Quantum Cheshire Cats

Scientists have created an effect comparable to a subatomic Cheshire cat. Rather than a grin that has been separated from its cat, they have created a property of magnetic moment (I’ll not pretend I understand what that is) separated from its neutron. As Stephen Luntz explains,

In the classical world we are familiar with the idea that a property like magnetic moment cannot be separated from its object – it would be like taking the taste away from a chocolate bar so that the bar produced no sensation on the tongue, but a disembodied taste could be detected somewhere quite distinct.

However, things work differently in the world of the very small. In the 1990s, Professor Yakir Aharonov of Tel Aviv University proposed the properties could indeed be detached from particles (his book explaining it is delightfully subtitled Quantum Theory for the Perplexed). The idea develops on Schrödinger’s famous feline thought-experiment. However, instead of ending up with a live and dead cat, you have a cat without its properties, and properties without the cat. The naming after Carroll’s Cheshire moggy was inevitable.

Thus,

Denkmayr and his co-authors…temporarily removed the magnetic moment from the neutrons using an interferometer. They used a silicon crystal to split a neutron beam and reported, “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.” The beams were then reunited, leaving no disembodied magnetic moments prowling the universe.

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