quantum internet by Ahmedmaged3000


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									Quantum Internet
Author(s): Peter Weiss
Source: Science News, Vol. 155, No. 14 (Apr. 3, 1999), pp. 220-221
Published by: Society for Science & the Public
Stable URL: http://www.jstor.org/stable/4011480
Accessed: 28/10/2010 11:46

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                                                                                                   formation via entanglement.
                                                                                                      Teleportation also requires a classical
                                                                                                   transfer of information-in Kimble's ex-
                                                                                                   periment, along wires. By correctly com-
                                                                                                   bining the information from the wires
                                                                                                   and the beams, the scientists recreate
                                                                                                   the message at the receiving end.
       The    quirks                            of         quantum                                    Along the classical path, information
                                                                                                   flows no faster than the speed of light.
   mechanics         may                              lead      to better                          So, quantum teleportation still obeys
                                                                                                   that universal speed limit.
           computer                                  networks
                                                                                                      A lthough light-based quantum-infor-
                                   By PETER WEISS                                                          mation processing seems promis-
                                                                                                           ing, the quantum-Internet may not
                                                                                                   ultimately use light as its medium.
Feverish                    now under equivalent of sending just one quantum
              experimentation                                                                      Attempts to use photons as bits in rudi-
      way in labs around the world may one           bit, or qubit, worth of information. Unlike   mentary quantum-computing experiments
      day lead to quantum computers.                 a conventional bit, which must represent      have run into some serious snags. In an
These extraordinarilypowerful calculating            either 0 or 1, a qubit represents a mixture   alternative pursued by some researchers,
machines would employ as their bits not              of 0 and 1 called a superposition. Only       the quantum Internet might slosh more
electric circuits but particles that obey the        when a measurement is actually made,          than blink.
strange rules of quantum mechanics. These            which destroys the superposition, is the         A number of scientific teams are ex-
devices are years away at best-maybe                 qubit forced into a specific value.           ploring quantum computing and commu-
decades, maybe more.                                    While wonderfully versatile, a qubit       nication using atoms in liquids manipu-
   Scientists dare to dream, anyway-                 still packs only one nugget of informa-       lated via nuclear magnetic resonance
not only of quantum computers but al-                tion. Recently Kimble and his colleagues      (NMR). The technique is also used in
so of linking them together into net-                have shown experimentally that quan-          medicine to make images of body parts.
works. The connections between the                   tum teleportation using light beams,          With strong magnetic fields and radio-
machines would operate on quantum                    made up of many photons, may be able          wave pulses, NMRmanipulates the spins
mechanical principles, too.                          to carry a great deal more information,       of atomic nuclei.
   Fuelingthose dreams is a growing ability          enough perhaps to support practical              In the Nov. 5, 1998 NATURE,  researchers
to transfer delicate quantum information             computing.                                    from Los Alamos (N.M.) National Labora-
from one place to another. New experi-                  Kimble's team and scientists from          tory and the University of New Mexico in
ments that stretch quantum mechanical ef-            Aarhus University in Denmark and the          Albuquerque reported a short-distance
fects across distances of kilometers are             University of Wales in Bangor shipped a       example of teleportation. They transmit-
providing encouragement.                             characteristic of a pulse of light across a   ted a characteristic known as spin orien-
   Theorists are fanning the flames as               lab bench to another pulse a meter away.      tation from one atom to another within a
well. Studies of how such hypothetical               Although the distance is short, in princi-    molecule. The scientists manipulated
networks would compare with conven-                  ple the same technique could work over        molecules of trichloroethylene dissolved
tional ones hint that greater computing              unlimited spans, Kimble says. The re-         in chloroform.
power waits to be unleashed.                         searchers described their experiment in          "We'veused different nuclei to transfer
   H. Jeff Kimble, an experimenter and               the Oct. 23, 1998 SCIENCE.                    the information, not photons or electro-
theorist at the California Institute of                 "With our quantum scheme, we could         magnetic fields. We're the first ones to do
Technology in Pasadena, foresees such                take the whole output of a quantum com-       that," says Raymond Laflamme of Los
networks having a widespread impact.                 puter and teleport it," says Christopher      Alamos.
"One could imagine a quantum Internet                A. Fuchs, one of the Caltech researchers.        In a manner analogous to the optical ex-
in the future," he says. It would be a                  To achieve teleportation, scientists ex-   periments, the researchers created a quan-
more complex web than the one that                   ploit another of the quantum realm's          tum conduit by entangling two atoms.
currently spans the globe and would                  strange aspects. Known as entanglement,       Then, they allowed another atom, which
employ communication capabilities not                it creates a correlation between quantum      carried the spin message, to interact with
possible with conventional technology.               objects that, in theory, persists no matter   one of the entangled pair,automatically af-
   "Such a network can do heroic                     how far apart those entities become. The      fecting the other via the quantum link.
things," he predicts.                                correlation arises because the objects           Although no wires were involved, a
                                                     occupy a joint quantum state. When the        classical ingredient was still present. A
                                                     entanglement ends-because         of a mea-   combination of radiofrequency pulses
Less     than 2 years ago, scientists suc-           surement, for example-the once-entan-         and quiescent periods guided the mole-
      ceeded for the first time in mak-              gled states must adopt related values.        cule into a final state that depends on the
      ing information appear to leap in-             Two formerly entangled photons would          arrangement of spins caused by the ini-
stantaneously from one place to another              take on predictable characteristics-for       tial message interaction. Those influ-
without passing through the intervening              instance, opposite values.                    ences finally nudged the target atom into
space. In independent experiments, scien-               Kimble's team split a single laser beam    the message's spin state.
tists in two European laboratories trans-            to create an entangled pair of beams.            The Caltech and Los Alamos achieve-
ferred a characteristic of one photon-               One blazed into the sending station and       ments are both "great experimental tours
the elementary particle of light-to anoth-           the other into the receiving station.         de force in learning how to control these
er photon via a technique called quan-               When a new pulse, which can be thought        things," says Charles H. Bennett of the
tum teleportation (SN: 1/17/98, p. 41).              of as the message, interacts with the         IBM Thomas J. Watson Research Center
Researchers say quantum teleportation                sending half of the original beam, entan-     in Yorktown Heights, N.Y. Bennett is one
will be an essential ingredient of both              glement requires that the receiving part      of six theorists who in 1993 came up with
quantum computers and networks.                      be affected, too. In essence, the receiver    the idea of quantum teleportation (SN:
   Teleporting a photon's state is the               gets a part of the message as quantum in-     4/10/93, p. 229).

220                                                        SCIENCE NEWS, VOL. 155                                            APRIL3, 1999
   Kimble,  however,harborsgravedoubts goes farbeyond interatomicdistances,al-             Early last year, however, a trio of com-
about the NMRexperiment. "Inmy view, beit withoutcomingclose to practicalnet-              puter scientists examined how quantum
it's not a demonstrationof teleportation, work dimensions. Moreover,"the same              computers would solve the problem and
it's a simulation,"he says. He contends procedurewe used for 3 photons can now             reported that the number of bits needed
that entanglements can't survive in the be generalized" possibly as manyas 10
                                                              to                           would be significantly below n.
disorderlysea of molecules constitutinga photons,Zeilinger       says.                        "By using quantum bits, rather than
typical liquid. NMRproponents counter                                                      classical bits, you can save on commu-
that Kimbleand his fellow skeptics have                                                    nication," says Richard Cleve of the Uni-
chosen to ignore other analyses showing                ould quantum networks be            versity of Calgary in Alberta, a member
that entanglements survive.                       W    worth the work that it will take    of the research team. For this particular
                                                       to develop the quantum links        problem, however, he notes, the quan-
                                             that they will need?Theoristsare probing      tum treatment requires more exchanges
Teleporting across a molecule-or how model networksmight performand                        among the computers than a classical
      even a workbench-won't suffice comparing them with conventional, or                  solution does.
      for making practical networks. classical,computernetworks.                             An analysis of a more esoteric problem
Researchers are building up to greater          Each node of a quantum network             by Ran Raz of the Weizmann Institute in
leaps, however,by testing the notion that would be a quantumcomputer.Such ma-              Rehovot, Israel, concludes that a quantum
entanglementhas an unlimitedrange.           chines would calculate and performlogi-       interaction saves on both the number of
   Wolfgang  Titteland his colleaguesat the cal operations using delicate strings of       bits exchanged and the number of ex-
University Genevaholdthe worldrecord entangled qubits, each in a superposi-
            of                                                                             changes. Raz is scheduled to present his
for extendingentanglementacross space. tion of many states. So far no more than            work in May in Atlanta at the 31st Annual
Usingexistingopticalfibersthat had been three-qubit, rough-hewncalculating ex-             Association for Computing Machinery's
installedfor telecommunications, sci- perimentshave appearedin labs. Not un-
                                    the                                                    Symposium on Theory of Computing.
entificteamsplitup entangled    pairsof pho- til that qubit number grows to thirty or        Another example of a possible quan-
tons producedin Genevaand sent themon forty and a robust technology emerges                tum-network edge emerged at a January
separate paths to Bellevue and                                                                    workshop on algorithms in quan-
Bernex, two villages outside Geneva Tj  THEY  4IoWEP 14OW              L-AN
                                                              ARiTHUR(P A5K MGRLM        TO tum information processing at De-
(SN: 2/10/96, p. 90). The Swiss re- ffiAI<P- JRIF
                                                A                                                 Paul
                                                           OF/ 4LA7T CALCULATION*,i University in Chicago.
searchers used a differentcharacter- J At1D   14OW   ART94UJR CHECK A J4WER!!5 Some computing researchers
                                                               CAN         T$E
istic of photons than that transmit-                                                              study ways in which computers
ted in the teleportation experiments.
                                        Fai1 COg5VF#IECy WI4TH         5XACMOTHFP, WIThOUT
                                                                                                  can evaluate the validity of mathe-
   Measurements at the destinations ACTUALL-/        VGRIF%/1N& ACCURAC%/.
                                                                  TfWIR                           matical proofs. In the interactive
determined that the quantum states WIAr'-r 6            AN>6-                                     method, two computers, named
remained correlated throughout the                                                                Arthur and Merlin after the leg-
photons' journeys. In the May 1998                                                                endary king and sorcerer, have a
PHysIcAL   REVIEW the researchers
                  A,                                                                   ~ID        chat. Merlin, who is wise but not al-
concluded, borrowing a phrase from                                                                ways honest, presents the proof to
Albert Einstein, that the "spooky ac-                                                             Arthur. Limited both in brains and
tion at a distance" between their en-          [R~~~~~~~0                                         time, Arthur queries Merlin in an at-
tangled photons does not break                                                                    tempt to verify the proof.
down across the 10.9 kilometers be-                                                                  Daunted by the proof itself,
tween the villages.                                                                               Arthur asks Merlin to carry out re-
   Scientists are planning to test                                                                lated calculations instead. By check-
longer entanglements. Anton Zeil-                                                                 ing for consistency among Merlin's
inger of the University of Vienna Quantum         networkscould quicklydeterminewhether           answers, Arthur can discern if the
says that his group is gearing up Merlin's      proof is valid.                                   proof is valid.
for exDeriments at distances be-                                                                     In the case of conventional com-
yond 20 km.He led one of the firstexperi- will quantum computers begin to make puters, the number of rounds of question-
ments in photon teleportationmore than their mark,scientists say.                          and-answer grows as the mathematical
a year ago, while at the University of           At that point, teleportationwould pro- statement or equation under considera-
Innsbruck in Austria. His newly estab- vide the thread to tie the computers to- tion becomes more complicated.
lished Viennalab will collaborate on the gether. How far those threads might                  At the DePaul conference, however,
projectwith the Genevaresearchers and stretch remains to be seen. Tittel thinks John Watrous of the University of Mon-
other scientists.                              50 km is possible with current optical treal reported that a quantum Arthur and
   To go beyond entanglement,the Vien- fibertechnology.                                    Merlin duo could determine the validity
na researchers are also laying plans for         If quantum computers start talkingto of the proof, no matter how convoluted
the first teleportation of a photon's char- each other, what would come next? its mathematical expression, in only two
acteristics across kilometer distances, Computer scientists have begun to ad- rounds of questioning. Watrous says that
Zeilingersays.                                 dress that question, although on a very the finding rests on a widely accepted as-
   Those experimentswould follow on an abstract level.                                     sumption that there is a certain type of
achievement completed while he was                In one sort of problem that they pon- complexity in the mathematics.
still at Innsbruckbut just reported in the der, several very busy people try to               Watrous's new evidence of latent quan-
Feb. 15 PHYSIcAL  REVIEW  LETTERS. The Inns- arrangeto meet for lunch. They let their tum network power has impressed Bennett.
bruck team simultaneously entangled computers,which knowtheir jam-packed "Thisis another major step along the way,"
three photons, with distances of roughly schedules, interactwith each other in or- he says. For more than two computers, Wa-
20 centimetersbetween each of them.            der to find a time slot in which all three trous says, he expects a quantum approach
   It'snot the first report of three-particle people are free.                             also to yield a bonus, but he hasn't yet ana-
entanglement. Laflamme and his col-              For conventional computers, re- lyzed that situationin detail.
leagues made that claim in a NMR     experi- searchers had already proved years ago           If researchers ultimately find ways to
ment last year involvingthree atoms in a that for schedules with some number,n, make quantum information leap far
molecule (SN: 9/12/98, p. 165).                of time slots, no fewer than n bits would enough and wide enough, a quantum leap
   The Innsbruck experiment, however, have to be exchanged by the machines. for networks may not be far behind.                      DG

APRIL3, 1999                                        SCIENCE NEWS, VOL. 155                                                        221

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