276 research outputs found
Multipartite entanglement and few-body Hamiltonians
We investigate the possibility to obtain higly multipartite-entangled states
as nondegenerate eigenstates of Hamiltonians that involve only short-range and
few-body interactions. We study small-size systems (with a number of qubits
ranging from three to five) and search for Hamiltonians with a Maximally
Multipartite Entangled State (MMES) as a nondegenerate eigenstate. We then find
conditions, including bounds on the number of coupled qubits, to build a
Hamiltonian with a Greenberger-Horne-Zeilinger (GHZ) state as a nondegenerate
eigenstate. We finally comment on possible applications.Comment: 15 pages, 3 figures. Proceedings of IQIS 2013 to appear on IJQ
Quantum Typicality and Initial Conditions
If the state of a quantum system is sampled out of a suitable ensemble, the
measurement of some observables will yield (almost) always the same result.
This leads us to the notion of quantum typicality: for some quantities the
initial conditions are immaterial. We discuss this problem in the framework of
Bose-Einstein condensates.Comment: 8 page
Correlation Plenoptic Imaging With Entangled Photons
Plenoptic imaging is a novel optical technique for three-dimensional imaging
in a single shot. It is enabled by the simultaneous measurement of both the
location and the propagation direction of light in a given scene. In the
standard approach, the maximum spatial and angular resolutions are inversely
proportional, and so are the resolution and the maximum achievable depth of
focus of the 3D image. We have recently proposed a method to overcome such
fundamental limits by combining plenoptic imaging with an intriguing
correlation remote-imaging technique: ghost imaging. Here, we theoretically
demonstrate that correlation plenoptic imaging can be effectively achieved by
exploiting the position-momentum entanglement characterizing spontaneous
parametric down-conversion (SPDC) photon pairs. As a proof-of-principle
demonstration, we shall show that correlation plenoptic imaging with entangled
photons may enable the refocusing of an out-of-focus image at the same depth of
focus of a standard plenoptic device, but without sacrificing
diffraction-limited image resolution.Comment: 12 pages, 5 figure
Long-lived entanglement of two multilevel atoms in a waveguide
We study the presence of nontrivial bound states of two multilevel quantum
emitters and the photons propagating in a linear waveguide. We characterize the
conditions for the existence of such states and determine their general
properties, focusing in particular on the entanglement between the two
emitters, that increases with the number of excitations. We discuss the
relevance of the results for entanglement preservation and generation by
spontaneous relaxation processes.Comment: 6 pages, 1 figur
Huygens' principle and Dirac-Weyl equation
We investigate the validity of Huygens' principle for forward propagation in
the massless Dirac-Weyl equation. The principle holds for odd space dimension
n, while it is invalid for even n. We explicitly solve the cases n=1,2 and 3
and discuss generic . We compare with the massless Klein-Gordon equation and
comment on possible generalizations and applications.Comment: 7 pages, 1 figur
Correlation plenoptic imaging
Plenoptic imaging is a promising optical modality that simultaneously
captures the location and the propagation direction of light in order to enable
three-dimensional imaging in a single shot. However, in classical imaging
systems, the maximum spatial and angular resolutions are fundamentally linked;
thereby, the maximum achievable depth of field is inversely proportional to the
spatial resolution. We propose to take advantage of the second-order
correlation properties of light to overcome this fundamental limitation. In
this paper, we demonstrate that the momentum/position correlation of chaotic
light leads to the enhanced refocusing power of correlation plenoptic imaging
with respect to standard plenoptic imaging.Comment: 6 pages, 3 figure
Typical observables in a two-mode Bose system
A class of k-particle observables in a two-mode system of Bose particles is
characterized by typicality: if the state of the system is sampled out of a
suitable ensemble, an experimental measurement of that observable yields
(almost) always the same result. We investigate the general features of typical
observables, the criteria to determine typicality and finally focus on the case
of density correlation functions, which are related to spatial distribution of
particles and interference.Comment: 8 pages, 1 figur
Resolution Limit of Correlation Plenoptic Imaging between Arbitrary Planes
Correlation plenoptic imaging (CPI) is an optical imaging technique based on intensity correlation measurement, which enables detecting, within fundamental physical limits, both the spatial distribution and the direction of light in a scene. This provides the possibility to perform tasks such as three-dimensional reconstruction and refocusing of different planes. Compared with standard plenoptic imaging devices, based on direct intensity measurement, CPI overcomes the problem of the strong trade-off between spatial and directional resolution. Here, we study the resolution limit in a recent development of the technique, called correlation plenoptic imaging between arbitrary planes (CPI-AP). The analysis, based on Gaussian test objects, highlights the main properties of the technique, as compared with standard imaging, and provides an analytical guideline to identify the limits at which an object can be considered resolved
Phase Transitions in Gauge Models: Towards Quantum Simulations of the Schwinger-Weyl QED
We study the ground-state properties of a class of lattice
gauge theories in 1 + 1 dimensions, in which the gauge fields are coupled to
spinless fermionic matter. These models, stemming from discrete representations
of the Weyl commutator for the group, preserve the unitary
character of the minimal coupling, and have therefore the property of formally
approximating lattice quantum electrodynamics in one spatial dimension in the
large- limit. The numerical study of such approximated theories is important
to determine their effectiveness in reproducing the main features and
phenomenology of the target theory, in view of implementations of cold-atom
quantum simulators of QED. In this paper we study the cases by
means of a DMRG code that exactly implements Gauss' law. We perform a careful
scaling analysis, and show that, in absence of a background field, all
models exhibit a phase transition which falls in the Ising
universality class, with spontaneous symmetry breaking of the symmetry. We
then perform the large- limit and find that the asymptotic values of the
critical parameters approach the ones obtained for the known phase transition
the zero-charge sector of the massive Schwinger model, which occurs at negative
mass.Comment: 15 pages, 18 figure
Signal-to-noise properties of correlation plenoptic imaging with chaotic light
Correlation Plenoptic Imaging (CPI) is a novel imaging technique, that
exploits the correlations between the intensity fluctuations of light to
perform the typical tasks of plenoptic imaging (namely, refocusing out-of-focus
parts of the scene, extending the depth of field, and performing 3D
reconstruction), without entailing a loss of spatial resolution. Here, we
consider two different CPI schemes based on chaotic light, both employing ghost
imaging: the first one to image the object, the second one to image the
focusing element. We characterize their noise properties in terms of the
signal-to-noise ratio (SNR) and compare their performances. We find that the
SNR can be significantly higher and easier to control in the second CPI scheme,
involving standard imaging of the object; under adequate conditions, this
scheme enables reducing by one order of magnitude the number of frames for
achieving the same SNR.Comment: 12 pages, 3 figure
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