  We present theoretical results based on mean-field and exact many-body
approaches showing that in bilayer triangular graphene quantum dots with zigzag
edges the magnetism can be controlled by an external vertical electric-field.
We demonstrate that without electric field the spins of the two layers of the
quantum dot interact ferromagnetically. At a critical value of the
electric-field, the total spin of the bilayer structure can be turned off or
reduced to a single localized spin, a qubit isolated from contacts and free
from interaction with nuclear spins.
