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D. Salgado

Publications and source records attributed to D. Salgado.

At least 19 recordsLinked to original sources
arXiv2023

Scalar-tensor theory with EGB term from Einstein Chern-Simons gravity

It is shown that the compactification a la Randall Sundrum of the so called, five dimensional Einstein Chern Simons action gravity leads to an action for a four dimensional scalar tensor gravity that includes a Gauss Bonnet term, which belongs to a particular case of the action of the Horndeski theory. The five dimensional action includes new gravitational degrees of freedom that were introduced requiring that the action be invariant under symmetries greater than the usual Poincare or (A)dS symmetries, namely the so called generalized Poincare algebras B5.

hep-th↗
arXiv2022

Generalized Einstein gravities and generalized AdS symmetries

We consider the curvatures 2 form asociated with AdSL4 valued one-form gauge connetion, and then we construct a four-dimensional action that generalize the Einstein-Hilbert gravity. It is shown that the Maxwell extension of Einstein gravity can be obtained from AdSL4-gravity making use of the Inonu-Wigner contraction method. In the same way, by gauging the AdSL5 spacetime algebra, the Einstein-Hilbert gravity is extended including the vector fields kab and ha which are associated with non-Abelian tensors and non Abelian vectors charges in the AdSL5 algebra. The B5 extension of Einstein gravity can be obtained from AdSL5 gravity using of the above mentioned contraction procedure. Some aspects of a gravity based on the algebra AdSL6 are considered in an appendix.

hep-th↗
arXiv2022

Use of Simulation Models for the Development of a Statistical Production Framework for Mobile Network Data with the simutils Package

We propose to use agent-based simulation models for the development of statistical methods in Official Statistics, especially in relation with the new digital data sources. We present a mobile network data simulator which is managed through the simutils R package which provides geospatial representations of the simulated data. While the synthetic data are produced by an external tool, our simutils package allows an R user to parameterize and run this external simulation tool, to build geospatial data structures from the simulation output or to compute several aggregates. The geospatial data structures were designed with the purpose of using them in a visualization package too. Useful simulation models require the incorporation of real metadata from mobile telecommunication networks driving us to the inclusion of functionalities allowing the user to specify and validate them. All metadata are specified using XML file whose structure are defined in corresponding XSD files. Our R package includes example data sets and we show here how validate the metadata, how to run a simulation and how build the geospatial data structures and how to compute different aggregates.

stat.AP↗
arXiv2013

The Relevance of the Preparation Concept in the Interpretation of Quantum Formalism

The preparation procedure, an undefined notion in quantum theory, has not had the relevance that it deserves in the interpretation of quantum mechanical formalism. Here we utilize the concepts of identical and similar preparation procedures to show the conceptual differences and mutual interconnections between the statistical and the conventional interpretation of quantum formalism. Although the statistical understanding, and its final logical consequence, hidden variables theories (this connexion being explained in the text), have a great intuitive appeal due to its fewer ontological difficulties, both recent experimental results and some theoretical developments seem to support an epistemic alternative closer to the conventional one. Nevertheless, we must not rule out the possibility that new theorems or new explanatory principles may modify the reigning supremacy of this interpretation.

quant-ph↗
arXiv2011

A Critical Discussion About The Methodology Of Quantum Theory

It is argued that the traditional "realist" methodology of physics, according to which human concepts, laws and theories can grasp the essence of reality, is incompatible with the most fruitful interpretation of quantum formalism. The proof rests on the violation by quantum mechanics of the foundational principles of that methodology. An alternative methodology, in which the construction of sciences finishes at the level of human experience, as standard quantum theory strongly suggests, is then conjectured.

quant-ph↗
arXiv2010

A cone approach to the quantum separability problem

Exploiting the cone structure of the set of unnormalized mixed quantum states, we offer an approach to detect separability independently of the dimensions of the subsystems. We show that any mixed quantum state can be decomposed as $ρ=(1-λ)C_ρ+λE_ρ$, where $C_ρ$ is a separable matrix whose rank equals that of $ρ$ and the rank of $E_ρ$ is strictly lower than that of $ρ$. With the simple choice $C_ρ=M_{1}\otimes M_{2}$ we have a necessary condition of separability in terms of $λ$, which is also sufficient if the rank of $E_ρ$ equals 1. We give a first extension of this result to detect genuine entanglement in multipartite states and show a natural connection between the multipartite separability problem and the classification of pure states under stochastic local operations and classical communication (SLOCC). We argue that this approach is not exhausted with the first simple choices included herein.

quant-ph↗
arXiv2008

Sequential Implementation of Global Quantum Operations

We study the possibility for a global unitary applied on an arbitrary number of qubits to be decomposed in a sequential unitary procedure, where an ancillary system is allowed to interact only once with each qubit. We prove that sequential unitary decompositions are in general impossible for genuine entangling operations, even with an infinite-dimensional ancilla, being the controlled-NOT gate a paradigmatic example. Nevertheless, we find particular nontrivial operations in quantum information that can be performed in a sequential unitary manner, as is the case of quantum error correction and quantum cloning.

quant-ph↗
arXiv2008

Quantum Mechanics, is it magic?

We show that quantum mechanics is the first theory in human history that violates the basic a priori principles that have shaped human thought since immemorial times. Therefore although it is more contrary to magic than any body of knowledge could be, what could be called its magic precisely resides in this violation.

physics.hist-ph↗
arXiv2007

Sequential Quantum Cloning

Not all unitary operations upon a set of qubits can be implemented by sequential interactions between each qubit and an ancillary system. We analyze the specific case of sequential quantum cloning 1->M and prove that the minimal dimension D of the ancilla grows linearly with the number of clones M. In particular, we obtain D = 2M for symmetric universal quantum cloning and D = M+1 for symmetric phase-covariant cloning. Furthermore, we provide a recipe for the required ancilla-qubit interactions in each step of the sequential procedure for both cases.

quant-ph↗
arXiv2007

Inductive Entanglement Classification of Four Qubits under SLOCC

Using an inductive approach to classify multipartite entangled states under stochastic local operations and classical communication introduced recently by the authors [Phys. Rev. A 74, 052336 (2006)], we give the complete classification of four-qubit entangled pure states. Apart from the expected degenerate classes, we show that there exist eight inequivalent ways to entangle four qubits. In this respect, permutation symmetry is taken into account and states with a structure differing only by parameters inside a continuous set are considered to belong to the same class.

quant-ph↗
arXiv2006

Inductive classification of multipartite entanglement under SLOCC

We propose an inductive procedure to classify N-partite entanglement under stochastic local operations and classical communication (SLOCC) provided such a classification is known for N-1 qubits. The method is based upon the analysis of the coefficient matrix of the state in an arbitrary product basis. We illustrate this approach in detail with the well-known bi- and tripartite systems, obtaining as a by-product a systematic criterion to establish the entanglement class of a given pure state without resourcing to any entanglement measure. The general case is proved by induction, allowing us to find an upper bound for the number of N-partite entanglement classes in terms of the number of entanglement classes for N-1 qubits.

quant-ph↗
arXiv2005

Another dual formulation of the separability problem

We show how the separability problem is dual to that of decomposing any given matrix into a conic combination of rank-one partial isometries, thus offering a duality approach different to the positive maps characterization problem. Several inmediate consequences are analyzed: (i) a sufficient criterion for separability for bipartite quantum systems, (ii) a complete solution to the separability problem for pure states also of bipartite systems independent of the classical Schmidt decomposition method and (iii) a natural generalization of these results to multipartite systems.

quant-ph↗
arXiv2005

On nonlinear evolution and supraluminal communication between finite quantum systems

We revise the 'no-signaling' condition for the supraluminal communication between two spatially separated finite quantum systems of arbitrary dimensions, thus generalizing a similar preceding approach for two-qubits: non-linear evolution does not necessarily imply the possibility of supraluminal communication between any sort of finite quantum systems.

quant-ph↗
arXiv2004

A formula for the Bloch vector of some Lindblad quantum systems

Using the Bloch representation of an N-dimensional quantum system and immediate results from quantum stochastic calculus, we establish a closed formula for the Bloch vector, hence also for the density operator, of a quantum system following a Lindblad evolution with selfadjoint Lindblad operators.

quant-ph↗
arXiv2002

Expressing Decoherence with Spectral and Stochastic Methods

We suggest a novel proposal to express decoherence in open quantum systems by jointly employing spectral and stochastic methods. This proposal, which basically perturbs the unitary evolution operator in a random fashion, allows us to embrace both markovian and nonmarkovian situations with little extra effort. We argue that it can be very suitable to deal with models where an approximation neglecting some degrees of freedom is undertaken. Mathematical simplicity is also obtained both to solve some master equations and to arrive at experimentally measured decoherence functions.

quant-ph↗
arXiv2002

Comment on ``Dynamics of open quantum systems initially entangled with environment: Beyond the Kraus representation'' [PRA 64, 062106 (2001)]

We correct a mistake in a result reported in [PRA 64, 062106 (2001)], where it is rightfully argued that initial correlations between a system and its environment may render the system reduced dynamics not completely positive. We prove how not only these initial correlations but also the specific joint dynamics does play a significant role in the question of the complete positivy of the reduced dynamics.

quant-ph↗