Quantum information technology | Enigma variations | Economist.com - The Diigo Meta page

• 28 Jul 08
  

  Takuya Homma

  Science

  • Quantum cryptography, however, will soon pass into the quotidian realm if Andrew Shields and his colleagues at Toshiba’s research laboratory in Cambridge have anything to do with it. Over the past few years they have been working on the various bits and pieces needed. And, as they report in Nature Photonics, an important part of the puzzle has just fallen into place.

  • Such a photon counter is essential if quantum cryptography is to work, because it will allow what are known as quantum repeaters to be built. In a classical telecommunications system the signal has to be boosted by a repeater every 80km or so. But a traditional repeater destroys the quantum states of the photons, such as their planes of polarisation. That does not matter for classical telecoms, but matters very much for quantum cryptography, which relies on the fact that no eavesdropper can intercept the message without changing those quantum states, and thus giving away the fact that he is on the line.

      
  • Now that there is one, the eavesdropper’s days may be numbered.

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