  Quantum random walks (QRWs) can be used to perform both quantum simulations
and quantum algorithms. In order to exploit this potential, quantum walks on
different types of graphs must be physically implemented. To this end we
design, model and experimentally fabricate, using the femtosecond laser
direct-write technique, a 3D tubular waveguide array within glass to implement
a photonic quantum walk on a circle. The boundary conditions of a QRW on a
circle naturally suggests a 3D waveguide implementation - allowing much simpler
device design than what could be achieved using a 2D waveguide architecture. We
show that, in some cases, three-dimensional photonic circuits can be more
suited to the simulation of complex quantum phenomena.
