Quantum computing with incoherent resources and quantum jumps

Spontaneous emission and the inelastic scattering of photons are two natural processes usually associated with decoherence and the reduction in the capacity to process quantum information. Here we show that when suitably detected, these photons are sufficient to build all the fundamental blocks needed to perform quantum computation in the emitting qubits while protecting them from deleterious dissipative effects. We exemplify by showing how to teleport an unknown quantum state and how to efficiently prepare graph states for the implementation of measurement-based quantum computation.Comment: 5 pages, 5 figure

A Heuristic Strategy to Compute Ensemble of Trajectories for 3D Low Cost Earth-Moon Transfers

The problem of finding optimal trajectories is essential for modern space mission design. When considering multibody gravitational dynamics and exploiting both low-thrust and high-thrust and alternative forms of propulsion such as solar sailing, sets of good initial guesses are fundamental for the convergence to local or global optimal solutions, using both direct or indirect methods available to solve the optimal control problem. This paper deals with obtaining preliminary trajectories that are designed to be good initial guesses as input to search optimal low-energy short-time Earth-Moon transfers with ballistic capture. A more realistic modelling is introduced, in which the restricted four-body system Sun-Earth-Moon-Spacecraft is decoupled in two patched planar Circular Restricted Three-Body Problems, taking into account the inclination of the orbital plane of the Moon with respect to the ecliptic. We present a heuristic strategy based on the hyperbolic invariant manifolds of the Lyapunov orbits around the Lagrangian points of the Earth- Moon system to obtain ballistic capture orbits around the Moon that fulfill specific mission requirements. Moreover, quasi-periodic orbits of the Sun-Earth system are exploited using a genetic algorithm to find optimal solutions with respect to total Dv, time of flight and altitude at departure. Finally, the procedure is illustrated and the full transfer trajectories assessed in view of relevant properties. The proposed methodology provides sets of low-cost and shorttime initial guesses to serve as inputs to compute fully optimized three-dimensional solutions considering different propulsion technologies, such as low, high, and hybrid thrust, and/or using more realistic models

The Geometry of Entanglement Sudden Death

In open quantum systems, entanglement can vanish faster than coherence. This phenomenon is usually called sudden death of entanglement. In this paper sudden death of entanglement is discussed from a geometrical point of view, in the context of two qubits. A classification of possible scenarios is presented, with important known examples classified. Theoretical and experimental construction of other examples is suggested as well as large dimensional and multipartite versions of the effect.Comment: 6 pages, 2 figures, references added, initial paragraph corrected, sectioning adopted, some parts rewritten; accepted by New J. Phy

Asymptotic Entanglement Dynamics and Geometry of Quantum States

A given dynamics for a composite quantum system can exhibit several distinct properties for the asymptotic entanglement behavior, like entanglement sudden death, asymptotic death of entanglement, sudden birth of entanglement, etc. A classification of the possible situations was given in [M. O. Terra Cunha, {\emph{New J. Phys}} {\bf{9}}, 237 (2007)] but for some classes there were no known examples. In this work we give a better classification for the possibile relaxing dynamics at the light of the geometry of their set of asymptotic states and give explicit examples for all the classes. Although the classification is completely general, in the search of examples it is sufficient to use two qubits with dynamics given by differential equations in Lindblad form (some of them non-autonomous). We also investigate, in each case, the probabilities to find each possible behavior for random initial states.Comment: 9 pages, 2 figures; revised version accepted for publication in J. Phys. A: Math. Theo

New foliose and gelatinous red macroalgae (Rhodophycota) from the Azores: morphological and geographical observations.

Copyright © 2002 Published by Elsevier Science B.V.The following four species of foliose and gelatinous red algae (Rhodophycota) are newly recorded for the Azores archipelago (North Atlantic Ocean): Gracilaria multipartita (Clemente) Harvey, Meristotheca decumbens Grunow (Solieriaceae), Asteromenia peltata (W.R. Taylor) Huisman and A.J.K. Millar (Rhodymeniaceae), and Agardhinula browneae (J. Agardh) De Toni (Faucheaceae). The species are described, and information on reproductive status, ecology and biogeographical relationships is provided

Soil Carbon and Nitrogen Dynamics of Integrated Crop-Pasture Systems with Annual and Perennial Forages

Increased demand for food and bioenergy crops and the subsequent intensification of crop production creates a challenge for the conservation of natural resources in Latin America and the world. In Uruguay, no-till cash-crop production area has increased from 0.4 to 1.5 million ha in the last decade (DIEA 2011) mostly at the expense of pastureland through expanding grain production to soils with lower land use capability. Production systems based on crop-pasture rotations shifted to a longer annual cropping phase with a shorter pasture phase, or to continuous annual crop-ping. Long-term experiments in the country have shown that the rotation of annual crops and perennial pastures minimizes soil erosion in tilled systems, maintaining a positive long-term soil carbon (C) and nitrogen (N) balance that contrasts with C and N losses in annual cropping systems (García-Préchac et al. 2004). Research and extension on soil conservation in crop-pasture systems have led to a massive adoption of no-tillage practices, reaching about 90% of cash crop area by the 2009 growing season (DIEA 2011). However, the gradual increase in no-till adoption by farm operators has been associated with a dramatic increase in continuous annual cropping to the detriment of the pasture phase of the rotation. Our overarching question is: What is the impact of an increased frequency of annual crops in the C and N cycling of these systems? The objective of this study was to assess the impact of the pasture phase and cropping intensity on the soil C and N cycling of an Oxyaquic Argiudoll soil of eastern Uruguay using long term field experimental data and a cropping systems simulation model

Do Groups Matter? An Agent-based Modeling Approach to Pedestrian Egress

Festivals in city parks attended by individuals and families are a universal feature of urban life. These venues often have the common attributes of vendors and other obstacles that restrict pedestrian movement through certain areas, as well as fixed number of exits. In this study, the authors build an agent-based model (ABM) that incorporates group cohesion forces into this type of pedestrian egress scenario. The scenario considered was an evacuation of 500 people through a single exit. This allowed an investigation into the use of two different simulated pedestrian\u27s heading updating rules

A Hybridized Approach to Validation: The Role of Sociological Research Methods in Pedestrian Modeling

Pedestrian and crowd-movement models are difficult to validate using traditional empirical methods because of data-related issues such as generalizability, collection ethics, and costs. Commonly used validation methods make strong assumptions about emergence and the importance of crowd structure, leaving a gap in validation literature. The paper reviews the most common methods of validating pedestrian models and proposes a hybridized qualitative approach to validating models that covers more complex group dynamics and possible situations of panic