All Annotations of [Preview]

saved by17 people, first byDan McCrea on 2006-07-04, last byWilliam Hummel on 2008-07-24

• The field of quantum information processing has made
  numerous promising advancements since its conception, including the building
  of two- and three-qubit quantum computers capable of some simple arithmetic
  and data sorting. 
  However, a few potentially large obstacles still
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  remain that prevent us from "just building one," or more precisely, building
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  a quantum computer that can rival today's modern digital computer.
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  Among these difficulties, error correction, decoherence, and hardware architecture
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  are probably the most formidable.  Error correction is rather self
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  explanatory, but what errors need correction?  The answer is primarily
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  those errors that arise as a direct result of
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  decoherence
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  ,
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  or the tendency of a quantum computer to decay from a given quantum state
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  into an incoherent state as it interacts, or entangles, with the state
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  of the environment.  These interactions between the environment and
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  qubits are unavoidable, and induce the breakdown of information stored
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  in the quantum computer, and thus errors in computation.  Before any
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  quantum computer will be capable of solving hard problems, research must
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  devise a way to maintain decoherence and other potential sources of error
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  at an acceptable level.
  >  Thanks to the theory (and now reality) of
  quantum error correction, first proposed in 1995 and continually developed
  since, small scale quantum computers have been built and the prospects
  of large quantum computers are looking up.  Probably the most important
  idea in this field is the application of error correction in phase
  coherence as a means to extract information and reduce error in a quantum
  system without actually measuring that system.  In 1998, researches
  at Los Alamos National Laboratory
  and MIT led by Raymond
  Laflamme managed to spread a single bit of quantum information (qubit)
  across three nuclear spins in each molecule of a liquid solution of alanine
  or trichloroethylene molecules.  They accomplished this using the
  techniques of nuclear magnetic resonance (NMR).  This experiment is
  significant because spreading out the information actually made it harder
  to corrupt.  Quantum mechanics tells us that directly measuring the
  state of a qubit invariably destroys the superposition of states in which
  it exists, forcing it to become either a 0 or 1.  The technique of
  spreading out the information allows researchers to utilize the property
  of entanglement to study the interactions between states as an indirect
  method for analyzing the quantum information.  Rather than a direct
  measurement, the group compared the spins to see if any new differences
  arose between them without learning the information itself.  This
  technique gave them the ability to detect and fix errors in a qubit's
  phase
  coherence, and thus maintain a higher level of coherence in the quantum
  system.  This milestone has provided argument against skeptics, and
  hope for believers.  Currently, research in quantum error correction
  continues with groups at Caltech (Preskill,
  Kimble),
  Microsoft,
  Los
  Alamos, and elsewhere.
• At present, quantum computers and quantum information
  technology remains in its pioneering stage.  At this very moment obstacles
  are being surmounted that will provide the knowledge needed to thrust quantum
  computers up to their rightful position as the fastest computational machines
  in existence.  Error correction has made promising progress to date,
  nearing a point now where we may have the tools required to build a computer
  robust enough to adequately withstand the effects of decoherence. 
  Quantum hardware, on the other hand, remains an emerging field, but the
  work done thus far suggests that it will only be a matter time before we
  have devices large enough to test Shor's and other quantum algorithms. 
  Thereby, quantum computers will emerge as the superior computational devices
  at the very least, and perhaps one day make today's modern computer obsolete.  
  Quantum computation has its origins in highly specialized fields of theoretical
  physics, but its future undoubtedly lies in the profound effect it will
  have on the lives of all mankind.
• In a quantum computer, the fundamental unit of information
  (called a quantum bit or qubit), is not binary but rather more quaternary
  in nature.  This qubit property arises as a direct consequence of
  its adherence to the laws of quantum mechanics which differ radically from
  the laws of classical physics.  A qubit can exist not only in a state
  corresponding to the logical state 0 or 1 as in a classical bit, but also
  in states corresponding to a blend or superposition of these classical
  states.  In other words, a qubit can exist as a zero, a one, or simultaneously
  as both 0 and 1, with a numerical coefficient representing the probability
  for each state. 

• on 2007-03-28 Mrxtrace
  A nice piece on the basics of Quantum computing and how it will make encryption obsolete as it has been shown already that RSA can be broken through quantum computing however serious limitations have to be overcome before it hits the shelves. a nice comparison between classic computers and quantum computers.