190 research outputs found
Planetary stations and Abyssal Benthic Laboratories: An overview of parallel approaches for long-term investigation in extreme environments
In spite of the apparent great differences between deep ocean and space environment, significant similarities can be recognized when considering the possible solutions and technologies enabling the development of remote automatic stations supporting the execution of scientific activities. In this sense it is believed that mutual benefits shall be derived from the exchange of experiences and results between people and organizations involved in research and engineering activities for hostile environments, such as space, deep sea, and polar areas. A significant example of possible technology transfer and common systematic approach is given, which describes in some detail how the solutions and the enabling technologies identified for an Abyssal Benthic Laboratory can be applied for the case of a lunar or planetary station
Realization of a Knill-Laflamme-Milburn C-NOT gate -a photonic quantum circuit combining effective optical nonlinearities
Quantum information science addresses how uniquely quantum mechanical
phenomena such as superposition and entanglement can enhance communication,
information processing and precision measurement. Photons are appealing for
their low noise, light-speed transmission and ease of manipulation using
conventional optical components. However, the lack of highly efficient optical
Kerr nonlinearities at single photon level was a major obstacle. In a
breakthrough, Knill, Laflamme and Milburn (KLM) showed that such an efficient
nonlinearity can be achieved using only linear optical elements, auxiliary
photons, and measurement. They proposed a heralded controlled-NOT (CNOT) gate
for scalable quantum computation using a photonic quantum circuit to combine
two such nonlinear elements. Here we experimentally demonstrate a KLM CNOT
gate. We developed a stable architecture to realize the required four-photon
network of nested multiple interferometers based on a displaced-Sagnac
interferometer and several partially polarizing beamsplitters. This result
confirms the first step in the KLM `recipe' for all-optical quantum
computation, and should be useful for on-demand entanglement generation and
purification. Optical quantum circuits combining giant optical nonlinearities
may find wide applications across telecommunications and sensing.Comment: 6pages, 3figure
An Algebraic Approach to Linear-Optical Schemes for Deterministic Quantum Computing
Linear-Optical Passive (LOP) devices and photon counters are sufficient to
implement universal quantum computation with single photons, and particular
schemes have already been proposed. In this paper we discuss the link between
the algebraic structure of LOP transformations and quantum computing. We first
show how to decompose the Fock space of N optical modes in finite-dimensional
subspaces that are suitable for encoding strings of qubits and invariant under
LOP transformations (these subspaces are related to the spaces of irreducible
unitary representations of U(N)). Next we show how to design in algorithmic
fashion
LOP circuits which implement any quantum circuit deterministically. We also
present some simple examples, such as the circuits implementing a CNOT gate and
a Bell-State Generator/Analyzer.Comment: new version with minor modification
Les perles dâĂ©mail: aspects ultrastructuraux et hypothĂšses de morphogenĂšse
Five enamel pearls were examined by Scanning Electron Microscope. Some external pearls presented a bare enamel surface, others were covered by a thin layer of cementum.The enamel pearls showed irregular dystrofic enamel surface or a thin layer without structure, rows of irregular Tomeâs processes pits, enamel caps and focal holes. Some enamel pearls revealed little areas of enamel surface resorption like-resorbing lacunae with, in some cases, areas of tissue repair.La perle dâĂ©mail est une masse circulaire de matĂ©riel calcifiĂ© qui apparait le plus souvent dans la bifurcation des molaires et est attachĂ©e Ă la surface externe de la dent. Elle peut aussi ĂȘtre interne mais nous en savons trĂšs peu Ă ce sujet Ă cause du manque de publications. Cinq perles externes ont Ă©tĂ© observĂ©es au microscope Ă©lectronique Ă balayage.Tandis que certaines perles externes prĂ©sentent une surface Ă nu, dâautres sont recouvertes dâune fine couche de cĂ©ment qui les protĂšge. La surface de la perle dâĂ©mail prĂ©sente des zones irrĂ©guliĂšres dâhypominĂ©ralisation ou une fine couche sans structure, des rangĂ©es de petits trous irrĂ©guliers des processus de Tome et des trous focaux et des cratĂšres
SAS multipass interferometry for monitoring seabed deformation using a high-frequency imaging sonar
Abstract-. This paper presents the results of a two years project led and funded by Eni from 2008 to 2010 with the aim of supporting
the development and experimentation of innovative technology for environmental monitoring. The problem addressed is the precise estimate of possible altimetric variations of the seabed through long-term monitoring. The selected methodology consists in the application of repeat-track interferometry to high-resolution, high-frequency sonar data collected from an AUV during repeated surveys of a seafloor area of interest. The paper describes the experimental measurements conducted at sea, the SAS and interferometry methodologies developed, and the results obtained on artificial objects sitting on the seabed. The quality of the achieved focusing is analyzed. The achieved repeat-pass SAS interferograms are shown and analyzed. The coherence along time of the particular
kind of seabed (silty sand) characterizing the experimental area is presented and the utility of artificial reflectors for long-term SAS interferometry is discussed.Published673-6832.5. Laboratorio per lo sviluppo di sistemi di rilevamento sottomariniN/A or not JCRreserve
NEMO-SN1 (Western Ionian Sea, off Eastern Sicily): A Cabled Abyssal Observatory with Tsunami Early Warning Capability
The NEMO-SN1 (NEutrino Mediterranean Observatory - Submarine
Network 1) seafloor observatory is located in the central
Mediterranean, Western Ionian Sea, off Eastern Sicily Island (Southern
Italy) at 2100 m water depth, 25 km from the harbour of the city of
Catania. It is a prototype of cabled deep-sea multiparameter
observatory, and the first operating with real-time data transmission in
Europe since 2005. NEMO-SN1 is also the first-established node of
EMSO (European Multidisciplinary Seafloor Observatory,
http://emso-eu.org), one of the European large-scale research
infrastructures. EMSO will address long-term monitoring of
environmental processes related to marine ecosystems, climate change
and geo-hazards. NEMO-SN1 will perform geophysical and
environmental long-term monitoring by acquiring seismological,
geomagnetic, gravimetric, accelerometric, physico-oceanographic,
hydro-acoustic, bio-acoustic measurements to study earthquake and
tsunami generation, and to characterize ambient noise which includes
marine mammal sounds, and environmental and anthropogenic sources.
NEMO-SN1 is also equipped with a prototype tsunami detector, based
on the simultaneous measurement of the seismic and bottom pressure
signals and a new high performance tsunami detection algorithm.
NEMO-SN1 will be a permanent tsunami early warning node in
Western Ionian Sea, an area where very destructive earthquakes have
occurred in the past, some of them tsunamigenic (e.g., 1693, M=7.5;
1908, M=7.4).
Another important feature of NEMO-SN1 is the installation of a low
frequency-high sensibility hydrophone and two (scalar and vector,
respectively) magnetometers. The objective is to improve the tsunami
detection capability of SN1 through the recognition of tsunami-induced
hydro-acoustic and electro-magnetic precursors.SubmittedRhodes, Greece3A. Ambiente Marinorestricte
An innovative tsunami detector operating in tsunami generation environment
On August 25th 2007 a tsunami detector installed onboard the multi-parameter observatory GEOSTAR was successfully deployed at 3200 b. s. l. in the Gulf of Cadiz, Portugal. This activity is within the NEAREST EC Project (http://nearest.bo.ismar.cnr.it/ ). Among other deliverables, the NEAREST project will produce and test the basic parts of an operational prototype of a near field tsunami warning system. This system includes an onshore warning centre, based on the geophysical monitoring networks which are already operating, and a tsunami detector deployed on board GEOSTAR at the sea bottom. On land the warning centre is in charge of collecting, integrating, and evaluating data recorded at sea. At the sea bottom data is recorded and processed by an advanced type of tsunami detector which includes: a pressure sensor, a seismometer and two accelerometers. The detector communicates acoustically with a surface buoy in two-way mode. The buoy is equipped with meteo station, GPS and tiltmeter and is connected to a shore station via satellite link. The prototype is designed to operate in tsunami generation areas for detection-warning purpose as well as for scientific measurements. The tsunami detector sends a near real time automatic alert message when a seismic or pressure threshold are exceeded. Pressure signals are processed by the tsunami detection algorithm and the water pressure perturbation caused by the seafloor motion is taken into account. The algorithm is designed to detect small tsunami waves, less than one centimetre, in a very noisy environment. Our objective is to combine a novel approach to the tsunami warning problem, with a study of the coupling between the water column perturbations and sea floor motion, together with the long term monitoring of geophysical, geochemical and oceanographic parameters
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
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