Using spin bias to manipulate and measure spin in quantum dots

A double quantum dot coupled to electrodes with spin-dependent splitting of chemical potentials (spin bias) is investigated theoretically by means of the nonequilibrium Kyldysh Green's function formalism. By applying a large spin bias, the quantum spin in a quantum dot (dot 1) can be manipulated in a fully electrical manner. To noninvasively monitor the manipulation of the quantum spin in dot 1, it is proposed that the second quantum dot (dot 2) is weakly coupled to dot 1. In the presence of the exchange interaction between the two dots, the polarized spin in dot 1 behaves like an effective magnetic field and weakly polarizes the spin in the nearby quantum dot 2. By applying a very small spin bias to dot 2, the spin-dependent transport through dot 2 can be probed, allowing the spin polarization in dot 1 to be identified nondestructively. These two steps form a complete scheme to manipulate a trapped spin while permitting this manipulation to be monitored in the double-dot system using pure electric approaches.