Without quite the drama of Alexander Graham Bell calling out, “Mr. Watson, come here!” or the charm of the original “Star Trek” television show, scientists have nonetheless achieved a milestone in communication: teleporting the quantum identity of one atom to another a few feet away.
The contraption is a Rube Goldberg-esque mix of vacuum chambers, fiber optics, lasers and semitransparent beam splitters in a laboratory at the Joint Quantum Institute in Maryland.
Even in the far future, “Star Trek” transporters will probably remain a fantasy, but the mechanism could form an important component in new types of communication and computing.
Quantum teleportation depends on entanglement, one of the strangest of the many strange aspects of quantum mechanics. Two particles can become “entangled” into a single entity, and a change in one instantaneously changes the other even if it is far away.
Previously, physicists have shown that they could use teleportation to transfer information from one photon to another or between nearby atoms. In the new research, the scientists used light to transfer quantum information between two well-separated atoms.
“It’s that hybrid approach that we’ve demonstrated that looks to be an interesting way to proceed,” said Christopher Monroe, a University of Maryland physicist and the senior author of a paper describing the research in the Jan. 23 issue of the journal Science.
Present-day digital computers store information as zeroes and ones. In a future quantum computer, a single bit of information could be both zero and one at the same time. (In essence, a quantum coin toss would be both heads and tails until someone actually looked at the coin, at which time the coin instantly becomes one or the other.) In theory, a quantum computer could calculate certain types of problems much more quickly than digital computers.
In the experiment, two ytterbium ions, cooled to a fraction of a degree above absolute zero, served as the two quantum coins. A microwave pulse wrote quantum information onto one; a second microwave pulse placed the ion into a state of equal probabilities of heads and tails.
A laser then induced each ion to emit exactly one photon, collected by a lens and guided through fiber optics to a beam splitter that could reflect the photons or let them pass through. Two detectors then captured and recorded the photons. Because it was not known which photon came from which atom, the photons became “entangled,” meaning that the behavior of the two particles became wrapped up in a single equation even though they were not in the same place. And, oddly, because the photons were emitted by the ions, the two ions also became entangled.
“That’s the magic of entanglement,” Dr. Monroe said. “Now, the atoms are entangled. The photons are gone and out of the picture.”
The information in the first ion was then measured in a way that did not reveal the information and that teleported the information to the second ion. (If that did not make any sense, take a look at this animated graphic.)
By repeating the experiment many times and taking many measurements of the second ion, the researchers, from Maryland and the University of Michigan, confirmed that the second ion contained the information that had been originally written to the first ion.
The method is not particularly practical at the moment, because it fails almost all of the time. Only 1 of every 100 million teleportation attempts succeed, requiring 10 minutes to transfer one bit of quantum information.
“We need to work on that,” Dr. Monroe said.
But he said that a success rate of just 1 in 10,000 would be high enough for some uses. Such systems could be used as “quantum repeaters” — reading the information from one photon and then imprinting it on a new photon for the next leg of its communications journey.
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