117,599 research outputs found
X-entanglement: the non-factorable spatio-temporal structure of biphoton correlation
No full textIn this work we turn our attention to the genuine quantum properties of PDC, and we demonstrate the hyperbolic
geometry underlying the spatio-temporal structure of the PDC entanglement and its non-factorability with
respect to space and time [1,2]. As for the macroscopic X-waves, the X-shape of the biphoton correlation is
imposed by the phase-matching mechanism governing the PDC process, and following this analogy we coined
the name of X-entanglement
[1] A. Gatti, E. Brambilla, L. Caspani, O. Jedrkiewicz, and L.A. Lugiato, Phys. Rev. Lett. 102, 223601 (2009) ;
e-print arXiv:0812.3533v1
[2] L. Caspani, E. Brambilla and A. Gatti, Tailoring the spatio-temporal structure of biphoton entanglement in
type I PDC , Phys. Rev A, 81, 033808 (2010
X-entanglement of PDC photon pairs: the nonfactorable spatiotemporal structure of biphoton correlation
No full textMastering the techniques involving sources of entangled photon pairs has become vital for the implementations of many quantum networks and quantum computing schemes. So far, parametric down-conversion (PDC) demonstrated the most efficient room-temperature source of entangled photon pairs, employed in successful implementation of quantum communication schemes. At the very heart of such technologies lies the quantum interference
between photonic wave functions, which depends crucially on the spatio-temporal
mode structure of the photons.
In this work, this issue is addressed from a peculiar and novel point of view, that is, the
non factorability in space and time of the PDC bi-photon entanglement. The idea is driven
by recent investigations in nonlinear optics [1] that outlined how in nonlinear media the angular dispersion relations impose a hyperbolic geometry involving temporal and spatial
degrees of freedom in a non-factorable way. The wave object that captures such a geometry is the so-called X-wave (the X being formed by the asymptotes of the hyperbola).
Here we turn our attention to the genuine quantum properties of PDC, and we demonstrate the hyperbolic geometry underlying the spatio-temporal structure of the PDC entanglement
and its non-factorability with respect to space and time [2]. As for the X-waves encountered in nonlinear optics, the X-shape of the bi-photon correlation is imposed by the phase-matching mechanism governing the PDC process, and following this analogy
we coined the name of X-entanglement. This represents a entirely new concept, because investigations on the quantum state of of PDC have been performed to date mostly in a purely either temporal or spatial framework. Our approach, which takes into account
the nonfactorability of the state in space and time, leads to relevant elements of novelty,
namely i) the possibility of tailoring the temporal bandwidth of the bi-photons by
manipulating their spatial degrees of freedom, or viceversa and ii) the extreme relative
localization of the X-entanglement in time and space, with bi-photon correlation times and lengths in the femtosecond and micrometer range, respectively. It should be stressed that both the non-factorability and the extreme localization are not present in the detection schemes used so far, which usually select small angular portions of the PDC fluorescence.
In the metrology domain, our researches have high potentialities for e.g. ultra-precise measurements of time delays and clock synchronizations, due to the ultra-short localization
in time of the entangled photons.
[1] For a review see C.Conti and S.Trillo in Localized-Waves, p. 243, H.E.Hernandez-
Figuroa, M.Zamboni-Rached and E.Recami eds.
[2] E. Brambilla, L. Caspani, O. Jedrkiewicz, L.A. Lugiato and A. Gatti, X-entanglement
of PDC photon pairs, e-print arXiv:0812.3533v
Counterpropagating frequency mixing with terahertz waves in diamond
No full textFrequency conversion by means of Kerr nonlinearity is one of the most common and exploited nonlinear optical processes in the UV, visible, IR, and mid-IR spectral regions. Here we show that wave mixing of an optical field and a terahertz wave can be achieved in diamond, resulting in the frequency conversion of the terahertz radiation either by sum-or difference-frequency generation. In the latter case, we show that this process is phase matched and most efficient in a counterpropagating geometry. (C) 2013 Optical Society of America</p
Improved Visibility of Spectral Two-photon Quantum Interference Introduced by Multiphoton Components
No full textSpectral two-photon quantum interference between a thermal field and a heralded state is studied theoretically and experimentally, demonstrating visibility enhancements as a result of the contribution of multiphoton components within the heralded photon state
Heat stress : characteristics, pathophysiology and avoidable mistakes
No full textIn August 2003 an exceptional heatwave was recorded in Europe. The authors would like to describe 6 patients for which the intensivist was called as a consultant. All patients had a skin temperature >40 degrees C, central nervous system impairment, severe hyponatremia [124.7 mEq/l+/-5.6 (range 117-130)] and severe metabolic acidosis [BE -6.28 mEq/l+/-3.55 (range -9.5-0), HCO3- 17.75 mEq/l+/-3.25 (range 13.4-21.9)]. All patients had decreased platelet count and coagulation abnormalities. Two patients were hypertensive, 4 hypotensive. The heat stress due to the hot environment is characterized by systemic inflammatory response (as in severe sepsis) and hemodynamic impairment (as in hypovolemic shock). The association between hypovolemia and altered microcirculation leads to cell energy failure with metabolic lactic acidosis. The energy failure may induce structural irreversible damage of mitochondria. It is possible to differentiate, during energy failure, the irreversible or reversible condition by volume loading and vasoactive drugs challenge tests. In fact, if the hemodynamic correction is associated with normalization of SvO2 with disappearance of metabolic acidosis, this suggests hemodynamic impairment with intact mitochondrial function. In contrast, if the hemodynamic improvement with normalization of SvO2 is associated and acidosis persists, this suggests irreversible structural mitochondrial damage. The threshold between reversibility and irreversibility is likely time dependent, as suggested by biochemical consideration and by 2 large randomized studies on hemodynamic treatment. The comparative analysis of these 2 studies suggests that the time of intervention may lead to significant differences in mortality. In these patients time is essential
Quantum signatures in the interference of macroscopic signal-idler beams
No full textThe interference of signal and idler waves produced by optical parametric down-conversion was the object of a classic paper by Ghosh and Mandel [Phys. Rev. Lett. 1987, 59, 1903-1905] many years ago. In this paper we investigate the problem in the continuous variable regime, with the aim of identifying quantum signatures that arise from the entanglement of signal and idler waves. By using a model which allows for analytical calculations we show first of all that no quantum features appear for the interference in the fourth-order correlation function in the high-gain regime of parametric down-conversion. The quantum signatures emerge instead from the spatio-temporal correlation function of a generic quadrature component, and we demonstrate that they are clearly linked to the signal/idler entanglement. Relevant and useful links with the theory of quantum images complete the picture
Contribution of red blood cells to the compensation for hypocapnic alkalosis through plasmatic strong ion diff erence variations
No full textIntroduction Chloride shift is the movement of chloride between red
blood cells (RBC) and plasma (and vice versa) caused by variations in
pCO2. The aim of our study was to investigate changes in plasmatic
strong ion diff erence (SID) during acute variations in pCO2 and their
possible role in the compensation for hypocapnic alkalosis.Methods Patients admitted in this year to our ICU requiring extracorporeal
CO2 removal were enrolled. Couples of measurements
of gases and electrolytes on blood entering (v) and leaving (a) the
respiratory membrane were analyzed. SID was calculated as [Na+]
+ [K+] + 2[Ca2+] – [Cl–] – [Lac–]. Percentage variations in SID (SID%)
were calculated as (SIDv – SIDa) x 100 / SIDv. The same calculation was
performed for pCO2 (pCO2%). Comparison between v and a values was
performed by paired t test or the signed-rank test, as appropriate.
Results Analysis was conducted on 205 sample-couples of six enrolled
patients. A signifi cant diff erence (P <0.001) between mean values of
v–a samples was observed for pH (7.41 ± 0.05 vs. 7.51 ± 0.06), pCO2
(48 ± 6 vs. 35 ± 7 mmHg), [Na+] (136.3 ± 4.0 vs. 135.2 ± 4.0 mEq/l), [Cl–]
(101.5 ± 5.3 vs. 102.8 ± 5.2 mEq/l) and therefore SID (39.5 ± 4.0 vs.
36.9 ± 4.1 mEq/l). pCO2% and SID% signifi cantly correlated (r2 = 0.28,
P <0.001). Graphical representation by quartiles of pCO2% is shown in
Figure 1.
Conclusions As a reduction in SID decreases pH, the observed
movement of anions and cations probably limited the alkalinization
caused by hypocapnia. In this model, the only source of electrolytes
are blood cells (that is, no interstitium and no infl uence of the kidney
is present); it is therefore conceivable to consider the observed
phenomenon as the contribution of RBC for the compensation of acute
hypocapnic alkalosi
Entanglement of PDC photon pairs
No full textWe investigate the spatio-temporal structure of the biphoton entanglement in parametric down-conversion (PDC) and we demonstrate its non-factorable X-shaped geometry. Such a structure gives access to the ultrabroad bandwidth of PDC, and can be exploited to achieve a biphoton temporal localization in the femtosecond range. This extreme localization is conditioned by our ability to resolve the photon positions in the source near field. The nonfactorability opens the possibility of tailoring the temporal entanglement by acting on the spatial degrees of freedom of twin photons. We also put in evidence distinctive features that characterize type II with respect to type I PD
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