Non-Dissipative Logic Device NOT Based on Two Coupled Quantum Dots
  Non-dissipative dynamics of interacting electrons in two tunnel-coupled quantum dots is studied theoretically within the framework of the Hubbard model. Various values of intra-dot Coulomb repulsion energy $U$ and inter-dot tunneling energy $V$ are considered, which correspond to various size of the dots and to various distance between them. In the ground state, the average value of the spin projection (magnetic moment) at each dot is zero. The input signal (the local external magnetic field $H$) applied to one of the dots at a time $t=0$ causes the electronic subsystem to evolve in such a way that magnetic moments of quantum dots become oriented in the opposite directions at any time $t>0$. For any set of $U$ and $V$, there exist optimal values of $H$ and $t$ which maximize the absolute values of magnetic moments at both dots, and magnetic moments become almost saturated. Thus, the antiferromagnetic-like spin ordering can be realized at the stage of coherent temporal evolution, well before the relaxation to a new ground state at the sacrifice of inelastic processes. This effect ("dynamical antiferromagnetism") may be used for implementation of a logic function NOT in an extremely short time. A possibility to use the arrays of quantum dots as high-speed single-electron devices of new generation is discussed. 
L.A.Openov and A.M.Bychkov (Moscow State Engineering Physics   Institute)