  One of the key challenges for the implementation of scalable quantum
information processing is the design of scalable architectures that support
coherent interaction and entanglement generation between distant quantum
systems. We propose a nanotube double quantum dot spin transducer that allows
to achieve steady-state entanglement between nitrogen-vacancy center spins in
diamond with spatial separations over micrometers. The distant spin
entanglement further enables us to design a scalable architecture for
solid-state quantum information processing based on a hybrid platform
consisting of nitrogen-vacancy centers and carbon-nanotube double quantum dots.
