1,563 research outputs found
A quantum delayed choice experiment
Quantum systems exhibit particle-like or wave-like behaviour depending on the
experimental apparatus they are confronted by. This wave-particle duality is at
the heart of quantum mechanics, and is fully captured in Wheeler's famous
delayed choice gedanken experiment. In this variant of the double slit
experiment, the observer chooses to test either the particle or wave nature of
a photon after it has passed through the slits. Here we report on a quantum
delayed choice experiment, based on a quantum controlled beam-splitter, in
which both particle and wave behaviours can be investigated simultaneously. The
genuinely quantum nature of the photon's behaviour is tested via a Bell
inequality, which here replaces the delayed choice of the observer. We observe
strong Bell inequality violations, thus showing that no model in which the
photon knows in advance what type of experiment it will be confronted by, hence
behaving either as a particle or as wave, can account for the experimental
data
Some remarks on the spectral functions of the Abelian Higgs Model
We consider the unitary Abelian Higgs model and investigate its spectral
functions at one-loop order. This analysis allows to disentangle what is
physical and what is not at the level of the elementary particle propagators,
in conjunction with the Nielsen identities. We highlight the role of the
tadpole graphs and the gauge choices to get sensible results. We also introduce
an Abelian Curci-Ferrari action coupled to a scalar field to model a massive
photon which, like the non-Abelian Curci-Ferarri model, is left invariant by a
modified non-nilpotent BRST symmetry. We clearly illustrate its non-unitary
nature directly from the spectral function viewpoint. This provides a
functional analogue of the Ojima observation in the canonical formalism: there
are ghost states with nonzero norm in the BRST-invariant states of the
Curci-Ferrari model.Comment: 32 pages, 12 figure
The nonrelativistic limit of the Majorana equation and its simulation in trapped ions
We analyze the Majorana equation in the limit where the particle is at rest.
We show that several counterintuitive features, absent in the rest limit of the
Dirac equation, do appear. Among them, Dirac-like positive energy solutions
that turn into negative energy ones by free evolution, or nonstandard
oscillations and interference between real and imaginary spinor components for
complex solutions. We also study the ultrarelativistic limit, showing that the
Majorana and Dirac equations mutually converge. Furthermore, we propose a
physical implementation in trapped ions.Comment: 7 pages, 1 figure. Proceedings of 18th Central European Workshop on
Quantum Optics (CEWQO 2011), Madrid, Spai
Quality assurance for CMS Tracker LV and HV Power Supplies
This work describes the quality assurance measurements that have been carried out on about 2000 Power Supply Units produced in CAEN technology for the CMS Silicon Tracker Detector. The automate procedure and the characteristics of the dedicated Test Fixture developed for this activity are described in details. Magnetic field tolerance and radiation hardness of Tracker power supply units is also discussed at length
Design of the new electromagnetic measurement system for RFX-mod upgrade
A major modification of the RFX-mod toroidal load assembly has been decided in order to improve passive MHD control and to minimize the braking torque on the plasma, thus extending the operational space in both RFP and Tokamak configurations. With the removal of the vacuum vessel, the support structure will be modified in order to obtain a new vacuum-tight chamber and the first wall tiles will be directly in front of the passive stabilizing shell inside of it, so increasing both the poloidal cross section and the plasma-shell proximity.
This implies the design of a new vacuum fit electromagnetic measurement system. The new local probes will be installed in vacuum onto the copper shell, behind the graphite tiles, and shall operate up to a maximum temperature of 180\ub0C to allow for baking cycles for first wall conditioning. Because of the reduced room available, tri-axial pickup probes have been designed, with the additional advantage of allowing the minimization of alignment errors.
The paper describes the detailed design of the new probe set, in particular highlighting advantages and effectiveness of different probe solutions. Preliminary tests carried out on local probe prototypes to characterize their electromagnetic behaviour are also reported
Coherent Time Evolution and Boundary Conditions of Two-Photon Quantum Walks
Multi-photon quantum walks in integrated optics are an attractive controlled
quantum system, that can mimic less readily accessible quantum systems and
exhibit behavior that cannot in general be accurately replicated by classical
light without an exponential overhead in resources. The ability to observe time
evolution of such systems is important for characterising multi-particle
quantum dynamics---notably this includes the effects of boundary conditions for
walks in spaces of finite size. Here we demonstrate the coherent evolution of
quantum walks of two indistinguishable photons using planar arrays of 21
evanescently coupled waveguides fabricated in silicon oxynitride technology. We
compare three time evolutions, that follow closely a model assuming unitary
evolution, corresponding to three different lengths of the array---in each case
we observe quantum interference features that violate classical predictions.
The longest array includes reflecting boundary conditions.Comment: 7 pages,7 figure
Experimental Setup and Measuring System to Study SolitaryWave Interaction with Rigid Emergent Vegetation
The aim of this study is to present a peculiar experimental setup, designed to investigate
the interaction between solitary waves and rigid emergent vegetation. Flow rate changes due to the
opening and closing of a software-controlled electro-valve generate a solitary wave. The complexity of
the problem required the combined use of different measurement systems of water level and velocity.
Preliminary results of the experimental investigation, which allow us to point out the effect of the
vegetation on the propagation of a solitary wave and the effectiveness of the measuring system, are also
presented. In particular, water level and velocity field changes due to the interaction of the wave with
rigid vegetation are investigated in detail
Small-scale characterization of vine plant root water uptake via 3-D electrical resistivity tomography and mise-à-la-masse method
The investigation of plant roots is inherently difficult and often neglected.
Being out of sight, roots are often out of mind. Nevertheless, roots play a key role
in the exchange of mass and energy between soil and the atmosphere, in addition to
the many practical applications in agriculture. In this paper, we propose a
method for roots imaging based on the joint use of two electrical
noninvasive methods: electrical resistivity tomography (ERT) and
mise-à-la-masse (MALM). The approach is based on the key assumption that the
plant root system acts as an electrically conductive body, so that injecting
electrical current into the plant stem will ultimately result in the injection
of current into the subsoil through the root system, and particularly through
the root terminations via hair roots. Evidence from field data, showing that
voltage distribution is very different whether current is injected into the
tree stem or in the ground, strongly supports this hypothesis. The proposed
procedure involves a stepwise inversion of both ERT and MALM data that
ultimately leads to the identification of electrical resistivity (ER)
distribution and of the current injection root distribution in the
three-dimensional soil space. This, in turn, is a proxy to the active (hair)
root density in the ground. We tested the proposed procedure on synthetic
data and, more importantly, on field data collected in a vineyard, where the
estimated depth of the root zone proved to be in agreement with literature on
similar crops. The proposed noninvasive approach is a step forward towards a
better quantification of root structure and functioning.</p
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