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Macroscopic Quantum Entanglement
meckardt writes: "We laugh at the science fiction of such programs as Star Trek, but it can almost be stated as a truism that what is fiction today may be science tomorrow and engineering next week. Researchers at the University of Aarhus in Denmark report in the science journal Nature that they have been able to cause particles to interact over a distance using lasers. The effect, called quantum entanglement, has been observed before, but never with such large amounts of matter. Don't expect transporters next week, but it is interesting that this report hits the streets the same day that Enterprise debuts."
I think their goal may be practical to quantum computing. I could explain this here, but I already did it here. Basically, you need to be able to create a quantum copier to create a quantum computer. Building a quantum copier is difficult because, due to the no-cloning theorem, arbitrary quantum states cannot be copied perfectly every time. You can either clone a subset of quantum states perfectly or you can copy arbitrary states with a certain probability of failure.
Clarification:
Quantum entanglement involves creating a system in which the state (polarization, spin, etc.) of two or more particles are 'dependent on' each other. Measuring the state of one particle defines the state of the other, 'magically', over some distance.
HOWEVER make no mistake, nothing in quantum mechanics or entanglement theory allows anything resembling faster-than-light information traveling, nor teleportation as we understand it. This is pure fantasy that many physicists subtly or not-so-subtly use to solicit grants, or at least popular press. (There's plenty of this nonsense in sci-tech magazines.) It certainly worked here.
Here's another example of macroscopic 'quantum entanglement'. I have a bag with two billiard balls, one black, one white. I close my eyes, pull one out and put it in a second bag. Then, I hand you the first bag, and walk across the room with the second bag, and open it. Once I look at the color of the billiard ball in my bag, the color of the ball in your bag 'magically' changes color and assumes a defined state. These billiard balls are entangled, very much like subatomic particles are.
Can you ever transport information faster than light using this method? NO. Can matter be teleported? NO. I really wish these pop-sci articles would put an end to these misconceptions once and for all...
This was presented at the
International Conference on Quantum Information
June 10-13, 2001 at the University of Rochester campus in Rochester, New York.
Further information and links at the research group from Austria that ran the first experimental verification of quantum teleportation.
You don't change their spin, you measure it and find that it is the same. Usually you measure a quantity that has a fifty fifty chance to give one or the other result. The interesting thing is that it always comes out the same for the entangled particles. No matter how far their separation in time and space.
You can't convey any information that way since you don't know what the result of the measurement will be. But somehow the particles "know".
For more information see their paper at http://xxx.lanl.gov/abs/quant-ph/0106057
and references therein
***Quis custodiet ipsos custodes***
Well, this will get us into some of the most dangerous neighborhoods of quantum mechanics, but I'll see what I can do.
The quantum entanglement of two particles means that (just as you say) the behavior of one particle becomes perfectly correlated with the behavior of another. In the classic example case, two photons are generated with opposite polarizations. If you can transmit them a distance apart without any interference, then the photons will remain entangled, and a measurement of the polarization of one photon will have immediate implications for the polarization of the other.
Although this is very useful for quantum cryptography, please note that it will NOT allow you to transmit information any faster than the speed of light. To take the cryptographic example, it allows you to generate a safe one-time pad, known to both sides and to no one else, but you still have to transmit your actual message separately.
How can quantum entanglement be used for something like teleportation? Well, let us agree first that if I can produce a perfect quantum replica of a distant system, that is equivalent to teleporting the system. Any given electron (for example) is indistinguishable (in a very deep sense) from every other electron in the universe. So for teleportation all we need to do is reproduce a quantum state. You might say it's more akin to a quantum xerox machine than to most people's classical idea of teleportation.
Okay, so here's how it works: take your two quantum-entangled photons, and instead of simply measuring the polarization of the one nearby, get it to interact with a "target photon" that you want to teleport. If you set things up properly, and observe the outcome very carefully, then the interaction of the two photons on your end will cause the entangled photon - an arbitrary distance away - to enter a new state which is perfectly correlated with the state that your target photon had. Then, once you tell your distant collaborator about the exact outcome of the photon interaction on your side, your collaborator will be able to apply that knowledge to her entangled photon, and produce an exact quantum replica of your original target photon. Voila! Teleportation.
Note again that no faster-than-light communication is enabled by this. You still have to communicate a regular light-speed message between collaborators to get this to work. The actual experiment was carried out several years ago and is old hat by now. The current experiment improves upon previous efforts by entangling so many more (trillions!) particles.
The quantum entanglement of so many particles makes the actual teleportation of a similar number feasible, but one final note - even trillions of particles is many orders of magnitude less than the 10^27 or so particles in your average Starship Captain.
-Renard
The homepage:
http://www.dfi.aau.dk/amo/qoptics/qoptics.htm
Direct links, that looked related:
http://www.dfi.aau.dk/amo/qoptics/qa.htm
http://www.dfi.aau.dk/amo/qoptics/
http://www.dfi.aau.dk/amo/qoptics/title.html
http://www.qubit.org/intros/comm/comm.html
(Centre for quantum computation)
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"Since the beginning of time, man has yearned to destroy the sun"
...
-- J. Montgomery Burns
Ignoring the fact that this technology does not permit the transmission of matter, only information
If one could teleport matter, how much cadmium or other neutron absorber would one have to teleport into the sun in order to quench the nuclear reaction and make Burns' dream a reality? Or would it just not work at all?
Believe it or not, our memories and knowledge are not stored via black-magic in an unknown mystical misty substance in our heads, but by good old solid molecules etc that physically make up our brains. An exact replica would have ALL of that, just like an exact replica of a hard disk would have all of that hard disks information. Believe it or not, human memory is not a mystical force that defies physics, our brains are subject to precisely the same physics laws as every other part of our body. Nope, no defying-of-physics going on inside our heads. Its good old plain old real matter in there, and its certainly not "vaporous" (with the exception of the presence of some gasses, which are of course, once again, just good old molecules, plain old matter, the same electrons/protons/neutrons that our "skin and bones and blood" are made up of).
Dude, take some chemistry courses and physics courses. Our brains are not mystical metaphysical things. The existence of sentience (related to "consciousness") eludes explanation of course, and thats where it might get a little dicy, but memories and knowledge and thinking and reasoning are things that are, unfortunately, made up of matter and have not been granted exemption to the laws of physics.
All of which is why, of course, the brain is still so subject to modification and damage, e.g. a little bit of brain damage can seriously affect all of memory, knowledge, thinking and reasoning. Which "proves" in at least some way that the memory and thinking and reasoning was the result of the *physical* configuration of the particles in the brain, not something vaporous or non-matter. It also explains why not only thinking and reasoning, but CONSCIOUSNESS itself (might be called a "soul" by some) is so horribly easy to influence even with a few simple drugs. If our "souls" are so absolute, then why would it be even possible for a small amount of a single specific chemical (i.e. alcohol and drugs) to have such drastic influences on the way we *experience* consciousness? Consciousness itself must surely be a simple product of chemistry if it is so easily modified by chemicals. Same applies to emotions; if emotions are as mystical as many religous people portray, how can chemicals so easily directly modify emotion?
..
And things like MRI scans *reveal* a "concrete", physical structure to thought and reasoning. Chemistry analysis reveals concrete chemical causality of emotions.
Only the unified holistic *experience* of all of these things combined, which is our "consciousness", defies explanation by existing scientific knowledge, otherwise, if we can "feel", its arguable that a computer would be able to also. Where do "I" stop and my "body" begins? Where do "I" stop and the world begin? Bodies can be extended by prosthetics, even nerve endings extended by artifical "nerves", there is no reason to suspect the brain will not be "extendible" in future by more advanced electronics. Would such electronics become an integral part of an individuals consciousness?
Anyway, just some random thoughts related to the question
There is a mirror of the paper here at the arXiv.org e-Print archive. 11 pages of pdf fun can be found:
HERE
Have fun!
I find it gratifying that an earlier comment of mine about quantum entanglement was rudely put down as "impossible outside of science fiction and dilbert cartoons" is now receiving some front-page lovin'