Realistic continuous-variable quantum teleportation with non-Gaussian resources

We present a comprehensive investigation of nonideal continuous-variable quantum teleportation implemented with entangled non-Gaussian resources. We discuss in a unified framework the main decoherence mechanisms, including imperfect Bell measurements and propagation of optical fields in lossy fibers, applying the formalism of the characteristic function. By exploiting appropriate displacement strategies, we compute analytically the success probability of teleportation for input coherent states, and two classes of non-Gaussian entangled resources: Two-mode squeezed Bell-like states (that include as particular cases photon-added and photon-subtracted de-Gaussified states), and two-mode squeezed cat-like states. We discuss the optimization procedure on the free parameters of the non-Gaussian resources at fixed values of the squeezing and of the experimental quantities determining the inefficiencies of the non-ideal protocol. It is found that non-Gaussian resources enhance significantly the efficiency of teleportation and are more robust against decoherence than the corresponding Gaussian ones. Partial information on the alphabet of input states allows further significant improvement in the performance of the non-ideal teleportation protocol.Comment: 14 pages, 6 figure

Optimization of the transmission of observable expectation values and observable statistics in Continuous Variable Teleportation

We analyze the statistics of observables in continuous variable quantum teleportation in the formalism of the characteristic function. We derive expressions for average values of output state observables in particular cumulants which are additive in terms of the input state and the resource of teleportation. Working with Squeezed Bell-like states, which may be optimized in a free parameter for better teleportation performance we discuss the relation between resources optimal for fidelity and for different observable averages. We obtain the values of the free parameter which optimize the central momenta and cumulants up to fourth order. For the cumulants the distortion between in and out states due to teleportation depends only on the resource. We obtain optimal parameters for the second and fourth order cumulants which do not depend on the squeezing of the resource. The second order central momenta which is equal to the second order cumulants and the photon number average are optimized by the same resource. We show that the optimal fidelity resource, found in reference (Phys. Rev. A {\bf 76}, 022301 (2007)) to depend also on the characteristics of input, tends for high squeezing to the resource which optimizes the second order momenta. A similar behavior is obtained for the resource which optimizes the photon statistics which is treated here using the sum of the squared differences in photon probabilities of input and output states as the distortion measure. This is interpreted to mean that the distortions associated to second order momenta dominates the behavior of the output state for large squeezing of the resource. Optimal fidelity and optimal photon statistics resources are compared and is shown that for mixtures of Fock states they are equivalent.Comment: 25 pages, 11 figure

Hierarchies of Geometric Entanglement

We introduce a class of generalized geometric measures of entanglement. For pure quantum states of $N$ elementary subsystems, they are defined as the distances from the sets of $K$-separable states ($K=2,...,N$). The entire set of generalized geometric measures provides a quantification and hierarchical ordering of the different bipartite and multipartite components of the global geometric entanglement, and allows to discriminate among the different contributions. The extended measures are applied to the study of entanglement in different classes of $N$-qubit pure states. These classes include $W$ and $GHZ$ states, and their symmetric superpositions; symmetric multi-magnon states; cluster states; and, finally, asymmetric generalized $W$-like superposition states. We discuss in detail a general method for the explicit evaluation of the multipartite components of geometric entanglement, and we show that the entire set of geometric measures establishes an ordering among the different types of bipartite and multipartite entanglement. In particular, it determines a consistent hierarchy between $GHZ$ and $W$ states, clarifying the original result of Wei and Goldbart that $W$ states possess a larger global entanglement than $GHZ$ states. Furthermore, we show that all multipartite components of geometric entanglement in symmetric states obey a property of self-similarity and scale invariance with the total number of qubits and the number of qubits per party.Comment: 16 pages, 7 figures. Final version, to appear in Phys. Rev.

Quantum characterization of bipartite Gaussian states

Gaussian bipartite states are basic tools for the realization of quantum information protocols with continuous variables. Their complete characterization is obtained by the reconstruction of the corresponding covariance matrix. Here we describe in details and experimentally demonstrate a robust and reliable method to fully characterize bipartite optical Gaussian states by means of a single homodyne detector. We have successfully applied our method to the bipartite states generated by a sub-threshold type-II optical parametric oscillator which produces a pair of thermal cross-polarized entangled CW frequency degenerate beams. The method provide a reliable reconstruction of the covariance matrix and allows to retrieve all the physical information about the state under investigation. These includes observable quantities, as energy and squeezing, as well as non observable ones as purity, entropy and entanglement. Our procedure also includes advanced tests for Gaussianity of the state and, overall, represents a powerful tool to study bipartite Gaussian state from the generation stage to the detection one

Developmental perspectives on Europe

The crisis of 2008–2009 has ended, stockmarkets skyrocketed in 2012–2013, while growth of the real sector remained sluggish in Europe. This article attempts to explain the latter puzzle. Analyzing long term factors, the costs of short-termism in crisis management become obvious. The limitations of EU as a growth engine are highlighted

Prospect theory and tax evasion: a reconsideration of the Yitzhaki puzzle

The standard expected utility (EUT) model of tax evasion predicts that evasion is decreasing in the marginal tax rate (the Yitzhaki puzzle). Recent literature shows cases in which incorporating prospect theory (PT) does and does not overturn the Puzzle. In a general environment that nests both PT and EUT preferences, we provide a detailed study of how the elements of PT affect the Puzzle. PT does not always reverse the Puzzle, hence we give and interpret conditions for when it does and does not. When allowing for stigma and/or variable audit probability, PT reverses the Puzzle in the same way and with the same limitations as does EUT, if equally augmented

Quality Assurance Driving Factors as Antecedents of Knowledge Management: a Stakeholder-Focussed Perspective in Higher Education

Similar to many other types of organisations, the successful development of higher education institutions generally depends on proactive multi-stakeholder management strategy. As a social responsibility of universities, quality assurance (QA) of higher education is already an established research domain. However, the issues that serve as driving factors in higher education’s quality are acknowledged in this vast knowledge stream in a dispersed way. An objective of this paper is to provide a quick snapshot of the major QA driving factors in higher education. Another objective here is to discuss the significance of these existing QA driving factors in higher education as prospective antecedents of knowledge management among the key stakeholders in the higher education sector and beyond. An inductive constructivist approach is followed to review the relevant QA driving factors from the extant scholarly views. A number of relevant factors are précised from the literature that would be instrumental to uphold quality in higher education. The discussion demonstrates that these factors are also significant to transfer and share knowledge between the key stakeholders not only for universities, but also for businesses, governments and other organisational stakeholders. The paper proposes a framework of the QA drivers’ application for meaningful knowledge transfer between diverse stakeholders and clarifies the framework’s managerial implications. This conceptual framework specifies different scenarios and perspectives of QA drivers’ application in the global education sector. The academic novelty is based on the inductive approach applied in the paper. QA practitioners will be able to follow these factors as steering phenomena to effectively assure quality, in relation to their multi-stakeholder relationships in higher education and beyond

Multipartite entangled states in particle mixing

In the physics of flavor mixing, the flavor states are given by superpositions of mass eigenstates. By using the occupation number to define a multiqubit space, the flavor states can be interpreted as multipartite mode-entangled states. By exploiting a suitable global measure of entanglement, based on the entropies related to all possible bipartitions of the system, we analyze the correlation properties of such states in the instances of three- and four-flavor mixing. Depending on the mixing parameters, and, in particular, on the values taken by the free phases, responsible for the CP-violation, entanglement concentrates in preferred bipartitions. We quantify in detail the amount and the distribution of entanglement in the physically relevant cases of flavor mixing in quark and neutrino systems. By using the wave packet description for localized particles, we use the global measure of entanglement, suitably adapted for the instance of multipartite mixed states, to analyze the decoherence induced by the free evolution dynamics on the quantum correlations of stationary neutrino beams. We define a decoherence length as the distance associated with the vanishing of the coherent interference effects among massive neutrino states. We investigate the role of the CP-violating phase in the decoherence process.Comment: 18 pages, 7 figure

A study of the efficiency of the class of WW-states as a quantum channel

Recently, a new class of $W$-states has been defined by Agarwal and Pati \cite{agarwal} and it has been shown that they can be used as a quantum channel for teleportation and superdense coding. In this work, we identify those three-qubit states from the set of the new class of $W$-states which are most efficient or suitable for quantum teleportation. We show that with some probability $|W_1>=(1/2)(|100>+|010>+\sqrt{2}|001>)$ is best suited for teleportation channel in the sense that it does not depend on the input state.Comment: 7 pages, Late