Spin Information Achieved by Energy Transfer via Optical Near Fields Between Quantum Dots and Its Robustness

We discuss the mechanism of the spin and excitation energy transfer in a quantum dot pair driven by optical near fields. When one member of the pair is excited by either an optical near field or effectively by a propagating far field, the energy and spin information of the induced exciton can be transferred to the other quantum dot via the near-field optical interaction. Intriguingly, it is possible to select the spin state of the electron, e.g., to preserve or flip the electron spin in the transfer process without applying a magnetic field, by selecting an appropriate incident angle of pumping light and the resonant state of the energy levels of the quantum dots. Thus, we present the electron spin selection rules, the spin and excitation energy transfer rates between a quantum dot pair, and the spin polarization after the transfer in terms of the exciton polariton basis to describe the optical near fields. We also examine the effects of spin relaxation due to interactions with the environment, indicating that there are cases where the spin transfer via optical near fields is robust against the depolarization channel.