Spin relaxation of conduction electrons in coupled quantum wells

The spin of the conduction-band electrons in a quantum well constitutes a promising two-level system for realizing a quantum bit in the solid state. One of the important parameters in the spin dynamics is their relaxation time. It is desired to develop models and semiconductor structures in order to control it. There are several reported examples of spin lifetime control in quantum wells. Double quantum wells in a semiconductor heterostructure allow the modulation of the relaxation time. By changing the relative thicknesses of the wells in the double quantum well system, the wave function for the lowest-energy level of the conduction band can be distributed symmetrically or asymmetrically with respect to the coupling barrier between the quantum wells to control the Dresselhaus and Rashba components of the spin-orbit coupling and, consequently, the relaxation time. To detect and characterize this effect, circularly polarized photoluminescence was used at low temperatures (19 K). The results reported in the present paper suggest that this coupled double quantum well system enables the design of structures that allows for the control of the relaxation time and the performance of the electron spin as a quantum bit.