Wednesday, August 8, 2012

'Noise' may boost research towards quantum computer

For most people, quantum physics is weird and hard to understand. That is not surprising, because our observations at the sub-atomic level are radically different from what we have come to expect in the 'real' world. A famous example is quantum entanglement; a weird interaction between two particles, that assume each other's opposite form regardless of how far away they are from each other. This sort of behaviour makes instant teleportation of data a possibility, as has recently been shown by transferring data over 100km without a 'physical' connection. When particles on the quantum level interact, that is not only due to entanglement, but also due to something called quantum discord. Often regarded as background noise, but scientists have now found that it may actually be even more useful than applications of entanglement.

Quantum discord is not something new, as it has been observed by scientists many years ago. However, it did not receive a lot of attention, while other famous examples of quantum weirdness have. To put it in simple terms, discord is a form of noise, that can be used as a measurement to find out how much two particles are correlated with each other. Basically, it can be regarded as a form of background noise, or interference, that is not due to entanglement. So far, scientists have used it to establish a so-called signal-to-noise ratio.

In order to encode information in quantum computers using quantum bits, scientists often use entanglement. However, researchers have now discovered that the discord between two particles may actually be easier to use for such computers. Their experiments point out that quantum discord is more accessible than entanglement and can be used as a more robust phenomenon to encode information, which they achieved by using laser light. This indicates that the phenomenon described as discord is not just noise: it is probably due to our lack of understanding of the mechanisms involved that we have come to call it like that.

In order to get a quantum computer to work, one needs the equivalent of the bits and bytes that conventional computers work with. Quantum bits, or qubits, are a working concept, but using entanglement to store, modify and retrieve information is not that easy. Because of the other quantum interactions, previously considered as unhelpful background noise, this may be made easier. Though, scientists do first need to show that they can put it into practice.
A basic explanation of quantum entanglement. On the picture are two particles that became entangled with each other, but were separated afterwards. When Alice measures her particle at her location, she measures 0 or 'down'. At that exact same moment, the second particle of the pair will become the exact opposite: Bob will then measure 1, or 'up'. This works without any form of physical interaction between the two entangled particles; it 'just' happens.

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