KentuckyFC writes "Last year, a group of theoretical physicists suggested a bizarre experiment based on a quantum phenomenon known as weak measurement. Unlike ordinary measurements that always change the state of a quantum object, a weak measurement extracts such a small amount of information that it leaves the quantum state intact. For example, a weak measurement can detect the presence of a photon by the deflection it causes when it bounces off a mirror. However, this does not change the photon's quantum state. The new idea was to make two weak measurements on a quantum system that is in a superposition of states, the goal being to separate the location of this quantum system from its properties, like a Cheshire cat. Now a group of experimentalists say they've observed a quantum Cheshire cat for the first time in an experiment involving neutrons. They passed a beam of neutrons through a magnetic field to align their spins and then sent them through an interferometer in which the neutrons pass down both arms of the experiment at the same time. They then used weak measurements to locate the neutrons in one arm while measuring their magnetic properties in the other. Voila! A quantum Cheshire cat."
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