02.15.08

Teleportation Friday!

So I've two timely snippets on teleportation in my newly minted Teleportation Friday! series. (Um, it's a limited series...of one).

The first is, in light of Doug Liman's new movie "Jumper", where there's lot of people teleporting around (I've heard), to answer the questions about whether teleportation is physically real or just another thing the movie and tv writers have gotten carried away with. The answer depends upon how you're defining teleportation. Most people these days envision something akin to what happens in Star Trek, where a person or object is dematerialized and turned into pure information which is then transmitted and used to reconstruct a perfect copy elsewhere. Ok, let's take that definition. So what's the answer, then? Well, the answer is actually a (highly qualified), YES. But here's the bit that qualifies the answer. Prior to not so long ago, the answer would have been an unqualified NO, for a good reason or matter of principle. We teleport things all the time, in a sense, for example when we make a phone call or send a fax. Your voice is being copied, turned into information, and used to reconstruct a copy of your voice elsewhere. Similarly for that picture of the cat you're faxing to grandma. Neither the voice nor the picture are travelling down the line to the other end. Information that can be used to reconstruct them is being transmitted instead. The objection about being able to do what is done in Star Trek would have come when you realize that you'd need to get not just the approximate details right, but every last detail about every subatomic particle in their body down to at least the atomic level. Putting aside the (still unsurmountable) matter of just how much information there is in all that, there's the issue that you'd need to somehow measure the fully quantum information about all of those particles, and that's not possible without destroying that information, even in principle. (This is the old business of opening the box to see whether Schrodinger's cat is dead or alive... you'll only ever know one or the other, not the actual quantum state that mixes deadness and aliveness. Look it up, I can't explain all of quantum physics here.)  And it is well known in the trade that you can't make multiple copies of quantum states, so... no teleportation?

Well, there's a loophole... while you can't duplicate quantum information, you can actually transfer it from one place to another in a way that is very analogous to the Star Trek picture of teleportation, and this is what is called "Quantum Teleportation", discovered by Bennett et.al. inn 1993. The net effect is to make a perfect copy at teh expense of destroying the original, but the  process acheives dematerializing or destroying the quantum state in one place, and reconstructing it elsewhere, arbitrarily far away at some later time. (I'll get back to what "arbitrarily" means in a moment.) Real physicists in real laboratories around the world do this. Yes, for real. So the objection that we can't teleport things because we cannot duplicate the quantum information contained in its atoms and so forth is sidestepped by not duplicating but doing the Star-Trekian dematerialization. Nice, eh?

So what are the caveats? Well, to get useful benefits of the process, first you have to prepare things properly, and in advance. The receiver and transmitter people must have previously arranged to each have part of what's called an entangled state. (Think of this as a system of separable parts, all of which are nevertheless part of a single quantum system that you've done no measurements on. Have a dig on the web for more background.)  Such a situation, which is in principle easy to prepare,  is the key agent to the whole process. They then go off on their separate ways, and later when they want to teleport quantum information about something, like say an atom in your finger, the fact that they each have a piece of this pre-prepared entangled state will allow them to do this. Think of that as their fax machines, or if you prefer, their Star Trek transporters.  The other thing they'll need is a normal means of communication, because the transmitter will need to send a piece of classical (not quantum) information, essentially the result of a certain measurement done on the entangled state and state to be transmitted (which conveniently destroys the state and stops them from ending up with two copies of it in the end). Think of this as the phone line connecting their fax machines, or the whatever-it-is that the Star Trek people use to transmit over their communicators (presumably just regular radio waves or similar?).

With this piece of classical information, transmitted by ordinary means, and the pre-prepared shared entangled state, the quantum teleportation is possible. Note, finally, that this means that you can't teleport instantaneously. This information cannot be sent over distances faster than the speed of light. This is easy to see since  you need that crucial bit of classical communication (over the phone line or similar) as part of the infrastructure. So no Laws of Physics are hurt in this process.

So teleportation Star-Trek style is in principle possible, but you can't do it faster than the speed of light (do they ever do that in Star Trek?). Yes, really. There's of course the little matter of how long it would take to transmit all the information contained in even your finger.... much longer than the lifetime of the universe....not to mention that they'd have to have previously exchanged at least as many pre-prepared quantum entangled states as the amount they'd later want to transmit, which represents an equally humongous storage problem  but let's not worry about that just yet.

So I have to be the spoilsport  and explain these limitations to an excited audience tonight. Doug Liman's people are doing a private screening of the movie here in LA with a panel of filmmakers and a scientist to talk about the film at the end. I'll be, er, playing the role of the scientist.


So I said two teleportation items. What was the second one? Well, I learned the other day that  the actress Marlene Forte (who generously has played many times the role of Lucha in readings of the play "Dark Matters" that I co-wrote and developed with playwright Oliver Mayer*) has been cast as the Transporter Chief in the upcoming new Star Trek Movie. Well Done, Marlene!

Bit of a weird coincidence, isn't it?

-cvj

(*See more about that by searching over on Asymptotia. More on an early reading can be found here.)

Tags: doug liman, jumper, star trek, teleportation

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