"People are generally very interested in this very absurd picture that was painted by one of the founding fathers of quantum mechanics," Yale University's Chen Wang, lead author of the study published Thursday in Science, told The Washington Post.
It goes a little something like this: A cat sits in a box, along with some kind of poison. The poison's release is set to be triggered by the radioactive decay of a subatomic particle. But scientists know that these tiny particles are capable of being in multiple states at once – meaning that a particle could be decaying or not decaying at the same time. It follows that the poison could simultaneously be released and not released, and by extension, the cat could be dead and not dead.
"It's understandable that people don't understand it," Wang said. "You can't understand it using common sense. We can't either."
But the math shows that such a thing must be possible – at the microscopic level, anyway. "And we just follow the math," Wang said.
When Austrian physicist Erwin Schrödinger spun this paradoxical tale in 1935, he wasn't saying that cats can be simultaneously dead and alive. He was actually criticizing the prevailing school of thought in quantum mechanics, the Copenhagen interpretation, by showing how preposterous it would be when scaled up to affect objects in the visible world. The Copenhagen interpretation suggested that particles existed in all possible states (different positions, energies or speeds) until they were observed, at which point they collapsed into one set state. If that were true, he was arguing, you'd be able to have a cat that was simultaneously dead and alive until you opened your creepy cat-killing box to check on it.
Unfortunately for our buddy Erwin, the ridiculousness of his analogy hasn't kept the whole dead-and-alive-until-proven-otherwise-and-then-suddenly-you're-either-dead-or-alive thing from being true, at least at the microscopic scale.
Wang and his colleagues paired the famous cat paradox with another tenet of quantum mechanics: quantum entanglement, the phenomenon Einstein referred to as “spooky action at a distance." When two interacting subatomic particles become entangled, any change induced in one will be inflicted upon the other, no matter how distantly they're separated.
The Yale team built a tiny chamber with two aluminum cavities for subatomic particles to bounce around inside, then connected them with a superconducting chip made of sapphire. They were able to use electricity to induce a particular state on the particles in each chamber — two states at once, in fact, because quantum mechanics is weird. And because the chambers were linked by spooky action, both states could be inflicted at once in two places at once.
To get back to the cat, you can think of it this way: The fact that a cat in one box is simultaneously dead and alive causes another cat in another box to also be simultaneously dead and alive.
Your brain probably hurts too much to wonder why Wang and his fellow researchers care about these wacky particles, but here it is: They hope their findings can help advance the field of quantum computing.
A typical computer is made up of "bits" that can be coded as either zeroes or ones. But in theory, a quantum computer — one built using the crazy dead-and-alive particles we've been talking about — could have bits that were zeroes and ones at the same time. These computers would likely be much faster and more powerful than the computers we have today, at least for certain processes, because the machines would be able to simultaneously run many different calculations.
But since these particles lock into a single state when they're observed, you need a way to correct errors without, you know, checking for errors.
"It's well understood that 99 percent of computation or more will be done to correct for errors, rather than computation itself," Wang told Live Science. But his team hopes that inducing these simultaneous "cat" states in redundant particles could help keep things in check.
“It turns out ‘cat’ states are a very effective approach to storing quantum information redundantly, for implementation of quantum error correction. Generating a cat in two boxes is the first step towards logical operation between two quantum bits in an error-correctible manner,” study co-author Robert Schoelkopf said in a statement.