LOST AND FOUND

摘要

As weird as the quantum world is, something happened last year in the shadow of the French Alps that caused even hardened quantum physicists to do a double take. At the Institut Laue-Langevin in Grenoble, France, where a nuclear reactor spews out the world's most intense beam of neutrons, physicists made these particles perform a trick that until now had only existed in the fevered imaginations of theorists. In doing so, they have upset our notion of reality. The international team of physicists coaxed the neutrons to shed their quantum properties, getting the particles to go one way and their spins another way. It's as if you took one path and your personality another. Theorists have predicted the possibility of such strange behaviour for more than a decade. They even named it the quantum Cheshire cat phenomenon, after the cat in Alice's Adventures in Wonderland, which would disappear leaving only its grin behind. Now, for the first time, the quantum Cheshire cat is smirking at us in experiments, posing fundamental questions about the nature of the quantum world.