The Quantum Zoo

Schrödinger’s feline companion may (or may not) be turning in his grave when he hears that two new animals have stamped their name onto world of quantum theory.

The infamous Schrödinger’s Cat refers to a thought experiment created by Edwin Schrödinger in which a cat was put into a box with a radioactive element and a flask of poison. Should the radioactive element decay, then the flask would break, releasing the poison and killing the cat. From inside the box, if the atom does not decay and the cat is not poisoned. Yet from outside of the box, Schrödinger would experience the cat being both dead and alive at the same time. The experiment was designed to illustrate the flaws of the ‘Copenhagen interpretation’ of quantum mechanics, which states that a particle exists in all states at once until observed.

Now scientists at the Institut Laue-Langevin in Grenoble, France have managed to separate a particle from one of its physical properties for the first time – creating the ‘’quantum Cheshire Cat’’. In a nod to the character in Lewis Carroll’s Alice in Wonderland, where the Cheshire Cat gradually vanishes leaving only its grin, researchers have managed to get neutrons to shed their quantum properties, separating them from their magnetic moment  – in essence getting the particles to go one way and their spins another way. An outline of the experiment can be found here.

While scientists were still purring at these new findings, an international team of physicists led by Yakir Aharonov have come up with another peculiar scenario which they have called the “quantum-pigeonhole effect“. The paradox begins with the observation that when you put three pigeons in two pigeonholes, there will always be at least two pigeons in the same hole. However, according to the team’s quantum analysis, it is possible for none of the pigeons to share a hole.

According to Jeff Tollaksen, one of the physicists behind the experiment, intuition dictates that if you put three pigeons into two pigeonholes, one hole must contain two pigeons. On a quantum level, however, even basic “counting” becomes peculiar, as “You can put an infinite number of pigeons in two boxes, and no two pigeons will be in the same box. . .  It seems to be impossible, but it is a direct consequence of quantum mechanics.” This observation is leading many physicists to re-examine some of the foundational principles of quantum mechanics. While the paradox, like Schrödinger’s, will help physicists, mathematicians, and philosophers develop more accurate theories of quantum correlation and of the relationship between particles and their observer.