273 research outputs found
Physics-based simulation of narrow and wide band gap photonic devices
Historically, infrared (IR) detector technologies are connected mainly with controlling and night-vision problems: in a first stage, applications concerned simply with detection of IR radiation, but very soon capabilities to form IR images were developed, opening the way to systems for recognition and surveillance, especially for military purposes. Since the last decade of the twentieth century, the use of IR imaging systems for civil and peaceful purposes have increased continuously: these include medical and industrial applications, detection of earth resources, earth and universe sciences, etc. As an example, IR imaging is widely used in astronomy, to study interstellar medium and first-stages of stellar evolution; in medicine, IR thermography – IR imaging of the human body – is employed to detect cancers or other trauma; IR detectors are also widely used in automotive industry, chemical process monitoring, global monitoring of environmental pollution and climate changes, etc. The discovery in 1959 by Lawson and co-workers of the wide tunability of the HgCdTe alloy allowed this compound to become one of the most important and versatile materials for detector applications over the entire IR range. A critical contribution to research is given by Technology Computer-Aided Design (TCAD), modeling and simulation. In the first part of this thesis, I present the main part of my research activity, focused on the development of abilities and methodologies for the simulation of realistic three-dimensional HgCdTe-based infrared photodetectors. The purpose is the investigation of generation-recombination (GR) mechanisms and modeling of spectral photoresponse in narrow-gap HgCdTe-based photodetectors, with one-, two and three-dimensional (1D, 2D, 3D) realistic TCAD models (Chapters 1-5).
Another important topic of industrial research in semiconductor physics deals with nitride-based light-emitting diodes (LEDs). From automotive to streetlights, from lights in our houses to the displays of TVs and smartphones, LED-based technology is making its way in the market. This proliferation would have been impossible without GaN-based LEDs, whose invention by Isamu Akasaki, Hiroshi Amano and Shuji Nakamura has been rewarded with the 2014 Nobel Prize in Physics. Nevertheless, GaN-based LEDs performanceis limited by a reduction (droop) of their internal quantum efficiency (IQE) as the driving current density is increased beyond 10 A/cm2, whose physical origin is still under intense debate. In the second part of this thesis, I present a quantum model, based on condensed matter many-body theory, that allowed to obtain the electron capture time and hot-electron intraband relaxation times in a quantum well (QW)-barrier heterostructure, for longitudinal optic (LO) phonon emission, as function of carrier density. The interaction was described in the Single Plasmon Pole of the Random Phase Approximation, retaining the full density-, energy- and wavevector-dependent form of the dielectric function (Chapters 6-7)
Loss tolerant device-independent quantum key distribution: a proof of principle
We here present the rate analysis and a proof of principle realization of a
device-independent quantum key distribution (QKD) protocol requiring the lowest
detection efficiency necessary to achieve a secure key compared to
device-independent protocols known so far. The protocol is based on
non-maximally entangled state and its experimental realization has been
performed by two-photon bipartite entangled states. The improvement with
respect to protocols involving maximally entangled states has been estimated.Comment: 8 pages, 4 figure + appendi
Source-device-independent heterodyne-based quantum random number generator at 17 Gbps
For many applications, quantum random number generation should be fast and independent from assumptions on the apparatus. Here, the authors devise and implement an approach which assumes a trusted detector but not a trusted source, and allows random bit generations at ~17 Gbps using off-the-shelf components
Experimental Realization of Polarization Qutrits from Non-Maximally Entangled States
Based on a recent proposal [Phys. Rev. A 71, 062337 (2005)], we have
experimentally realized two photon polarization qutrits by using non-maximally
entangled states and linear optical transformations. By this technique high
fidelity mutually unbiased qutrits are generated at a high brilliance level.Comment: RevTex, 8 pages, 6 figure
High-Visibility Time-Bin Entanglement for Testing Chained Bell Inequalities
The violation of Bell's inequality requires a well-designed experiment to
validate the result. In experiments using energy-time and time-bin
entanglement, initially proposed by Franson in 1989, there is an intrinsic
loophole due to the high postselection. To obtain a violation in this type of
experiment, a chained Bell inequality must be used. However, the local realism
bound requires a high visibility in excess of 94.63 percent in the time-bin
entangled state. In this work, we show how such a high visibility can be
reached in order to violate a chained Bell inequality with 6, 8 and 10 terms.Comment: 8 pages, 4 figure
Fast and simple qubit-based synchronization for quantum key distribution
We propose Qubit4Sync, a synchronization method for Quantum Key Distribution
(QKD) setups, based on the same qubits exchanged during the protocol and
without requiring additional hardware other than the one necessary to prepare
and measure the quantum states. Our approach introduces a new cross-correlation
algorithm achieving the lowest computational complexity, to our knowledge, for
high channel losses. We tested the robustness of our scheme in a real QKD
implementation
Trench width dependant deeply etched surface-defined InP gratings for low-cost high speed DFB/DBR
In this paper we are reporting a fabrication process for multi-section telecom lasers based on surface defined lateral gratings, which is compatible with low-cost high-throughput nano-imprint lithography. A new grating definition process is developed, which allow a better control of the cross section geometry to obtain higher coupling strength
Interference at the Single Photon Level Along Satellite-Ground Channels
Quantum interference arising from superposition of states is a striking
evidence of the validity of Quantum Mechanics, confirmed in many experiments
and also exploited in applications. However, as for any scientific theory,
Quantum Mechanics is valid within the limits in which it has been
experimentally verified. In order to extend such limits, it is necessary to
observe quantum interference in unexplored conditions such as moving terminals
at large distance in Space. Here we experimentally demonstrate single photon
interference at a ground station due to the coherent superposition of two
temporal modes reflected by a rapidly moving satellite thousand kilometers
away. The relative speed of the satellite induces a varying modulation in the
interference pattern. The measurement of the satellite distance in real time by
laser ranging allowed us to precisely predict the instantaneous value of the
interference phase. We then observed the interference patterns with visibility
up to with three different satellites and with path length up to 5000
km. Our results attest the viability of photon temporal modes for fundamental
tests of Physics and Quantum Communications in Space.Comment: Version accepted for publication in Phys. Rev. Let
Elucidating molecular connetion between IAHSP onset and Alsin protein by means of Homology Modelling and Molecular Dynamics
The Infantile-onset Ascending Hereditary Spastic Paralysis (IAHSP) is an incurable rare neurodegerative disease related to a mutation-driven aberrant behaviour of the Alsin protein. The lack of information on Alsin atomic structure limits a complete understanding on pathology mechanisms. In this work, molecular modelling techniques have been applied to shed lights on Alsin folding dynamics and misfunction induced by aberrant mutations
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