  We explore the possibility of achieving a significant nonlinear phase shift
among photons propagating in nanoscale waveguides exploiting interactions among
photons that are mediated by vibrational modes and induced through Stimulated
Brillouin Scattering (SBS). We introduce a configuration that allows slowing
down the photons by several orders of magnitude via SBS involving sound waves
and two pump fields. We extract the conditions for maintaining vanishing
amplitude gain or loss for slowly propagating photons while keeping the
influence of thermal phonons to the minimum. The nonlinear phase among two
counter-propagating photons can be used to realize a deterministic phase gate.
