Spin Decoherence and Maxwell Angels

The advantages of a quantum machine are rooted in the coherent superposition of its states. In the paradigmatic quantum system of a single-electron in the environment of a quantum dot of interacting nuclear spins, how does its spin coherence decay? Is the coherence doomed to dissipate (the H-theorem)? I shall present a theory of decoherence with a simple quantum explanation with no a priori stochastic assumption, based on two solutions [1,3] of the many-body dynamics of the single electron spin and a mesoscopic number of nuclear spins. The theory is followed by a description of the principle of how the coherence lost can be restored by controlling only the electron spin [2,4]. Work done in collaboration with Wang Yao, Renbao Liu, and Semion Saikin. \newline \newline [1] Wang Yao, Ren-Bao Liu, and L. J. Sham, Phys. Rev. B \textbf{74}, 195301 (2006). \newline [2] Wang Yao, Ren-Bao Liu, and L. J. Sham, Phys. Rev. Lett. \textbf{98}, 077602 (2007). \newline [3] S. K. Saikin, Wang Yao, and L. J. Sham, Phys. Rev. B \textbf{75}, 125314 (2007). \newline [4] Ren-Bao Liu, Wang Yao, and L. J. Sham, New J. Phys. \textbf{9}, 226 (2007).