  Propagation of an electron wave packet through a quantum point contact (QPC)
defined by electrostatic gates in bilayer graphene is investigated. The gates
provide a bias between the layers, in order to produce an energy gap. If the
gates on both sides of the contact produce the same bias, steps in the electron
transmission probability are observed, as in the usual QPC. However, if the
bias is inverted on one of the sides of the QPC, only electrons belonging to
one of the Dirac valleys are allowed to pass, which provides a very efficient
valley filtering.
