Quantum discord and related measures of quantum correlations in XY chains

We examine the quantum correlations of spin pairs in the ground state of finite XY chains in a transverse field, by evaluating the quantum discord as well as other related entropic measures of quantum correlations. A brief review of the latter, based on generalized entropic forms, is also included. It is shown that parity effects are of crucial importance for describing the behavior of these measures below the critical field. It is also shown that these measures reach full range in the immediate vicinity of the factorizing field, where they become independent of separation and coupling range. Analytical and numerical results for the quantum discord, the geometric discord and other measures in spin chains with nearest neighbor coupling and in fully connected spin arrays are also provided.Comment: accepted in Int. J. Mod. Phys. B, special issue "Classical Vs Quantum correlations in composite systems" edited by L. Amico, S. Bose, V. Korepin and V. Vedra

Entanglement generation resonances in XY chains

We examine the maximum entanglement reached by an initially fully aligned state evolving in an XY Heisenberg spin chain placed in a uniform transverse magnetic field. Both the global entanglement between one qubit and the rest of the chain and the pairwise entanglement between adjacent qubits is analyzed. It is shown that in both cases the maximum is not a monotonous decreasing function of the aligning field, exhibiting instead a resonant behavior for low anisotropies, with pronounced peaks (a total of [n/2] peaks in the global entanglement for an $n$-spin chain), whose width is proportional to the anisotropy and whose height remains finite in the limit of small anisotropy. It is also seen that the maximum pairwise entanglement is not a smooth function of the field even in small finite chains, where it may exhibit narrow peaks above strict plateaus. Explicit analytical results for small chains, as well as general exact results for finite n-spin chains obtained through the Jordan-Wigner mapping, are discussed

Quantum correlations and least disturbing local measurements

We examine the evaluation of the minimum information loss due to an unread local measurement in mixed states of bipartite systems, for a general entropic form. Such quantity provides a measure of quantum correlations, reducing for pure states to the generalized entanglement entropy, while in the case of mixed states it vanishes just for classically correlated states with respect to the measured system, as the quantum discord. General stationary conditions are provided, together with their explicit form for general two-qubit states. Closed expressions for the minimum information loss as measured by quadratic and cubic entropies are also derived for general states of two-qubit systems. As application, we analyze the case of states with maximally mixed marginals, where a general evaluation is provided, as well as X states and the mixture of two aligned states.Comment: 10 pages, 3 figure

Conditional purity and quantum correlation measures in two qubit mixed states

We analyze and show experimental results of the conditional purity, the quantum discord and other related measures of quantum correlation in mixed two-qubit states constructed from a pair of photons in identical polarization states. The considered states are relevant for the description of spin pair states in interacting spin chains in a transverse magnetic field. We derive clean analytical expressions for the conditional local purity and other correlation measures obtained as a result of a remote local projective measurement, which are fully verified by the experimental results. A simple exact expression for the quantum discord of these states in terms of the maximum conditional purity is also derived.Comment: 16 pages, 5 figures, minor changes, to be published in J. Phys.

Generalized entropic measures of quantum correlations

We propose a general measure of non-classical correlations for bipartite systems based on generalized entropic functions and majorization properties. Defined as the minimum information loss due to a local measurement, in the case of pure states it reduces to the generalized entanglement entropy, i.e., the generalized entropy of the reduced state. However, in the case of mixed states it can be non-zero in separable states, vanishing just for states diagonal in a general product basis, like the Quantum Discord. Simple quadratic measures of quantum correlations arise as a particular case of the present formalism. The minimum information loss due to a joint local measurement is also discussed. The evaluation of these measures in a few simple relevant cases is as well provided, together with comparison with the corresponding entanglement monotones.Comment: 9 pages, 2 figure

Shell Model Monte Carlo Investigation of Rare Earth Nuclei

We utilize the Shell Model Monte Carlo (SMMC) method to study the structure of rare earth nuclei. This work demonstrates the first systematic ``full oscillator shell plus intruder'' calculations in such heavy nuclei. Exact solutions of a pairing plus quadrupole hamiltonian are compared with mean field and SPA approximations in several Dysprosium isotopes from A=152-162, including the odd mass A=153. Basic properties of these nuclei at various temperatures and spin are explored. These include energy, deformation, moments of inertia, pairing channel strengths, band crossing, and evolution of shell model occupation numbers. Exact level densities are also calculated and, in the case of 162 Dy, compared with experimental data.Comment: 40 pages; 24 figures; 2 tables. Update includes correction of figure labe

Virtual Network organizations and e-Procurement: A New Outsourcing Perspective

The make-or-buy dilemma represents one of the most important topic in the IS research field. The IT function, in fact, has been one of the first business areas to be outsourced. In this paper, we consider the outsourcing process not only as an economic decision driven by efficacy or efficiency but a real strategic move, driven by new business scenarios. In this new perspective, we consider ICT as a main factor enabling this change, where outsourcing is no longer a one-to-one relationship between two actors who regulate their transaction by a contract which establish terms and conditions of the exchange, but a one-to-X relationship where the outsourcing process is mediated by a technological interface such as the electronic marketplace which establish terms and condition of any transaction regulating the participation to e-marketplac

In-farm cost of an outbreak of diarrhoea in lambs

This article analyses the cost of diarrhoea in lambs on dairy sheep farms located in Grosseto (Italy). Farmers’ profits have recently declined due to a stable product price but increasing production costs. Animal diseases have a cascade of effects on farm productivity. Lamb enteric disease outbreaks, which result in mortality in the herd and reduced weight gain, can drastically compromise the income of farmers. An economic analysis of the impact of an outbreak of diarrhoea in lambs was thus performed, evaluating the cost of disease based on the main visible production losses (such as mortality, reduced weight gain and variation in milk production). A sensitivity analysis was also conducted by applying different observed ranges of prevalence and mortality associated with the disease. Finally, an economic scenario analysis was performed, considering different in-farm management options for delivering lambs to the abattoir, i.e. early, standard and late delivery. The results showed that a dairy sheep farm with around 300 lambs that delivers them to the abattoir at 30 days of age would experience a loss of between 50 and 1200 Euro during an outbreak of diarrhoea with a prevalence of 34.21 (23.54–44.88)% and a mortality of 15.69 (9.98–21.4)%