Authors 
X.D. Cai, C. Weedbrook, Z.E. Su, M.C. Chen, Mile Gu, M.J. Zhu, Li Li, NaiLe Liu, ChaoYang Lu, and JianWei Pan 
Journal No. 
Phys. Rev. Lett. 110, 230501 (2013) 
Keywords 

Abstract 
Solving linear systems of equations is ubiquitous in all areas of science and engineering. With rapidly growing data sets, such a task can be intractable for classical computers, as the best known classical algorithms require a time proportional to the number of variables N. A recently proposed quantum algorithm shows that quantum computers could solve linear systems in a time scale of order log(N), giving an exponential speedup over classical computers. Here we realize the simplest instance of this algorithm, solving 2×2 linear equations for various input vectors on a quantum computer. We use four quantum bits and four controlled logic gates to implement every subroutine required, demonstrating the working principle of this algorithm. 