237 research outputs found
Microoptical Realization of Arrays of Selectively Addressable Dipole Traps: A Scalable Configuration for Quantum Computation with Atomic Qubits
We experimentally demonstrate novel structures for the realisation of
registers of atomic qubits: We trap neutral atoms in one and two-dimensional
arrays of far-detuned dipole traps obtained by focusing a red-detuned laser
beam with a microfabricated array of microlenses. We are able to selectively
address individual trap sites due to their large lateral separation of 125 mu
m. We initialize and read out different internal states for the individual
sites. We also create two interleaved sets of trap arrays with adjustable
separation, as required for many proposed implementations of quantum gate
operations
Atom Optics with Microfabricated Optical Elements
We introduce a new direction in the field of atom optics, atom interferometry, and neutral-atom quantum information processing. It is based on the use of microfabricated optical elements. With these elements versatile and integrated atom optical devices can be created in a compact fashion. This approach opens the possibility to scale, parallelize, and miniaturize atom optics for new investigations in fundamental research and application. It will lead to new, compact sources of ultracold atoms, compact sensors based on matter wave interference and new approaches towards quantum computing with neutral atoms. The exploitation of the unique features of the quantum mechanical behavior of matter waves and the capabilities of powerful state-of-the-art micro- and nanofabrication techniques lend this approach a special attraction
Coherent Patterning of Matter Waves with Subwavelength Localization
We propose the Subwavelength Localization via Adiabatic Passage (SLAP)
technique to coherently achieve state-selective patterning of matter waves well
beyond the diffraction limit. The SLAP technique consists in coupling two
partially overlapping and spatially structured laser fields to three internal
levels of the matter wave yielding state-selective localization at those
positions where the adiabatic passage process does not occur. We show that by
means of this technique matter wave localization down to the single nanometer
scale can be achieved. We analyze in detail the potential implementation of the
SLAP technique for nano-lithography with an atomic beam of metastable Ne* and
for coherent patterning of a two-component 87Rb Bose-Einstein condensate.Comment: 6 pages, 5 figure
Atomtronics with holes: Coherent transport of an empty site in a triple well potential
We investigate arrays of three traps with two fermionic or bosonic atoms. The
tunneling interaction between neighboring sites is used to prepare multi-site
dark states for the empty site, i.e., the hole, allowing for the coherent
manipulation of its external degrees of freedom. By means of an ab initio
integration of the Schr\"odinger equation, we investigate the adiabatic
transport of a hole between the two extreme traps of a triple-well potential.
Furthermore, a quantum-trajectory approach based on the de Broglie-Bohm
formulation of quantum mechanics is used to get physical insight into the
transport process. Finally, we discuss the use of the hole for the construction
of a coherent single hole diode and a coherent single hole transistor.Comment: 9 pages, 6 figure
Mapping of the range of operational conditions for Cu-, Fe-, and Ni-based oxygen carriers in chemical-looping combustion
Available online September 14, 2006.- El pdf del artÃculo es la versión post-printChemical-looping combustion (CLC) is a two-step combustion process that produces a pure CO2 stream, ready for compression and sequestration. A CLC system is composed by two reactors, an air and a fuel reactor, and an oxygen carrier (OC) circulating between the reactors, which transfers the oxygen necessary for the fuel combustion from the air to the fuel. This system can be designed similar to a circulating fluidised bed, but with the addition of a bubbling fluidised bed on the return side. A mapping of the range of operational conditions, design values, and OC characteristics is presented for the most usual metal oxides (CuO, Fe2O3, and NiO) and different fuel gases (CH4, H2, and CO). The pressure operation of a CLC system is also considered. Moreover, a comparison of the possible use of three high reactive OCs (Cu10Al-I, Fe45Al-FG, Ni40Al-FG) previously characterised is carried out. It was found that the circulation rates and the solids inventories are linked, and the possible operating conditions are closely dependent on the reactivity of the OCs. The operational limits of the solids circulation rates, given by the mass and heat balances in the system, were defined for the different type of OCs. Moreover, a plot to calculate the solids inventories in a CLC system, valid for any type of OC and fuel gas, is proposed. The minimum solids inventories depended on the fuel gas used, and followed the order CH4 > CO > H2. Values of minimum solids inventories in a range from 40 to 133 kg / MWf were found for the OCs used in this work, excepting for the reaction of Fe45Al-FG with CH4, which needs a higher amount of solids because of its low reactivity. From the economic analysis carried out it was found the cost of the OC particles does not represent any limitation to the development of the CLC technology. © 2006 Elsevier Ltd. All rights reserved.This work was carried out with financial support from the European Coal and Steel Community (Project 7220-PR/125), and the Spanish Ministry of Education and Science (Project CTQ2004- 04034).Peer Reviewe
Kinetic and morphological differentiation of Ettringites in plain and blended Portland cements using Metakaolin and the ASTM C 452-68 test. Part I: kinetic differentiation.
22 pages, 3 figures, 5 tables.[ES] En esta Parte I de la investigación, se han logrado verifi-
car mediante el ensayo ASTM C 452-68, los resultados
obtenidos en anteriores investigaciones realizadas con
DRX y SEM y el ensayo Le Chatelier-Ansttet. Para ello, a
10 cementos Portland –6 CPO y 4 CPRS– se les añadió
20%, 30% y 40% de metakaolÃn (MK). Tanto los 10 CP
como los 30 de sus mezclas con metakaolÃn (MK), se
ensayaron durante 2 años, mediante dicho método ASTM
C 452-68, y a sus probetas no sólo se les determinó su
incremento porcentual de longitud, ∆L(%), sino además,
el contenido de sulfatos de sus aguas de conservación.
Otras determinaciones complementarias fueron: análisis
quÃmico de los materiales cementiceos utilizados y pro-
piedades especÃficas de algunos cementos ensayados.
Los resultados experimentales, ∆L(%) frente al tiempo,
han confirmado de nuevo que la velocidad de formación
de la ettringita de origen alúmina reactiva, Al2O3 r-, de las
puzolanas, tiene que ser considerablemente mayor que la
velocidad de formación de la ettringita de origen C3A de
los CP, lo que ha sido verificado por la evolución durante
todo el ensayo, del contenido de sulfatos de las aguas de
conservación de las probetas. Debido a ello, se ha pro-
puesto denominar a ambos tipos de ettringitas, ettringita
de rápida formación, ett-rf, y ettringita de lenta forma-
ción, ett-lf, respectivamente.[EN] In this first part of the study, the results obtained in prior
research with XRD and SEM, as well as the Le Chatelier-
Ansttet test were confirmed with the ASTM C 452-68 test.
To this end, 20%, 30% and 40% metakaolin (MK) was
added to ten Portland cements, six OPCs and four SRPCs.
Both the ten plain PCs and the 30 metakaolin (MK) blends
were tested for two years under ASTM C 452-68 specifications,
determining not only the percentage increase in
length, ΔL(%), of the specimens, but also the sulphate
content in the curing water. Other parameters studied
included: chemical analysis of the cementitious materials
used and specific properties of some of the cements tested.
The experimental results, ΔL(%) versus time, re-confirmed
that the formation rate of ettringite from the reactive
alumina, Al2O3
r-, present in the pozzolan must be substantially
higher than the formation rate of ettringite from
the C3A present in the PC. This was verified by the variation
of the sulphate content in the specimen curing water
throughout the test. In light of those findings, in this article
these two types of ettringite are denominated rapid
forming ettringite or ett-rf, and slow forming ettringite
or ett-lf.Peer reviewe
Coherent manipulation of atomic qubits in optical micropotentials
We experimentally demonstrate the coherent manipulation of atomic states in
far-detuned dipole traps and registers of dipole traps based on two-dimensional
arrays of microlenses. By applying Rabi, Ramsey, and spin-echo techniques, we
systematically investigate the dephasing mechanisms and determine the coherence
time. Simultaneous Ramsey measurements in up to 16 dipole traps are performed
and proves the scalability of our approach. This represents an important step
in the application of scalable registers of atomic qubits for quantum
information processing. In addition, this system can serve as the basis for
novel atomic clocks making use of the parallel operation of a large number of
individual clocks each remaining separately addressable.Comment: to be published in Appl. Phys.
Implications of SU(2) symmetry on the dynamics of population difference in the two-component atomic vapor
We present an exact many body solution for the dynamics of the population
difference induced by an rf-field in the two-component atomic cloud
characterized by equal scattering lengths. This situation is very close to the
actual JILA experiments with the two-component Rb vapor. We show that no
intrinsic decoherence exists for , provided the exact SU(2) symmetry
holds. This contrasts with finite dissipation of the normal modes even in the
presence of the SU(2) symmetry. The intrinsic decoherence for \ may
occur as long as deviations from the exact SU(2) symmetry are taken into
account. Such decoherence, however, should be characterized by very long times
governed by the smallness of the deviations from the symmetry. We suggest
testing the evolution of by conducting echo-type experiments.Comment: 5 RevTex pages, no figures, typos correcte
Multiple micro-optical atom traps with a spherically aberrated laser beam
We report on the loading of atoms contained in a magneto-optic trap into
multiple optical traps formed within the focused beam of a CO_{2} laser. We
show that under certain circumstances it is possible to create a linear array
of dipole traps with well separated maxima. This is achieved by focusing the
laser beam through lenses uncorrected for spherical aberration. We demonstrate
that the separation between the micro-traps can be varied, a property which may
be useful in experiments which require the creation of entanglement between
atoms in different micro-traps. We suggest other experiments where an array of
these traps could be useful.Comment: 10 pages, 3 figure
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