Quantum Trick Allows Researchers to 'Pet' Schrödinger's Cat Without Killing It

In this thought experiment, it works out OK for the cat. ansik [CC BY 2.0]/Flickr

It's the thought experiment that has long made animal lovers cringe: Schrödinger's cat. The thought experiment, first imagined by physicist Erwin Schrödinger in 1935, goes like this: A cat is sealed in a dark box, accompanied only by a quantum "booby trap" that will release a poison the moment a radioactive atom within it decays.

Of course, the experiment was never actually meant to be implemented. Rather, it was intended as a mockery of the prevailing theory in quantum physics called the Copenhagen interpretation. According to that interpretation, quantum states exist only as probabilities until they are observed; it is the act of observation that fixes a particle's state.

Since Schrödinger's cat is locked in an observation-proof box, and since the cat's fate depends upon the probability of an atom's decay, it therefore follows from the Copenhagen interpretation that the cat must be simultaneously alive and dead — which is, presumably, an absurdity. In other words, so long as the cat is not observed, its existence stands in limbo. Only when the box is opened, and the cat is observed, can it be either alive or dead.

If your head is spinning, you're not alone. It's all just another bizarre chapter in the book of quantum physics. But now, 75 years after Erwin Schrödinger first considered the fate of his poor cat, a group of researchers from the University of California, Berkeley, have conceived of a quantum "trick" that could allow Schrödinger to "pet" his boxed cat for the first time without the threat of killing it, reports New Scientist.

The trick, according to researcher R. Vijay, is to "only partially open the box." Basically, researchers used a new kind of amplifier that let them turn up the signal without contamination. This, presumably, allowed them to indirectly observe what was happening inside the box in a manner that did not disrupt, or fix, the quantum states of the particles within.

In other words, Vijay and colleagues believe they can observe what is happening inside the box without really observing it. It's a logical juxtaposition that seems as paradoxical as the thought experiment it purports to solve. It sounds like cheating, a little bit. But the researchers are adamant that their method is a success.

If the results pan out, the discovery will not only be significant for Schrödinger's much-maligned cat, but also for the development of quantum computing. One of the obstacles to developing a quantum computer is that quantum bits are fragile. Whenever researchers attempt to control quantum bits long enough to perform a calculation, the bits become fixed much in the same way that opening the box seals Schrödinger's cat's fate. But by discovering a way around this dilemma, researchers could effectively control quantum bits without destroying them.

"This demonstration shows we are almost there, in terms of being able to implement quantum error controls," said Vijay.