5,375 research outputs found
Automated background subtraction technique for electron energy-loss spectroscopy and application to semiconductor heterostructures
Electron energy-loss spectroscopy (EELS) has become a stan-dard tool for identification and sometimes also quantificationof elements in materials science. This is important for un-derstanding the chemical and/or structural composition ofprocessed materials. In EELS, the background is often mod-elled using an inverse power-law function. Core-loss ioniza-tion edges are superimposed on top of the dominating back-ground, making it difficult to quantify their intensities. Theinverse power-law has to be modelled for each pre-edge regionof the ionization edges in the spectrum individually ratherthan for the entire spectrum. To achieve this, the prerequisiteis that one knows all core losses possibly present. The aim ofthis study is to automatically detect core-loss edges, model thebackground and extract quantitative elemental maps and pro-files of EELS, based on several EELS spectrum images (EELS SI)without any prior knowledge of the material. The algorithmprovides elemental maps and concentration profiles by makingsmart decisions in selecting pre-edge regions and integrationranges. The results of the quantification for a semiconduc-tor thin film heterostructure show high chemical sensitivity,reasonable group III/V intensity ratios but also quantificationissues when narrow integration windows are used withoutdeconvolution
Strong-driving-assisted multipartite entanglement in cavity QED
We propose a method of generating multipartite entanglement by considering
the interaction of a system of N two-level atoms in a cavity of high quality
factor with a strong classical driving field. It is shown that, with a
judicious choice of the cavity detuning and the applied coherent field
detuning, vacuum Rabi coupling produces a large number of important
multipartite entangled states. It is even possible to produce entangled states
involving different cavity modes. Tuning of parameters also permits us to
switch from Jaynes-Cummings to anti-Jaynes-Cummings like interaction.Comment: Last version with minor changes and added references. Accepted for
publication in Phys. Rev. Letter
Heralded generation of entangled photon pairs
Entangled photons are a crucial resource for quantum communication and linear
optical quantum computation. Unfortunately, the applicability of many
photon-based schemes is limited due to the stochastic character of the photon
sources. Therefore, a worldwide effort has focused in overcoming the limitation
of probabilistic emission by generating two-photon entangled states conditioned
on the detection of auxiliary photons. Here we present the first heralded
generation of photon states that are maximally entangled in polarization with
linear optics and standard photon detection from spontaneous parametric
down-conversion. We utilize the down-conversion state corresponding to the
generation of three photon pairs, where the coincident detection of four
auxiliary photons unambiguously heralds the successful preparation of the
entangled state. This controlled generation of entangled photon states is a
significant step towards the applicability of a linear optics quantum network,
in particular for entanglement swapping, quantum teleportation, quantum
cryptography and scalable approaches towards photonics-based quantum computing
Binaural sound source localisation using a Bayesian-network-based blackboard system and hypothesis-driven feedback
An essential aspect of Auditory Scene Analysis is the localisation of sound sources in relation to the
position of the listener in the surrounding environment. The human auditory system is capable of
precisely locating and separating different sound sources, even in noisy and reverberant environments,
whereas mimicking this ability by computational means is still a challenging task. In this work, we
investigate a Bayesian-network-based approach in the context of binaural sound source localisation.
We extend existing solutions towards a Bayesian network based blackboard system that includes expert
knowledge inspired by insights into the human auditory system. In order to improve estimation
of source positions and reduce uncertainty caused by front-back ambiguities, hypothesis-driven feedback
is used. This is accomplished by triggering head movements based on inference results provided
by the Bayesian network. We evaluate the performance of our approach in comparison to existing
solutions in a sound-source localisation task within a virtual acoustic environment
Combining photonic crystal and optical Monte Carlo simulations: implementation, validation and application in a positron emission tomography detector
This paper presents a novel approach towards incorporating photonic crystals (PhCs) into optical Monte Carlo (MC) simulations. This approach affords modeling the full diffractive nature of PhCs including their reflection and transmission behavior as well as the manipulation of the photon trajectories through light scattering. The main purpose of this tool is to study the impact of PhCs on the light yield and timing performance of scintillator-based detectors for positron emission tomography (PET). To this end, the PhCs are translated into look-up tables and implemented into the optical MC algorithm. Our simulations are validated in optical experiments using PhC samples fabricated with electron beam lithography. The experimental results indicate that the simulations match the measurements within the accuracy of the experiments. The application of the combined simulation technique to a PET detector module predicts an increase of the total light yield by up to 23% for PhC coatings versus the reference without PhCs. Timing calculations reveal an improvement of the coincident resolving time by up to 6%. The results underline the potential of PhCs to improve light yield and timing of PET detector modules
Genuine Counterfactual Communication with a Nanophotonic Processor
In standard communication information is carried by particles or waves.
Counterintuitively, in counterfactual communication particles and information
can travel in opposite directions. The quantum Zeno effect allows Bob to
transmit a message to Alice by encoding information in particles he never
interacts with. The first suggested protocol not only required thousands of
ideal optical components, but also resulted in a so-called "weak trace" of the
particles having travelled from Bob to Alice, calling the scalability and
counterfactuality of previous proposals and experiments into question. Here we
overcome these challenges, implementing a new protocol in a programmable
nanophotonic processor, based on reconfigurable silicon-on-insulator waveguides
that operate at telecom wavelengths. This, together with our telecom
single-photon source and highly-efficient superconducting nanowire
single-photon detectors, provides a versatile and stable platform for a
high-fidelity implementation of genuinely trace-free counterfactual
communication, allowing us to actively tune the number of steps in the Zeno
measurement, and achieve a bit error probability below 1%, with neither
post-selection nor a weak trace. Our demonstration shows how our programmable
nanophotonic processor could be applied to more complex counterfactual tasks
and quantum information protocols.Comment: 6 pages, 4 figure
Measure of phonon-number moments and motional quadratures through infinitesimal-time probing of trapped ions
A method for gaining information about the phonon-number moments and the
generalized nonlinear and linear quadratures in the motion of trapped ions (in
particular, position and momentum) is proposed, valid inside and outside the
Lamb-Dicke regime. It is based on the measurement of first time derivatives of
electronic populations, evaluated at the motion-probe interaction time t=0. In
contrast to other state-reconstruction proposals, based on measuring Rabi
oscillations or dispersive interactions, the present scheme can be performed
resonantly at infinitesimal short motion-probe interaction times, remaining
thus insensitive to decoherence processes.Comment: 10 pages. Accepted in JPhys
Cryo-Preparation and Planar Magnetron Sputtering for Low Temperature Scanning Electron Microscopy
Cryo-preparation is a reliable technique for the structural investigation of food products in low temperature scanning electron microscopy (SEM). Artifacts, such as, the segregation of water/non-water ingredients, occur during the freezing process by the crystallization of ice; they can be helpful for correct interpretation of visualized details, e.g., the detection of water containing compartments. The size of the segregation structures depends on water concentration and specimen thickness. The condensation of water vapor (ice contamination) is influenced by the specimen temperature and the partial pressure of the water inside the vacuum system. Furthermore, the evaporation (sublimation, etching) of specimen water can be regulated by monitoring the specimen temperature. Sublimation under SEM observation, i.e., in situ etching at low acceleration voltage, allows the progress of etching to be observed continuously, prior to the coating of the specimen inside a dedicated cryo-preparation system attached to the SEM. Coating of specimens provides superior structural resolution compared with the observation of uncoated samples. A coating layer of platinum ( ~ 1-2 nm thick), deposited on a cold substrate by planar magnetron sputtering, is almost homogenous and has a density close to that of the solid metal. Its use allows bulk biological specimens to be observed in low temperature SEM with a structural resolution up to the visualization of transmembrane proteins
Cavity losses for the dissipative Jaynes-Cummings Hamiltonian beyond Rotating Wave Approximation
A microscopic derivation of the master equation for the
Jaynes-Cummings model with cavity losses is given, taking into account the
terms in the dissipator which vary with frequencies of the order of the vacuum
Rabi frequency. Our approach allows to single out physical contexts wherein the
usual phenomenological dissipator turns out to be fully justified and
constitutes an extension of our previous analysis [Scala M. {\em et al.} 2007
Phys. Rev. A {\bf 75}, 013811], where a microscopic derivation was given in the
framework of the Rotating Wave Approximation.Comment: 12 pages, 1 figur
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