1,606 research outputs found
Demonstration of a programmable source of two-photon multiqubit entangled states
We suggest and demonstrate a novel source of two-photon multipartite
entangled states which exploits the transverse spatial structure of spontaneous
parametric downconversion together with a programmable spatial light modulator
(SLM). The 1D SLM is used to perform polarization entanglement purification and
to realize arbitrary phase-gates between polarization and momentum degrees of
freedom of photons. We experimentally demonstrate our scheme by generating
two-photon three qubit linear cluster states with high fidelity using a diode
laser pump with a limited coherence time and power on the crystal as low as
2.5$mW.Comment: 5 pages, 4 figures, to appear on PR
Programmable entanglement oscillations in a non Markovian channel
We suggest and demonstrate an all-optical experimental setup to observe and
engineer entanglement oscillations of a pair of polarization qubits in a
non-Markovian channel. We generate entangled photon pairs by spontaneous
parametric downconversion (SPDC), and then insert a programmable spatial light
modulator in order to impose a polarization dependent phase-shift on the
spatial domain of the SPDC output and to create an effective non-Markovian
environment. Modulation of the enviroment spectrum is obtained by inserting a
spatial grating on the signal arm. In our experiment, programmable oscillations
of entanglement are achieved, with the maximally revived state that violates
Bell's inequality by 17 standard deviations.Comment: 4 pages, 4 figure
Programmable purification of type-I polarization-entanglement
We suggest and demonstrate a scheme to compensate spatial and spectral
decoherence effects in the generation of polarization entangled states by
type-I parametric downconversion. In our device a programmable spatial light
modulator imposes a polarization dependent phase-shift on different spatial
sections of the overall downconversion output and this effect is exploited to
realize an effective purification technique for polarization entanglement.Comment: published versio
Optical interferometry in the presence of large phase diffusion
Phase diffusion represents a crucial obstacle towards the implementation of
high precision interferometric measurements and phase shift based communication
channels. Here we present a nearly optimal interferometric scheme based on
homodyne detection and coherent signals for the detection of a phase shift in
the presence of large phase diffusion. In our scheme the ultimate bound to
interferometric sensitivity is achieved already for a small number of
measurements, of the order of hundreds, without using nonclassical light
Experimental estimation of one-parameter qubit gates in the presence of phase diffusion
We address estimation of one-parameter qubit gates in the presence of phase
diffusion. We evaluate the ultimate quantum limits to precision, seek for
optimal probes and measurements, and demonstrate an optimal estimation scheme
for polarization qubits. An adaptive method to achieve optimal estimation in
any working regime is also analyzed in details and experimentally implemented.Comment: revised version, to appear on PR
Distributed Storage for the Provision of Ancillary Services to the Main Grid: Project PRESTO
AbstractThis paper presents the three-year PRESTO research project (2013-2015). PRESTO is a self-funded project developed by the Department of Energy of Politecnico di Milano in cooperation with FIAMM Storage, Elvi Energy and MCM Energy Lab (an Italian spin-off). Within the project, experimental tests and numerical simulations were performed in order to evaluate the effectiveness of an Energy Storage System (ESS) in the provision of ancillary services to the main grid. This paper focuses specifically on the experimental and numerical analyses carried out in the project to develop an innovative control law for the primary frequency regulation, able to maximize the performances of the regulating service and effectively manage the ESS state of charge
Towards a random laser with cold atoms
Atoms can scatter light and they can also amplify it by stimulated emission.
From this simple starting point, we examine the possibility of realizing a
random laser in a cloud of laser-cooled atoms. The answer is not obvious as
both processes (elastic scattering and stimulated emission) seem to exclude one
another: pumping atoms to make them behave as amplifier reduces drastically
their scattering cross-section. However, we show that even the simplest atom
model allows the efficient combination of gain and scattering. Moreover,
supplementary degrees of freedom that atoms offer allow the use of several gain
mechanisms, depending on the pumping scheme. We thus first study these
different gain mechanisms and show experimentally that they can induce
(standard) lasing. We then present how the constraint of combining scattering
and gain can be quantified, which leads to an evaluation of the random laser
threshold. The results are promising and we draw some prospects for a practical
realization of a random laser with cold atoms.Comment: Accepcted for publication by J. Opt. A for the special issue on
nanolasers and random lasers (to be published early 2010
Threshold of a random laser based on Raman gain in cold atoms
We address the problem of achieving a random laser with a cloud of cold
atoms, in which gain and scattering are provided by the same atoms. In this
system, the elastic scattering cross-section is related to the complex atomic
polarizability. As a consequence, the random laser threshold is expressed as a
function of this polarizability, which can be fully determined by spectroscopic
measurements. We apply this idea to experimentally evaluate the threshold of a
random laser based on Raman gain between non-degenerate Zeeman states and find
a critical optical thickness on the order of 200, which is within reach of
state-of-the-art cold-atom experiments
Determination of the anisotropic permeability of a carbon cloth gas diffusion layer through X-ray computer micro-tomography and single-phase lattice Boltzmann simulation
An investigation of the anisotropic permeability of a carbon cloth gas diffusion layer (GDL) based on the integration of X-ray micro-tomography and lattice Boltzmann (LB) simulation is presented. The method involves the generation of a 3D digital model of a carbon cloth GDL as manufactured using X-ray shadow images acquired through X-ray micro-tomography at a resolution of 1.74 µm. The resulting 3D model is then split into 21 volumes and integrated with a LB single-phase numerical solver in order to predict three orthogonal permeability tensors when a pressure difference is prescribed in the through-plane direction. The 21 regions exhibit porosity values in the range of 0.910–0.955, while the average fibre diameter is 4 µm. The results demonstrate that the simulated through-plane permeability is about four times higher than the in-plane permeability for the sample imaged and that the corresponding degrees of anisotropy for the two orthogonal off-principal directions are 0.22 and 0.27. The results reveal that flow channelling can play an important role in gas transport through the GDL structure due to the non-homogeneous porosity distribution through the material. The simulated results are also applied to generate a parametric coefficient for the Kozeny–Carman (KC) method of determining permeability. The current research reveals that by applying the X-ray tomography and LB techniques in a complementary manner, there is a strong potential to gain a deeper understanding of the microscopic fluidic phenomenon in representative models of porous fuel cell structures and how this can influence macroscopic transport characteristics which govern fuel cell performance
A novel method to investigate how the spatial correlation of the pump beam affects the purity of polarization entangled states
We present an innovative method to address the relation between the purity of
type-I polarization entangled states and the spatial properties of the pump
laser beam. Our all-optical apparatus is based on a spatial light modulator,
and it offers unprecedented control on the spatial phase function of the
entangled states. In this way, we demonstrate quantitatively the relation
between the purity of the generated state and spatial correlation function of
the pump beam.Comment: 3 pages, 3 figure
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