  Single particle interference lies at the heart of quantum mechanics. The
archetypal double-slit experiment has been repeated with electrons in vacuum up
to the more massive $C_{60}$ molecules. Mesoscopic rings threaded by a magnetic
flux provide the solid-state analogous. Intra-molecular interference has been
recently discussed in molecular junctions. Here we propose to exploit
interference to achieve all-electrical control of a single electron spin in
quantum dots, a highly desirable property for spintronics and spin-qubit
applications. The device consists of an interference single electron transistor
(ISET), where destructive interference between orbitally degenerate electronic
states produces current blocking at specific bias voltages. We show that in the
presence of parallel polarized ferromagnetic leads the interplay between
interference and the exchange coupling on the system generates an effective
energy renormalization yielding different blocking biases for majority and
minority spins. Hence, by tuning the bias voltage full control over the spin of
the trapped electron is achieved.
