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Interweb prepared for quantum leap

Once its photons are all lined up
Tue Apr 15 2008, 17:47

SCIENCE BOFFINS HAVE been dreaming about quantum computers since the beginning of the 1980s, but now advances in the field mean that the working reality could be that much closer, and not just in isolated lab experiments, either.

A professor of electrical engineering and computer science at Northwestern University, Prem Kumar, has just published new research in the journal Physical Review Letters, detailing how his team managed to put together a quantum logic gate, essential for quantum computing, inside optical fibre. According to Technology Review, this sort of gate could now be used either as part of a circuit, able to transmit data securely over hundreds of kilometers, from one quantum computer to another, or individually, to crack really hard math problems.

Quantum computers are quite a bit different to the classic computers most people are used to, using ‘qubits’ as their units of information instead of the electronic ‘bits’ of either 1 or 0. Because qubits can be both "1" and a "0" simultaneously, they can purportedly process much more information than classic computers, and can also manipulate certain bizarre quantum-mechanical particle properties like electrons and photons. Seeing as the processing ability of a quantum computer doubles for every extra qubit, quantum computers only need a handful (or a couple of hundred) of qubits to give even today’s fastest supercomputers a run for their money.

Kumar and his boffins have fashioned a gate which they’ve dubbed a NOT gate, which uses a classical-computing analogue for flipping a bit "1" to "0", and the opposite. The team reckon that this gate will let them run specific applications and plan to test it even further by running a complex auction over a secure quantum network.

Kumar and his team manage to set up the gates by making qubits out of photons that are "entangled". What this means in a practical sense is that certain of the photons’ characteristics link up in a sort of ying-yang combo, whereby when one photon assumes a certain state, whilst the other will take on the opposite one. This works really well in polarisation for example, and photons entangled in this way can remain so for about 100km.

Coordinator of the quantum information program at the National Institute of Standards and Technology, Carl Williams, also told Technology Review that the important thing about the new research “is that it's in fiber. This is a big deal because it could lead to distributed networks. ... The obvious application is for long-distance quantum communication between two smaller quantum computers." He added that Kumar’s quantum gate could potentially be used as a repeater inside a circuit, to amplify a signal without un-entangling the photons.

A leading researcher in quantum computation and a professor of mechanical engineering at MIT, Seth Lloyd, also spoke to TR and said that "This is an important step toward constructing a quantum Internet," adding that “communication over the quantum Internet would be automatically secure". µ

Technology Review


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