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Harness vast power of quantum computers… for sums

作者：马柒 时间：2019-03-13 02:10:02 人气： ℃

By Jacob Aron Quantum computers sound exotic but their power may lie in solving mundane equations – fast. Until now these systems have been geared towards tasks such as factorising huge numbers, which would not be much use outside cryptography. In 2009, Seth Lloyd at the Massachusetts Institute of Technology and colleagues devised a quantum algorithm for solving systems of linear equations, such as determining two unknown variables that appear in two separate equations. This example is classroom algebra, but scale it up to millions of variables and the same mathematics drives weather forecasting, image processing and traffic analysis. Lloyd’s team showed that while the number of steps in the classical algorithm scales with the number of equations, for the quantum version, it scales with the logarithm of that number – equivalent to solving a trillion equations in a few hundred steps. “You basically take a classical algorithm that sucks and do it in quantum parallel,” says Lloyd, taking advantage of the fact that a quantum computer can perform multiple calculations at the same time. Now Stefanie Barz’s team at the University of Vienna, Austria, has got Lloyd’s algorithm working on a very simple quantum computer, using two entangled photons to solve a system of two equations (arxiv.org/abs/1302.1210). Though too simple to be useful in itself, it is a neat demonstration. “It is very nice that they’ve been able to implement it,” says Lloyd. Meanwhile, Jiangfeng Du’s team at the University of Science and Technology of China, Hefei, has demonstrated Lloyd’s algorithm with a four-equation system (arxiv.org/abs/1302.1946). But they used a quantum computer based on the spins of atomic nuclei that some physicists fear won’t scale. More on these topics: