The phenomenon is named after the curious feline in Alice in Wonderland, who vanishes leaving only its grin. Researchers took a beam of neutrons and separated them from their magnetic moment, like passengers and their baggage at airport security. They describe their feat in Nature Communications.
The same separation trick could in principle be performed with any property of any quantum object, say researchers from Vienna University of Technology. Their technique could have a useful application in metrology - helping to filter out disturbances during high-precision measurements of quantum systems.
The idea of a "quantum Cheshire Cat" was first proposed in 2010 by Dr Jeff Tollaksen from Chapman University, a co-author on this latest paper. In the world familiar to us, an object and its properties are always bound together. A rotating ball, for instance, cannot become separated from its spin.
"We find the cat in one place, and its grin in another," as the researchers once put it. The feline analogy is a nod to Schrodinger's Cat - the infamous thought experiment in which a cat in a box is both alive and dead simultaneously - illustrating a quantum phenomenon known as superposition.
To prove that the Cheshire Cat is not just a cute theory, the researchers used an experimental set-up known as an interferometer, at the Institute Laue-Langevin (ILL) in Grenoble, France.
A neutron beam was passed through a silicon crystal, sending it down two different paths - like passengers and their luggage at airport security.
By applying filters and a technique known as "post-selection", they were able to detect the physical separation of the neutrons from their magnetic moment - as measured by the direction of their spin.
"The system behaves as if the neutrons go through one beam path, while their magnetic moment travels along the other," the researchers reported.