Qubit-portraits of qudit states and quantum correlations

The machinery of qubit-portraits of qudit states, recently presented, is consider here in more details in order to characterize the presence of quantum correlations in bipartite qudit states. In the tomographic representation of quantum mechanics, Bell-like inequalities are interpreted as peculiar properties of a family of classical joint probability distributions which describe the quantum state of two qudits. By means of the qubit-portraits machinery a semigroup of stochastic matrices can be associated to a given quantum state. The violation of the CHSH inequalities is discussed in this framework with some examples, we found that quantum correlations in qutrit isotropic states can be detected by the suggested method while it cannot in the case of qutrit Werner states.Comment: 12 pages, 4 figure

Invariant measures on multimode quantum Gaussian states

We derive the invariant measure on the manifold of multimode quantum Gaussian states, induced by the Haar measure on the group of Gaussian unitary transformations. To this end, by introducing a bipartition of the system in two disjoint subsystems, we use a parameterization highlighting the role of nonlocal degrees of freedom -- the symplectic eigenvalues -- which characterize quantum entanglement across the given bipartition. A finite measure is then obtained by imposing a physically motivated energy constraint. By averaging over the local degrees of freedom we finally derive the invariant distribution of the symplectic eigenvalues in some cases of particular interest for applications in quantum optics and quantum information.Comment: 17 pages, comments are welcome. v2: presentation improved and typos corrected. Close to the published versio

On the classical capacity of quantum Gaussian channels

The set of quantum Gaussian channels acting on one bosonic mode can be classified according to the action of the group of Gaussian unitaries. We look for bounds on the classical capacity for channels belonging to such a classification. Lower bounds can be efficiently calculated by restricting to Gaussian encodings, for which we provide analytical expressions.Comment: 10 pages, IOP style. v2: minor corrections, close to the published versio

Non-existence of isometry-invariant Hadamard states for a Kruskal black hole in a box and for massless fields on 1+1 Minkowski spacetime with a uniformly accelerating mirror

We conjecture that (when the notion of Hadamard state is suitably adapted to spacetimes with timelike boundaries) there is no isometry-invariant Hadamard state for the massive or massless covariant Klein-Gordon equation defined on the region of the Kruskal spacetime to the left of a surface of constant Schwarzschild radius in the right Schwarzschild wedge when Dirichlet boundary conditions are put on that surface. We also prove that, with a suitable definition for ‘boost-invariant Hadamard state’ (which we call ‘strongly boost-invariant globally-Hadamard’) which takes into account both the existence of the timelike boundary and the special infra-red pathology of massless fields in 1+1 dimensions, there is no such state for the massless wave equation on the region of 1+1 Minkowski space to the left of an eternally uniformly accelerating mirror – with Dirichlet boundary conditions at the mirror. We argue that this result is significant because, as we point out, such a state does exist if there is also a symmetrically placed decelerating mirror in the left wedge (and the region to the left of this mirror is excluded from the spacetime). We expect a similar existence result to hold for Kruskal when there are symmetrically placed spherical boxes in both right and left Schwarzschild wedges. Our Kruskal no-go conjecture raises basic questions about the nature of the black holes in boxes considered in black hole thermodynamics. If true, it would lend further support to the conclusion of B. S. Kay ‘Instability of enclosed horizons’, Gen. Rel. Grav. 47, 1-27 (2015) (arXiv: 1310.7395) that the nearest thing to a description of a black hole in equilibrium in a box in terms of a classical spacetime with quantum fields propagating on it has, for the classical spacetime, the exterior Schwarzschild solution, with the classical spacetime picture breaking down near the horizon. Appendix B to the paper points out the existence of, and partially fills, a gap in the proofs of the theorems in B. S. Kay and R. M. Wald, ‘Theorems on the uniqueness and thermal properties of stationary, nonsingular, quasifree states on spacetimes with a bifurcate Killing horizon’, Phys. Rep. 207, 49-136 (1991)

Stakeholder discourse and water management ? implementation of the participatory model CATCH in a Northern Italian alpine sub-catchment

International audienceThe Water Framework Directive (WFD, directive 2000/60/EC) was created to ensure the sustainable use of water resources in the European Union. A central guideline included throughout the directive is a call for the participation of stakeholders in the management of these resources. Involving stakeholders is an important step to ensure that catchment management plans take into consideration local experience in the development of these plans and the impact of the plans on local interests. This paper describes and analyses the results of a series of workshops to facilitate implementation of the WFD at a catchment level based on the stakeholder participation model, CATCH. To test the usefulness of the CATCH model, developed for water management in a catchment area, a sub-catchment in an alpine valley in the north-east of Italy, the Alta Valsugana in the Province of Trento, was chosen as the setting for a series of workshops. In this valley water is fundamental for activities associated with agriculture, domestic use, energy production, sports and recreation. In the recent past the valley has had serious problems related to water quality and quantity. Implementation of water management plans under the WFD may lead to conflicts within the catchment between different stakeholder interest groups. Including stakeholders in the development of management plans not only follows the guidelines of the WFD but also could result in a more locally adapted and acceptable plan for the catchment. A new stakeholder analysis methodology was developed and implemented in order to identify the relevant stakeholders of the area and then two sets of workshops involving the key stakeholders identified were conducted in Spring 2006. The CATCH meetings were a new experience for the participants, who had to deal with both the principles of the WFD in general and the participation requirement in particular. During the meetings, the CATCH model played a very important role in structuring the participatory process. It provided a general framework consisting of a sequence of steps that helped the participants to reach the goal of the process: the identification and evaluation of measures to improve water management in the catchment. This test of the CATCH model showed it to be a dynamic and flexible tool, useful for structuring and guiding the participation process, without imposing undue restrictions on influencing the outcome of stakeholder participation in a small catchment

Stakeholder discourse and water management in a catchment in northern Italy

International audienceThe Water Framework Directive (WFD; directive 2000/60/EC) was created to ensure the sustainable use of water resources in the European Union. A central guideline included throughout the directive is a call for the participation of stakeholders in the management of these resources. Involving stakeholders is an important step to ensure that catchment management plans take into consideration local experience in the development of these plans and the impact of the plans on local interests. This paper describes and analyses the results of a series of workshops to facilitate implementation of the WFD at a catchment level based on the stakeholder participation model, CATCH. To test the usefulness of the stakeholder participation model CATCH for water management in a catchment area, a sub-catchment in an alpine valley in the north-east of Italy, the Alta Valsugana in the Province of Trento, was chosen as the setting for a series of workshops. In this valley water is fundamental for activities associated with agriculture, domestic use, energy production, sports and recreation. In the recent past the valley has had serious problems related to water quality and quantity. Implementation of water management plans under the WFD may lead to conflicts within the catchment between different stakeholder interest groups. Including stakeholders in the development of management plans not only follows the guidelines of the WFD but also could result in a more locally adapted and acceptable plan for the catchment. A new stakeholder analysis methodology was developed and implemented in order to identify the relevant stakeholders of the area and then two sets of workshops involving the key stakeholders identified were conducted in Spring 2006. The CATCH meetings were a new experience for the participants, who had to deal with both the principles of the WFD in general and the participation requirement in particular. During the meetings, the CATCH model played a very important role in structuring the participatory process. It provided a general framework consisting of a sequence of steps that helped the participants to reach the goal of the process; the identification and evaluation of measures to improve water management in the catchment. This test of the CATCH model showed it to be a dynamic and flexible tool, useful for structuring and guiding the participation process, without imposing undue restrictions on influencing the outcome of stakeholder participation in a small catchment

The Application of a Simple Method for the Verification of Weather Forecasts and Seasonal Variations in Forecast Accuracy

The evaluation of weather forecast accuracy has always been a difficult subject to address for many reasons. In this study, a simple semiobjective method is used to examine the accuracy of zone forecasts issued by the Weldon Spring (Saint Louis) National Weather Service (NWS) Office for mid-Missouri over a period of 416 days with the goal of demonstrating the utility of this method. Zone forecasts were chosen because these forecasts are typically what the public will receive either directly or indirectly from various media outlets. Not surprising, the evaluation method used here demonstrates that forecasts issued by the NWS and the Nested Grid Model (NGM) model output statistics (MOS) represent a considerable improvement over persistence or climatological baseline forecasts. NWS forecasts were slightly better than NGM MOS forecasts, especially when considering temperature and precipitation only. All forecasts showed distinct seasonal variability. The NWS winter-season forecasts were superior to those issued in the summer season, and this superiority was found to be a function of the precipitation forecast parameter. This technique might represent an easily understandable and concise method for providing weather forecast performance information to the general public in such a way that it would instill or reinforce public confidence in the accuracy of weather forecasts

Memory effects in attenuation and amplification quantum processes

With increasing communication rates via quantum channels, memory effects become unavoidable whenever the use rate of the channel is comparable to the typical relaxation time of the channel environment. We introduce a model of a bosonic memory channel, describing correlated noise effects in quantum-optical processes via attenuating or amplifying media. To study such a channel model, we make use of a proper set of collective field variables, which allows us to unravel the memory effects, mapping the n-fold concatenation of the memory channel to a unitarily equivalent, direct product of n single-mode bosonic channels. We hence estimate the channel capacities by relying on known results for the memoryless setting. Our findings show that the model is characterized by two different regimes, in which the cross correlations induced by the noise among different channel uses are either exponentially enhanced or exponentially reduced.Comment: 10 pages, 7 figures, close to the published versio