1,720,993 research outputs found
Analytical expression of genuine tripartite quantum discord for symmetrical X-states
No full textThe 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
Quantum correlations of identical particles subject to classical environmental noise
No full textAbstract In this work, we propose a measure for the quantum discord of indistinguishable
particles, based on the definition of entanglement of particles given in
Wiseman and Vaccaro (Phys Rev Lett 91:097902, 2003. doi:10.1103/PhysRevLett.91.
097902). This discord of particles is then used to evaluate the quantum correlations in
a system of two identical bosons (fermions), where the particles perform a quantum
random walk described by the Hubbard Hamiltonian in a 1D lattice. The dynamics of
the particles is either unperturbed or subject to a classical environmental noise—such
as random telegraph, pink or brown noise. The observed results are consistent with
those for the entanglement of particles, and we observe that on-site interaction between
particles have an important protective effect on correlations against the decoherence
of the system
Time-dependent simulation and analytical modelling of electronic Mach-Zehnder interferometry with edge-states wave packets
No full textWe 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 Schrödinger 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—controlled
via magnetic field and/or area variation—reproduces the one of (Ji et al 2003 Nature 422
415). 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
Intrinsic Electric Oscillations of Ovonic Devices towards the TeraHerz limit
No full textThe time-dependent response of Ovonic devices to an electric potential ramp signal
is analysed by means of an enhanced version of a previously published time-dependent charge-
transport model proposed by the authors. Depending on the inevitable parasitics of the system,
either stable or oscillating solutions are found according to the position of the load line. The
model also allows for speculations on the potential of Ovonic materials in the design of high-
frequency oscillating circuits close to the terahertz range
A fifth-order method for 1D device solution
No full textThe so called Numerov process provides an inexpensive, accurate discretization scheme for second-order equations. In this paper the Numerov process has been made applicable to practical cases with typical applications to numerical solution of the coupled Schroedinger Poisson equations. Here the feasibility of the 5-th order method is proved for the longitudinal part of the wave equation
Magnetophotoluminescence in GaAs/AlAs core-multishell nanowires: A theoretical investigation
Full text linkThe magnetophotoluminescence in modulation doped core-multishell nanowires is predicted as a function of
photoexcitation intensity in nonperturbative transverse magnetic fields. We use a self-consistent field approach
within the effective mass approximation to determine the photoexcited electron and hole populations, including
the complex composition and anisotropic geometry of the nanomaterial. The evolution of the photoluminescence
is analyzed as a function of (i) photoexcitation power, (ii) magnetic field intensity, (iii) type of doping, and
(iv) anisotropy with respect to field orientation
Time-dependent transport in amorphous semiconductors: instability in the field-controlled regime
No full textA time-dependent trap-limited conduction scheme is used to analyze the transient behavior of bistable homogeneous amorphous semiconductors when either the electric field or the current density is prescribed. Numerical outcomes confirm that, for a current-controlled system, the working point is unique and stable in any region of the current-voltage characteristic, while in a field-controlled system the negative differential-resistance region is unstable even in absence of circuit parasitics. The proposed theoretical approach represents a valid tool to grasp the relevant time-dependent features of the Ovonic switching in chalcogenide materials
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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