  Transistors are key elements for enabling computational hardware in both
classical and quantum domains. Here, we propose a voltage-gated spin transistor
using itinerant electrons in the Hubbard model which acts at the level of
single electron spins. Going beyond classical spintronics, it enables the
controlling of the flow of quantum information between distant spin qubits. The
transistor has two modes of operation, open and closed, which are realized by
two different charge configurations in the gate of the transistor. In the
closed mode, the spin information between source and drain is blocked while in
the open mode we have free spin information exchange. The switching between the
modes takes place within a fraction of the operation time which allows for
several subsequent operations within the coherence time of the transistor. The
system shows good resilience against several imperfections and opens up a
practical application for quantum dot arrays.
