  We investigate the viability of coupled waveguides as basic units of quantum
circuits. In particular, we study the dynamics of entanglement for the single
photon state, and single mode squeezed vacuum state. We further consider the
case of entangled inputs in terms of the two mode mode squeezed vacuum states
and the two photon NOON state. We present explicit analytical results for the
measure of entanglement in terms of the logarithmic negativity. We also address
the effect of loss on entanglement dynamics of waveguide modes. Our results
indicate that the waveguide structures are reasonably robust against the effect
of loss and thus quite appropriate for quantum architectures as well as for the
study of coherent phenomena like random walks. Our analysis is based on
realistic structures used currently.
