Conductance quantization in V-groove quantum wires

We have observed and studied ballistic one-dimensional (1D) electron transport in V-grooved ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}-\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterostructures. In two different regimes of quantum wire confinement the conductance varies in a steplike manner, with the number of populated 1D subbands controlled by a gate voltage. For weak lateral confinement, the conductance steps nearly attain the ${2e}^2/h$ value, whereas for stronger confinement the values of the conductance steps are suppressed. Our results suggest that a poor coupling between the 1D states of the wire and the 2D states of the reservoirs outside the gated region is responsible for the conductance suppression for strong lateral confinement.