Scientists 'beam up' an atom, sort of
Teleportation marks a giant leap %>(not for traveling, but computing)
Thursday, June 17, 2004
BY AMY ELLIS NUTT
Star-Ledger Staff
Legend has it that Gene Roddenberry, creator of "Star Trek," invented the transporter -- the means by which Captain Kirk and the other members of the Enterprise traveled instantaneously from place to place -- merely as a convenience. It was a lot less expensive to show Roddenberry's television characters being "beamed" down to the surface of another planet than to create another spacecraft to do the job.
Physicists at the U.S. Department of Commerce's National Institute of Standards and Technology needed no such excuse. In an article appearing today in the journal Nature, government researchers report that for the first time, they have succeeded in teleporting key properties of one atom to another, nearly instantaneously and without the use of a physical link.
A "transporter" that can beam a person from home to work is still countless years away, but the demonstration of atomic teleportation is the most significant step taken to date in the quest to create the world's first quantum computer.
The importance of teleportation has less to do with the movement of objects than with the speed of information. Quantum information is one of the most rapidly developing areas in physics, and its reliance on teleportation is the basis for all future information technology.
Classical computers are binary -- that is, they deal with bits of information, each taking one of two values, 0 or 1. Quantum computers, on the other hand, deal in "qubits," or quantum bits, when performing calculations or storing information. In a quantum computer, atoms or molecules could be manipulated to be in several different states, or superpositions, simultaneously. This means they could process and store exponentially more information than a classical binary computer.
A quantum computer could run an operation on 1 million inputs, all at the same time, using only as many qubits as a binary-based computer would need to run an operation on just one input.
Using teleportation instead of wires, a quantum computer would mean the advent of truly unbreakable security codes. Able to sort through exponentially more variables and in drastically shorter amounts of time, such a computer also could solve in seconds complex mathematical problems that would take a conventional computer millions of years.
And perhaps most important of all, quantum computers could usher in a new era of technological development: modeling chemical combinations in the search for life- saving drugs, or engineering photoelectric cells so efficient as to make global warming moot.
MEASURE FOR MEASURE
How does teleportation work? For one thing, it does not involve beaming a person -- or any other object -- from one place to another, but rather, the information about that object. Teleporting means replicating that information (an object's properties or characteristics) at a distance.
To do that, the properties first must be observed or measured. The problem is that, according to the theory of quantum mechanics, which governs matter and energy at the subatomic level, it is impossible to know all the properties of an object at any one time. According to Heisenberg's uncertainty principle, when we measure an object we interact with it and therefore change it ever so slightly. And if we cannot know or measure all those properties accurately, we can hardly replicate them. Teleportation, therefore, would seem to be impossible.
But what if something could be measured indirectly? Charles H. Bennett of IBM proposed this idea in 1993. In the demonstration at the Institute of Standards and Technology, this kind of quantum teleportation was achieved by making use of something physicists call "entanglement."
A laser beam can be squeezed and split in such a way that it creates a pair of entangled subatomic particles. These particles, no matter how far apart they travel, mysteriously remain linked. Like psychic twins, when one particle's spin or velocity is changed, so will the other's -- even if the two wind up at opposite sides of the universe.
"Einstein called it 'spooky action at a distance,'" said David Wineland, chief author of the Nature article. "Entanglement is even weird for physicists. Nevertheless it does exist."
The particles used by Wineland's team were electrically charged beryllium atoms, or ions. In attempting to teleport the spin and position of beryllium ion A, the team entangled two additional ions, B and C, through the use of laser beams.
Instead of directly measuring A, which would make teleportation impossible, the team instead measured a joint feature of A and ion B. And because ion C was entangled with B, the joint measurement of A and B became the joint measurement of A and C, from which the properties of A could be extracted. Meanwhile, the original properties of A were destroyed by the interaction -- which was all that was needed to say that A had been teleported to C.
"One way to think about these states is: Think of them as little arrows pointing in the same direction in space," said Wineland. "We can have them pointing in any direction. In an entangled state, what happens is, if you separate the particles and put them in widely different locations, when one is measured the arrow points up, then instantly the other is pointing up, too. The first will measure up and down with random probability, but as soon as it is measured, the other one will measure the same way.
"You'll still find plenty of people who say that (quantum computing) is fantasy," he continued. "It's extremely hard -- the technological problems -- and yet, having said that, there's no fundamental reason we can't do this. It's where all the technology is headed. We want to make smaller and smaller devices and control them better and better, and that's where it's headed. I'll be lucky to see a useful device in my lifetime, but I believe it will happen."
