Coherent Distribution Research Articles

Distribution and monogamy of quantum coherence for open three-qubit systems under local noisy channels

We study the distribution and monogamous relations of quantum coherence for three-qubit systems under the influence of local amplitude-damping, phase-damping and random unitary channels, respectively. We find that under the influence of the considered channels, the W state has both global and bipartite coherence, and its monogamy is always equal to zero. For the Greenberger–Horne–Zeilinger) state, however, there is only global coherence in the time evolution and the monogamy is always positive. We also present a partially entangled state, , which has global, bipartite, and monomeric coherences and negative monogamy during the whole time evolution.

The heuristic vulnerability model: fragility curves for masonry buildings

In the framework of seismic risk analyses at large scale, among the available methods for the vulnerability assessment the empirical and expert elicitation based ones still represent one of most widely used options. In fact, despite some drawbacks, they benefit of a direct correlation to the actual seismic behaviour of buildings and they are easy to handle also on huge stocks of buildings. Within this context, the paper illustrates a macroseismic vulnerability model for unreinforced masonry existing buildings that starts from the original proposal of Lagomarsino and Giovinazzi (Bull Earthquake Eng 4(4):445–463, 2006) and has further developed in recent years. The method may be classified as heuristic, in the sense that: (a) it is based on the expertise that is implicit in the European Macroseismic Scale (EMS98), with fuzzy assumptions on the binomial damage distribution; (b) it is calibrated on the observed damage in Italy, available in the database Da.D.O. developed by the Italian Department of Civil Protection (DPC). This approach guarantees a fairly well fitting with actual damage but, at the same time, ensures physically consistent results for both low and high values of the seismic intensity (for which observed data are incomplete or lacking). Moreover, the method provides a coherent distribution between the different damage levels. The valuable data in Da.D.O. allowed significant improvements of the method than its original version. The model has been recently applied in the context of ReLUIS project, funded by the DPC to support the development of Italian Risk Maps. To this aim, the vulnerability model has been applied for deriving fragility curves. This step requires to introduce a correlation law between the Macroseismic Intensity (adopted for the calibration of the model from a wide set of real damage data) and the Peak Ground Acceleration (at present, one of most used instrumental intensity measures); this conversion further increases the potential of the macroseismic method. As presented in the paper, the first applications of the model have produced plausible and consistent results at national scale, both in terms of damage scenarios and total risk (economic loss, consequences to people).

Distribution and Evolution of Quantum Coherence for Open Multi‐Qubit Systems in Non‐Inertial Frames

AbstractThe distribution and evolution of quantum coherence for multi‐qubit W and GHz states of Dirac fields in the non‐inertial frames and under the action of local environments is studied. It is found that the N‐qubit W state has all orders of coherence (from bipartite to N‐partite subsystems), and the coherence of the whole system is equal to the sum of all the bipartite coherences in the whole time evolution. However, the evolved N‐qubit GHz state has its coherence belonged only to the whole system and no coherence resides in any subsystems. Further, it is found that the expressions of coherence for both W and GHz states are covariant with respect to the transformation of decaying rates.

2D DOA Estimation of Coherently Distributed Sources for Planar Arrays Based on Blind Signal Separation

A novel method is presented to estimate the direction-of-arrival (DOA) of coherently distributed (CD) sources for planar arrays. In the proposed method, the two-dimensional (2D) angular parameters are obtained by making use of the estimated generalized array manifold matrix, which is separated from the received observation data based on blind signal separation algorithm. The proposed method offers a number of advantages. First, the 2D central DOAs and angular spread variances can be estimated simultaneously. Second, the deterministic angular distributed functions (DADFs) of the CD sources do not need to know. Third, the special array geometries are not required, as the method is applicable to planar arrays. Computer simulations are shown to verify the efficacy of the proposed method.

Distribution and Generation of Quantum Coherence for Gaussian States in de Sitter Space

AbstractThe distribution and generation of quantum coherence for two‐mode and multi‐mode Gaussian states in de Sitter space are studied. It is found that the quantum coherence is redistributed among the mode in different open charts under the curvature effect of de Sitter space. In particular, the Gaussian coherence for the initially correlated state is found to survive in the limit of infinite curvature, while quantum entanglement vanishes in this limit. Unlike entanglement and steering, the coherence of a massive scalar field is more robust than a massless field under the influence of curvature of de Sitter space. In addition, it is shown that the curvature generates two‐mode Gaussian state and three‐mode Gaussian state quantum coherence among the open charts, even though the observers are localized in causally disconnected regions. It is worth noting that the gravity‐generated three‐mode coherence is extremely sensitive to the curvature effect for the conformal and massless scalar fields, which may be in principle employed to design an effective detector for the space curvature.

Propagation of a rectangular Laguerre-Gaussian correlated Schell-model beam in uniaxial crystal

The analytical equation of a rectangular Laguerre-Gaussian correlated Schell-model (LGCSM) beam in uniaxial crystal orthogonal to the optical axis is derived. The intensity and coherence properties of a rectangular LGCSM beam in uniaxial crystal are investigated by numerical simulations. It is shown that the symmetry of intensity and coherence distribution can be modulated by the ne/no. When ne/no>1 of uniaxial crystal, the multiple beams generating by a rectangular LGCSM beam will spread faster along x-direction than y-direction at the longer distance. The physical explanations of evolutions are analyzed in detail.

Spin-orbit coupled bosons in a double-well potential

We study the quantum phase coherence and atomic distribution of two-component spin-orbit coupled bosons in a disordered double-well potential. For the spin-orbit coupled bosons have the equal intraspecies interaction, i.e., U↑↑=U↓↓, the quantum phase coherence exhibits the single periodical oscillation behavior and has the local maxima at certain values of disorder without the interspecies interaction. Considering the interspecies interaction, the single periodical oscillation evolved into the double periodical oscillations when the intraspecies interaction larger than the interspecies interaction. For the spin-orbit coupled bosons have the unequal intraspecies interaction, i.e., U↑↑≠U↓↓, the quantum phase coherence shows a triple periodical oscillations behavior without the interspecies interaction. After adding the interspecies interaction, the quantum phase coherence evolves from the triple periodical oscillations to the double periodical oscillations or the single periodical oscillation. The resonance feature of the quantum phase coherence becomes significant when the strengths of the intraspecies and interspecies interactions are comparable. The atomic distribution shows the stairs character.

DOA estimation of coherently distributed sources in massive MIMO systems with unknown mutual coupling

In this paper, a direction of arrival (DOA) estimation algorithm for coherent distributed (CD) sources considering unknown mutual coupling in massive MIMO systems is proposed. By utilizing an enhanced sample covariance matrix (SCM) that matches well with massive MIMO systems, the proposed algorithm constructs a perturbed model and further exploits the sparse total east squares (STLS) technique to achieve DOA and angular spread estimation. With the DOA and angular spread estimates, the mutual coupling coefficients are given by solving the constrained minimization problem. Compared with the other state-of-the-art algorithms, the proposed algorithm not only can provide improved DOA estimation performance, but also can conquer the deficient scenario in a much easier way. Theoretical performance analysis and numerical examples validate the effectiveness of the proposed algorithm.

Semantic-based topic representation using frequent semantic patterns

Topic modeling discovers the hidden topics in a document collection. Most of the existing topic models focus only on word usage and generate the topics based on the word frequency and co-occurrence without considering the meaning of the text. In this paper, we propose a novel approach to generate a semantic pattern-based topic representation based on the meaning of the text to represent the topics in a document collection. The proposed approach considers both the semantics and co-occurrence of words to generate a set of frequent semantic patterns to represent each topic. The semantics are captured by matching the words in each topic with concepts in the Probase ontology. A set of frequent semantic patterns in each topic is generated based on the co-occurrence of the matched words to represent the topic. Hence, our approach differs from traditional topic models because of the meaningful frequent semantic patterns generated based on the ontology. The proposed topic representation was evaluated in terms of topic quality and information filtering performance against a set of state-of-the-art systems. Perplexity, coherence, and topic word distribution were examined in the topic quality evaluation. The generated frequent semantic patterns were used as features for the information filtering evaluation. Our topic representation outperformed in all the evaluations.

Results from the Ice Thickness Models Intercomparison eXperiment Phase 2 (ITMIX2)

Knowing the ice thickness distribution of a glacier is of fundamental importance for a number of applications, ranging from the planning of glaciological fieldwork to the assessments of future sea-level change. Across spatial scales, however, this knowledge is limited by the paucity and discrete character of available thickness observations. To obtain a spatially coherent distribution of the glacier ice thickness, interpolation or numerical models have to be used. Whilst the first phase of the Ice Thickness Models Intercomparison eXperiment (ITMIX) focused on approaches that estimate such spatial information from characteristics of the glacier surface alone, ITMIX2 sought insights for the capability of the models to extract information from a limited number of thickness observations. The analyses were designed around 23 test cases comprising both real-world and synthetic glaciers, with each test case comprising a set of 16 different experiments mimicking possible scenarios of data availability. A total of 13 models participated in the experiments. The results show that the inter-model variability in the calculated local thickness is high, and that for unmeasured locations, deviations of 16% of the mean glacier thickness are typical (median estimate, three-quarters of the deviations within 37% of the mean glacier thickness). This notwithstanding, limited sets of ice thickness observations are shown to be effective in constraining the mean glacier thickness, demonstrating the value of even partial surveys. Whilst the results are only weakly affected by the spatial distribution of the observations, surveys that preferentially sample the lowest glacier elevations are found to cause a systematic underestimation of the thickness in several models. Conversely, a preferential sampling of the thickest glacier parts proves effective in reducing the deviations. The response to the availability of ice thickness observations is characteristic to each approach and varies across models. On average across models, the deviation between modeled and observed thickness increase by 8.5% of the mean ice thickness every time the distance to the closest observation increases by a factor of 10. No single best model emerges from the analyses, confirming the added value of using model ensembles.

High resolution location of deep low-frequency tremors beneath the Kii Peninsula, Nankai subduction zone, Japan, using data from a dense seismic array

SUMMARY This study performs detection and location of deep low-frequency tremors beneath the Kii Peninsula, Nankai subduction zone, Japan, using data from a dense seismic array. We set a quantitative threshold for the tremor detection based on the Gaussian distribution of waveform coherence among stations to distinguish between tremor signal and noise. Then, we estimated slownesses and arrival azimuths by applying the Multiple Signal Classification method and performed hypocentre determination by backprojection onto the plate interface. During the analysed period of 2 yrs from July 2012 to July 2014, we detected 25155 tremor events which are approximately 2.2 times more than those in the AIST-tremor catalogue based on the conventional envelope correlation method ( 11475 events). This improvement is due to the detection of even weak amplitude tremors owing to the array analysis scheme, which uses recorded waveform’s phase information. Our high-resolution tremor catalogue leads to the following findings of the tremor activity in the Kii Peninsula. A few tremor episodes show continuous updip migration in the initial stage. The updip migration speed depends on whether the tremor migrates in the along-strike direction after the updip migration: approximately 1.0 km hr –1 for tremors that develop into the along-strike migration, and approximately 0.5 km hr–1 for those that do not. Estimated radiated energies are found to increase gradually with propagation into the updip direction. These findings suggest the depth dependence of the frictional strength on the plate interface. Furthermore, we noticed that accumulated radiated energies are positively correlated with the updip migration speed, and this relationship implies that fluid migration might play a role in the updip migration.

Remobilization and hypoxia-dependent migration of phosphorus at the coastal sediment-water interface

Sediment internal phosphorus (P) loading can be tightly associated with overlying water hypoxia. However, the effects of long-term seasonal hypoxia on the geochemical transition of P in P-poor coastal sediment and how this transition is linked to the early diagenesis of iron (Fe), sulfur (S) and carbon are still poorly understood. Here, we conducted a one-year monthly field investigation to study the (im)mobilization and migration of P among coastal sediment, porewater and overlying water. The coherent distribution of soluble Fe and mobile P and decoupled distribution of labile S (soluble sulfide) and mobile P in the depth profiles indicate that the redox cycling of Fe (but not S) dominates P mobility. Nevertheless, the monthly variation in the porewater soluble reactive P (SRP) presented significant positive correlations with that of the overlying water SRP. This finding highlights that hypoxia-fueled SRP migration from overlying water rather than weak diagenetic P mobilization due to deficient organic matter and solid labile P is the crucial factor responsible for internal P mobility over long time scales. Although SRP tends to migrate from overlying water to porewater, the potential risk of sediment labile P remobilization and reliberation to the overlying water is considerable.

A Low Complexity DOA Estimation Method of CD Sources in Impulsive Noise

Direction of arrival (DOA) estimation, as the main technology of passive radio monitoring and positioning, has been deeply investigated. However, the DOA for distributed sources is challenging to estimate in environments with impulsive noise. Although many methods have been proposed for DOA estimation, most of them assume that array output signals contain Gaussian noise. Therefore, the performance of these methods is often poor for alpha-stable distributed impulsive noise. Furthermore, subspace-based DOA estimation methods for distributed sources require a two-dimensional (2D) peak search, which increases the consumption of system computing resources. In this paper, a Q-function-based kernel function is proposed, and its properties are derived. On this basis, a novel DOA estimation method is proposed for coherently distributed (CD) sources in impulsive noise. To reduce computational complexity, a Lagrangian quadratic optimization function is derived by approximating the generalized array manifold of the CD source. By solving this optimization function, a 2D peak search can be reduced to several one-dimensional (1D) peak searches. The simulation results illustrate that the accuracy and robustness of the proposed method outperform those of existing methods.

Unambiguous State Discrimination with Intrinsic Coherence

We investigate the simulation of pure-mixed (quantum filtering) and mixed-mixed state discriminations, by discriminating a pair of pure states and comparing the optimal success probability with the ones for pure-mixed and mixed-mixed discriminations. It is shown thatunder the equal-fidelity condition, the pure-pure state discrimination scheme is superior to the pure-mixed (mixed-mixed) one. With respect to the simulation of filtering, the coherence is detrimental to the state discrimination for lower dimensional systems; while it is the opposite for the mixed-mixed case with symmetrically distributed coherence. This result is due to the different distribution of the intrinsic coherence in the two schemes. Extending this problem to infinite-dimensional systems, we find that the coherence which is detrimental to state discrimination may become helpful and vice versa.

Intensity and Coherence Characteristics of a Radial Phase-Locked Multi-Gaussian Schell-Model Vortex Beam Array in Atmospheric Turbulence

The theoretical descriptions for a radial phase-locked multi-Gaussian Schell-model vortex (RPLMGSMV) beam array is first given. The normalized intensity and coherence distributions of a RPLMGSMV beam array propagating in free space and atmospheric turbulence are illustrated and analyzed. The results show that a RPLMGSMV beam array with larger total number N or smaller coherence length σ can evolve into a beam with better flatness when the beam array translating into the flat-topped profile at longer distance z and the flatness of the flat-topped intensity distribution can be destroyed by the atmospheric turbulence at longer distance z. The coherence distribution of a RPLMGSMV beam array in atmospheric turbulence at the longer distance will have Gaussian distribution. The research results will be useful in free space optical communication using a RPLMGSMV beam array.

Understanding of Various Type of Unambiguous Discrimination in View of Coherence Distribution.

Unambiguous quantum state discrimination is a strategy where the conclusive result can always be trusted. This strategy is very important, since it can be used for various quantum information protocols, including quantum key distribution. However, in the view of quantumness, it is not clear what is going on in performing unambiguous quantum state discrimination. To answer the question, we investigate coherence distribution when unambiguous discrimination is performed by generalized measurement. Specially, we study coherence distribution in three cases, which consist of unambiguous quantum state discrimination, sequential quantum state discrimination, and assisted optimal discrimination, which are considered to be a family of unambiguous quantum state discrimination. In this investigation, we show that the structure of generalized measurements performing various types of unambiguous quantum state discrimination can be understood in terms of coherence distribution. Our result is not limited to the discrimination of two pure quantum states, but it is extended to the discrimination of two mixed states.

Evaluation of SAR C-band interferometric coherence time-series for coastal wetland hydropattern mapping

South America is the continent of wetlands, which represents more than 20% of its surface. Since the ecological integrity of wetlands strongly depends on their water sources and dynamics, it is fundamental to understand their hydrology. Large wetlands are usually located in inaccessible areas where remote sensing results are a fundamental tool for wetland monitoring, providing information over a broad range of spatial and temporal scales. Radar spaceborne sensors provide an excellent all-weather tool for monitoring and recent investigations have also shown that Interferometric SAR (InSAR) can be very valuable for wetland monitoring in addition to its regular uses in DEM generation and surface deformation analyses. The availability of new SAR satellites such as the Sentinel 1 and SAOCOM missions, with short revisit times and open data policies, repeat-pass interferometry can now provide long time-series of coherence for wetland monitoring. In this article, we used a SOM neural network to cluster a yearly series of Sentinel 1 B coherence images from the coastal plain of Samborombón Bay, Argentina, into temporal coherence patterns. The timing and coherence values of these patterns were interpreted in terms of landcover, vegetation phenology, water sources, and waterlogged condition. Although the SOM patterns did not show a one to one relationship with landcover types nor with the main water sources, their spatial distribution and temporal signature of coherence gave information on wetlands with different water dynamics. A key outcome of our study was that temporal patterns of coherence could be used to assess the impacts of land-use practices on wetland functioning, which deserves further exploration. The spatial distribution of the temporal coherence patterns can be used as a hypothesis for wetland hydropatterns, a key to hydrological functional type wetland classification. This approach can help us gain a better understanding of complex wetlands and foster their sustainable management, particularly combined with in situ fieldwork and other remote sensing sources, particularly repeat pass L-band coherence, which can give a better indication of soil wetness.

DOA Tracking of Two-Dimensional Coherent Distribution Source Based on Fast Approximated Power Iteration

Aiming at two-dimensional (2D) coherent distributed (CD) sources, this paper has proposed a direction of arrival (DOA) tracking algorithm based on signal subspace updating under the uniform rectangular array (URA). First, based on the hypothesis of small angular spreads of distributed sources, the rotating invariant relations of the signal subspace of the receive vector of URA are derived. An ESPRIT-like method is constructed for DOA estimation using two adjacent parallel linear arrays of URA. Through the synthesis of estimation by multiple groups of parallel linear arrays within URA arrays, the DOA estimation method for 2D CD sources based on URA is obtained. Then, fast approximated power iteration (FAPI) subspace tracking algorithm is used to update the signal subspace. In this way, DOA tracking of 2D CD sources can be realized by DOA estimation through signal subspace updating. This algorithm has a low computational complexity and good real-time tracking performance. In addition, the algorithm can track multiple CD sources without knowing the angular signal distribution functions, which is robust to model errors.

Coherence and Entanglement Dynamics in Training Variational Quantum Perceptron.

In quantum computation, what contributes supremacy of quantum computation? One of the candidates is known to be a quantum coherence because it is a resource used in the various quantum algorithms. We reveal that quantum coherence contributes to the training of variational quantum perceptron proposed by Y. Du et al., arXiv:1809.06056 (2018). In detail, we show that in the first part of the training of the variational quantum perceptron, the quantum coherence of the total system is concentrated in the index register and in the second part, the Grover algorithm consumes the quantum coherence in the index register. This implies that the quantum coherence distribution and the quantum coherence depletion are required in the training of variational quantum perceptron. In addition, we investigate the behavior of entanglement during the training of variational quantum perceptron. We show that the bipartite concurrence between feature and index register decreases since Grover operation is only performed on the index register. Also, we reveal that the concurrence between the two qubits of index register increases as the variational quantum perceptron is trained.

Twenty Years of Spanish Geoparks: Analysis and Future Prospects

Considering the number of UNESCO Global Geoparks, Spain is the second country in the world and the first country in Europe. This paper describes the historical development and the current reality of Spanish Geoparks with a geographical, geological, administrative and sociological analysis and explains the main reasons that have contributed to the successful spread of Spanish UNESCO Global Geoparks. This analysis describes also the main challenges for the future and introduces a fundamental question that will have to be discussed in many countries with an important number of Geoparks: the criteria to define a sustainable number of UNESCO Global Geoparks (UGGp) at the national level. The representativeness of the national geological main features and its geological heritage in UGGp is one the main factors that can contribute to defining a well-balanced and impartial strategy for a sustainable growth. Thus, the relevance of a national geosite inventory rises up as one of the important tools to organize a coherent national distribution and to help on the definition of the boundaries of UGGp.