881 research outputs found
Surface Acoustic Wave induced Transport in a Double Quantum Dot
We report on non-adiabatic transport through a double quantum dot under
irradiation of surface acoustic waves generated on-chip. At low excitation
powers, absorption and emission of single and multiple phonons is observed. At
higher power, sequential phonon assisted tunneling processes excite the double
dot in a highly non-equilibrium state. The present system is attractive for
studying electron-phonon interaction with piezoelectric coupling.Comment: 4 pages, 3 figure
Non-adiabatic two-parameter charge and spin pumping in a quantum dot
We study DC charge and spin transport through a weakly coupled quantum dot,
driven by a non-adiabatic periodic change of system parameters. We generalize
the model of Tien and Gordon to simultaneously oscillating voltages and tunnel
couplings. When applying our general result to the two-parameter charge pumping
in quantum dots, we find interference effects between the oscillations of the
voltage and tunnel couplings. Furthermore, we discuss the possibility to
electrically pump a spin current in presence of a static magnetic field.Comment: 4.1 pages, 4 figure
Spin injection and perpendicular spin transport in graphite nanostructures
Organic and carbon-based materials are attractive for spintronics because
their small spin-orbit coupling and low hyperfine interaction is expected to
give rise to large spin-relaxation times. However, the corresponding
spin-relaxation length is not necessarily large when transport is via weakly
interacting molecular orbitals. Here we use graphite as a model system and
study spin transport in the direction perpendicular to the weakly bonded
graphene sheets. We achieve injection of highly (75%) spin-polarized electrons
into graphite nanostructures of 300-500 nm across and up to 17 nm thick, and
observe transport without any measurable loss of spin information. Direct
visualization of local spin transport in graphite-based spin-valve sandwiches
also shows spatially uniform and near-unity transmission for electrons at 1.8
eV above the Fermi level
The connection between noise and quantum correlations in a double quantum dot
We investigate the current and noise characteristics of a double quantum dot
system. The strong correlations induced by the Coulomb interaction create
entangled two-electron states and lead to signatures in the transport
properties. We show that the interaction parameter phi, which measures the
admixture of the double-occupancy contribution to the singlet state and thus
the degree of entanglement, can be directly accessed through the Fano factor of
super-Poissonian shot noise.Comment: 5 pages, major revision, to be published in Phys. Rev.
Coherent single electron spin control in a slanting Zeeman field
We consider a single electron in a 1D quantum dot with a static slanting
Zeeman field. By combining the spin and orbital degrees of freedom of the
electron, an effective quantum two-level (qubit) system is defined. This
pseudo-spin can be coherently manipulated by the voltage applied to the gate
electrodes, without the need for an external time-dependent magnetic field or
spin-orbit coupling. Single qubit rotations and the C-NOT operation can be
realized. We estimated relaxation () and coherence () times, and
the (tunable) quality factor. This scheme implies important experimental
advantages for single electron spin control.Comment: 4 pages, 3 figure
Entanglement distillation by adiabatic passage in coupled quantum dots
Adiabatic passage of two correlated electrons in three coupled quantum dots
is shown to provide a robust and controlled way of distilling, transporting and
detecting spin entanglement, as well as of measuring the rate of spin
disentanglement. Employing tunable interdot coupling the scheme creates, from
an unentangled two-electron state, a superposition of spatially separated
singlet and triplet states. A single measurement of a dot population (charge)
collapses the wave function to either of these states, realizing entanglement
to charge conversion. The scheme is robust, with the efficiency close to 100%,
for a large range of realistic spectral parameters.Comment: 5 pages, 4 figure
Time-dependent magnetotransport of a wave packet in a quantum wire with embedded quantum dots
We consider wave packet propagation in a quantum wire with either an embedded
antidot or an embedded parallel double open quantum dot under the influence of
a uniform magnetic field. The magnetoconductance and the time evolution of an
electron wave packet are calculated based on the Lippmann-Schwinger formalism.
This approach allows us to look at arbitrary embedded potential profiles and
illustrate the results by performing computational simulations for the
conductance and the time evolution of the electron wave packet through the
quantum wire. In the double-dot system we observe a long-lived resonance state
that enhances the spatial spreading of the wave packet, and quantum
skipping-like trajectories are induced when the envelop function of the wave
packet covers several subbands in appropriate magnetic fields.Comment: RevTeX, 9 pages with 8 included postscript figure
AC-driven double quantum dots as spin pumps and spin filters
We propose and analyze a new scheme of realizing both spin filtering and spin
pumping by using ac-driven double quantum dots in the Coulomb blockade regime.
By calculating the current through the system we demonstrate that the spin
polarization of the current can be controlled by tuning the parameters
(amplitude and frequency) of the ac field. We also discuss spin relaxation and
decoherence effects in the pumped current.Comment: 5 pages, 4 figure
Exchange-controlled single-electron-spin rotations in quantum dots
We show theoretically that arbitrary coherent rotations can be performed
quickly (with a gating time ~1 ns) and with high fidelity on the spin of a
single confined electron using control of exchange only, without the need for
spin-orbit coupling or ac fields. We expect that implementations of this scheme
would achieve gate error rates on the order of \eta ~ 10^{-3} in GaAs quantum
dots, within reach of several known error-correction protocolsComment: 4+ pages, 3 figures; v2: Streamlined presentation, final version
published in PRB (Rapid Comm.
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