Physicists seem to be obsessed with cats. James Clerk Maxwell, the father of electrodynamics, studied falling felines to investigate how they turned as they fell. Many physics teachers have used a cat’s fur and a hard rubber rod to explain the phenomenon of frictional electricity. And Erwin Schrödinger famously illustrated the strangeness of quantum physics with a thought experiment involving a cat that is neither dead nor alive.
So it hardly seems surprising that physicists turned to felines once again to name a newly discovered quantum phenomenon in a paper published in the New Journal of Physics in 2013. Their three-sentence study abstract reads, “In this paper we present a quantum Cheshire Cat. In a pre- and post-selected experiment we find the Cat in one place, and its grin in another. The Cat is a photon, while the grin is its circular polarization.”
The newfound phenomenon was one in which certain particle features take a different path from their particle—much like the smile of the Cheshire Cat in Alice’s Adventures in Wonderland, written by Lewis Carroll—a pen name of mathematician Charles Lutwidge Dodgson—and published in 1865. To date, several experiments have demonstrated this curious quantum effect. But the idea has also drawn significant skepticism. Critics are less concerned about the theoretical calculations or experimental rigor than they are about the interpretation of the evidence. “It seems a bit bold to me to talk about disembodied transmission,” says physicist Holger Hofmann of Hiroshima University in Japan. “Instead we should revise our idea of particles.”
Recently researchers led by Yakir Aharonov of Chapman University took the debate to the next level. Aharonov was a co-author of the first paper to propose the quantum Cheshire effect. Now, on the preprint server arXiv.org, he and his colleagues have posted a description of theoretical work that they believe demonstrates that quantum properties can move without any particles at all—like a disembodied grin flitting through the world and influencing its surroundings—in ways that bypass the critical concerns raised in the past.
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