Schrödinger's cat is probably the most famously tragic figure in all of quantum theory. First envisioned by Erwin Schrödinger in 1935, the thought experiment involves a kitty being sealed in a box that is rigged with a quantum booby trap. Once triggered, the trap releases a poison that will kill our hapless feline friend.
Well, now researchers have taken it one cruel step further. Apparently, Schrödinger's cat now has a twin, and both of their lives are on the line, reports the Washington Post.
The trick to the original experiment is that the trap's mechanism relies on radioactive decay, which according to quantum theory is actually a probabilistic event that can both happen and not happen at the same time. According to one interpretation of quantum theory, it only becomes an actual event (that is, the decay either happens or not) when the process is observed. Something about the power of observation collapses the suspended quantum state.
In other words, so long as the box with the cat inside remains sealed, and therefore unobserved, the cat cannot be said to be alive or dead. In fact, the cat is theoretically both alive and dead at the same time. It's a weird experiment to think about, but that's quantum mechanics for you.
Now researchers have upped the ante by adding another weird quantum effect to the mix: entanglement. This is a concept that Einstein famously called "spooky action at a distance" because it involves two separated particles that are nevertheless linked to one another, such that any change induced in one will be inflicted upon the other at exactly the same time. It doesn't make any intuitive sense, but again: that's quantum mechanics for you.
The new experiment, performed by Yale University's Chen Wang and colleagues, replaced the cat (thankfully) with a subatomic particle in one box that was entangled with another particle in a different box. This added a whole new layer to the old experiment because now the fate of one particle (or cat, if a cat was used) in one box became inextricably tied to the other.
This is profound because it means that you only need to open up one of the boxes to affect the state of the particle in the other, even though the events inside the second box remain unobserved. In other words, the probabilistic quantum state in the second box did not have to be collapsed by direct observation in order to "check in on it," so to speak.
The principal application of the experiment, aside from giving you a mind-blast, involves the development of quantum computing. Basically, quantum computing aims to make use of entangled bits so that processing times can be virtually eliminated, leading to ultra-fast computers of the future. The only problem is that entanglement is a very difficult state to maintain, so errors in a quantum computer are difficult to correct. The Yale team's experiment offers a way around this problem.
"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," explained study co-author Robert Schoelkopf.