86 research outputs found
Interference at the Single Photon Level Along Satellite-Ground Channels
Quantum interference arising from superposition of states is a striking
evidence of the validity of Quantum Mechanics, confirmed in many experiments
and also exploited in applications. However, as for any scientific theory,
Quantum Mechanics is valid within the limits in which it has been
experimentally verified. In order to extend such limits, it is necessary to
observe quantum interference in unexplored conditions such as moving terminals
at large distance in Space. Here we experimentally demonstrate single photon
interference at a ground station due to the coherent superposition of two
temporal modes reflected by a rapidly moving satellite thousand kilometers
away. The relative speed of the satellite induces a varying modulation in the
interference pattern. The measurement of the satellite distance in real time by
laser ranging allowed us to precisely predict the instantaneous value of the
interference phase. We then observed the interference patterns with visibility
up to with three different satellites and with path length up to 5000
km. Our results attest the viability of photon temporal modes for fundamental
tests of Physics and Quantum Communications in Space.Comment: Version accepted for publication in Phys. Rev. Let
Towards Quantum Communication from Global Navigation Satellite System
Satellite-based quantum communication is an invaluable resource for the
realization of a quantum network at the global scale. In this regard, the use
of satellites well beyond the low Earth orbits gives the advantage of long
communication time with a ground station. However, high-orbit satellites pose a
great technological challenge due to the high diffraction losses of the optical
channel, and the experimental investigation of such quantum channels is still
lacking. Here, we report on the first experimental exchange of single photons
from Global Navigation Satellite System at a slant distance of 20000
kilometers, by exploiting the retroreflector array mounted on GLONASS
satellites. We also observed the predicted temporal spread of the reflected
pulses due to the geometrical shape of array. Finally, we estimated the
requirements needed for an active source on a satellite, aiming towards quantum
communication from GNSS with state-of-the-art technology.Comment: Revte
Large-scale optical interferometry in general spacetimes
We introduce a convenient formalism to evaluate the frequency-shift affecting
a light signal propagating on a general curved background. Our formulation,
which is based on the laws of geometric optics in a general relativistic
setting, allows to obtain a transparent generalization of the Doppler
frequency-shift without requiring to perform Local Lorentz transformations. It
is easily applicable to stationary spacetimes, and in particular to the
near-Earth experiments where geometry is described in the parametrized
post-Newtonian approximation. We apply our recipe to evaluate the phase-shift
arising in large-scale optical interferometric experiments, as the optical
version of the Colella-Overhauser-Werner experiment.Comment: 8 pages, 3 figure
Proposal for an Optical Test of the Einstein Equivalence Principle
The Einstein Equivalence Principle (EEP) underpins all metric theories of
gravity. Its key element is the local position invariance of non-gravitational
experiments, which entails the gravitational red-shift. Precision measurements
of the gravitational red-shift tightly bound violations of the EEP only in the
fermionic sector of the Standard Model, however recent developments of
satellite optical technologies allow for its investigation in the
electromagnetic sector. Proposals exploiting light interferometry traditionally
suffer from the first-order Doppler effect, which dominates the weak
gravitational signal necessary to test the EEP, making them unfeasible. Here,
we propose a novel scheme to test the EEP, which is based on a double
large-distance optical interferometric measurement. By manipulating the
phase-shifts detected at two locations at different gravitational potentials it
is possible to cancel-out the first-order Doppler effect and observe the
gravitational red-shift implied by the EEP. We present the detailed analysis of
the proposal within the post-Newtonian framework and the simulations of the
expected signals obtained by using two realistic satellite orbits. Our proposal
to overcome the first-order Doppler effect in optical EEP tests is feasible
with current technology.Comment: manuscript improve
Extending Wheeler's delayed-choice experiment to Space
Gedankenexperiments have consistently played a major role in the development
of quantum theory. A paradigmatic example is Wheeler's delayed-choice
experiment, a wave-particle duality test that cannot be fully understood using
only classical concepts. Here, we implement Wheeler's idea along a
satellite-ground interferometer which extends for thousands of kilometers in
Space. We exploit temporal and polarization degrees of freedom of photons
reflected by a fast moving satellite equipped with retro-reflecting mirrors. We
observed the complementary wave-like or particle-like behaviors at the ground
station by choosing the measurement apparatus while the photons are propagating
from the satellite to the ground. Our results confirm quantum mechanical
predictions, demonstrating the need of the dual wave-particle interpretation,
at this unprecedented scale. Our work paves the way for novel applications of
quantum mechanics in Space links involving multiple photon degrees of freedom.Comment: 4 figure
Postselection-loophole-free Bell violation with genuine time-bin entanglement
Entanglement is an invaluable resource for fundamental tests of physics and
the implementation of quantum information protocols such as device-independent
secure communications. In particular, time-bin entanglement is widely exploited
to reach these purposes both in free-space and optical fiber propagation, due
to the robustness and simplicity of its implementation. However, all existing
realizations of time-bin entanglement suffer from an intrinsic postselection
loophole, which undermines their usefulness. Here, we report the first
experimental violation of Bell's inequality with "genuine" time-bin
entanglement, free of the postselection loophole. We introduced a novel
function of the interferometers at the two measurement stations, that operate
as fast synchronized optical switches. This scheme allowed to obtain a
postselection-loophole-free Bell violation of more than nine standard
deviations. Since our scheme is fully implementable using standard fiber-based
components and is compatible with modern integrated photonics, our results pave
the way for the distribution of genuine time-bin entanglement over long
distances.Comment: RevTe
Insulin resistance, diabetic kidney disease, and all-cause mortality in individuals with type 2 diabetes. a prospective cohort study
BACKGROUND: It is unclear whether insulin resistance (IR) contributes to excess mortality in patients with type 2 diabetes independent of diabetic kidney disease (DKD), which is strongly associated with IR and is a major risk factor for cardiovascular disease (CVD), the main cause of death in these individuals. We tested this hypothesis in patients with type 2 diabetes from the Renal Insufficiency And Cardiovascular Events Italian Multicentre Study.METHODS: This observational, prospective, cohort study enrolled 15,773 patients with type 2 diabetes attending 19 Italian Diabetes Clinics in 2006-2008. Insulin sensitivity was assessed as estimated glucose disposal rate (eGDR), which was validated against the euglycaemic-hyperinsulinemic clamp technique. Vital status on October 31, 2015, was retrieved for 15,656 patients (99.3%). Participants were stratified by eGDR tertiles from T1 (≥ 5.35mg/kg/min) to T3 (≤ 4.14mg/kg/min, highest IR).RESULTS: CVD risk profile was worse in T2 and T3 vs T1. eGDR tertiles were independently associated with micro- and macroalbuminuria and the albuminuric DKD phenotypes (albuminuria with preserved or reduced estimated glomerular filtration rate [eGFR]) as well as with eGFR categories or the nonalbuminuric DKD phenotype. Over a 7.4-year follow-up, unadjusted death rates and mortality risks increased progressively across eGDR tertiles, but remained significantly elevated after adjustment only in T3 vs T1 (age- and gender- adjusted death rate, 22.35 vs 16.74 per 1000 person-years, p<0.0001, and hazard ratio [HR] adjusted for multiple confounders including DKD, 1.140 [95% confidence interval [CI], 1.049-1.238], p=0.002). However, eGDR was independently associated with mortality in participants with no DKD (adjusted HR, 1.214 [95% CI, 1.072-1.375], p=0.002) and in those with nonalbuminuric DKD (1.276 [1.034-1.575], p=0.023), but not in those with the albuminuric DKD phenotypes. Moreover, the association was stronger in males and in younger individuals and was observed in those without but not with prior CVD, though interaction was significant only for age.CONCLUSIONS: The proxy of insulin sensitivity eGDR predicts all-cause mortality in type 2 diabetes, independent of confounders including DKD. However, the impact of IR in individuals with albuminuric DKD may be mediated by its relationship with albuminuria.TRIAL REGISTRATION: ClinicalTrials.gov , NCT00715481, retrospectively registered 15 July 2008
Independent association of atherogenic dyslipidaemia with all-cause mortality in individuals with type 2 diabetes and modifying effect of gender. a prospective cohort study
Atherogenic dyslipidaemia has been implicated in the residual risk for cardiovascular morbidity and mortality, which remains despite attainment of LDL cholesterol goals especially in individuals with type 2 diabetes. However, its relationship with all-cause death has not been sufficiently explored. This analysis evaluated the independent association of increased triglycerides and triglyceride:HDL cholesterol ratio (TG:HDL) and decreased HDL cholesterol with total mortality and the possible modifying effect of gender in a large cohort of patients with type 2 diabetes
Intermodal quantum key distribution field trial with active switching between fiber and free-space channels
Intermodal quantum key distribution enables the integration of fiber networks
and free-space channels, which are both necessary elements for the development
of a global quantum network. We present a field trial of an intermodal quantum
key distribution system - comprised of two polarization-based transmitters and
a single receiver - in which the active channel is alternately switched between
a free-space link of 620 m and a 17km-long deployed fiber in the metropolitan
area of Padova. The performance of the free-space channel is evaluated against
the atmospheric turbulence strength. The field trial lasted for several hours
in daylight conditions, attesting the intermodal functionality between fiber
and free-space channels. Our switching system represents a cost-effective
solution for a trusted quantum key distribution network, reducing the number of
necessary devices in different network topologies
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