539 research outputs found
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
Dynamics of quantum correlations in colored environments
We address the dynamics of entanglement and quantum discord for two non
interacting qubits initially prepared in a maximally entangled state and then
subjected to a classical colored noise, i.e. coupled with an external
environment characterized by a noise spectrum of the form . More
specifically, we address systems where the Gaussian approximation fails, i.e.
the sole knowledge of the spectrum is not enough to determine the dynamics of
quantum correlations. We thus investigate the dynamics for two different
configurations of the environment: in the first case the noise spectrum is due
to the interaction of each qubit with a single bistable fluctuator with an
undetermined switching rate, whereas in the second case we consider a
collection of classical fluctuators with fixed switching rates. In both cases
we found analytical expressions for the time dependence of entanglement and
quantum discord, which may be also extended to a collection of flcutuators with
random switching rates. The environmental noise is introduced by means of
stochastic time-dependent terms in the Hamiltonian and this allows us to
describe the effects of both separate and common environments. We show that the
non-Gaussian character of the noise may lead to significant effects, e.g.
environments with the same power spectrum, but different configurations, give
raise to opposite behavior for the quantum correlations. In particular,
depending on the characteristics of the environmental noise considered, both
entanglement and discord display either a monotonic decay or the phenomena of
sudden death and revivals. Our results show that the microscopic structure of
environment, besides its noise spectrum, is relevant for the dynamics of
quantum correlations, and may be a valid starting point for the engineering of
non-Gaussian colored environments.Comment: 8 pages, 3 figure
Probing the sign of on-site Hubbard interaction by two-particle quantum walks
We consider two identical bosons propagating on a one-dimensional lattice and
address the prob- lem of discriminating whether their mutual on-site
interaction is attractive or repulsive. We suggest a probing scheme based on
the properties of the corresponding two-particle quantum walks, and show that
the sign of the interaction introduces specific and detectable features in the
dynamics of quantum correlations, thus permitting to discriminate between the
two cases. We also discuss how these features are connected to the
band-structure of the Hubbard Hamiltonian, and prove that discrimination may be
obtained only when the two walkers are initially prepared in a superposition of
localized states.Comment: 9 pages, 9 figure
Linear entropy as an entanglement measure in two-fermion systems
We describe an efficient theoretical criterion, suitable for
indistinguishable particles to quantify the quantum correlations of any pure
two-fermion state, based on the Slater rank concept. It represents the natural
generalization of the linear entropy used to treat quantum entanglement in
systems of non-identical particles. Such a criterion is here applied to an
electron-electron scattering in a two-dimensional system in order to perform a
quantitative evaluation of the entanglement dynamics for various spin
configurations and to compare the linear entropy with alternative approaches.
Our numerical results show the dependence of the entanglement evolution upon
the initial state of the system and its spin components. The differences with
previous analyses accomplished by using the von Neumann entropy are discussed.
The evaluation of the entanglement dynamics in terms of the linear entropy
results to be much less demanding from the computational point of view, not
requiring the diagonalization of the density matrix.Comment: 16 pages. Added references in section 1 Corrected typo
Entanglement dynamics of electron-electron scattering in low-dimensional semiconductor systems
We perform the quantitative evaluation of the entanglement dynamics in
scattering events between two insistinguishable electrons interacting via
Coulomb potential in 1D and 2D semiconductor nanostructures. We apply a
criterion based on the von Neumann entropy and the Schmidt decomposition of the
global state vector suitable for systems of identical particles. From the
timedependent numerical solution of the two-particle wavefunction of the
scattering carriers we compute their entanglement evolution for different spin
configurations: two electrons with the same spin, with different spin, singlet,
and triplet spin state. The procedure allows to evaluate the mechanisms that
govern entanglement creation and their connection with the characteristic
physical parameters and initial conditions of the system. The cases in which
the evolution of entanglement is similar to the one obtained for
distinguishable particles are discussed.Comment: 22 pages, 7 figures, submitted to Physical Review
Influence of Older Generation's Fertility Behaviours on Daughter's Desired Family Size in Bihar, India. VID Working Paper 04/2014
This paper investigates the associations between preferred family size of married women aged 16-34 in rural Bihar (India) and the fertility behaviours of their biological mother and mother-in-law. This information is based on scheduled interviews of 450 pairs of index women (i.e. women central in our analysis) and their mother-in-laws conducted in 2011. Preferred family size is first measured by Coombs scale, allowing us to capture latent desired number of children, and then categorized into three categories (low, medium, and high). Ordered logistic regression is employed to estimated the preferred family size of index women. We find that family size preferences of index woman is not associated with mother's fertility but with mother's education. Mother-in-law's desired number of grandchildren is positively associated with preferred family size of index woman and remains significant even after controlling for relevant socioeconomic characteristics. However, in the case where index woman has higher education than her mother-in-law, her preferred family size gets smaller. This suggests that education may provide women with greater autonomy in their decision making on childbearing
Intergenerational support among migrant families in Europe
Intergenerational support is important throughout the individual life course and a major mechanism of cultural continuity. In this study, we analyse support between older parents and their adult children among international migrant and non-migrant populations in North, Centre and Southern Europe. Data from the Survey of Health, Ageing and Retirement in Europe are used to compare upward and downward practical support, grandparenting, and frequency of contact among 62,213 parent–child dyads. Findings indicate limited differences in support between migrants and non-migrants as well as between migrants of various origins. However, persistent differences in intergenerational support across Europe along a north–south gradient are found irrespective of migrant status
Dynamics of copropagating edge states in a multichannel Mach-Zender interferometer
We study numerically a multichannel electronic Mach-Zender interferometer, where
an orthogonal magnetic field produces edge states. Our time-dependent model is based on the split-step Fourier method and describes the charge carrier as a Gaussian wavepacket of edge states, whose path is defined by split-gate induced potential profiles on the 2DEG at filling factor 2. We analyse a beam splitter with ∼ 50% inter-channel mixing and obtain Aharonov-Bohm oscillations in the transmission probability of the second channel
Noisy quantum walks of two indistinguishable interacting particles
We investigate the dynamics of continuous-time two-particle quantum walks on
a one-dimensional noisy lattice. Depending on the initial condition, we show
how the interplay between particle indistinguishability and interaction
determines distinct propagation regimes. A realistic model for the environment
is considered by introducing non-Gaussian noise as time-dependent fluctuations
of the tunneling amplitudes between adjacent sites. We observe that the
combined effect of particle interaction and fast noise (weak coupling with the
environment) provides a faster propagation compared to the noiseless case. This
effect can be understood in terms of the band structure of the Hubbard model,
and a detailed analysis as a function of both noise and system parameters is
presented.Comment: 9 pages, 8 figure
Carrier-carrier entanglement and transport resonances in semiconductor quantum dots
We study theoretically the entanglement created in a scattering between an
electron, incoming from a source lead, and another electron bound in the ground
state of a quantum dot, connected to two leads. We analyze the role played by
the different kinds of resonances in the transmission spectra and by the number
of scattering channels, into the amount of quantum correlations between the two
identical carriers. It is shown that the entanglement between their energy
states is not sensitive to the presence of Breit-Wigner resonances, while it
presents a peculiar behavior in correspondence of Fano peaks: two close maxima
separated by a minimum, for a two-channel scattering, a single maximum for a
multi-channel scattering. Such a behavior is ascribed to the different
mechanisms characterizing the two types of resonances. Our results suggest that
the production and detection of entanglement in quantum dot structures may be
controlled by the manipulation of Fano resonances through external fields.Comment: 8 pages, 6 figures, RevTex4 two-column format, submitte
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