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Properties Separated from Particles in Experiment

Category: Science & Technology
Posted: 05:33AM

In 2001 an idea was published that under quantum mechanics, particles could behave like the Cheshire Cat and have their properties separated from the particle, like the grin being found off of the cat from Alice's Adventure in Wonderland. Researchers at Chapman University and the Vienna University of Technology have finally demonstrated this phenomenon experimentally using neutrons.

Neutrons are subatomic particles lacking an electronic charge, but possessing a spin, so they are affected by magnetic fields. For some time researchers have been using neutron interferometers to measure quantum mechanics by splitting a beam of neutrons and recombining them. As the neutrons enter a superposition, they will take both paths until a measurement forces a decision. For this experiment the two beams were filtered so that the top beam consisted only of neutrons with spins parallel to the beam, with those in the bottom beam having antiparallel spins. (Returning to the Cheshire Cat, the cats in the top beam are all grinning and those in the bottom are all frowning.) When the beams recombine, the resulting beam contains neutrons of both spin directions, but only those with a parallel spin are counted, therefore they must have taken the top path. (Only grins are being counted, so the only cats being counted travelled the top path.)

To separate the properties from the particles, the researchers bring in a magnetic field to disrupt the spins a little. When applied to the top beam, nothing actually happens, but when applied to the bottom beam, they will actually interfere with the measurement. As only the spin parallel neutrons are being counted and only the spin antiparallel neutrons are being affected, there should be no interference. Unless, that is, the spins of the neutrons in the top beam are actually taking the bottom path, and being affected by the magnetic field such that there is interference when the beams recombine. (Some of the grins must be separated from their cats to take the bottom path, because the count of grins changes when applying the field to the bottom path, despite there being no grinning cats on the bottom path.)

What is any of this good for? Besides adding another cat to quantum mechanics experiments, it could also be used to create high precision experiments that are less susceptible to external perturbations.

Source: Chapman University

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