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Comment on: Observation of a quantum Cheshire Cat in a matter-wave interferometer experiment

W. M. Stuckey, Michael Silberstein, Timothy J. McDevitt

Published Oct 5, 2014• 1 citation
OpenAlex

Abstract

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.

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The quantum Cheshire Cat experiment of Denkmayr et al

W. M. Stuckey, Michael Silberstein, Timothy J. McDevitt

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.

•Oct 5, 2014•1 citation

Concerning Quadratic Interaction in the Quantum Cheshire Cat Experiment

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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.

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The validity of quantum-mechanical predictions has been confirmed with a high degree of accuracy in a wide range of experiments. Although the statistics of the outcomes of a measuring apparatus have been studied intensively, little has been explored and is known regarding the accessibility of quantum dynamics. For these sorts of fundamental studies of quantum mechanics, interferometry using neutron matter-waves in particular, provides almost ideal experimental circumstances. In this device quantum interference between spatially separated beams occurs on a macroscopic scale. Recently, the full determination of weak-values of neutrons 1 2 - spin adds a new aspect to the study of quantum dynamics. Moreover, a new counter-intuitive phenomenon, called quantum Cheshire Cat, is observed in an interference experiment. In this article, we present an overview of these experiments.

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Raul Correa Silva

Based on the concept of weak measurements, in 2013 Aharonov et al. proposed an experiment in which, according to their interpretation of the predicted results, a photon and its circular polarization were spatially separated, naming this phenomenon quantum Cheshire Cat [1]. This name is after a character in Lewis Carrolls novel Alice In Wonderland, the Cheshire Cat a cat whose grin can exist without the animal itself. Denkmayr et al., in 2014, claimed they realized experimentally the quantum Cheshire Cat, separating a neutron from its intrinsic magnetic moment [3]. We show how both results follow from interference effects, and thus the conclusion that a particle is separated from one of its intrinsic properties is not a necessary one. Making use of mostly undergraduate level quantum mechanics, we rule out the apparent paradox of the quantum Cheshire Cat.

•Feb 25, 2015•0 citations
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.
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.
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.
The validity of quantum-mechanical predictions has been confirmed with a high degree of accuracy in a wide range of experiments. Although the statistics of the outcomes of a measuring apparatus have been studied intensively, little has been explored and is known regarding the accessibility of quantum dynamics. For these sorts of fundamental studies of quantum mechanics, interferometry using neutron matter-waves in particular, provides almost ideal experimental circumstances. In this device quantum interference between spatially separated beams occurs on a macroscopic scale. Recently, the full determination of weak-values of neutrons 1 2 - spin adds a new aspect to the study of quantum dynamics. Moreover, a new counter-intuitive phenomenon, called quantum Cheshire Cat, is observed in an interference experiment. In this article, we present an overview of these experiments.
From its very beginning, quantum theory has been revealing extraordinary and counter-intuitive phenomena, such as wave-particle duality, Schrödinger cats and quantum non-locality. Another paradoxical phenomenon found within the framework of quantum mechanics is the 'quantum Cheshire Cat': if a quantum system is subject to a certain pre- and postselection, it can behave as if a particle and its property are spatially separated. It has been suggested to employ weak measurements in order to explore the Cheshire Cat's nature. Here we report an experiment in which we send neutrons through a perfect silicon crystal interferometer and perform weak measurements to probe the location of the particle and its magnetic moment. The experimental results suggest that the system behaves as if the neutrons go through one beam path, while their magnetic moment travels along the other.
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.
Based on the concept of weak measurements, in 2013 Aharonov et al. proposed an experiment in which, according to their interpretation of the predicted results, a photon and its circular polarization were spatially separated, naming this phenomenon quantum Cheshire Cat [1]. This name is after a character in Lewis Carrolls novel Alice In Wonderland, the Cheshire Cat a cat whose grin can exist without the animal itself. Denkmayr et al., in 2014, claimed they realized experimentally the quantum Cheshire Cat, separating a neutron from its intrinsic magnetic moment [3]. We show how both results follow from interference effects, and thus the conclusion that a particle is separated from one of its intrinsic properties is not a necessary one. Making use of mostly undergraduate level quantum mechanics, we rule out the apparent paradox of the quantum Cheshire Cat.