Abstract
A quantum theory of electron injection from a reservoir of higher dimension into a semi-infinite one-dimensional (1D) conductor is presented. Numerical results are given for simple models of narrow quantum channels in semiconductor heterostructures. It is shown that the injection process can strongly influence experimentally measured 1D conductances in ballistic or near-ballistic regimes. It should contribute in a major way to the observed deviations from perfect quantisation of the 1D ballistic conductance. The possibility of resonances in the conductance of finite channels is briefly discussed.