November 22, 2011 Leave a comment
So, a good friend and excellent science writer has started a feature where he solicits science questions and answers them by talking to NC State’s best scientists. I thought I’d throw out a good one with “how doe faster-than-light quantum communication work?” Short answer: it doesn’t. I was thinking of the very cool, related concept of quantum entanglement. I think this is perhaps the coolest scientific finding I’m aware of. Ship explains:
There are ways to prepare two subatomic particles so that they interact and are then separated. For example, under some circumstances a photon (or discrete packet of light energy) can be split into two photons, each of which has half the energy of the original photon.
Some of these paired photons are “entangled,” meaning that they have orthogonal, or perpendicular, polarizations. That means, for example, that if the electric field of one of the photons is vibrating vertically, its twin is vibrating horizontally. The same will hold true regardless of the polarization – if one is polarized to vibrate in a clockwise motion, the other vibrates in a counterclockwise motion, et cetera.
According to a common interpretation of quantum mechanics, both photons are in indeterminate states until you measure them. It is important to make this distinction: it’s not simply that you don’t know what the polarization of each photon is until you measure it; instead, the polarization does not take on a definite value until you measure it. No matter how far apart they are, when the polarization of one photon is determined by a measurement, somehow the other photon instantaneously “knows” the outcome and will always be found to be vibrating in a perpendicular direction.
Now, that’s pretty cool – but it can’t really be used for faster-than-light communication purposes for the simple reason that we cannot control the polarization of the entangled particles. And while it may seem that the two photons are able to communicate with each other in some way, we have no idea how.
That’s not just pretty cool, that’s super cool. Perhaps even cooler than faster than light neutrinos.