I really should be paying Brad DeLong a finders fee for the links he posts on his blog.  (Probably well over half the things I comment on here came to my attention via Brad’s blog.)  Today he posted a link to video from the University of Vienna of real-time imaging of quantum entanglement.  What is quantum entanglement?  From a recent article in Science:

Physicists have long known that quantum mechanics allows for a subtle connection between quantum particles called entanglement, in which measuring one particle can instantly set the otherwise uncertain condition, or “state,” of another particle—even if it’s light years away…

Entanglement is a kind of order that lurks within the uncertainty of quantum theory. Suppose you have a quantum particle of light, or photon. It can be polarized so that it wriggles either vertically or horizontally. The quantum realm is also hazed over with unavoidable uncertainty, and thanks to such quantum uncertainty, a photon can also be polarized vertically and horizontally at the same time. If you then measure the photon, however, you will find it either horizontally polarized or vertically polarized, as the two-ways-at-once state randomly “collapses” one way or the other.

Entanglement can come in if you have two photons. Each can be put into the uncertain vertical-and-horizontal state. However, the photons can be entangled so that their polarizations are correlated even while they remain undetermined. For example, if you measure the first photon and find it horizontally polarized, you’ll know that the other photon has instantaneously collapsed into the vertical state and vice versa—no matter how far away it is. Because the collapse happens instantly, Albert Einstein dubbed the effect “spooky action at a distance.”

So that’s quantum entanglement.  What’s special about real-time imaging of quantum entanglement?  THAT THEY’RE DOING IT IN REAL-TIME!  The authors don’t go into the lab, collect data, go back to their office and analyze it, then produce a neat movie a few weeks later.   The data they collect is the movie.  From their paper associated with the video:

Although, photonic entanglement is routinely studied in many experiments nowadays, its signature has been out of the grasp for real-time imaging. Here we show that modern technology, namely triggered intensified charge coupled device (ICCD) cameras are fast and sensitive enough to image in real-time the effect of the measurement of one photon on its entangled partner.

Without further ado, here’s their video:

When I was a grad student photofragment imaging was new and had a similar “Wow!” factor – at least for me.  (See here for an example of photofragment imaging.)  It’s neat to see how science progresses.