Liquid-State NMR Quantum Computing

Processing of digital information has progressed at an enormous speed over the last few decades and thus become an indispensable resource. Still, for some computational problems, no efficient algorithms are known for today's computers. If quantum mechanical systems are used instead of classical ones, some of these problems become solvable, with an exponential speedup over classical computers. Many different physical systems are being considered for implementing quantum algorithms, but so far, spins have proved most successful for storing and processing digital information. This feat may be tracked to two different causes: (i) spins are the only naturally occurring two-level systems and are therefore ideal qubits. (ii) magnetic resonance, in particular NMR, has developed a wide range of sophisticated techniques for coherent control of quantum systems. This article provides an introduction into the basic ideas that allow one to use quantum systems for computational purposes and discusses a few examples where NMR has been used for this purpose. © 2010 John Wiley & Sons, Ltd.