Transport properties of nanosystems with conventional and unconventional charge density waves

We report a systematic study of transport properties of nanosytems with charge density waves. We demonstrate, how the presence of density waves modifies the current-voltage characteristics. On the other hand hand, we show that the density waves themselves are strongly affected by the applied voltage. This self-consistent problem is solved within the formalism of the nonequilibrium Green functions. The conventional charge density waves occur only for specific, periodically distributed ranges of the voltage. Apart from the low voltage regime, they are incommensurate and the corresponding wave vectors decrease discontinuously when the voltage increases.Comment: 7 pages, 7 figures, revte

Spontaneous currents in a bosonic ring

Nonequilibrium dynamics of noninteracting bosons in a one-dimensional ring-shaped lattice is studied by means of the Kinetic Monte Carlo method. The system is approximated by the classical XY model (the kinetic term is neglected) and then the simulations are performed for the planar classical spins. We study the dynamics that follows a finite-time quench to zero temperature. If the quench is slow enough the system can equilibrate and finally reaches the ground state with uniform spin alignment. However, we show that if the quench is faster than the relaxation rate, the system can get locked in a current-carrying metastable state characterized by a nonzero winding number. We analyze how the zero-temperature state depends on the quench rate.Comment: 6 pages, 3 figure

Semiconductor quantum ring as a solid-state spin qubit

The implementation of a spin qubit in a quantum ring occupied by one or a few electrons is proposed. Quantum bit involves the Zeeman sublevels of the highest occupied orbital. Such a qubit can be initialized, addressed, manipulated, read out and coherently coupled to other quantum rings. An extensive discussion of relaxation and decoherence is presented. By analogy with quantum dots, the spin relaxation times due to spin-orbit interaction for experimentally accessible quantum ring architectures are calculated. The conditions are formulated under which qubits build on quantum rings can have long relaxation times of the order of seconds. Rapidly improving nanofabrication technology have made such ring devices experimentally feasible and thus promising for quantum state engineering.Comment: 16 pages, 3 figure 3 table