Quantum crypto broken?

Michael_Heyman at NAI.com Michael_Heyman at NAI.com
Fri Apr 26 10:36:22 EDT 2002

Would anybody with more knowledge care to comment on this?

This article leads one to believe that one can eavesdrop without being
detected and with nearly 5/6ths confidence of the data on a quantum crypto
communication. This is in contrast to the claim to fame of quantum crypto
that the receiver will know if there is an eavesdropper. (This is what makes
quantum crypto work when all public key crypto gets broken.)

Quantum crypto has "1 photon"="1 bit" with the polarization of the photon
giving the 1 or 0 of the bit.

It seems photon polarization state can be duplicated with nearly 5/6th



  Near-perfect copies of single photons have been made in 
  the lab for the first time...

  The Oxford team sent a photon from one such pair [of 
  entangled photons] into an optically active crystal 
  where it stimulated the emission of a further photon. 
  There is an increased chance that the new photon will 
  have the same polarization as the 'input' photon. In 
  contrast, photons that are emitted spontaneously are 
  equally likely to be in either polarization state. 

There is also an abstract at:

  Experimental Quantum Cloning of Single Photons 
    Antía Lamas-Linares, Christoph Simon, John C. Howell, 
    Dik Bouwmeester 

-Michael Heyman

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