Steve Bellovin wrote: > > A quantum computer has been built that has actually factored a number: 15. > It's not a very interesting number from a cryptographic perspective, > but it is real. http://www.nature.com/nature/links/011220/011220-2.html
Its worth noting that not only is the number not very interesting (15), but various properties of it have been used to make the quantum computer simpler. The quantum computer would not be capable of performing any other calculation. In particular, addition has been substituted for multiplication in one part of the calculation, and the other multiplication has been changed to a completely different operation (bit swapping). Once simplified thus, several operations were omitted because they were known to not actually influence the outcome or because enough of their inputs were known to make them guaranteed to be null operations. These changes are described as optimisations - but since in any real case they would involve performing most of the calculation on a classical computer (AFAICS), its difficult to see how this experiment demonstrates anything other than a remarkable ability to control and measure the quantum state of 7 atoms in a molecule. Which is impressive in itself, but it seems hardly fair to describe it is factorisation. Probably the coolest thing about this experiment is that they have produced what appears to be a very accurate model of the decoherence effects, which should allow quantum computers to be modelled with some certainty in the future. Cheers, Ben. -- http://www.apache-ssl.org/ben.html http://www.thebunker.net/ "There is no limit to what a man can do or how far he can go if he doesn't mind who gets the credit." - Robert Woodruff --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]
