(06/25/2004 12:00 PM EDT)
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PORTLAND, Ore. — Physicists at the National Institute of Standards and Technology (NIST) in the United States and the University of Innsbruck, Austria have demonstrated the transfer of information between two locations without any intervening physical medium.
The separate efforts mark the first teleportation of material states, a concept long postulated and one that could open new avenues for unbreakable encryption technology — information would never be eavesdropped upon because it is not actually being transmitted.
"We and another group at the University of Innsbruck are the first to demonstrate teleportation of quantum states from one location to another," said NIST physicist David Wineland. "Both groups have followed Bennett's original algorithm very closely, and we both successfully teleported qubits." Wineland was referring to a 1993 finding by IBM fellow Charles Bennett and five colleagues that because matter was based on quantum-mechanical waves, "beam me up, Scotty" teleportation was possible in principle. The caveat: The original of the item being teleported would be destroyed in the process.
According to Bennett, teleportation sidesteps the Heisenberg uncertainty principle, which maintains that measuring destroys matter's quantum-mechanical information, thereby making it impossible to accurately reproduce it.
Bennett maintained that by virtue of the Einstein-Podolsky-Rosen effect, it was possible to destroy the original while passing its measurements (energy level, motion, spin state, phase, superpositions, magnetic field and other physical properties that would otherwise be lost to Heisenberg's principle) to a third party that could teleport them to the terminus point. There the data could be used to construct the original anew — thereby achieving teleportation without replication.
Between 1997 and 2002, several groups demonstrated the technique for teleporting quantum-mechanical information — called qubits — using light polarization. However, the NIST and Innsbruck efforts are the first time the states of a qubit have been teleported from one physical atom to another. The groups did not teleport the physical matter itself, but only the quantum-mechanical description. "We think that quantum computers in the future will have to use teleportation, so we wanted to demonstrate the proof of principle so that we and others could start trying to build quantum gates and processors," said Wineland.
Entangled atoms
The approach used by both groups was to begin with a pair of "entangled" atoms — that is, two atoms ("A" and "B") whose quantum states are linked by the manipulations of a laser beam (for up to 4 milliseconds, they were inextricably linked by an invisible force Einstein called "spooky action at a distance").
Then they transferred the qubit information from atom A to point "C" — a beryllium ion for the NIST team, a calcium ion for the Austrian group — by performing a mathematical operation called a Bell-state measurement that destroys A's quantum-mechanical state (by accurately measuring it).
The results of the Bell-state measurement are then sent to the terminus point of the teleportation, where they interact with the entangled atom B to construct the original quantum state of A.
"We never know just what the qubits contain, only that their information was destroyed in the original but preserved during teleportation to the entangled ion," said Wineland.
If perfected, the technique could enable uncrackable encryption codes. Only someone in possession of the second entangled ion can decode the information. Both teams reported success rates of 75 percent to 78 percent during the teleportation process.
NIST achieved its goal by creating ion traps out of gold electrodes deposited on alumina. By shuttling ions among up to six traps, made from eight electrodes, NIST was able to repeatedly demonstrate successful teleportation of quantum states.
NIST's work was funded by the Advanced Research and Development Activity and the National Security Agency.
