Universal computation by quantum walk

Phys Rev Lett. 2009 May 8;102(18):180501. doi: 10.1103/PhysRevLett.102.180501. Epub 2009 May 4.


In some of the earliest work on quantum computing, Feynman showed how to implement universal quantum computation with a time-independent Hamiltonian. I show that this remains possible even if the Hamiltonian is restricted to be the adjacency matrix of a low-degree graph. Thus quantum walk can be regarded as a universal computational primitive, with any quantum computation encoded in some graph. The main idea is to implement quantum gates by scattering processes.