V. Luceri

Experimental verification of the feasibility of a quantum channel between space and Earth

Extending quantum communication to space environments would enable us to perform fundamental experiments on quantum physics as well as applications of quantum information at planetary and interplanetary scales. Here, we report on the first experimental study of the conditions for the implementation of the single-photon exchange between a satellite and an Earth-based station. We built an experiment that mimics a single photon source on a satellite, exploiting the telescope at the Matera Laser Ranging Observatory of the Italian Space Agency to detect the transmitted photons. Weak laser pulses, emitted by the ground-based station, are directed toward a satellite equipped with cube-corner retroreflectors. These reflect a small portion of the pulse, with an average of less- than-one photon per pulse directed to our receiver, as required for faint-pulse

Experimental Satellite Quantum Communications

Quantum communication (QC), namely, the faithful transmission of generic quantum states, is a key ingredient of quantum information science. Here we demonstrate QC with polarization encoding from space to ground by exploiting satellite corner cube retroreflectors as quantum transmitters in orbit and the Matera Laser Ranging Observatory of the Italian Space Agency in Matera, Italy, as a quantum receiver. The quantum bit error ratio (QBER) has been kept steadily low to a level suitable for several quantum information protocols, as the violation of Bell inequalities or quantum key distribution (QKD). Indeed, by taking data from different satellites, we demonstrate an average value of QBER=4.6% for a total link duration of 85 s. The mean photon number per pulse μ_{sat} leaving the satellites was estimated to be of the order of one. In addition, we propose a fully operational satellite QKD system by exploiting our communication scheme with orbiting retroreflectors equipped with a modulator, a very compact payload. Our scheme paves the way toward the implementation of a QC worldwide network leveraging existing receivers.

Mantle viscosity inferences from joint inversions of pleistocene deglaciatio‐induced changes in geopotential with a new SLR analysis and polar wander

Joint inversions of post-glacial rebound-induced secular changes in low degree harmonics of the geopotential and true polar wander (TPW) systematically indicate that the upper mantle viscosity has a value that is considerably smaller than 10 21 Pas. The lower mantle viscosity is about one order of magnitude larger than the upper mantle viscosity. Discrepancies in the viscosity profiles inferred from even and odd zonals are likely an indication of recent, unmodeled glacial forcings and/or insufficient precision in the evaluation of the mass loss from Pleistocene ice sheets. The influence of systematic errors in SLR data reduction due to thermal drag on the LAGEOS satellites for the uneven zonals of the geopotential is avoided by making use of the Starlette and Stella satellites to recover the uneven zonals and by considering lumped coefficients for these uneven terms.

Geodetic control on recent tectonic movements in the central Mediterranean area

Abstract During the Neogene and Quaternary, the western Mediterranean geodynamics was apparently dominated by the nearly eastward migration of the Apenninic arc and the associated opening (spreading) of the back-arc basin (Tyrrhenian Sea). However, during the last 5 My, the collision of the arc with the Apulian platform led to a dramatic change in the tectonic setting of the area. As geological processes require a long period of time to register the displacements of the different blocks, it is indispensable to take into account the present-day motion given by space geodesy data analysis in order to better constrain the geological models. Geodetic motions were derived from Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) observations collected from different networks. All the geodetic solutions have been computed and combined at the Centre of Space Geodesy (CGS), at Matera, Italy. The geodetic results show a NNE motion of the Adriatic plate with a small component of counter-clockwise rotation, in good agreement with the geological and geophysical observations. In the southern Tyrrhenian area, the lengthening of the Matera–Cagliari baseline should imply that convergence cannot be considered as the driving mechanism for the Apenninic subduction process. The estimated motion of Noto is in quite good agreement with the estimated motion of the African plate.

Measurement of LAGEOS-2 rotation by satellite laser ranging observations

The unprecedented single shot precision of the new-born Matera Laser Ranging Observatory (MLRO), that can reach a scattering down to a few millimeters on LAGEOS orbit, discloses new chances in studying the high frequency dynamics. In this work we present the very first LAGEOS-2 observations in terms of range residuals and discuss the cause of the high frequencies noticed since the testing phase of the MLRO system. There are sufficient theoretical and experimental evidences to interpret those signals as rotational signatures of the spinning satellite and the first quantitative results we obtained indicates a rotation period of 23.5 s on May 31, 2000.

The SLR secular gravity variations and their impact on the inference of mantle rheology and lithospheric thickness

A long history of SLR (Satellite Laser Ranging) observations of the geodetic satellites LAGEOS-I, LAGEOS-II, Starlette and Stella have been analyzed in order to estimate the time series of the low degree zonal coefficients in the Earth gravity field, up to degree six, and derive their secular drifts. The paper will point out the critical aspects of the analysis process and will compare the estimated zonal rates with other published results. Comparison of these zonal rates with the results of global, viscoelastic Earth models forced by Pleistocenic deglaciation, shows that the SLR retrieved zonals and the lumped odd zonals can be used to infer the upper mantle viscosity and lithospheric thickness. Discrepancies in the viscosity profiles, required to reproduce the different zonals, seem to indicate ongoing mass redistribution over the Earth.

ESTIMATION OF LOW DEGREE GEOPOTENTIAL COEFFICIENTS USING SLR DATA

Abstract Geodetic satellites have been providing the low frequency part of the geopotential models used for precise orbit determination purposes (e.g. JGM3, EGM96, …). Nevertheless they can be used to estimate the temporal variation of selected coefficients, helping to clarify the complex interrelations in the earth-ocean-atmosphere system. In this paper we present the two years long analysis of SLR data from the seven available geodetic satellites (Lageos I–II, Stella, Starlette, Ajisai, Etalon I–II) to recover monthly estimates of low degree geopotential coefficients; the results are obtained analysing the satellites separately and in proper combination. An accurate modelling of the satellite orbits is required in order to separate the geopotential coefficients: we assume as a priori geopotential the JGM3 model together with its associated tides and we take care of non-gravitational effects on the satellites by means of proper empirical estimated accelerations. The time series of the estimated coefficients (J2, J3, J4, J5) are inspected to detect the sub-annual perturbations related to seasonal variation of mass distribution. Huge residual seasonal signals in the orbit of Stella indicate a strong model deficiency related to the Suns influence on the environment. The remaining six satellites are homogeneously modelled and build up a three cycles per year oscillation on J2 and a seasonal oscillation (1 year and six month periods) revealed on the J4. The origin and possible causes of these signals are further discussed in the text. We also present a preliminary J 2 estimate, using twelve years of Lageos-I and Lageos-II observations, that is compared with previous obtained values.

Ice mass loss in Antarctica and stiff lower mantle viscosity inferred from the long wavelength time dependent gravity field

[1]xa0Long wavelength time variations of the gravity field detected by means of laser tracking of geodetic satellites provide nowadays the unique opportunity to infer simultaneously the upper and lower mantle viscosity and the mass imbalance between ice accumulation and loss in Antarctica and Greenland. Here we show that mantle viscosity inversion based on stratified viscoelastic Earth models of the Pleistocene deglaciation, on two independent Satellite Laser Ranging (SLR) solutions for the even and odd zonal components of the geopotential and on True Polar Wander (TPW), indicate that present day ice mass loss in Antarctica amounts to about −250 Gt/yr, equivalent to a global sea level rise of 0.7 mm/yr, and that the lower mantle is more viscous than the upper mantle. The odd zonals of the two SLR solutions and TPW indicate two admissible upper mantle viscosities, close to 1020 Pa s and to 1021 Pa s respectively.

A contribution in the estimation of tectonic motion in crucial areas: the CGS96 SLR solution

Abstract The CGS96 is a global SLR solution based on the reduction of the whole available data set for the Lageos I and II satellites, starting from 1986. The accurate modelling adopted and the huge quantity of data of continuously growing quality, lead to reliable estimates of geodetic and orbital parameters. The solution collects a wide variety of parameters, daily earth orientation parameters, coordinates and site velocities of almost 60 sites, plus coordinates for sites with short tracking history, orbital parameters and non-modelled acceleration for both satellites. The core of the paper is the review of the tectonic results and their comparison with the models: the pointers of the goodness of the solution are those results regarding sites centrally located on the major plates, henceforth comparable to model predictions, being a prerequisite for the reliability of the estimates for the crucial sites. The tectonic results are particularly interesting in those areas not suitably described by the global models, such as the Mediterranean, periodically occupied by mobile systems.

Experimental single photon exchange along a space link of 7000 km

Extending the single photon transmission distance is a basic requirement for the implementation of quantum communication on a global scale. In this work we report the single photon exchange from a medium Earth orbit satellite (MEO) at more than 7000 km of slanted distance to the ground station at the Matera Laser Ranging Observatory. The single photon transmitter was realized by exploiting the corner cube retro-reflectors mounted on the LAGEOS-2 satellite. Long duration of data collection is possible with such altitude, up to 43 minutes in a single passage. The mean number of photons per pulse ({mu}sat) has been limited to 1 for 200 seconds, resulting in an average detection rate of 3.0 cps and a signal to noise ratio of 1.5. The feasibility of single photon exchange from MEO satellites paves the way to tests of Quantum Mechanics in moving frames and to global Quantum Information.