  Developing alternative paradigms of electronics beyond silicon technology
requires the exploration of fundamentally new physical mechanisms, such as the
valley specific phenomena in hexagonal two-dimensional materials. We realize
ballistic valley Hall kink states in bilayer graphene and demonstrate
gate-controlled current transmission in a four-kink router device. The
operations of a waveguide, a valve and a tunable electron beam splitter are
demonstrated. The valley valve exploits the valley-momentum locking of the kink
states and reaches an on/off ratio of 8 at zero magnetic field. A magnetic
field enables a full-ranged tunable coherent beam splitter. These results pave
the path to building a scalable, coherent quantum transportation network based
on the kink states.
