Experimental realization of a ballistic spin interferometer based on the Rashba effect using a nanolithographically defined square loop array

The gate-controlled electron spin interference was observed in nanolithographically defined square loop (SL) arrays fabricated using In$_{0.52}$Al$_{0.48}$As/In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As quantum wells. In this experiment, we demonstrate electron spin precession in quasi-one-dimensional channels that is caused by the Rashba effect. It turned out that the spin precession angle $\theta$ was gate-controllable by more than 0.75$\pi$ for a sample with $L=1.5\mu$m, where $L$ is the side length of the SL. Large controllability of $\theta$ by the applied gate voltage as such is a necessary requirement for the realization of the spin FET device proposed by Datta and Das [Datta {\it et. al.}, Appl. Phys. Lett. {\bf 56}, 665 (1990)] as well as for the manipulation of spin qubits using the Rashba effect.