5 research outputs found
Nonequilibrium stabilization of charge states in double quantum dots
We analyze the decoherence of charge states in double quantum dots due to
cotunneling. The system is treated using the Bloch-Redfield generalized master
equation for the Schrieffer-Wolff transformed Hamiltonian. We show that the
decoherence, characterized through a relaxation and a dephasing time
, can be controlled through the external voltage and that the
optimum point, where these times are maximum, is not necessarily in
equilibrium. We outline the mechanism of this nonequilibrium-induced
enhancement of lifetime and coherence. We discuss the relevance of our results
for recent charge qubit experiments.Comment: 5 pages, 5 figure
Effect of inelastic scattering on parametric pumping
Pumping of charge in phase-coherent mesoscopic systems due to the
out-of-phase modulation of two parameters has recently found considerable
interest. We investigate the effect of inelastic processes on the adiabatically
pumped current through a two terminal mesoscopic sample. We find that the loss
of coherence does not suppress the pumped charge but rather an additional
physical mechanism for an incoherent pump effect comes into play. In a fully
phase incoherent system the pump effect is similar to a rectification effect
Charge and spin configurations in the coupled quantum dots with Coulomb correlations induced by tunneling current
We investigated the peculiarities of non-equilibrium charge states and spin
configurations in the system of two strongly coupled quantum dots (QDs) weakly
connected to the electrodes in the presence of Coulomb correlations. We
analyzed the modification of non-equilibrium charge states and different spin
configurations of the system in a wide range of applied bias voltage and
revealed well pronounced ranges of system parameters where negative tunneling
conductivity appears due to the Coulomb correlations.Comment: 10 pages, 6 figure
Nonlinear cotunneling through an artificial molecule
We study electron transport through a system of two lateral quantum dots
coupled in series. We consider the case of weak coupling to the leads and a
bias point in the Coulomb blockade. After a generalized Schrieffer-Wolf
transformation, cotunneling through this system is described using methods from
lowest-order perturbation theory. We study the system for arbitrary bias
voltages below the Coulomb energy. We observe a rich, non-monotonic behavior of
the stationary current depending on the internal degrees of freedom. In
particular, it turns out that at fixed transport voltage, the current through
the system is largest at weak-to-intermediate inter-dot coupling.Comment: 4 pages, 5 figure
Dissipation and noise in adiabatic quantum pumps
We investigate the distribution function, the heat flow and the noise
properties of an adiabatic quantum pump for an arbitrary relation of pump
frequency and temperature. To achieve this we start with the
scattering matrix approach for ac-transport. This approach leads to expressions
for the quantities of interest in terms of the side bands of particles exiting
the pump. The side bands correspond to particles which have gained or lost a
modulation quantum . We find that our results for the pump
current, the heat flow and the noise can all be expressed in terms of a
parametric emissivity matrix. In particular we find that the current
cross-correlations of a multiterminal pump are directly related a to a
non-diagonal element of the parametric emissivity matrix. The approach allows a
description of the quantum statistical correlation properties (noise) of an
adiabatic quantum pump