Quantum Teleportation Achieved Over Ten Miles of Free Space

[jayfish]

http://arstechnica.com/science/news/2010/05/quantum-teleportation-achieved-over-ten-miles-of-free-space.ars

Quantum teleportation has achieved a new milestone or, should we say, a new ten-milestone: scientists have recently had success teleporting information between photons over a free space distance of nearly ten miles, an unprecedented length. The researchers who have accomplished this feat note that this brings us closer to communicating information without needing a traditional signal, and that the ten miles they have reached could span the distance between the surface of the earth and space.

Amazing breakthrough. Some of the practical applications of this tech, once fully realized, would be pretty sweet. I can imagine th elimination of communication satellites and real-time CnC of robotic craft in deep space. ...just for starters.

JAy

[Uncle Joe]

1. Kicked and recommended.

Thanks for the thread, jayfish.:thumbsup:

[jayfish]

5. My Pleasure

I expect to see people who think they know everything come in and shit all over this thread. Don't listen to them. A Decade ago they would have said none of this was possible.

FSH

[bananas]

13. Last year, I asked "Poll question: Do you know about Quantum Teleportation?"

Here's the response: http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=389x5788884

[jayfish]

17. I Underestimated The Knowledge Level Of My Fellow DUers. I Am Sorry.

What a pleasant surprise.

FSH

[bananas]

25. No need to apologize, I know what you're talking about.

It's why I asked the poll.

[EXneoCON]

2. Beme Upscotti...

...Eddie Van Halen's nome de plume when checking into hotels.

This is really exciting stuff! :thumbsup: K&R

[Tuesday Afternoon]

3. truly awesome...K&R and bkmrkd. thanks for posting this

the Real News Story of the day. :patriot:

[lumberjack_jeff]

4. "quantum teleportation" suggests FTL communication?

E.G. "subspace radio"? Seriously?

[jayfish]

6. Subspace Radio Is Probably...

way, way off in the future, but I don't see why simple binary communication would be too far off.

FSH

[Ian David]

22. "Simple binary communication" can be morse code or digitally encoded data. n/t

[TheWraith]

7. Something like that.

If you want to be technical, it's not "faster than light" because the information never goes anywhere--it stops existing in one place, and starts existing in the other. Nothing travels faster than C in this, but the information still gets there.

[Orsino]

11. You'd think the story would use the word "instantaneously"...

...as long as it's explaining other basics.

[Ratty]

12. Nah.

Hmm, I'm not crazy about the phrase "The researchers who have accomplished this feat note that this brings us closer to communicating information without needing a traditional signal," since I can't tell from the article what they mean by traditional signal. But according to Wikipedia:

Quantum teleportation, or entanglement-assisted teleportation, is a technique used to transfer quantum information from one quantum system to another. It does not transport the system itself, nor does it allow communication of information at superluminal (faster than light) speed ... The prerequisites are a conventional communication channel capable of transmitting two classical bits (i.e. one of four states), and an entangled Bell pair (b,c) of qubits

Quantum teleportation has always required a second slower-than-light signal in order to extract any information. There's more on this in in the discussion section - it's a very very common misunderstanding.

[Lochloosa]

8. "Entanglement" This could lead to transporting energy without power lines.

Imagine getting rid of all those telephone poles.....:bounce:

http://www.smartplanet.com/business/blog/smart-takes/physicist-proves-that-teleportation-of-energy-is-possible/3967/

A physicist has demonstrated that teleportation of energy is possible, a discovery that has profound implications for the study of physics.

Masahiro Hotta at Tohoku University in Japan showed that teleportation of energy is possible by using the quantum principles to transport information.

Relying on the quantum phenomenon called “entanglement” — in which two particles share the same existence, meaning that a measurement on one particle immediately influences the other despite being light-years apart — Hotta’s idea involves making a measurement on each one an entangled pair of particles.

According to Hotta, the measurement on the first particle injects quantum energy into the system. By carefully choosing the measurement to do on the second particle, it is possible to extract the original energy, Hotta says

[TheMadMonk]

9. No real time. Causality is not violated. (Not yet anyways)

What it provides is a means of communication that is not subject to interception in any form.

However certain lightspeed limitations remain.

[lumberjack_jeff]

10. I don't understand

Quantum entanglement (as I understand it) is not subject to the speed of light. A change in state of particle "a" creates a change in state of particle "b" instantaneously, regardless of the distance between them.

[TheMadMonk]

16. And while it can be proven that tunneling is faster than light. Any measurement...

...will show that the average speed of the tunneling particle is always sublight.

Teh Kwontum does that.

While the change might be instantaneous, Einstein still manages to intervene in such a way that any two way exchange of information is at lightspeed or less.

[caraher]

14. Well...

First, you don't need entanglement to transmit energy wirelessly. Classical electromagnetic waves do that quite nicely.

Second, this kind of experiment is nothing that serious physicists would have called "impossible" or otherwise dismissed anytime in at least the last 15-20 years. It's not a case of "they said it couldn't be done," but an instance of systematically pushing the technology.

Third, it's worth noting that new distance records are probably less impressive advances than technologies that increase the size (in number of quanta) of the entangled systems.

Fourth, always remember - while you can say the wavefunction collapse in some meaningful sense is simultaneous at remote locations, that does not help you send signals FTL. The problem is that you cannot *control* the outcome; it is random. Suppose we're using polarization states of entangled photons... it may be the case that the instant I measure my photon to have horizontal polarization, yours collapses to be vertically polarized. But I didn't get to choose that result. We might have correlated random bit patterns known to one another instantly, but that doesn't mean I got to send you any information. So this doesn't help you do things like evade transmission lag in communicating with distant space probes; if you wanted to set a bit to tell your Mars rover to turn left or right, you don't get to choose whether it goes left or right without resorting to some lightspeed or slower phenomenon to transmit your wishes.

Finally, even the experts have big disagreements about terminology. Last year I was at talk by a big name in this field where he kept talking about teleportation, and afterwards other experts were scratching their head about *why* he called it teleportation - "Isn't he just talking about remote state preparation?" You get a lot further understanding these experiments if you just look at what they did, and ignore the fancy labels they make up for the experiments (which are designed as much to create a buzz and attract funding as they are to inform others about the experiments).

[jayfish]

19. Very Well Stated.

I can't dispute anything you've said here. I will say in regards to point four that we can't control the outcome yet. Who knows, in the future we may come up with a way. If not directly then by means of some type of outcome branch prediction or similar.

FSH

[Heywood J]

15. When did space become ten miles up?

Aside from that, it begs the question of how well entanglement handles a moving destination, or a significant difference in velocity for source and destination (if both are moving).

Given that it took radio almost 75 years to make it from invention to public awareness of the FM dial, plus over 100 years for phone system improvements like fiber-optics, cellular, and VOIP, it'll be awhile before the masses can make use of any practical entanglement benefits.

[Ian David]

18. I wonder if this makes my idea of Quantum SETI slightly more possible?

Here's my crazy idea:

1) Search for "traditional" SETI signals in the radio and optical wavelengths. You'd be looking for the "We Are Here" signals, like a string of prime numbers or something.
2) If you receive such a signal, capture the photons or electrons that were used to send the signal.
3) Analyze those particles to see if any of them are quantum entangled and being used to send signals in real time.

Also:

4) Capture and analyze random photons and electrons from optical and radio telescopes to see if any of them are intentionally quantum-entangled "on the other end" and being used to transmit a signal. For example, an electron spining up and then down in a way that represents a sequence of prime numbers.

At the BOSKONE convention, I had the chance to speak to a nuclear physicist, who explained to me that my idea is unworkable because by the act of observing the particle, we change the particle, thus making it impossible to receive a signal.

However, the beings on the other end of a quantum-entangled particle would be able to tell that the particle we have is being observed.

So, now I'm thinking...

Maybe the way to use quantum entanglement would to be to "observe" the particle in a sort of Morse code?

Imagine two quantum-entangled refrigerators with little lightbulbs inside that only turn on when the door is open. Now, imagine one refrigerator is on Earth, and the other on Omega 3. When the refrigerator on Omega 3 is opened (the bulb is observed), the light in both refrigerators turn on. So Melllvar (That's Melllvar, with three L's) on Omega 3 Opens the door on his fridge once. And then three times. Then five times. Then seven times...

[FiveGoodMen]

20. Can you give a little more detail regarding step 3?

How would the analysis be done?

[Ian David]

21. You would look for a particle exhibiting signs of being intelligently controlled

For example, spinning up/down in a way that represents a series of prime numbers.

[FiveGoodMen]

23. Alright, I'll buy that.

[caraher]

27. But it doesn't work that way

Measurement *breaks* the entanglement.

It's like this - suppose you have "entangled coins," each of the pair in its own opaque box. As soon as you open one box and see that it's either a head or a tail, that immediately determines whether the other coin is a head or a tail (let's say that it's automatically the opposite). So I could take one box, you could take the other, and we could travel any distance from each other you like. Say you open your box and it's a head; you then know that if I open my box, I'll see a tail.

Here's the first point: you have no way of knowing (from this alone) whether I opened my box before or after you opened your box - or whether I *ever* opened the box.

The second point is that as soon as *either* of us takes a peek, we're through with entangled coins. A lot of people seem to have the impression that I could take my coin and turn it over, and yours would instantaneously flip over as well. That's not true. A "measured" coin henceforth is no longer in an entangled head/tail state along with the other coin. It is just a "head" or a "tail" with no "memory" of its past life as an entangled coin.

[Canuckistanian]

24. Is there no way to PASSIVELY observe an entangled particle?

For instance, maybe we could observe that particle's effect on ANOTHER nearby particle?

[caraher]

26. Interesting thought...

It sounds vaguely like you're talking about quantum nondemolition measurements. That certainly lets you not *destroy* the particle you're measuring, and it does allow you to measure it more than once.

But the trouble is that the biggest problem is not preserving the particle, it's extracting information without changing its state. If you accept the postulates of quantum theory, this is really a math problem. And the math problem is this: measuring a property changes the state of the system to an eigenstate of the property you just measured. And once you do that, the property you measure ceases to be entangled!

Particles basically don't "remember" that they used to be entangled. Before the measurement you had a pair of entangled particles; no matter how you performed the measurement, it's no longer entangled (at least not in the degree of freedom you measured; you might have hyperentangled particles that might remain entangled in other degrees of freedom).