Bridging the gap to quantum world (BBC) {'macro' entanglement}

[eppur_se_muova]

By Jason Palmer
Science and technology reporter, BBC News

Scientists have "entangled" the motions of pairs of atoms for the first time.

Entanglement is an effect in quantum mechanics, a relatively new branch of physics that is based more in probability than in classical laws.

It describes how properties of two or more objects can be inextricably linked over "vast" distances.

The results, published in Nature, further bridge the gap between the world of quantum mechanics and the laws of everyday experience.

This is the first time entanglement has been seen in a so-called "mechanical system".
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more: http://news.bbc.co.uk/2/hi/science/nature/8081058.stm

http://arxiv.org/abs/0901.4779

[Mojo_electro]

1. Cool...

Even Einstein's term for entanglement was "spooky action at a distance".. just to give an idea of how strange it is.

I'd suggest reading about an experiment called the "delayed choice quantum eraser".. it's really heady stuff, but once you grasp the meaning of it, it's truly fascinating.

:fistbump:

[Taitertots]

2. Spooky at any distance

Doesn't that mean information can and has been send at speeds exceeding the speed of light?

Now we just need the entanglement internet. A universe wide entanglement supercomputer than sends information at the speed of light throughout the universe to anything entangled to it.

[Salviati]

3. As far as I know entaglement is not useful for transmitting info...

It's as if you had a pair of coins that when flipped always came up either both heads or tails, They seem to be passing information between each other, but there's no way to hijack that for other uses...

[Taitertots]

4. We haven't found ways to hijack it for other reasons

Imagine two "coins" one on the moon and one on earth. Each lands on a pad that turns on a light when it lands on one specific side. Put one on the moon and the other here. Flip the coin on earth until you receive three heads on earth. The person on the moon would see three flashes and know they should return to earth.

The information would have been sent instantly.


Now scale it out to the whole universe. A quantum supercomputer on earth is entangled with receivers in computers throughout the universe.

[caraher]

5. It doesn't work that way.

I assume the goal is to do FTL signaling. First, entanglement isn't something you get to use over and over again. It's not as though you can make two coins with this special property of entanglement that makes the results of all future measurements correlated (or anticorrelated) in some way. As an information resource you prepare the state and measure it, and after measurement you've broken the entanglement (the interaction with the measurement apparatus fundamentally changes the quantum state; it does so instantaneously for both particles, which is the nonlocal aspect, and you cannot "undo" it).

Getting a bit more realistic, let's presume you've prepared a huge ensemble of entangled paired "quantum coins" (in special opaque boxes that both prevent inadvertent "measurement" and preserve the coherence of their quantum states) and transport (without peeking) one coin of each pair to the moon, leaving one from each pair on Earth. You want to send this signal and start looking at the coins (which you've numbered so that your friends on the moon know the order in which to peek in their boxes). You open box 1 - tails. No problem, you open a few more boxes... heads... heads... tails. OK, this will take a little while, but we've got plenty of coins... T,T,H,H,T,H,T,T,H,H,H At last!

Your confederate starts opening boxes... H,H,T,T,T,H,H,T,H,T,T,H,H,H,H,T,T,H,H,T...

ummm... when do I stop opening boxes? For that matter, when should I start? For simplicity lets assume HHH is the only meaningful code here. I suppose we could assume that every (Earth) day they are to check for the "return home" signal at some agreed-upon time. The problem is that the sequence is utterly random, and while you can be assured that any particular pre-arranged sequence will (eventually) crop up to convey the desired signal, you need an additional signal to tell them that, say, they should only open the first 10 boxes (or boxes 8-10, if your code is a sequence of 3 straight heads).

Note that there is nothing special about your opening the boxes first! If I were your friend on the Moon, I could just look at all of them as soon as I got there (heck, even on the way there) and simply the record the sequence. There's no information in the random sequence until you tell me which part of it includes the message you want me to receive. And that's going to require another communication channel over which the maximum transmission speed is the speed of light in vacuum.

Of course, there are uses for entanglement in quantum computing that exploit the parallelism of multiple particle entanglement. There, the challenges are entangling enough particles to be useful and performing operations faster than the rate at which the entanglement is lost to undesired interactions with their environment. And there are uses in quantum information such as secure encryption key distribution. But nobody has been clever enough to come up with a way to generate FTL communication using entanglement. Quantum mechanics is nonlocal but does not provide a way to do superluminal signaling.