  Transport measurements were made on four-terminal devices fabricated from
InSb/Al_xIn_(1-x)Sb quantum well structures at temperatures from 1.5 to 300K.
Negative bend resistance, which is characteristic of ballistic transport, was
observed in devices of channel widths 0.2 or 0.5 {\mu}m. We have improved upon
the existing implementations of R-matrix theory in device physics by
introducing boundary conditions that dramatically speed convergence. By
comparison with R-matrix calculations, we show that the experimental
observations are consistent with quantum coherent transport.
