1,005 research outputs found
Methods for Estimating Capacities and Rates of Gaussian Quantum Channels
Optimization methods aimed at estimating the capacities of a general Gaussian
channel are developed. Specifically evaluation of classical capacity as maximum
of the Holevo information is pursued over all possible Gaussian encodings for
the lossy bosonic channel, but extension to other capacities and other Gaussian
channels seems feasible. Solutions for both memoryless and memory channels are
presented. It is first dealt with single use (single-mode) channel where the
capacity dependence from channel's parameters is analyzed providing a full
classification of the possible cases. Then it is dealt with multiple uses
(multi-mode) channel where the capacity dependence from the (multi-mode)
environment state is analyzed when both total environment energy and
environment purity are fixed. This allows a fair comparison among different
environments, thus understanding the role of memory (inter-mode correlations)
and phenomenon like superadditivity of the capacity. The developed methods are
also used for deriving transmission rates with heterodyne and homodyne
measurements at the channel output. Classical capacity and transmission rates
are presented within a unique framework where the rates can be treated as
logarithmic approximations of the capacity.Comment: 39 pages, 30 figures. New results and graphs were added. Errors and
misprints were corrected. To appear in IEEE Trans. Inf. T
Adoption of Innovation in Small-Scale Forestry: The Case of Portable-Sawmill-Based Microenterprises
Microenterprise development can be a valuable societal component not only in terms of filling important niche markets, but also by enhancing a society\u27s wellbeing through creating opportunities available to people who are marginalized by the labor force for one reason or another. Forest microenterprises, in particular, can enhance rural community development efforts, as well as forest conservation goals, by empowering local people to successfully manage their resources as well as offer the possibility of income enhancement (Salafsky, Cordes, Leighton, Henderson, Watt, & Cherry, 1997; Lupo, 2012). This paper explores the adoption of portable-sawmill-based forest microenterprises. Key findings include common factors motivating portable sawmill adoption, as well as a bimodal adoption pattern, supporting previously postulated arguments regarding the importance of creating multiple adoption theories
Qubit-portraits of qudit states and quantum correlations
The machinery of qubit-portraits of qudit states, recently presented, is
consider here in more details in order to characterize the presence of quantum
correlations in bipartite qudit states. In the tomographic representation of
quantum mechanics, Bell-like inequalities are interpreted as peculiar
properties of a family of classical joint probability distributions which
describe the quantum state of two qudits. By means of the qubit-portraits
machinery a semigroup of stochastic matrices can be associated to a given
quantum state. The violation of the CHSH inequalities is discussed in this
framework with some examples, we found that quantum correlations in qutrit
isotropic states can be detected by the suggested method while it cannot in the
case of qutrit Werner states.Comment: 12 pages, 4 figure
On the classical capacity of quantum Gaussian channels
The set of quantum Gaussian channels acting on one bosonic mode can be
classified according to the action of the group of Gaussian unitaries. We look
for bounds on the classical capacity for channels belonging to such a
classification. Lower bounds can be efficiently calculated by restricting to
Gaussian encodings, for which we provide analytical expressions.Comment: 10 pages, IOP style. v2: minor corrections, close to the published
versio
Partial scaling transform of multiqubit states as a criterion of separability
The partial scaling transform of the density matrix for multiqubit states is
introduced to detect entanglement of quantum states. The transform contains
partial transposition as a special case. The scaling transform corresponds to
partial time scaling of subsystem (or partial Planck's constant scaling) which
was used to formulate recently separability criterion for continous variables.A
measure of entanglement which is a generalization of negativity measure is
introduced being based on tomographic probability description of spin states.Comment: 16 pages, 5 figures, submitted to J. Phys. A: Math. Ge
Bell's inequalities in the tomographic representation
The tomographic approach to quantum mechanics is revisited as a direct tool
to investigate violation of Bell-like inequalities. Since quantum tomograms are
well defined probability distributions, the tomographic approach is emphasized
to be the most natural one to compare the predictions of classical and quantum
theory. Examples of inequalities for two qubits an two qutrits are considered
in the tomographic probability representation of spin states.Comment: 11 pages, comments and references adde
Influence of long- and short-term climatic changes on chernozem soils : Central Chernozem region of Russia
The main purpose of this article is the identification of forest-steppe and steppe chernozem soils (Eastern European Mollisols) reactions to climate change with different periodicitiesyesBelgorod State National Research Universit
Dynamical quantum phase transitions of the Schwinger model: real-time dynamics on IBM Quantum
Simulating real-time dynamics of gauge theories represents a paradigmatic use
case to test the hardware capabilities of a quantum computer, since it can
involve non-trivial input states preparation, discretized time evolution,
long-distance entanglement, and measurement in a noisy environment. We
implement an algorithm to simulate the real-time dynamics of a few-qubit system
that approximates the Schwinger model in the framework of lattice gauge
theories, with specific attention to the occurrence of a dynamical quantum
phase transition. Limitations in the simulation capabilities on IBM Quantum are
imposed by noise affecting the application of single-qubit and two-qubit gates,
which combine in the decomposition of Trotter evolution. The experimental
results collected in quantum algorithm runs on IBM Quantum are compared with
noise models to characterize the performance in the absence of error
mitigation
Quantumness tests and witnesses in the tomographic-probability representation
In view of the tomographic-probability representation of quantum states, we
reconsider the approach to quantumness tests of a single system developed in
[Alicki and Van Ryn 2008 J. Phys. A: Math. Theor. 41 062001]. For qubits we
introduce a general family of quantumness witnesses which are operators
depending on an extra parameter. Spin tomogram and dual spin tomographic
symbols are used to study qubit examples and the test inequalities which are
shown to satisfy simple relations within the framework of the standard
probability theory.Comment: 9 pages, 1 figure, LaTex file, submitted to Physica Script
Robustness against parametric noise of non ideal holonomic gates
Holonomic gates for quantum computation are commonly considered to be robust
against certain kinds of parametric noise, the very motivation of this
robustness being the geometric character of the transformation achieved in the
adiabatic limit. On the other hand, the effects of decoherence are expected to
become more and more relevant when the adiabatic limit is approached. Starting
from the system described by Florio et al. [Phys. Rev. A 73, 022327 (2006)],
here we discuss the behavior of non ideal holonomic gates at finite operational
time, i.e., far before the adiabatic limit is reached. We have considered
several models of parametric noise and studied the robustness of finite time
gates. The obtained results suggest that the finite time gates present some
effects of cancellation of the perturbations introduced by the noise which
mimic the geometrical cancellation effect of standard holonomic gates.
Nevertheless, a careful analysis of the results leads to the conclusion that
these effects are related to a dynamical instead of geometrical feature.Comment: 8 pages, 8 figures, several changes made, accepted for publication on
Phys. Rev.
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