2,161 research outputs found
Field-induced Coulomb coupling in semiconductor macroatoms: application to "single-electron" quantum devices
A novel approach for the control of exciton-exciton Coulomb coupling in
semiconductor macroatoms/molecules is proposed. We show that by applying
properly tailored external fields, we can induce ---or significantly
reinforce--- excitonic dipoles, which in turn allows to control and magnify
intra- as well as inter-dot few-exciton effects. Such dipole-dipole interaction
mechanism will be accounted for within a simple analytical model, which is
found to be in good agreement with fully three-dimensional calculations. The
proposed approach may play an important role for the design and realization of
fully-optical quantum gates as well as ultrafast optical switches
Dissipation through spin Coulomb drag in electronic spin dynamics
Spin Coulomb drag (SCD) constitutes an intrinsic source of dissipation for
spin currents in metals and semiconductors. We discuss the power loss due to
SCD in potential spintronics devices and analyze in detail the associated
damping of collective spin-density excitations. It is found that SCD
contributes substantially to the linewidth of intersubband spin plasmons in
parabolic quantum wells, which suggests the possibility of a purely optical
quantitative measurement of the SCD effect by means of inelastic light
scattering
Metric space analysis of systems immersed in a magnetic field
Understanding the behavior of quantum systems subject to magnetic fields is
of fundamental importance and underpins quantum technologies. However, modeling
these systems is a complex task, because of many-body interactions and because
many-body approaches such as density functional theory get complicated by the
presence of a vector potential into the system Hamiltonian. We use the metric
space approach to quantum mechanics to study the effects of varying the
magnetic vector potential on quantum systems. The application of this technique
to model systems in the ground state provides insight into the fundamental
mapping at the core of current density functional theory, which relates the
many-body wavefunction, particle density and paramagnetic current density. We
show that the role of the paramagnetic current density in this relationship
becomes crucial when considering states with different magnetic quantum
numbers, . Additionally, varying the magnetic field uncovers a richer
complexity for the "band structure" present in ground state metric spaces, as
compared to previous studies varying scalar potentials. The robust nature of
the metric space approach is strengthened by demonstrating the gauge invariance
of the related metric for the paramagnetic current density. We go beyond ground
state properties and apply this approach to excited states. The results suggest
that, under specific conditions, a universal behavior may exist for the
relationships between the physical quantities defining the system
Exact and LDA entanglement of tailored densities in an interacting one-dimensional electron system
We calculate the `exact' potential corresponding to a one-dimensional
interacting system of two electrons with a specific, tailored density. We use
one-dimensional density-functional theory with a local-density approximation
(LDA) on the same system and calculate densities and energies, which are
compared with the `exact' ones. The `interacting-LDA system' corresponding to
the LDA density is then found and its potential compared with the original one.
Finally we calculate and compare the spatial entanglement of the electronic
systems corresponding to the interacting-LDA and original interacting system.Comment: 7 pages, 4 figure
Dissipation through spin Coulomb drag in electronic spin transport and optical excitations
Spin Coulomb drag (SCD) constitutes an intrinsic source of dissipation for spin currents in metals and semiconductors. We discuss the power loss due to SCD in potential spintronics devices and analyze in detail the associated damping of collective spin-density excitations. It is found that SCD contributes substantially to the linewidth of intersubband spin plasmons in semiconductor quantum wells, which suggests the possibility of a purely optical quantitative measurement of the SCD effect in a parabolic well through inelastic light scattering
Intersubband spin-orbit coupling and spin splitting in symmetric quantum wells
In semiconductors with inversion asymmetry, spin-orbit coupling gives rise to
the well-known Dresselhaus and Rashba effects. If one considers quantum wells
with two or more conduction subbands, an additional, intersubband-induced
spin-orbit term appears whose strength is comparable to the Rashba coupling,
and which remains finite for symmetric structures. We show that the conduction
band spin splitting due to this intersubband spin-orbit coupling term is
negligible for typical III-V quantum wells
Feasibility of approximating spatial and local entanglement in long-range interacting systems using the extended Hubbard model
We investigate the extended Hubbard model as an approximation to the local
and spatial entanglement of a one-dimensional chain of nanostructures where the
particles interact via a long range interaction represented by a `soft' Coulomb
potential. In the process we design a protocol to calculate the
particle-particle spatial entanglement for the Hubbard model and show that, in
striking contrast with the loss of spatial degrees of freedom, the predictions
are reasonably accurate. We also compare results for the local entanglement
with previous results found using a contact interaction (PRA, 81 (2010) 052321)
and show that while the extended Hubbard model recovers a better agreement with
the entanglement of a long-range interacting system, there remain realistic
parameter regions where it fails to predict the quantitative and qualitative
behaviour of the entanglement in the nanostructure system.Comment: 6 pages, 5 figures and 1 table; added results with correlated hopping
term; accepted by EP
Effect of matrix parameters on mesoporous matrix based quantum computation
We present a solid state implementation of quantum computation, which
improves previously proposed optically driven schemes. Our proposal is based on
vertical arrays of quantum dots embedded in a mesoporous material which can be
fabricated with present technology. We study the feasibility of performing
quantum computation with different mesoporous matrices. We analyse which matrix
materials ensure that each individual stack of quantum dots can be considered
isolated from the rest of the ensemble-a key requirement of our scheme. This
requirement is satisfied for all matrix materials for feasible structure
parameters and GaN/AlN based quantum dots. We also show that one dimensional
ensembles substantially improve performances, even of CdSe/CdS based quantum
dots
The entanglement of few-particle systems when using the local-density approximation
In this chapter we discuss methods to calculate the entanglement of a system
using density-functional theory. We firstly introduce density-functional theory
and the local-density approximation (LDA). We then discuss the concept of the
`interacting LDA system'. This is characterised by an interacting many-body
Hamiltonian which reproduces, uniquely and exactly, the ground state density
obtained from the single-particle Kohn-Sham equations of density-functional
theory when the local-density approximation is used. We motivate why this idea
can be useful for appraising the local-density approximation in many-body
physics particularly with regards to entanglement and related quantum
information applications. Using an iterative scheme, we find the Hamiltonian
characterising the interacting LDA system in relation to the test systems of
Hooke's atom and helium-like atoms. The interacting LDA system ground state
wavefunction is then used to calculate the spatial entanglement and the results
are compared and contrasted with the exact entanglement for the two test
systems. For Hooke's atom we also compare the entanglement to our previous
estimates of an LDA entanglement. These were obtained using a combination of
evolutionary algorithm and gradient descent, and using an LDA-based
perturbative approach. We finally discuss if the position-space information
entropy of the density---which can be obtained directly from the system density
and hence easily from density-functional theory methods---can be considered as
a proxy measure for the spatial entanglement for the test systems.Comment: 12 pages and 5 figures
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