(Communication) ‘텔리포팅’의 진일보 ~ 몇 피트 떨어진 ‘이온’ 간에서

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By KENNETH CHANG ⓒ2009 New York Times News Service 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. ‘앨렉샌더 그래엄 벨’이 “Mr. Watson, come here”라고 외쳤을 때의 극적 장면이나 원조 “스타 트렉” TV 쇼와 같은 매력을 동반시키지는 않았지만, 과학자들은 여하튼 ‘커뮤니케이션’(communication)의 새 이정표를 이룩하는 데 성공했다: 즉 ‘양자 아이덴티티’(quantum identity)를 하나의 원자에서 몇 피트 떨어져 있는 또 하나의 원자로 이동시키는 데 성공한 것이다. 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. 이 작업을 해 낸 기기는 진공 체임버들, 광섬유, 레이저, 반투명한 ‘빔 스플리터’를 루브 골드버그 스타일로 혼합시켜 놓은 것으로 메릴랜드 주에 있는 합동 양자 연구소(the Joint Quantum Institute)의 한 연구실에 있다. 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. “스타 트렉”에 나오는 ‘트랜스포터’들은 앞으로 먼 장래까지도 아마 하나의 공상의 산물로 남게 될 것이지만, 이 기기는 새로운 형식의 통신과 컴퓨팅의 중요한 요소의 역할을 하게 될지 모른다. 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. (ⓒ2009 The New York Times) (ⓒ2009 usabriefing.net)
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