QUANTUM-MECHANICS OF LATTICE-GAS AUTOMATA - BOUNDARY-CONDITIONS AND OTHER INHOMOGENEITIES

We continue our analysis of the physics of quantum lattice gas automat a (QLGA). Previous work has been restricted to periodic or infinite la ttices; simulation of more realistic physical situations requires fini te sizes and nonperiodic boundary conditions. Furthermore, envisioning a QLGA as a nanoscale computer architecture motivates consideration o f inhomogeneities in the 'substrate'; this translates into inhomogenei ties in the local evolution rules. Concentrating on the one-particle s ector of the model, we determine the various boundary conditions and r ule inhomogeneities which are consistent with unitary global evolution . We analyse the reflection of plane waves from boundaries, simulate w avepacket refraction across inhomogeneities, and conclude by discussin g the extension of these results to multiple particles.