Quantum Google in a Complex Network

We investigate the behavior of the recently proposed quantum Google algorithm, or quantum PageRank, in large complex networks. Applying the quantum algorithm to a part of the real World Wide Web, we find that the algorithm is able to univocally reveal the underlying scale-free topology of the network and to clearly identify and order the most relevant nodes (hubs) of the graph according to their importance in the network structure. Moreover, our results show that the quantum PageRank algorithm generically leads to changes in the hierarchy of nodes. In addition, as compared to its classical counterpart, the quantum algorithm is capable to clearly highlight the structure of secondary hubs of the network, and to partially resolve the degeneracy in importance of the low lying part of the list of rankings, which represents a typical shortcoming of the classical PageRank algorithm. Complementary to this study, our analysis shows that the algorithm is able to clearly distinguish scale-free networks from other widespread and important classes of complex networks, such as Erd\H{o}s-R\'enyi networks and hierarchical graphs. We show that the ranking capabilities of the quantum PageRank algorithm are related to an increased stability with respect to a variation of the damping parameter $\alpha$ that appears in the Google algorithm, and to a more clearly pronounced power-law behavior in the distribution of importance among the nodes, as compared to the classical algorithm. Finally, we study to which extent the increased sensitivity of the quantum algorithm persists under coordinated attacks of the most important nodes in scale-free and Erd\H{o}s-R\'enyi random graphs

Growth of graph states in quantum networks

We propose a scheme to distribute graph states over quantum networks in the presence of noise in the channels and in the operations. The protocol can be implemented efficiently for large graph sates of arbitrary (complex) topology. We benchmark our scheme with two protocols where each connected component is prepared in a node belonging to the component and subsequently distributed via quantum repeaters to the remaining connected nodes. We show that the fidelity of the generated graphs can be written as the partition function of a classical Ising-type Hamiltonian. We give exact expressions of the fidelity of the linear cluster and results for its decay rate in random graphs with arbitrary (uncorrelated) degree distributions.Comment: 16 pages, 7 figure

Time-resolved photoluminescence of n-doped SrTiO_3

Following the recent surge of interest in n-doped strontium titanate as a possible blue light emitter, a time-resolved photoluminescence analysis was performed on nominally pure, Nb-doped and oxygen-deficient single-crystal SrTiO3 samples. The doping-effects on both the electronic states involved in the transition and the decay mechanism are respectively analyzed by comparing the spectral and dynamic features and the yields of the emission. Our time-resolved analysis, besides shedding some light on the basic recombination mechanisms acting in these materials, sets the intrinsic bandwidth limit of the proposed blue light emitting optoelectronic devices made of Ti-based perovskites heterostructures in the GHz range

Crustal deformation and <i>AE</i> monitoring: annual variation and stress-soliton propagation

International audienceThe stress propagation through the crust can be effectively monitored by means of acoustic mission (AE) techniques (ultrasounds). The \textit{AE} intensity is indicative of the amount of stress that affects some lithospheric and/or crustal slab of some (ultimately unknown) scale size. In principle, such scale size can be different in different areas, as it depends on their respective tectonic setting, by which a variety of prime causes ought to be considered: every cause can eventually prevail over others. Two basic phenomena are here reported. If the crust behaves like a comparatively ideal elastic body, an annual variation is observed, which appears in-phase and correlated, when comparing AE records collected at the Italian site and on the Cephallonia Island. It seems being astronomically modulated, hence it should display a planetary scale. One likely explanation is in terms of the loading tide. Such interpretation can be confirmed by some additional modelling and analysis upon considering the motion of the Sun and of the Moon. A second observed effect refers to the case in which the crust feels the effect of the fatigue that reduces its elastic performance. The phenomenon can be described in terms of stress solitons that cross the area being monitored. They can be unambiguously recognised, and the possibility is therefore envisaged of eventually using them for measuring the propagation speed of stress through the crust over continental or planetary scales. The residuals, with respect to such regularly recognisable effects, of the recorded AE signals are to be investigated in a few subsequent analyses (in progress), as they appear to contain additional relevant physical information, still being much different from any simple random noise. A final recommendation ought therefore to be stressed, for setting up some array of at least a few AE recording stations to be simultaneously operated over some continental scale area and for a few years at least. Their potential applications still appear much promising and to be still focused in their complete, specific, operative and physical details and interpretation

Acoustic emission and released seismic energy

International audienceIntense crises of crustal stress appear to cross large regions, and to precede by several months the eventual occurrence of some strong earthquake within them. The phenomenon is not linear, and the stress control reflects some wide scale-size rather than local effects. The stress propagation through the crust can be effectively monitored by means of acoustic emission (AE) techniques (ultrasounds). The correlation is here investigated between crustal stress crises and the total release of seismic energy within some space domain around the AE recording site. Some clear inferences can be envisaged, although a significant diagnosis of the state of the crust within a given region ought to request arrays of simultaneously operated AE recorders. Some case histories are described dealing with the Italian peninsula and with the Cephallonia Island

Ultrasound monitoring of applied forcing, material ageing, and catastrophic yield of crustal structures

International audienceA new kind of data analysis is discussed ? and a few case histories of actual application are presented ? concerning the physical information attainable by acoustic emission (AE) records in geodynamically active or volcanic areas. The previous analyses of such same kind of observations were reported in several papers appeared in the last few years, and here briefly recalled. They are concerned with the inference of the forcing ("F") acting on the physical system, and on the ageing ("T") or fatigue of its "solid" structures. The new analysis here discussed deals with the distinction between a state of applied stress ("hammer regime"), compared to state of "recovery regime" of the system while it seeks a new equilibrium state after having been perturbed. For instance, in the case of a seismic event ? and according to some kind of almost intuitive argument ? the "hammer regime" is the phenomenon leading to the main shock, while the "recovery regime" deals with the well known aftershocks. Such same intuitive inference, however, can be investigated by a much more formal algorithm, aimed at envisaging the minor changes of the behaviour of the system, during its history and during its present dynamic evolution. As a demonstrative application, detailed consideration is given of AE records ? each one lasting for a few years ? collected on the Italian peninsula vs. records collected on the Kefallinìa Island (western Greece). Such two areas are well known being characterised by some great comparative difference in their respective tectonic setting. When considering planetary scale phenomena, they appear comparatively very close to each other. Hence, they are likely being presumably affected by similar large-scale external actions, although they ought to be expected to respond in some completely different way. Such facts are clearly manifested by some substantially different AE responses of the local crustal structures. However, a full understanding of such entire set of geodynamic and tectonic details ought to require several year data series of AE records, and/or (maybe) also simultaneous AE records collected within some suitable array of AE stations. Such understanding ought to permit the inference of the spatial features of the crustal stress propagation ? including its diagnosis and "forecasting" ? in addition to the temporal diagnosis and "prevision" that can be attained by isolated point-like AE recording stations. Additional analyses are in progress

On the variability of HD 170699 - a possible COROT target

We present the analysis of the variability of HD 170699, a COROT star showing the characteristics of a non evolutionary Delta Scuti star with high rotational velocity. There is a clear period of 10.45 c/d with 5.29 mmag amplitude in the y filter. From the data, it can be seen that the star shows multi-periodicity and it is necessary to add more frequencies to adjust the observationsComment: To appear in RevMexAA(SC) in Proceedings of XII Reunion Regional Latinoamericana de la UAI held in Isla Margarita, Venezuela, October 22-26, 200