From: cjl <cjl@welchlink.welch.jhu.edu>
Date: Mon, 23 Oct 95 10:18:49 PDT
To: Cypherpunks mailing list <cypherpunks@toad.com>
Subject: Quantum Computation article
Message-ID: <Pine.SOL.3.91.951023122259.5612B-100000@welchlink.welch.jhu.edu>
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David P. DiVincenzo from the IBM Research Division has written an article 
in the 13th October issue of SCIENCE magazine (vol. 270, pg. 255-261) 
entitled "Quantum Computation".  The article is nicely divide into 
subsections:

- Building blocks of quantum logic
- Quantum circuits
- Peter Shor's prime factorization
- The decoherence problem
- Outlook

From the outlook section "It is evident from this survey of the current 
state of the art in quantum experimental physics that the construction of 
quantum computers is presently in the most rudimentary stage, and that to 
even think about a procedure like Shor factorization, which might require 
millions of operations on thousands of qubits, might be absurdly premature."

If that is the good news for Cypherpunks, then the great news is the 
following.

". . even a few bits of quantum computation will be very useful in 
performing so-called Bell measurements, which could be used to implement 
quantum teleportation, in which an unknown quantum state can be 
trasmitted to a remote location.  At perhaps the 10-qubit level, a 
quantum computer becomes capable of performing Schumacher's quantum 
coding, which would be of interest in the implementation of efficient 
quantum cryptography.  And at perhaps the 100-qubit level, a quantum 
computer becomes an efficient repeater for a noisy (that is partially 
decohered) quantum cryptographic link."

It looks like the advantages of quantum computing accrue to Alice and 
Bob, long before it becomes useful to Eve and Mallet.

A must read for aficianados of "alternative computing".

Here are some URLs from the references

http://vesta.physics.ucla.edu/~smolin/
(Quantum Information Page, Center for Advanced Accelerators)

http://eve.physics.ox.ac.uk/QChome.html
(Quantum Computation and Cryptography page, Clarendon Laboratory, Oxford 
University)

C. J. Leonard                     (    /      "DNA is groovy"
                                   \ /                - Watson & Crick
<cjl@welchlink.welch.jhu.edu>      / \     <--  major groove
                                  (    \
Finger for public key               \   )
Strong-arm for secret key             /    <--  minor groove
Thumb-screws for pass-phrase        /   )