Universal quantum computation by quantum walks on directed graphs

We propose a universal quantum computation using multi-particle bosonic/fermionic quantum walks with chirality.  The universal gates can be realized by single- or two-particle scatterings on directed graphs incorporating devices that operate the chirality. As a result, we can design a simple quantum architecture without any need for time-dependent control. An application of our procedure to quantum random access memory (qRAM) is also discussed.