QUANTUM CHESHIRE CAT

In the 1865 classic, Alice in Wonderland Lewis Carrol describes the Cheshire Cat’s mysterious way of disappearing as “A grin without a cat.” Physicists have been attempting to measure if an object can be separated from its properties such as the grin appears separated from the cat. Last year Tobias Denkmayr and coauthors carried out an experiment in which the neutrons seemed separated from their spin, this effect is called a “Quantum Cheshire Cat.” Learn how the separation of an object from its properties, also known as the Quantum Cheshire Cat, works below.

Where is the Cat …?

Neutrons are not electrically charged, but they carry a magnetic moment. They have a magnetic direction, the neutron spin, which can be influenced by external magnetic fields.

First, a neutron beam is split into two parts in a neutron interferometer. Then the spins of the two beams are shifted into different directions: The upper neutron beam has a spin parallel to the neutrons’ trajectory, the spin of the lower beam points into the opposite direction. After the two beams have been recombined, only those neutrons are chosen, which have a spin parallel to their direction of motion. All the others are just ignored. “This is called postselection”, says Hermann Geppert. “The beam contains neutrons of both spin directions, but we only analyse part of the neutrons.”

These neutrons, which are found to have a spin parallel to its direction of motion, must clearly have travelled along the upper path – only there, the neutrons have this spin state. This can be shown in the experiment. If the lower beam is sent through a filter which absorbs some of the neutrons, then the number of the neutrons with spin parallel to their trajectory stays the same. If the upper beam is sent through a filter, than the number of these neutrons is reduced.

… and Where is the Grin?

Things get tricky, when the system is used to measure where the neutron spin is located: the spin can be slightly changed using a magnetic field. When the two beams are recombined appropriately, they can amplify or cancel each other. This is exactly what can be seen in the measurement, if the magnetic field is applied at the lower beam – but that is the path which the neutrons considered in the experiment are actually never supposed to take. A magnetic field applied to the upper beam, on the other hand, does not have any effect.

“By preparing the neurons in a special initial state and then postselecting another state, we can achieve a situation in which both the possible paths in the interferometer are important for the experiment, but in very different ways”, says Tobias Denkmayr. “Along one of the paths, the particles themselves couple to our measurement device, but only the other path is sensitive to magnetic spin coupling. The system behaves as if the particles were spatially separated from their properties.”

Could the Cheshire Cat and Bigfoot hold similar secrets in their mysterious departures. Ron Morehead has been investigating the Bigfoot phenomena for over 4 decades and has come to believe the answers may lay in the further understanding of Quantum Physics.

SRC: Learn more about the Quantum Cheshire Cat experiment at: phys.org/news/2014-07-quantum-cheshire-cat-neutrons.html

Categories: Bigfoot