7 research outputs found
Adiabatic spin pumping through a quantum dot with a single orbital level
We investigate an adiabatic spin pumping through a quantum dot with a single
orbital energy level under the Zeeman effect. Electron pumping is produced by
two periodic time dependent parameters, a magnetic field and a difference of
the dot-lead coupling between the left and right barriers of the dot. The
maximum charge transfer per cycle is found to be , the unit charge in the
absence of a localized moment in the dot. Pumped charge and spin are different,
and spin pumping is possible without charge pumping in a certain situation.
They are tunable by changing the minimum and maximum value of the magnetic
field.Comment: RevTeX4, 5 pages, 3 figure
Quantum Pumping and Quantized Magnetoresistance in a Hall Bar
We show how a dc current can be generated in a Hall bar without applying a
bias voltage. The Hall resistance that corresponds to this pumped current
is quantized, just as in the usual integer quantum Hall effect (IQHE). In
contrast with the IQHE, however, the longitudinal resistance does not
vanish on the plateaus, but equals the Hall resistance. We propose an
experimental geometry to measure the pumped current and verify the predicted
behavior of and .Comment: RevTeX, 3 figure
Noise-assisted classical adiabatic pumping in a symmetric periodic potential
We consider a classical overdamped Brownian particle moving in a symmetric
periodic potential. We show that a net particle flow can be produced by
adiabatically changing two external periodic potentials with a spatial and a
temporal phase difference. The classical pumped current is found to be
independent of the friction and to vanish both in the limit of low and high
temperature. Below a critical temperature, adiabatic pumping appears to be more
efficient than transport due to a constant external force.Comment: six pages, 3 figure
Quantum spin pumping with adiabatically modulated magnetic barrier's
A quantum pump device involving magnetic barriers produced by the deposition
of ferro magnetic stripes on hetero-structure's is investigated. The device for
dc- transport does not provide spin-polarized currents, but in the adiabatic
regime, when one modulates two independent parameters of this device, spin-up
and spin-down electrons are driven in opposite directions, with the net result
being that a finite net spin current is transported with negligible charge
current. We also analyze our proposed device for inelastic-scattering and
spin-orbit scattering. Strong spin-orbit scattering and more so inelastic
scattering have a somewhat detrimental effect on spin/charge ratio especially
in the strong pumping regime. Further we show our pump to be almost noiseless,
implying an optimal quantum spin pump.Comment: 14 pages, 9 figures. Manuscript revised with additional new material
on spin-orbit scattering and inelastic scattering. Further new additions on
noiseless pumping and analytical results with distinction between weak and
strong pumping regimes. Accepted for publication in Physical Review
Adiabatic Transfer of Electrons in Coupled Quantum Dots
We investigate the influence of dissipation on one- and two-qubit rotations
in coupled semiconductor quantum dots, using a (pseudo) spin-boson model with
adiabatically varying parameters. For weak dissipation, we solve a master
equation, compare with direct perturbation theory, and derive an expression for
the `fidelity loss' during a simple operation that adiabatically moves an
electron between two coupled dots. We discuss the possibility of visualizing
coherent quantum oscillations in electron `pump' currents, combining quantum
adiabaticity and Coulomb blockade. In two-qubit spin-swap operations where the
role of intermediate charge states has been discussed recently, we apply our
formalism to calculate the fidelity loss due to charge tunneling between two
dots.Comment: 13 pages, 8 figures, to appear in Phys. Rev.
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
Charge Transport Through Open, Driven Two-Level Systems with Dissipation
We derive a Floquet-like formalism to calculate the stationary average
current through an AC driven double quantum dot in presence of dissipation. The
method allows us to take into account arbitrary coupling strengths both of a
time-dependent field and a bosonic environment. We numerical evaluate a
truncation scheme and compare with analytical, perturbative results such as the
Tien-Gordon formula.Comment: 14 pages, 6 figures. To appear in Phys. Rev.