Realistic operation of an entangler : a density matrix approach
  The detailed operation of an electron spin entangler is studied, using density matrix equations. The device is made of a superconductor, two quantum dots and two normal leads. The treatment takes into account coherent tunneling in a non-perturbative way, and analyzes the various parasitic effects, in addition to the main process (crossed Andreev reflection) : those include singlet pairs passing through a single dot, or cotunneling between dots through the superconductor. The optimum operation of the device is characterized. 
Olivier Sauret, Denis Feinberg, Thierry Martin