  Nanoscale channels realized at the conducting interface between LaAlO$_{3}$
and SrTiO$_{3}$ provide a perfect playground to explore the effect of
dimensionality on the electronic properties of complex oxides. Here we compare
the electric transport properties of devices realized using the AFM-writing
technique and conventional photo-lithography. We find that the lateral size of
the conducting paths has a strong effect on their transport behavior at low
temperature. We observe a crossover from metallic to insulating regime
occurring at about 50 K for channels narrower than 100 nm. The insulating
upturn can be suppressed by the application of a positive backgate. We compare
the behavior of nanometric constrictions in lithographically patterned channels
with the result of model calculations and we conclude that the experimental
observations are compatible with the physics of a quantum point contact.
