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Leaps in Quantum Computing

Leaps in Quantum Computing

Apr 2000

On December 29th 1959 Richard Feynman gave a visionary talk entitled "There's Plenty of Room at the Bottom"outlining the possibilities allowed by conventional laws of physics for a new type of computers.

"You realize, of course, that if we had a operational quantum computer today, nothing on the Internet would be safe. Our current methods of encrypting secret or personal data, like the RSA public key encryption algorithm currently usedin web browsers, would be nearly worthless."
Raymond Laflamme
NMR Quantum Computing Researcher

For decades advances in conventional computer technology have been following Moore'sLaw of doubling power every 18 months. However, to rescue Moore's Law in the nextcouple of decades will take some big advances - among other things we are soon going to be entangled in quantum mechanics rather than conventional electronics. However, quantum mechanics is also the key to a brand new technology with much higher capability.

May 4, 1998 after decades of theoretical physics, a 2 qubit quantum computer capable of loading data and reading out a result is announced.

Modern digital computers are based on bits - something which can be toggled back and forthbetween two states (e.g. magnetized or demagnetized). By representing these two states as 0 and 1, we can do binary arithmetic with sets of bits and the devices that toggle them. Everything else is built from there ... In quantum mechanics we see many physical systems as have two states (e.g. spin up or spin down). We refer to each such "bit" as a qubit. However, qubits are quantum mechanical and as such they behave much differently than bits. They exist in a superposition of 0 and 1 states simultaneously and may couple with neighboring qubits.

There is an old saying that "when all you have is a hammer, everything looks like a nail". To somebody trained in conventional computing a qubit might look completely impractical because they have learned to see problems in terms of how you can solve them with bits and bit operations. However, as we examine what can be done with qubits, there are many problems where they are clearly the superior tool to use.

An array of qubits operates as a parallel computer capable of performing a large calculation in one step, and the power grows rapidly with the number of qubits. One application is the factoring of numbers. This is significant because it is the basis of standard security schemes for encrypting numbers.A 30 qubit computer would be 5 times more powerful than the worlds fastest present supercomputer and could break any known code.

In the last couple of weeks there have been big announcements from rivals in the size of operating quantum computers. Mar. 16 scientists at the NIST (National Institute for Standards and Technology) announced the "quantum entanglement of four particles" - published in Nature. One week later scientistsat LANL (Los Alamos National Laboratory) announced a seven bit NMR quantum computer.

NIST physicist David Wineland predicts that while NMR has a headstart, it will hit a fundamentalblock at 15 qubits beyond which the interaction between the particles will start to disappear. That is why they are pursuing the trapped ion approach instead.

The future development of quantum computing is impossible to predict. Scientists in the field say useful computers could be a few years away, or they could be decades away. The history is too short to say whether Moore's Law is being followed or not, but 18 months ago the first 2-qubit computer was shortly followed by a 3-qubit computer and now a 4-qubit announcement was shortly followed by 7-qubit announcement. So far, doubling every 18 months looks pretty accurate. IF this rate should continue, we'll see that 30 qubit computer in three or four years.

Further Reading on Quantum Computing

Frequently Asked Questions about Quantum Computation
From the Centre for Quantum Computation - part of the University of Oxford.

Quantum Computing with Molecules
Scientific American article by Neil Gershenfeld and Isaac L. Chuang - developers of the first 2 qubit computer.

Quantum Computer Development
A review of the status, logic and prospects of quantum computing.

Quantum Leap in Computing
Mar 23, 2000 announcement of a 7 qubit computer

Quantum Logic
For those who know what a wavefunction is: how to implement AND/OR/NOT etc with qubits.

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