Coherent transport and manipulation of spins in indirect-exciton nanostructures

摘要

We report on the coherent control and transport of indirect-exciton (Ⅸ) spins in GaAs double quantum well (DQW) nanostructures. The spin dynamics was investigated by optically generating spins using a focused, circularly polarized light spot and by probing their spatial distribution using spatially and polarization resolved photoluminescence spectroscopy. Optically injected Ⅸ spins precess while moving over distances exceeding 20 μm from the excitation spot with a precession length that depends on the spin transport direction as well as on the bias applied across the DQW structure. This behavior is attributed to the spin precession in the effective magnetic field induced by the spin-orbit interaction. From the dependence of the spin dynamics on the transport direction, bias, and external magnetic fields we directly determined the Dresselhaus and Rashba electron spin splitting coefficients for the DQW structure. The precession dynamics is essentially independent of the Ⅸ density, thus indicating that the long spin lifetimes are not associated with Ⅸ collective effects. The long Ⅸ lifetimes, together with the negligible contribution of holes to the spin dynamics, are rather attributed to spatial separation of the electron and hole wave functions by the electric field, which reduces the electron-hole exchange interaction. If extended to the single-exciton regime, the present results on coherent spin precession over long transport distances as well as the control of the spin vector using electric and magnetic fields open the way for the application of Ⅸ spins in quantum information processing.