159 research outputs found
Wigner transport equation with finite coherence length
The use of the Wigner function for the study of quantum transport in open
systems present severe criticisms. Some of the problems arise from the
assumption of infinite coherence length of the electron dynamics outside the
system of interest. In the present work the theory of the Wigner function is
revised assuming a finite coherence length. A new dynamical equation is found,
corresponding to move the Wigner momentum off the real axis, and a numerical
analysis is performed for the case of study of the onedimensional potential
barrier.Comment: 14 pages, 1 figure. Revised text. Added new reference
Time-evolution of tripartite quantum discord and entanglement under local and non-local random telegraph noise
Few studies explored the dynamics of non-classical correlations besides
entanglement in open multipartite quantum systems. Here, we address the
time-evolution of quantum discord and entanglement in a model of three
non-interacting qubits subject to a classical random telegraph noise in common
and separated environments. Two initial entangled states of the system are
examined, namely the GHZ- and W-type states. The dynamics of quantum
correlations results to be strongly affected by the input configuration of the
qubits, the type of the system-environment interaction, and the memory
properties of the environmental noise. When the qubits are non-locally coupled
to the random telegraph noise, the GHZ-type states partially preserve, at long
times, both discord and entanglement, regardless the correlation time of the
environmental noise. The survived entangled states turn out to be also
detectable by means of suitable entanglement witnesses. On the other hand, in
the same conditions, the decohering effects suppress all the quantum
correlation of the W-type states which are thus less robust than the GHZ-type
ones. The long-time survival of tripartite discord and entanglement opens
interesting perspectives in the use of multipartite entangled states for
practical applications in quantum information science.Comment: 11 pages, 4 figure
Dynamics of electron entanglement in semiconductor nanostructures
Quantum entanglement, the most remarkable feature of quantum physics, is recognized as a resource for quantum information processing. The quest for quantum-computing devices has also produced great interest in entanglementformation in solid-state systems involving quantum effects. Indeed,the functionality of an increasing number of nanodevices is influenced by quantum correlations. In this work a theoretical approach developed in recent years to study the entanglement of fermions interacting via a Coulomb potential is presented, together with a number of applications to specific situations of physical interest in the field of charge transport in semiconductor nanostructures
Analytical expression of Genuine Tripartite Quantum Discord for Symmetrical X-states
The study of classical and quantum correlations in bipartite and multipartite
systems is crucial for the development of quantum information theory. Among the
quantifiers adopted in tripartite systems, the genuine tripartite quantum
discord (GTQD), estimating the amount of quantum correlations shared among all
the subsystems, plays a key role since it represents the natural extension of
quantum discord used in bipartite systems. In this paper, we derive an
analytical expression of GTQD for three-qubit systems characterized by a
subclass of symmetrical X-states. Our approach has been tested on both GHZ and
maximally mixed states reproducing the expected results. Furthermore, we
believe that the procedure here developed constitutes a valid guideline to
investigate quantum correlations in form of discord in more general
multipartite systems.Comment: 13 pages, 4 figures. v3: Added some references and corrected some
typo
Quantum correlations in continuos-time quantum walks of two indistinguishable particles
We evaluate the degree of quantum correlation between two fermions (bosons)
subject to continuous time quantum walks in a one-dimensional ring lattice with
periodic boundary conditions. In our approach, no particle-particle interaction
is considered. We show that the interference effects due to exchange symmetry
can result into the appearance of non-classical correlations. The role played
onto the appearance of quantum correlations by the quantum statistics of the
particles, the boundary conditions, and the partition of the system is widely
investigated. Quantum correlations also been investigated in a model mimicking
the ballistic evolution of two indistinguishable particles in a 1D continuous
space structure. Our results are consistent with recent quantum optics and
electron quantum optics experiments where the showing up of two-particle
non-classical correlations has been observed even in the absence of mutual
interaction between the particles.Comment: 12 pages, 5 figure
Entanglement creation in semiconductor quantum dot charge qubit
We study theoretically the appearance of quantum correlations in two- and
three-electron scattering in single and double dots. The key role played by
transport resonances into entanglement formation between the single-particle
states is shown. Both reflected and transmitted components of the scattered
particle wavefunction are used to evaluate the quantum correlations between the
incident carrier and the bound particle(s) in the dots. Our investigation
provides a guideline for the analysis of decoherence effects due to the Coulomb
scattering in semiconductor quantum dots structures.Comment: 8 pages, 5 figures, Proceedings of Quantum 2010:24-28, May, 2010
Torin
Time-dependent simulation and analytical modelling of electronic Mach-Zehnder interferometry with edge-states wave packets
We compute the exact single-particle time-resolved dynamics of electronic
Mach-Zehnder interferometers based on Landau edge-states transport, and assess
the effect of the spatial localization of carriers on the interference pattern.
The exact carrier dynamics is obtained by solving numerically the
time-dependent Schroedinger equation with a suitable 2D potential profile
reproducing the interferometer design. An external magnetic field, driving the
system to the quantum Hall regime with filling factor one, is included. The
injected carriers are represented by a superposition of edge states and their
interference pattern reproduces the results of Y.Ji et al.[Nature 422, 415
(2003)]. By tuning the system towards different regimes, we find two additional
features in the transmission spectra, both related to carrier localization,
namely a damping of the Aharonov-Bohm oscillations with increasing difference
in the arms length, and an increased mean transmission that we trace to the
energy-dependent transmittance of quantum point contacts. Finally, we present
an analytical model, also accounting for the finite spatial dispersion of the
carriers, able to reproduce the above effects.Comment: two-columns, 12 pages, 9 figures; added 10 refs.; main text modified;
corrected few typos; added 3 figures of Supplementary Dat
A measure of tripartite entanglement in bosonic and fermionic systems
We describe an efficient theoretical criterion suitable for the evaluation of
the tripartite entanglement of any mixed three-boson or -fermion state, based
on the notion of the entanglement of particles for bipartite systems of
identical particles. Our approach allows one to quantify the accessible amount
of quantum correlations in the systems without any violation of the local
particle number superselection rule. A generalization of the tripartite
negativity is here applied to some correlated systems including the
continuous-time quantum walks of identical particles (both for bosons and
fermions) and compared with other criteria recently proposed in the literature.
Our results show the dependence of the entanglement dynamics upon the quantum
statistics: the bosonic bunching results into a low amount of quantum
correlations while Fermi-Dirac statistics allows for higher values of the
entanglement.Comment: 19 pages, 3 figure
Non-Markovian continuous-time quantum walks on lattices with dynamical noise
We address the dynamics of continuous-time quantum walks on one-dimensional
disordered lattices inducing dynamical noise in the system. Noise is described
as time-dependent fluctuations of the tunneling amplitudes between adjacent
sites, and attention is focused on non-Gaussian telegraph noise, going beyond
the usual assumption of fast Gaussian noise. We observe the emergence of two
different dynamical behaviors for the walker, corresponding to two opposite
noise regimes: slow noise (i.e. strong coupling with the environment) confines
the walker into few lattice nodes, while fast noise (weak coupling) induces a
transition between quantum and classical diffusion over the lattice. A phase
transition between the two dynamical regimes may be observed by tuning the
ratio between the autocorrelation time of the noise and the coupling between
the walker and the external environment generating the noise. We also address
the non-Markovianity of the quantum map by assessing its memory effects, as
well as evaluating the information backflow to the system. Our results suggest
that the non-Markovian character of the evolution is linked to the dynamical
behavior in the slow noise regime, and that fast noise induces a Markovian
dynamics for the walker.Comment: 10 pages, 8 figure
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