1,721,079 research outputs found
Controllability of quantum walks on graphs
No full textIn this paper, we consider discrete time quantum walks on graphs with
coin, focusing on the decentralized model, where the coin operation is allowed to
change with the vertex of the graph. When the coin operations can be modified at
every time step, these systems can be looked at as control systems and techniques of
geometric control theory can be applied. In particular, the set of states that one can
achieve can be described by studying controllability. Extending previous results, we
give a characterization of the set of reachable states in terms of an appropriate Lie
algebra. Controllability is verified when any unitary operation between two states can
be implemented as a result of the evolution of the quantum walk. We prove general
results and criteria relating controllability to the combinatorial and topological properties
of the walk. In particular, controllability is verified if and only if the underlying
graph is not a bipartite graph and therefore it depends only on the graph and not on the
particular quantum walk defined on it.We also provide explicit algorithms for control
and quantify the number of steps needed for an arbitrary state transfer. The results of
the paper are of interest in quantum information theory where quantum walks are used
and analyzed in the development of quantum algorithms
Optimal steering for an extended class of nonholonomic systems using Lagrange functionals
No full text
Quantum Symmetries and Cartan Decompositions in Arbitrary Dimensions
No full textDecompositions of Lie groups are used in systems and control, both to analyse dynamics and to design control algorithms for systems with state varying on a Lie group. In this paper, we investigate the relation between Cartan decompositions of the unitary group and discrete quantum symmetries. To every Cartan decomposition, there corresponds a quantum symmetry which is the identity when applied twice. As an application, we describe a new and general method to obtain Cartan decompositions of the unitary group of evolutions of multipartite systems from Cartan decompositions on the single subsystems. The resulting decomposition, which we call of the odd - even type, contains, as a special case, the concurrence canonical decomposition (CCD) presented in [ 6 - 8] in the context of entanglement theory. The CCD is therefore extended from the case of a multipartite system of N qubits to the case where the component subsystems have arbitrary dimensions. We present an example of application of the results to control design for quantum systems
Families of solutions of matrix Riccati equations
No full textThe J. C. Willems-Coppel-Shayman geometric characterization of solutions of the algebraic Riccati equation (ARE) is extended to asymmetric Riccati dierential equations with time varying coefficients. The coefficients do not need to satisfy any definiteness, periodicity, or system-theoretic condition. More precisely, given any two solutions X1(t) and X2(t) of such equation on a given interval [t0; t1], we show how to construct a family of solutions of the same equation of the form X(t) = (I −(t))X1(t) + (t)X2(t), where is a suitable matrix-valued function. Even when
specialized to the case of X1 and X2 equilibrium solutions of a symmetric equation with constant coefficients, our results considerably extend the classical ones, as no further assumption is made on the pair X1, X2 and on the coefficient matrices
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Evoluzione del concetto di abitare: aspetti sanitari, progettuali e tecnologici
No full textATTI DEL 40°CONGRESSO NAZIONALE SITI
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