Electronic conductance of an orifice in a magnetic field

We study the two-terminal magnetoconductance of a two-dimensional noninteracting electron gas through an orifice. The approximate conductance quantization for ballistic transport at vanishing magnetic field remains in weak magnetic fields, but the resonance structure associated with the opening of new channels is attenuated and eventually subdued. At high magnetic field the quantization steps are less pronounced and lag behind the number of open channels. An intuitive interpretation of the structure of the conductance in terms of cyclotron orbits is presented.