Jacob Aron, reporter
(Image: Pasieka/Science Photo Library)
A quantum computer has correctly calculated how a protein folds up, which is crucial to understanding diseases such as Alzheimer's and Parkinson's. Don't throw away your ordinary computer just yet, though - the quantum computer could handle only a very small version of the problem, involving just a few amino acids, which conventional hardware can already solve easily.
The quantum computer in question is made by D-Wave of Burnaby, British Columbia, Canada. The company has attracted a lot of attention for selling quantum computers, which had previously been found in academic, rather than commercial, settings.
Chemists at Harvard University worked with D-Wave to find the lowest-energy configuration of a very small proteins. This can be calculated because it is generally believed that proteins naturally fold into shapes that require the least energy.
The researchers looked at the problem in two dimensions, meaning there were four possible directions that each protein fold could take, and used two quantum bits (qubits) to represent each of the four folds - "00" for down, "01" for right, and so on.
Arrays of qubits also have a lowest-energy state. The trick to calculating the energy required for a protein to take on a particular sequence of folds is to arrange the qubits so that the lowest-energy state of the quantum system corresponds to the lowest-energy state of the protein.
The D-Wave team managed to do this - but only for a very simple protein, consisting of just six amino acids. Even this was a stretch: the researchers had to break the problem into parts that could be processed separately by the quantum computer, and combine them at the end. By contrast, predicting the folds of a six-amino-acid protein in one go would be trivial for an ordinary computer.
There was a further limitation. Theoretically, the quantum computer should operate at a temperature of 0 kelvin, but such extreme cooling is impossible in practice, so D-Wave repeatedly ran the system at slightly above zero in the hope of reaching the lowest-energy state. Due to these higher temperatures the calculation got the right answer only 13 times after 10,000 attempts.
You may be starting to feel underwhelmed by D-Wave's achievement, but the company's Colin Williams says the fact that the calculation worked at all demonstrates the potential for quantum computers to beat conventional ones.
Ordinary computer algorithms for protein folding also attempt to find the lowest-energy state, but they can get stuck in local "valleys" that only appear to be the lowest, which is why other researchers have turned to gamers to provide creative assistance. "The D-Wave hardware, in contrast, is performing a quantum annealing process that allows it to tunnel through this energy landscape," explains Williams, exploiting a quantum shortcut unavailable to ordinary computers.
Journal reference: Scientific Reports, DOI: 10.1038/srep00571
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