Probing the sign of on-site Hubbard interaction by two-particle quantum walks

We consider two identical bosons propagating on a one-dimensional lattice and address the prob- lem of discriminating whether their mutual on-site interaction is attractive or repulsive. We suggest a probing scheme based on the properties of the corresponding two-particle quantum walks, and show that the sign of the interaction introduces specific and detectable features in the dynamics of quantum correlations, thus permitting to discriminate between the two cases. We also discuss how these features are connected to the band-structure of the Hubbard Hamiltonian, and prove that discrimination may be obtained only when the two walkers are initially prepared in a superposition of localized states.Comment: 9 pages, 9 figure

Experiencing the Presence: Degrees of Closeness in the Digital Biographies of Migration

Among the many representations of migration, relevant prominence has been acquired by multimedia biographic discourses and digital enriched documentaries that reproduce the direct experience of migrants and their relationship with hosting societies. This paper aims at proposing a scale of the possible degrees of proximity or closeness in the contemporary media discourses about migration. Drawing on the semiotics of media experience, we focus on how biographic theatrical video, digital artistic based VR installation, data visualization platforms and web documentaries contribute to shape the figure of the migrant and of the border, and how they challenge the dialectic opposition between presence and distance in regard of the migration experience. In this direction, contemporary discourses on migration and migrants\u2019 digital biographies are not only characterized by recovering the so called \u201ccapture of speech\u201d of migrants or what idea of border and Self has been produced. Indeed, they are marked by their capacity to generate effects of presence of and to the direct experience of the migrants\u2019 lives

Continuous-time quantum walks on planar lattices and the role of the magnetic field

We address the dynamics of continuous-time quantum walk (CTQW) on planar two-dimensional (2D) lattice graphs, i.e., those forming a regular tessellation of the Euclidean plane (triangular, square, and honeycomb lattice graphs). We first consider the free particle: On square and triangular lattice graphs we observe the well-known ballistic behavior, whereas on the honeycomb lattice graph we obtain a sub-ballistic one, although still faster than the classical diffusive one. We impute this difference to the different amount of coherence generated by the evolution and, in turn, to the fact that, in 2D, the square and the triangular lattices are Bravais lattices, whereas the honeycomb one is non-Bravais. From the physical point of view, this means that CTQWs are not universally characterized by the ballistic spreading. We then address the dynamics in the presence of a perpendicular uniform magnetic field and study the effects of the field by two approaches: (i) introducing the Peierls phase factors, according to which the tunneling matrix element of the free particle becomes complex or (ii) spatially discretizing the Hamiltonian of a spinless charged particle in the presence of a magnetic field. Either way, the dynamics of an initially localized walker is characterized by a lower spread compared to the free particle case; larger fields correlate to more localized stays of the walker. Remarkably, upon analyzing the dynamics by spatial discretization of the Hamiltonian (vector potential in the symmetric gauge), we obtain that the variance of the space coordinate is characterized by pseudo-oscillations, a reminiscence of the harmonic oscillator behind theHamiltonian in the continuum, whose energy levels are the well-known Landau levels

Enterprise Eco-watching and Appraisal: Asset Modelling and Sustainability Assessment

AbstractAt the millennium turnover, the ecology globalisation shows the impeding threats of over-depletion/pollution: the sustainable growth requires supply-chain visibility, resource bookkeeping and renovation planning. The lifecycle starts when the idea of a product is born and lasts until complete disposal after realisation and operation. In the musts’ specification/analysis, the basic design (global plan, detailed design, assembly design, etc.) are followed by manufacturing, assembly, testing, diagnostics and operation, advertising, service, maintenance, etc.; then, disassembly and firing are scheduled, requiring reclamation and recovery, by re-cycling (material reprocessing) or re-using (part refurbishing). The present paper provides pilot clues for understanding the product-process agendas, using the TYPUS metrics and the KILT model, developed by the authors, in previous works

Universality of the fully connected vertex in Laplacian continuous-time quantum walk problems

A fully connected vertex w in a simple graph G of order N is a vertex connected to all the other N − 1 vertices. Upon denoting by L the Laplacian matrix of the graph, we prove that the continuous-time quantum walk (CTQW)—with Hamiltonian H = γL—of a walker initially localized at |w does not depend on the graph G. We also prove that for any Grover-like CTQW—with Hamiltonian H = γL + w λw|w w|—the probability amplitude at the fully connected marked vertices w does not depend on G. The result does not hold for CTQW with Hamiltonian H = γA (adjacency matrix). We apply our results to spatial search and quantum transport for single and multiple fully connected marked vertices, proving that CTQWs on any graph G inherit the properties already known for the complete graph of the same order, including the optimality of the spatial search. Our results provide a unified framework for several partial results already reported in literature for fully connected vertices, such as the equivalence of CTQWand of spatial search for the central vertex of the star and wheel graph, and any vertex of the complete graph