1,028 research outputs found
Distilling entanglement from cascades with partial "Which Path" ambiguity
We develop a framework to calculate the density matrix of a pair of photons
emitted in a decay cascade with partial "which path" ambiguity. We describe an
appropriate entanglement distillation scheme which works also for certain
random cascades. The qualitative features of the distilled entanglement are
presented in a two dimensional "phase diagram". The theory is applied to the
quantum tomography of the decay cascade of a biexciton in a semiconductor
quantum dot. Agreement with experiment is obtained
Banking activity in the conditions of economy digitalization
В економічній сфері фінансовий сектор є лідером з впровадження та використання інноваційних технологій.
Метою дослідження є визначення змін і тенденцій у банківській сфері внаслідок діджиталізації економіки. Використано
такі загальнонаукові та спеціальні методи, як узагальнення, системний метод, статистичний аналіз, графічний метод.
В результаті проведеного дослідження розглянуто та узагальнено різні теоретичні підходи до тлумачення поняття
цифровізації, виокремлено характерні риси даного процесу та запропоновано власне визначення цифровізації у банку.
Визначено основні наслідки цифровізації банківського сектору, а також охарактеризовано нових конкурентів банківських
установ. Практична значимість отриманих результатів полягає в необхідності врахування банками окреслених тенденцій
розвитку фінансової сфери та перспектив співпраці з FinTech-компаніями.The reason for the digitalization of banking is the change in the economic environment of financial institutions caused
by the rapid development and introduction of information technologies. The purpose of the study is analysis of the economy
digitalization impact on banking. The study dealed with systematic approach, generalization, statistical analysis, graphic method,
expert estimates. The essence of digitalization concept, its purpose and ways of implementation are considered. Digitalization in
banking is the process of implementing innovative technological solutions in any sphere of banking activity in order to increase the
efficiency of banking and maintain a competitive position on the market. This will help banks increase their competitiveness and
profitability, as well as expand their customer base. The main prerequisites contributing to the implementation of digitalization
in the banking sector are highlighted. The result of the study is the determination of the active digitization consequences for the
financial and banking sector, such as an increase in the volume of non-cash transactions using payment cards and their structure
by types, a decrease in the number of structural divisions of banks, and an increase in competition in the banking sector due to
the appearance of new participants. The best examples in the essay are the new participants of the financial markets - BigTech,
neobanks and FinTech - which can act as competitors or partners for banks. The main point is the cooperation between the
banks and FinTech startups is mutually beneficial: the examples of such cooperation in Ukraine are discussed in the article. Our
investigation shows that the digital transformation of the banking business is an objective necessity for maintaining competitiveness
in the era of information technology. The practical significance of the obtained results lies in the need to take into account the
outlined trends in the development of the financial sphere by the banks and the prospects for cooperation with FinTech companies
Nanowire quantum dots tuned to atomic resonances
Quantum dots tuned to atomic resonances represent an emerging field of hybrid
quantum systems where the advantages of quantum dots and natural atoms can be
combined. Embedding quantum dots in nanowires boosts these systems with a set
of powerful possibilities, such as precise positioning of the emitters,
excellent photon extraction efficiency and direct electrical contacting of
quantum dots. Notably, nanowire structures can be grown on silicon substrates,
allowing for a straightforward integration with silicon-based photonic devices.
In this work we show controlled growth of nanowire-quantum-dot structures on
silicon, frequency tuned to atomic transitions. We grow GaAs quantum dots in
AlGaAs nanowires with a nearly pure crystal structure and excellent optical
properties. We precisely control the dimensions of quantum dots and their
position inside nanowires, and demonstrate that the emission wavelength can be
engineered over the range of at least around . By applying an
external magnetic field we are able to fine tune the emission frequency of our
nanowire quantum dots to the transition of Rb. We use the Rb
transitions to precisely measure the actual spectral linewidth of the photons
emitted from a nanowire quantum dot to be , under
non-resonant excitation. Our work brings highly-desirable functionalities to
quantum technologies, enabling, for instance, a realization of a quantum
network, based on an arbitrary number of nanowire single-photon sources, all
operating at the same frequency of an atomic transition.Comment: main text (20 pages, 3 figures) plus supplementary information, Nano
Letters (2018
Polarization sensitive spectroscopy of charged Quantum Dots
We present an experimental and theoretical study of the polarized
photoluminescence spectrum of single semiconductor quantum dots in various
charge states. We compare our high resolution polarization sensitive spectral
measurements with a new many-carrier theoretical model, which was developed for
this purpose. The model considers both the isotropic and anisotropic exchange
interactions between all participating electron-hole pairs. With this addition,
we calculate both the energies and polarizations of all optical transitions
between collective, quantum dot confined charge carrier states. We succeed in
identifying most of the measured spectral lines. In particular, the lines
resulting from singly-, doubly- and triply- negatively charged excitons and
biexcitons. We demonstrate that lines emanating from evenly charged states are
linearly polarized. Their polarization direction does not necessarily coincide
with the traditional crystallographic direction. It depends on the shells of
the single carriers, which participate in the recombination process.Comment: 11 pages, 9 figures. Revised versio
Detecting ionospheric TEC perturbations caused by natural hazards using a global network of GPS receivers: The Tohoku case study
Recent advances in GPS data processing have demonstrated that ground-based GPS receivers are capable of detecting ionospheric TEC perturbations caused by surface-generated Rayleigh, acoustic and gravity waves. There have been a number of publications discussing TEC perturbations immediately following the M 9.0 Tohoku earthquake in Japan on March 11, 2011. Most investigators have focused on the ionospheric responses up to a few hours following the earthquake and tsunami. In our research, in addition to March 11, 2011 we investigate global ionospheric TEC perturbations a day before and after the event. We also compare indices of geomagnetic activity on all three days with perturbations in TEC, revealing strong geomagnetic storm conditions that are also apparent in processed GEONET TEC observations. In addition to the traveling ionospheric disturbances (TIDs)produced by the earthquake and tsunami, we also detect “regular” TIDs across Japan about 5 hours following the Tohoku event, concluding these are likely due to geomagnetic activity. The variety of observed TEC perturbations are consistent with tsunami-generated gravity waves, auroral activity, regular TIDs and equatorial fluctuations induced by increased geomagnetic activity. We demonstrate our capabilities to monitor TEC fluctuations using JPL’s real-time Global Assimilative Ionospheric Model (GAIM) system. We show that a real-time global TEC monitoring network is able to detect the acoustic and gravity waves generated by the earthquake and tsunami. With additional real-time stations deployed, this new capability has the potential to provide real-time monitoring of TEC perturbations that could potentially serve as a plug-in to enhance existing early warning systems
Calculations of He+p Elastic Cross Sections Using Microscopic Optical Potential
An approach to calculate microscopic optical potential (OP) with the real
part obtained by a folding procedure and with the imaginary part inherent in
the high-energy approximation (HEA) is applied to study the He+p elastic
scattering data at energies of tens of MeV/nucleon (MeV/N). The neutron and
proton density distributions obtained in different models for He are
utilized in the calculations of the differential cross sections. The role of
the spin-orbit potential is studied. Comparison of the calculations with the
available experimental data on the elastic scattering differential cross
sections at beam energies of 15.7, 26.25, 32, 66 and 73 MeV/N is performed. The
problem of the ambiguities of the depths of each component of the optical
potential is considered by means of the imposed physical criterion related to
the known behavior of the volume integrals as functions of the incident energy.
It is shown also that the role of the surface absorption is rather important,
in particular for the lowest incident energies (e.g., 15.7 and 26.25
MeV/nucleon).Comment: 11 pages, 7 figures, accepted for publication in Physical Review
Charge and matter distributions and form factors of light, medium and heavy neutron-rich nuclei
Results of charge form factors calculations for several unstable neutron-rich
isotopes of light, medium and heavy nuclei (He, Li, Ni, Kr, Sn) are presented
and compared to those of stable isotopes in the same isotopic chain. For the
lighter isotopes (He and Li) the proton and neutron densities are obtained
within a microscopic large-scale shell-model, while for heavier ones Ni, Kr and
Sn the densities are calculated in deformed self-consistent mean-field Skyrme
HF+BCS method. We also compare proton densities to matter densities together
with their rms radii and diffuseness parameter values. Whenever possible
comparison of form factors, densities and rms radii with available experimental
data is also performed. Calculations of form factors are carried out both in
plane wave Born approximation (PWBA) and in distorted wave Born approximation
(DWBA). These form factors are suggested as predictions for the future
experiments on the electron-radioactive beam colliders where the effect of the
neutron halo or skin on the proton distributions in exotic nuclei is planned to
be studied and thereby the various theoretical models of exotic nuclei will be
tested.Comment: 26 pages, 11 figures, 3 tables, accepted for publication in Phys.
Rev.
Ionospheric Simulation System for Satellite Observations and Global Assimilative Modeling Experiments (ISOGAME)
ISOGAME is designed and developed to assess quantitatively the impact of new observation systems on the capability of imaging and modeling the ionosphere. With ISOGAME, one can perform observation system simulation experiments (OSSEs). A typical OSSE using ISOGAME would involve: (1) simulating various ionospheric conditions on global scales; (2) simulating ionospheric measurements made from a constellation of low-Earth-orbiters (LEOs), particularly Global Navigation Satellite System (GNSS) radio occultation data, and from ground-based global GNSS networks; (3) conducting ionospheric data assimilation experiments with the Global Assimilative Ionospheric Model (GAIM); and (4) analyzing modeling results with visualization tools. ISOGAME can provide quantitative assessment of the accuracy of assimilative modeling with the interested observation system. Other observation systems besides those based on GNSS are also possible to analyze. The system is composed of a suite of software that combines the GAIM, including a 4D first-principles ionospheric model and data assimilation modules, an Internal Reference Ionosphere (IRI) model that has been developed by international ionospheric research communities, observation simulator, visualization software, and orbit design, simulation, and optimization software. The core GAIM model used in ISOGAME is based on the GAIM++ code (written in C++) that includes a new high-fidelity geomagnetic field representation (multi-dipole). New visualization tools and analysis algorithms for the OSSEs are now part of ISOGAME
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