Using spin bias to manipulate and measure quantum 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 Green's functions formalism. By applying a large spin bias, the quantum spin in a quantum dot (the dot 1) can be manipulated in a fully electrical manner. To noninvasively monitor the manipulation of the quantum spin in the dot 1, it is proposed that the second quantum dot (the dot 2) is weakly coupled to the dot 1. In the presence of the exchange interaction between the two dots, the polarized spin in the 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 the dot 2, the spin-dependent transport through the dot 2 can be probed, allowing the spin polarization in the 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.