X-Message-Number: 6110 Date: Sun, 21 Apr 1996 13:16:14 -0700 From: John K Clark <> Subject: SCI.CRYONICS Quantum Computers -----BEGIN PGP SIGNED MESSAGE----- In the April 12 1996 issue of Science there is an article on Quantum Computers. It makes clear that a practical Quantum Computer has not been proven to be possible, nevertheless the article had a very optimistic tone, an optimism I did not see just one year ago. If such a machine could be built the ramifications are mind boggling. When a conventional 64 bit single processor computer performs an operation, it does it on ONE 64 bit number at a time. When a 64 bit (actually a 64 qubit) single processor QUANTUM computer performs an operation it does it on ALL 64 bit numbers at the same time, all 2^64 of them, more than a billion billion, and any increase in the number of qubits the computer can handle will increase it's already astronomical power exponentially. It gets even wilder, because the quantum mechanical state of the matter in the machine's memory determines the output, Seth Lloyd of MIT thinks you could run the machine in reverse and the result would be a quantum mechanical micromanipulator. Despite this enormous increase in performance and a possible short cut to Nanotechnology, most weren't very interested because it didn't seem like a Quantum Computer could ever be built. The slightest error or interaction with the outside environment would render the machine inoperative, conventional error correcting codes don't work for in the quantum domain and most said that correcting codes for quantum mechanical information was impossible. They were wrong. Late last year Peter Shor of ATT showed how to encode a piece of quantum information in a 9 qubit system so that the information is retained even if there is an error in one of the 9 qubits. A few months later researchers at IBM refined Shor's technique so that only 5 qubits was needed, and found ways to correct for multiple errors. We still don't know for sure if a Quantum Computer is possible because these error correcting codes work for storing and transmitting quantum information not for the actual calculation, but most now think the problem is solvable. In fact both Shor and Lloyd have privately circulated ideas on how to do this but have not yet published. If this problem could be solved then we just need someone to put all the pieces together and make a machine. I find all this very exciting, it must have been like this in the late 1930's when reports trickled in about nuclear fission and the idea occurred to people that a bizarre device like a nuclear bomb might actually be able to exist in the real world. John K Clark -----BEGIN PGP SIGNATURE----- Version: 2.6.i iQCzAgUBMXqVsn03wfSpid95AQEftQTuI6QlxNTLtatYQjbRF+vzs3Ab56j7YAM6 QkpACSuwC0CMJOHD6Z1dAKCP4fDOF2Jj+wQ556vXarvTVYi0GOWSD63QmMwwti1n /UxCAXYo5QRFPzj+r5+1rbu8CBtGjs226Hd1q6xGcc6K4oU9ED9P9FSypFYfTWGM FX4MxbCQ3zAddenXW92R9JX4wOLKwF6Oko6P3DNUCM3hbi/CtXg= =L3mz -----END PGP SIGNATURE----- Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=6110