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arXiv:1202.4894

Twin Quantum Cheshire Photons

Issam Ibnouhsein, Alexei Grinbaum

Published Feb 22, 2012• 5 citations
arXivHTMLPDF

Abstract

In an experiment with both pre- and post-selection one can find a photon (the cat) in one place and its polarization (the smile) in another. Aharonov et al. asked recently whether more than two degrees of freedom could be separated in the same way. We show that this is possible and that the separation of properties from objects that carry them is in some situations even stronger.

DOI
10.48550/arxiv.1202.4894

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In an experiment with both pre- and post-selection one can find a photon (the cat) in one place and its polarization (the smile) in another. Aharonov et al. asked recently whether more than two degrees of freedom could be separated in the same way. We show that this is possible and that the separation of properties from objects that carry them is in some situations even stronger.
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.
The quantum Chesire cat has drawn quite a deal of attention over the past few years, challenging the common sense perception that a physical system is inseparable from its physical properties. In this work we propose a thought experiment based on the quantum Chesire cat, which shows that suitable pre- and post-selections can not only separate a physical system from its properties, but also even separate the wave and particle attributes of a physical system. The enduring view about the wave-particle duality has suggested that a quantum entity behaves like both a wave and a particle. However, the wave-particle duality can be spatially separated under such pre- and post-selection conditions, thus allowing us to dismantle these two fundamental attributes of nature.
Abstract A common-sense perception of a physical system is that it is inseparable from its physical properties. The notion of quantum Cheshire cat challenges this, as far as quantum systems are concerned. It shows that a quantum system can be decoupled from its physical property under suitable pre and postselections. However, in the quantum Cheshire cat setup, the decoupling is not permanent. The photon, for example, and its circular polarization is separated and then recombined. In this paper, we present a thought experiment where we decouple two photons from their respective polarizations and then interchange them during recombination. Thus, our proposal shows that that the belongingness of a property for a physical system is very volatile in the quantum world. This raises the question of reality of an observable at a much deeper level.