Non-Empty Quantum Dot as a Spin-Entangler

We consider a three-port single-level quantum dot system with one input and two output leads. Instead of considering an empty dot, we study the situations that two input electrons co-tunnel through the quantum dot occupied by one or two dot electrons. We show that electron entanglement can be generated via the co-tunneling processes when the dot is occupied by two electrons, yielding non-local spin-singlet states at the output leads. When the dot is occupied by a single electron, net spin-singlet final states could be generated by injecting polarized electrons to the dot system. When the input electrons are unpolarized, we show that by carefully arranging model parameters non-local spin-triplet electrons can also be obtained at the output leads if the dot-electron spin remains unchanged in the final state.