TELEPORTATION may inspire images of instant travel, but physicists today see it more as a component of quantum computers.
Image: PHIL SAUNDERS Space Channel Ltd.
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The sci-fi dream (or utter fantasy) of getting from one place to another instantaneously continued this February 14, with the opening of Doug Liman's film Jumper, based on the novel by Steven Gould. We asked quantum physicist H. Jeff Kimble of the California Institute of Technology to explain how physicists understand quantum teleportation, which turns out to be more relevant to computing than to commuting. Note: This is an expanded version of a Q&A published in the March 2008 print edition of Scientific American.
Scientific American: What's the biggest misconception about teleportation?
Jeff Kimble: That the object itself is being sent. We're not sending around material stuff. If I wanted to send you a Boeing 757, I could send you all the parts, or I could send you a blueprint showing all the parts, and it's much easier to send a blueprint. Teleportation is a protocol about how to send a quantum state—a wave function—from one place to another.
Is transmitting a quantum state hard to do?
The most straightforward way to do it would be to imagine it was an electron: just shoot the electron from point A to point B and it takes its quantum state with it. But that’s not always so good, because the state gets messed up in the process.
How does teleportation get around the disruption of the quantum state?
The special resource that enables teleportation is entanglement. You're Alice [in location A], and I hand you an electron in an unknown quantum state. Your job is to send the quantum state (not the electron) to location B, which is Bob. If you try to measure it directly, you necessarily disturb it.
You and Bob also share a pair of electron—you have one, Bob has the other—and they're in an entangled state such that if yours is spinning up, his is spinning down and conversely.
You make a joint measurement of two electrons—the one I handed you and the one you're sharing with Bob. And that gives you two bits of information. You call up Bob on the cell phone and give him those two bits, and he uses them to manipulate his electron. And bingo, in the ideal case he can perfectly re-create the state of the electron that I handed you.
Why doesn't Alice just copy the quantum state and store the copy?
There are uncertainty relations like Heisenberg's uncertainty principle. When I hand my electron to Alice, what she might think to do is just keep a copy—clone it. The more information she tries to get about the state, the less good is the teleportation. If she tries to keep a perfect copy, then Bob would create a state that is perfectly random.
Why would you want to transmit a quantum state? What are the applications?
Imagine you want to build a quantum computer. A quantum computer is going to have parts just like a computer on your desktop. They have to be wired together quantum mechanically. The quantum memory's got to talk to the quantum processor. Teleportation is just a fancy quantum wire.
Why not just shoot electrons around?
If I carry this electron from the memory to the processor and I make a mistake—say it collides with some impurity in the wire—then I've lost more than just the state of that one electron. That one spin is entangled, potentially, with all the spins in the computer.
How has the field advanced since the first demonstrations of quantum teleportation in 1997?
All the initial work was done with light. In 1998 my team demonstrated teleportation of a beam of light. I would say that was the first bona fide demonstration. A beam of light came in, and a beam of light came out. In the experiments your magazine covered, there was never a moment you could say, aha, the state has emerged and been teleported.
A few years ago [in 2004] a group led by David J. Wineland at the National Institute of Standards and Technology in Boulder, Colo.—and simultaneously with that, a group led by Rainer Blatt in Innsbruck, Austria—teleported the internal spin of a trapped ion. It’s the first time teleportation had been done with the state of a massive particle. The quantum state of one ion was teleported to a second ion using a third ion in the middle as an intermediate.
More recently [in 2006], the group of Eugene S. Polzik at the University of Copenhagen teleported the quantum state of light directly into a material system. All the other experiments had been teleportation from an atom or a photon to exactly the same kind of particle.
Do these demonstrations have any practical value?
It has practical implications, because a quantum computer is going to be a hybrid system. Light is good for propagating from one place to the other with very low loss, but it's really hard to store light. Some quantum information protocols require you to take light and map it into some material system, where you can store it for a long time. Then if you want to communicate across your computer or across the country, you map it back into light.
I should tell you one other experiment. A scientist named Akira Furusawa* at the University of Tokyo teleported entanglement. He had one beam of light that was entangled to a second beam; he teleported the first beam and he could show it was still entangled with the partner that wasn't teleported.
How would keeping a teleported object entangled with its unteleported partner be useful?
The quantum computer's working on thousands of entangled spins and from time to time I need to teleport the state of the 561st electron to another place. Well that's not as simple as just thinking it's that one electron.
Switching gears—this new movie, Jumper, is about a kid, and some other people, who teleport from place to place.
I didn't know that.
If you saw X-Men, with Nightcrawler…
I haven't seen X-Men either.
See what we're tweeting about
14 Comments
Add CommentThis should not be called teleportation ... I could just as easily fax the electron spin information and get the same result.
Reply | Report Abuse | Link to thisnope
Reply | Report Abuse | Link to thishelp
Reply | Report Abuse | Link to this@axualalien
Reply | Report Abuse | Link to thisno. you could not. you cannot measure properties of the electron to fax them because as soon as you do, they are not what you measured. Thats why the intermediary particle is required and why it relies on entanglement.
amazing!!
Reply | Report Abuse | Link to thisIn Star Trek they used a Heisenberg compensator.
Reply | Report Abuse | Link to this"the base of our society is information commerce"
Reply | Report Abuse | Link to thisthats a very short explanation on how such a thing will be incredibly useful and utilized in all kinds of fields during the next ten years.
the very face of commerce itself (as we know it) is about to change substantially.
It's a good thing that physical teleportation isn't what we are talking about. Teleportation of the physical object moving variety is the ultimate superweapon that would remake world politics in a matter of days and change warfare forever. Those who got this capability would have a strike anywhere instantly capability with no trail indicating who did it. For instance, on a small scale teleporting a little piece of a heart into a location 2 centimeters away would kill. On a large scale, teleporting a city to the far side of the moon for 30 minutes and then right back where it was to begin with would kill everyone.
Reply | Report Abuse | Link to thisSo it's a good tihing that's not what this "teleportation" business is talking about.
Pythagoras, Euclid also, concluded that zero time occurs between any two or more points on the real line which is still the fundamental mathematical system for analysis of teleportation of objects in the vector universe. I think we may have two or three schools of science thought: vector holographic systems, digital pixel systems and quantum based energy systems. Since magnetism lacks a door to human life, i.e. Philadelphia invisibility experiments, the vector hologram system will probably win out in the future. Why? because the time between any two points on the line (in the universe) is 1-millionth second on two sides: into the tunnel and out of the tunnel. Thus, nobody would die or freeze to death or need to be taken apart to traverse any distance. BRB.
Reply | Report Abuse | Link to thisScience Fiction has a way to predict what will NOT happen in the comming years, Quantum teleportation is the key to secure communications, data storage (as in the "frozen photon" experiments), and probably supraluminic comunication (if you could somehow make an entangled particle "dance" like a cartesian diver), but you won't be seeing a disappearing act a la Kirk because the particles you use must be entangled first, that would mean you have to send an equal mass to your average Redshirt down to the planet before sending him, and then what is the purposse of such a maneuver? you still need a shuttle to haul down an even more fragile mass than your redshirt.
Reply | Report Abuse | Link to thisNever say never.
Reply | Report Abuse | Link to thisA few years before the Wright's brothers first flight
the top British Scientist of the day declared that manned flight is impossible.
An other one said around the same time"everything that can be invented has been invented".
I really dont understand the difference between teleporting the quantum state vs. sending a signal by transmission. I see the original entanglement will still be at point A and perhaps electron 532 state will be transported but what exactly does that mean? The information will get there anyway right?
Reply | Report Abuse | Link to thishow true!
Reply | Report Abuse | Link to thisthis is Not teleportation, it is replication.
What if entaglement is nothing more than the flow of space-time between two particles no matter how small they are,and space-time is so called dark energy?An excample would be eletromagnitism where S-pole is outward flow,and N-pole is inward flow,thus you couldn't have a monepole,because it's just a matter of direction of flow.
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