Thursday, October 19, 2006

Quantum entanglement demonstrated

Another milestone in our quantum history...


PORTLAND, Ore. — The National Institute of Standards and Technology (NIST) said it has demonstrated what it claims is the world's first entangled atoms that could be used to communicate information nondestructively.

By creating multiple pairings of entangled atoms, NIST scientist Dietrich Leibfried was able to transmit quantum data and verify its reception from one pair without destroying the information in the other pair.

"The distance between the pairs is about a micron, but we are the first group to demonstrate high success rates in an ion trap design that we think can scaled up to build a quantum computer," Liebfried claimed.

Entanglement—referred to by Albert Einstein as "spooky action at a distance"—is a quantum phenomenon in which two particles—atoms or photons in close proximity—take on identical internal states. The synchronization, if conditions are right, can persist even if the particles are separated so that information processed by one pair is simultaneously processed by the other.

Researchers believe the phenomenon could serve as the basis for enabling quantum computing capabilities.

Still, almost any operation performed to determine the state of an entangled particle also destroys the synchronization, meaning that information read-out at any step in a computation destroys the synchronization of the quantum information, halting computations. Conversely, not reading out information makes the computation useless.

So far, schemes to sidestep the quantum entanglement Catch-22—which involve making more than one entangled pair, performing the same operations on each, then destructively reading out only from one pair—has only been demonstrated by pairs or entangled photons. NIST claims it has demonstrated a method that works for atoms too, opening the possibility of building future quantum computers using its approach.

The process, called data "purification," used two pairs of beryllium ions held in electromagnetic traps on a chip surface. The complex procedure enable the entanglement of two pairs which perform a quantum processing step, then read out the results from one pair while maintaining the integrity of original information in the first pair.

The purification procedure, which worked in one out of three attempts, compared to once in a million attempts in previous experiments with photons, employed special error-correction procedures that enabled information to become more secure at each iteration, perhaps enabling long multi-step quantum computationsin future quantum computers.

NIST researchers will next seek to apply the purification procedure to quantum computer development using other subsystems already designed, including ion traps. They will also demonstrate working algorithms for uncrackable data encryption or quantum teleportation of information.


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