1,500 research outputs found
Shape dependence and anisotropic finite-size scaling of the phase coherence of three-dimensional Bose-Einstein condensed gases
We investigate the equilibrium phase-coherence properties of Bose-condensed
particle systems, focusing on their shape dependence and finite-size scaling
(FSS). We consider three-dimensional (3D) homogeneous systems confined to
anisotropic L x L x L_a boxes, below the BEC transition temperature . We
show that the phase correlations develop peculiar anisotropic FSS for any
, in the large- limit keeping the ratio \lambda = L_a/L^2 fixed. This
phenomenon is effectively described by the 3D spin-wave (SW) theory. Its
universality is confirmed by quantum Monte Carlo simulations of the 3D
Bose-Hubbard model in the BEC phase. The phase-coherence properties of very
elongated BEC systems, \lambda>>1, are characterized by a coherence length
\xi_a \sim A_t \rho_s/T where A_t is the transverse area and \rho_s is the
superfluid density.Comment: 7 page
Hyperentanglement witness
A new criterium to detect the entanglement present in a {\it hyperentangled
state}, based on the evaluation of an entanglement witness, is presented. We
show how some witnesses recently introduced for graph states, measured by only
two local settings, can be used in this case. We also define a new witness
that improves the resistance to noise by increasing the number of local
measurements.Comment: 6 pages, 2 figures, RevTex. v2: new title, minor changes in the
explanation of the witness for hyperentangled states, more comments in the
conclusions sectio
Hyperentanglement of two photons in three degrees of freedom
A 6-qubit hyperentangled state has been realized by entangling two photons in
three degrees of freedom. These correspond to the polarization, the
longitudinal momentum and the indistinguishable emission produced by a
2-crystal system operating with Type I phase matching in the spontaneous
parametric down conversion regime. The state has been characterized by a
chained interferometric apparatus and its complete entangled nature has been
tested by a novel witness criterium specifically introduced for hyperentangled
states. The experiment represents the first realization of a genuine
hyperentangled state with the maximum entanglement between the two particles
allowed in the given Hilbert space.Comment: 4 pages, 2 figures, Revtex
First measurement of the 14N/15N ratio in the analogue of the Sun progenitor OMC-2 FIR4
We present a complete census of the 14N/15N isotopic ratio in the most
abundant N-bearing molecules towards the cold envelope of the protocluster
OMC-2 FIR4, the best known Sun progenitor. To this scope, we analysed the
unbiased spectral survey obtained with the IRAM-30m telescope at 3mm, 2mm and
1mm. We detected several lines of CN, HCN, HNC, HC3N, N2H+, and their
respective 13C and 15N isotopologues. The lines relative fluxes are compatible
with LTE conditions and moderate line opacities have been corrected via a
Population Diagram method or theoretical relative intensity ratios of the
hyperfine structures. The five species lead to very similar 14N/15N isotopic
ratios, without any systematic difference between amine and nitrile bearing
species as previously found in other protostellar sources. The weighted average
of the 14N/15N isotopic ratio is 270 +/- 30. This 14N/15N value is remarkably
consistent with the [250-350] range measured for the local galactic ratio but
significantly differs from the ratio measured in comets (around 140).
High-angular resolution observations are needed to examine whether this
discrepancy is maintained at smaller scales. In addition, using the CN, HCN and
HC3N lines, we derived a 12C/13C isotopic ratio of 50 +/- 5.Comment: Accepted for publication in ApJ ; 19 pages, 5 tables, 12 figure
Custom silicon technology for SPAD-arrays with red-enhanced sensitivity and low timing jitter
Single-photon detection is an invaluable tool for many applications ranging
from basic research to consumer electronics. In this respect, the Single Photon
Avalanche Diode (SPAD) plays a key role in enabling a broad diffusion of these
techniques thanks to its remarkable performance, room-temperature operation,
and scalability. In this paper we present a silicon technology that allows the
fabrication of SPAD-arrays with an unprecedented combination of low timing
jitter (95 ps FWHM) and high detection efficiency at red and near infrared
wavelengths (peak of 70% at 650 nm, 45% at 800 nm). We discuss the device
structure, the fabrication process, and we present a thorough experimental
characterization of the fabricated detectors. We think that these long-awaited
results can pave the way to new exciting developments in many fields, ranging
from quantum optics to single molecule spectroscop
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