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The Quantum Physics of TeleportationMost of the science has been covered in the brief analysis. But teleportation is the most complicated, and needs much more space, so it will be presented here. It is in fact a fascinating subject, and there now is some actual real science concerning the subject which was recently discovered only a little over 1 year ago. In short, EFC was completely irresponsible in their presentation, and probably completely oblivious to this recently discovered effect (clinging to Star Trek garbage). Nonetheless, this discovery is quite amazing and we hope you will find the article interesting.
In an attempt to make this article more readable, the math has been removed. To be honest however, it has been a fair number of years since any of us here at The Companion have studied quantum physics, and the actual theory behind teleportation goes well beyond any courses we once took. So I admit, I am not completely sure about all the details I will present, so I hope you will bear with me. (If you happen to understand this theory and think you can tell it better or have corrections, please email us.)
Introduction to Quantum Teleportation and Entanglement
On December 11, 1997, a group of researchers led by Anton Zeilinger at the University of Innsbruck in Austria published a paper on the successful experiment of the teleportation of photons. The idea was introduced by a team of researchers from IBM in 1993. Before this, the problem seen with teleportation was that it seemed to violate the Uncertainty Principle. The Uncertainty Principle basically states that for very small particles, you cannot know both its position and its momentum beyond a specific degree of certainty at a single point in time. This is because if you make an attempt to learn both pieces of this information, your observation will actually directly affect the particle changing its characteristics. (Sorry I was going to leave the equation out, but the following episode, "Friendly Fire" has Augur bastardize the Uncertainty Principle, so I feel compelled to add it. (delta p)(delta x) >= h/2PI, where p is momentum, x is position, PI is the constant pi=3.14...., and h is Plank's constant (which is a very very small number). This means that the product of the precision in the measurement of position with the precision of the measurement of momentum can never be smaller than h/2PI. The point is that this requirement is very, very small, and would have no useful application to anything in the macroscopic world, like a space shuttle.)
So it was believed that to teleport a particle, you need to know its exact information in order to reproduce an exact copy. More specifically, in quantum physics, objects exhibit properties of both particles and waves. An object is considered to be both a particle and a wave. Thus, to teleport, it seems you would need to know its particlelike properties such as its position, and you would need to know its wavelike properties, such as momentum. But this is a violation of the Uncertainty Principle.
The IBM researchers suggested an "end-run" (a way around the Uncertainty Principle without violating it). They posed the question, "Is there a way to transfer properties without needing to know what the properties are?" The answer lies in a paper published by Einstein-Podolsky-Rosen in the 1930s and a theory referred to as "entanglement". Ironically, it appears that this paper was written to mock the concept of quantum mechanics because it allowed for very strange things to happen. Einstein-Podolsky-Rosen proposed that under certain conditions, when two particles come into contact, they can become "entangled". This means what happens to the state of one particle directly affects the state of the other, even if they are no longer in proximity to each other. Einstein referred to this as "spooky action at a distance" and found the concept quite absurd. However, once again, Einstein is wrong, and also right at the same time.
Entanglement is very important to the workings of the quantum teleportation, so I will elaborate a little more. Experimentalists can create the "entanglement" on photons (light particles/packets of energy) by taking a single photon and splitting it into two photons of lower energy. For the purpose of teleportation, these two particles become "complements" of each other. In a generic sense, the specific properties of particles can be referred to as "polarization". Polarization is expressed in angles, such as 45 degrees. So if we find two particles of the same type (e.g. both are photons), and both have a polarization of 45 degrees, then they are considered to equivalent. (This will be important later for the actual teleportation.) And in very simplistic terms, to be "complements" of each other means one particle is in an opposite state of another. (An example of this is listed below in the text of the actual experiment.)
One of the experiments to help determine if entanglement (and "spooky action at a distance") was real was to separate two entangled photons with initially undefined energies and channel them through two separate fiber optic wires, separating them a total distance of 10km. Once they both reach the far ends of their fiber optic cable, the scientists can measure one of the particles and discover that it had instantaneously determined the energy of its counterpart 10 km away.
It is very important to note that this change was instantaneous. There were tests to make sure data did not travel from one particle to another at the speed of light to tell what each other's state is. The changes beat the speed of light and were indeed instantaneous.
However, there is another important fact to notice. The photons sent through the fiber optic cable were still constrained to the speed of light. It still takes time to actually send the particles. So even though "spooky action" between the two keeps their states intertwined, they still need to be transported via conventional means at conventional speeds.
The University of Innsbruck Experiment
With entanglement in mind, the researchers at the University of Innsbruck devised a plan. The idea is to separate the two entangled particles like before, but introduce a third particle that contains the data you wish to "teleport" and force it to interact with one of the two entangled particles. Thus, the other particle will react and become the same as the data you wished to teleport. It is important to emphasize that this method does not physically teleport (relocate) the photon itself. This method only transfers its properties to a remote photon. But in quantum physics, two of the same kind of particles in exactly the same states are identical, so teleportation is achieved. (The indistinguishability of identical particles is a consequence of the wave nature of particles, because in a collision region, the fuzziness from the uncertainty principle makes it impossible to tell which path a specific particle took. This is verified by another principle called the Pauli Exclusion Principle.)
I will now refer to some diagrams which will hopefully help the explanation along. The first diagram is the diagram of the actual experiment (published by the University of Innsbruck). This is how it was really done. The second diagram (obtained from IBM's website) is a simplification of the process. Note there is an arrow labeled "send data" connecting the two particles in diagram 2. I personally found this misleading because it seemed like something physical was actually traveling along that line. This is not true. This is the "spooky action at a distance".
To gather an appreciation of the ramifications and limitations of this discovery, I believe it helps to go through how the teleportation works in slightly more precise detail than you have seen above. This means I will be referring to diagram 1 more often. So to start with, "Alice" is the sending station which sends the particle we wish to teleport. "Bob" is the receiving station where we want the teleported particle to appear at the end. (The names "Alice" and "Bob" seem to be a standard convention.) There is another device in the picture between Alice and Bob. This is a device that emits "entangled" photons.
So the first step in the experiment is to create a photon we want to teleport. Alice sends and encodes a photon (which is called "Photon M") with a specific state. For this example, 45 degrees polarization is the specific state. We give the photon a specific state because we want to compare the teleported photon at the end of the experiment to make sure it is identical (meaning it also must have a state of 45 degrees).
Meanwhile, another special device generates two "entangled" photons which are called "Photon A" and "Photon B". These two photons are in "fuzzy" states meaning that we don't really know what their specific states are. This is our "end-run" around the Uncertainty Principle. Though we don't know their exact states, we do know they are entangled, meaning if we measure one photon later and it has a horizontal polarization (0 degrees), then the other photon must "collapse" into the complementary state of vertical polarization (90 degrees). Photon A is sent to the beam splitter to meet Photon M and Photon B is sent to Bob (the final destination).
This next part is a little hairy, and left solely to me, I would completely misrepresent the process. To get through the next part, I will quote directly from an article found at Physics News Update, and the muddle through a translation.
Entangled photon A arrives at the beam splitter at the same time as the message photon M. The beam splitter causes each photon to either continue towards detector 1 or change course and travel to detector 2. In 25% of all cases, in which the two photons go off into different detectors, Alice does not know which photon went to which detector. This inability for Alice to distinguish between the two photons causes quantum weirdness to kick in. Just by the very fact that the two photons are now indistinguishable, the message photon M loses its original identity and becomes entangled with A. The polarization value for each photon is now indeterminate, but since they travel towards different detectors Alice knows that the two photons must have complementary polarizations.
The general idea seems to be that photons A and M need to be entangled, but that only happens when the photons land in different detectors. (This is probably related to the Exclusion Principle mentioned earlier.) There seems to be some kind of mathematical limitation which allows the process to have only a 25% probability of actually becoming entangled (which is perhaps the probability of landing in two different detectors rather than landing in the same detectors or none at all?). This seems to suggest that teleportation might not always work. But when it does work, photon M and photon A now become entangled and M and A must have complementary polarizations.
Finally, since photon A has become entangled with photon M (becoming complements) and photon A and photon B were already entangled (complements), photon B experiences "spooky action at a distance". "M" is the complement of "A". And "B" is the complement of "A". This means that "B" must conform to be the same as "M" (45 degrees). Thus the "spooky action" changes "B" into the state that "M" was, completing the teleportation. Since photons in the same polarization are indistinguishable from another, this transformation of "B" is the teleportation.
An important additional note however, is that photon A and photon M are now in unknown, fuzzy states. It seems that the new entanglement breaks the connection with photon B after B's instantaneous transformation. This is shown more clearly in diagram 2. This means that the original "message" to be teleported was completely destroyed! This means the dual person paradox presented in the "Mars Teleporter" story above could never happen with this process.
It is also important to note that teleportation does not allow faster-than-light communication to anywhere. Photon B must still travel by conventional methods (like a fiber optic cable).
The Limitations and Realities of Quantum Teleportation
This discovery is quite amazing and quite shocking. However, there are some serious limitations which make the teleportation of large objects highly unlikely. The major problem is that the technique is dependent on "entanglement". But entanglement is dependent on the "wavelike" properties of matter which quickly break down as an object scales up to macroscopic sizes. One might speculate that you might be able to deal with quantum particles separately, but reconstructing them to reconstruct the original larger object seems to require you to violate the Uncertainty Principle. And as a side thought, if teleportation of humans was possible, you have to wonder how painful the process might be since you are essentially being destroyed.
Another issue is that teleportation is not necessarily able to transport things into random places, because you need the exact 2 particles (A and B) that you started with. As seen in the experiment, "Photon B" must be sent to a location before the teleportation occurs. This means you will need some kind of network such as fiber optic cables to send the photon so you don't lose it. Or you will need some kind of storage device for the particle so you can deliver it at your convenience. (This is actually something that is being explored.)
Though this discovery doesn't seem to offer teleportation of large objects, there is hope that this can be applied to "Quantum Computers". The idea is that traditional computers must use 0's or 1's which make many operations (like factoring) difficult. But since a quantum particle can be both a 0 and 1 (for those with some quantum background, think double slit experiment), it allows for instantaneous and free parallelization, which permits quantum based computers to calculate very differently, or at the very least compute more quickly. And with entanglement and teleportation, it is believed that states can be changed instantaneously in different parts of a system that rely on each other.
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Last updated: March 27, 1999
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