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Physicists add ‘quantum Cheshire Cats’ to list of quantum paradoxes

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Posted November 26, 2013
Physicists add ‘quantum Cheshire Cats’ to list of quantum paradoxes
In the proposed experimental set-up, the quantum Cheshire Cat paradox is demonstrated when photons travel through the left arm of the interferometer while photon polarizations travel through the right arm. Some measurements disturb the photons and cause them to travel through the right arm with their polarizations, making the paradox seem to disappear. However, weak measurements that do not cause this disturbance bring the paradox back to life. Credit: Aharonov, et al. ©2013 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Given all the weird things that can occur in quantum mechanics—from entanglement to superposition to teleportation—not much seems surprising in the quantum world. Nevertheless, a new finding that an object’s physical properties can be disembodied from the object itself is not something we’re used to seeing on an everyday basis. In a new paper, physicists have theoretically shown that this phenomenon, which they call a quantum Cheshire Cat, is an inherent feature of quantum mechanics and could prove useful for performing precise quantum measurements by removing unwanted properties.

The physicists, Yakir Aharonov at Tel Aviv University in Tel Aviv, Israel, and Chapman University in Orange, California, US, and his coauthors have published a paper on quantum Cheshire Cats in a recent issue of the New Journal of Physics.

The physicists begin their paper with an excerpt from Lewis Carroll’s 1865 novel Alice in Wonderland:

‘All right’, said the Cat; and this time it vanished quite slowly, beginning with the end
of the tail, and ending with the grin, which remained some time after the rest of it had
gone.

‘Well! I’ve often seen a cat without a grin’, thought Alice, ‘but a grin without a cat!
It’s the most curious thing I ever saw in my life!’

Just as the grin is a property of a cat, polarization is a property of a photon. In their paper, the physicists explain how, “in the curious way of quantum mechanics, photon polarization may exist where there is no photon at all.”

Disturbing measurements

In their proposed experimental set-up, the physicists show that a photon will travel through the left arm of an interferometer with 100% certainty, yet its polarization can be detected in the right arm, where there is 0% probability of the photon traveling. That is, the photon is in one place while its polarization is in another.

Read more at: Phys.org

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