Quantum Dynamics in a Fluctuating Environment

We theoretically investigate the dynamics of a quantum system which is coupled to a fluctuating environment based on the framework of Kubo-Anderson spectral diffusion. By employing the projection operator technique, we derive two types of dynamical equations, namely, time-convolution and time-convolutionless quantum master equations, respectively. We derive the exact quantum master equations of a qubit system with both diagonal splitting and tunneling coupling when the environmental noise is subject to a random telegraph process and a Ornstein-Uhlenbeck process, respectively. For the pure decoherence case with no tunneling coupling, the expressions of the decoherence factor we obtained are consistent with the well-known existing ones. The results are significant to quantum information processing and helpful for further understanding the quantum dynamics of open quantum systems.

ALL-ELECTRICAL SPIN CONTROL IN A TRIPLE-TERMINAL QUANTUM DOTS RING: EFFECT OF THE INTERDOT COUPLING AND SPIN FLIP

The electron spin polarization in two quantum dots, which are inserted in one arm of a mesoscopic ring, is investigated by means of the non-equilibrium Keldysh Green's function technique. We find that the spin accumulations in the two dots Δni=ni↑-ni↓, where niσ is the spin-σ electron occupation number in dot i, can be efficiently tuned in terms of the applied bias voltage V, the interdot tunneling coupling strength tc and the phase induced by the Rashba spin-orbit interaction. By adjusting these parameters, Δn1 and Δn2 can be generated and manipulated either simultaneously or separately, which may have real usage in spintronics or quantum information devices. We interpret the origin of the spin accumulation in terms of the spin-dependent total effective coupling strengths between the leads and the dots.