-neutron interferometry experiment [T. Denkmayr {\sl et al.}, Nat. Commun. 5, 4492 (2014)] and provides a logically consistent, paradox-free, cause-and-effect explanation of the quantum Cheshire cat effect without invoking the notion that the neutron and its magnetic moment separate. Describing the experimental neutron data using weak-measurement theory is shown to be useless for unravelling the quantum Cheshire cat effect.

DOI
10.1166/jctn.2017.6819

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It is shown that discrete-event simulation accurately reproduces the experimental data of a single-neutron interferometry experiment [T. Denkmayr {\sl et al.}, Nat. Commun. 5, 4492 (2014)] and provides a logically consistent, paradox-free, cause-and-effect explanation of the quantum Cheshire cat effect without invoking the notion that the neutron and its magnetic moment separate. Describing the experimental neutron data using weak-measurement theory is shown to be useless for unravelling the quantum Cheshire cat effect.
In a July 2014 Nature Communications paper, Denkmayr et al. claim to have instantiated so-called quantum Cheshire Cat experiment using neutron interferometry. Crucial to this claim are weak values which must imply quantum Cheshire Cat interpretation, i.e., the neutron and its spin are spatially separated in their experiment. While they measured correct weak values for quantum Cheshire Cat interpretation, corresponding implications do not obtain because, as we show, those weak values were measured with both a quadratic and a linear magnetic field Bz interaction. We show explicitly how those weak values imply quantum Cheshire Cat if Bz interaction is linear and then we show how quadratic Bz interaction destroys quantum Cheshire Cat implications of those weak values. Since both linear and quadratic Bz interactions contribute equally to neutron intensity in this experiment, deviant weak value implications are unavoidable. Because weak values were used successfully to compute neutron intensities for weak Bz in this experiment, it is clearly case that one cannot make ontological inferences from weak values without taking into account corresponding interaction strength.
A discrete-event approach, which has already been shown to give a cause-and-effect explanation of many quantum optics experiments, is applied to single-neutron interferometry experiments. The simulation algorithm yields a logically consistent description in terms of individual neutrons and does not require the knowledge of the solution of a wave equation. It is shown that the simulation method reproduces the results of several single-neutron interferometry experiments, including experiments which, in quantum theoretical language, involve entanglement. Our results demonstrate that classical (non-Hamiltonian) systems can exhibit correlations which in quantum theory are associated with interference and entanglement, also when all particles emitted by the source are accounted for.
In a recent work, Aharonov et al suggested that a photon could be separated from its polarization in an experiment involving pre- and post-selection (Aharonov et al 2013 New J. Phys. 15 113015 ). They named the effect 'quantum Cheshire Cat', in a reference to the cat that is separated from its grin in the novel Alice ' s Adventures in Wonderland . Following these ideas, Denkmayr et al performed a neutron interferometric experiment and interpreted the results suggesting that neutrons were separated from their spin (Denkmayr et al 2014 Nat. Commun. 5 4492 ). Here we show that these results can be interpreted as simple quantum interference, with no separation between the quantum particle and its internal degree of freedom. We thus hope to clarify the phenomenon with this work, by removing these apparent paradoxes.
A discrete-event approach, which has already been shown to give a cause-and-effect explanation of many quantum optics experiments, is applied to single-neutron interferometry experiments. The simulation algorithm yields a logically consistent description in terms of individual neutrons and does not require the knowledge of the solution of a wave equation. It is shown that the simulation method reproduces the results of several single-neutron interferometry experiments, including experiments which, in quantum theoretical language, involve entanglement. Our results demonstrate that classical (non-Hamiltonian) systems can exhibit correlations which in quantum theory are associated with interference and entanglement, also when all particles emitted by the source are accounted for.
In a July 2014 Nature Communications paper, Denkmayr et al. claim to have instantiated the so-called quantum Cheshire Cat experiment using neutron interferometry. Crucial to this claim are the weak values which must imply the quantum Cheshire Cat interpretation, i.e., "the neutron and its spin are spatially separated" in their experiment. While they measured the correct weak values for the quantum Cheshire Cat interpretation, the corresponding implications do not obtain because, as we show, those weak values were measured with both a quadratic and a linear magnetic field Bz interaction. We show explicitly how those weak values imply quantum Cheshire Cat if the Bz interaction is linear and then we show how the quadratic Bz interaction destroys the quantum Cheshire Cat implications of those weak values. Since both linear and quadratic Bz interactions contribute equally to the neutron intensity in this experiment, the deviant weak value implications are unavoidable. Because weak values were used successfully to compute neutron intensities for weak Bz in this experiment, it is clearly the case that one cannot make ontological inferences from weak values without taking into account the corresponding interaction strength.