  Photons and electrons are the key quantum media for the quantum information
processing based on solid state devices. The essential ingredients to
accomplish the quantum repeater were investigated and their underlying physics
were revealed. The relevant elementary processes of the quantum state transfer
between a single photon and a single electron were analyzed, to clarify the
conditions to be satisfied to achieve the high fidelity of the quantum state
transfer. An optical method based on the Faraday rotation was proposed to carry
out the Bell measurement of two electrons which is a key operation in the
entanglement swapping for the quantum repeater and its feasibility was
confirmed. Also investigated was the quantum dynamics in the electron-nuclei
coupled spin system in quantum dots and a couple of new phenomena were
predicted related to the correlations induced by the hyperfine interaction,
namely, bunching and revival in the electron spin measurements. These findings
will pave the way to accomplish the efficient and robust quantum repeater and
nuclear spin quantum memory.
