2,664 research outputs found
Non-Markovian entanglement dynamics in the presence of system-bath coherence
A complete treatment of the entanglement of two-level systems, which evolves
through the contact with a thermal bath, must include the fact that the system
and the bath are not fully separable. Therefore, quantum coherent
superpositions of system and bath states, which are almost never fully included
in theoretical models, are invariably present when an entangled state is
prepared experimentally. We show their importance for the time evolution of the
entanglement of two qubits coupled to independent baths. In addition, our
treatment is able to handle slow and low-temperature thermal baths.Comment: Accepted for publication in Phys. Rev. Lett
Interference of multi-mode photon echoes generated in spatially separated solid-state atomic ensembles
High-visibility interference of photon echoes generated in spatially
separated solid-state atomic ensembles is demonstrated. The solid state
ensembles were LiNbO waveguides doped with Erbium ions absorbing at 1.53
m. Bright coherent states of light in several temporal modes (up to 3) are
stored and retrieved from the optical memories using two-pulse photon echoes.
The stored and retrieved optical pulses, when combined at a beam splitter, show
almost perfect interference, which demonstrates both phase preserving storage
and indistinguishability of photon echoes from separate optical memories. By
measuring interference fringes for different storage times, we also show
explicitly that the visibility is not limited by atomic decoherence. These
results are relevant for novel quantum repeaters architectures with photon echo
based multimode quantum memories
Do Spin-Offs Make the Academics’ Heads Spin?: The Impacts of Spin-Off Companies on Their Parent Research Organisation
As public research organisations are increasingly driven by their national and regional governments to engage in knowledge transfer, they have started to support the creation of companies. These research based spin-off companies (RBSOs) often keep contacts with the research institutes they originate from. In this paper we present the results of a study of four research institutes within two universities and two non-university public research organisations (PROs) in the Netherlands. We show that research organisations have distinct motivations to support the creation of spin-off companies. In terms of resources RBSOs contribute, mostly in a modest way, to research activities by providing information, equipment and monetary resources. In particular, RBSOs are helpful for researchers competing for research grants that demand participation of industry. Furthermore, RBSOs may be seen as a proactive response by Dutch public research organisations to demands of economic relevance from their institutional environment. RBSOs enhance the prestige of their parent organisations and create legitimacy for public funds invested in PROs. At the same time, most RBSOs do not have a significant impact on the direction of the research conducted at the PROs
Perfil logístico de Colombia
El presente documento ofrece un estudio del perfil logístico de Colombia con la finalidad de dar a conocer el estado de arte de las ciudades, puertos e infraestructura principal para facilitar la toma de decisiones de los empresarios. Para el desarrollo de este trabajo se determinaron a partir de un análisis competitivo del país; las principales ciudades y puertos; logrando establecer un inventario de maquinaria y equipo e infraestructura logística; enmarcados en retos ya establecidos en las políticas públicas.This document provides a profile study logistics Colombia in order to present the state of art of the cities, ports and infrastructure in facilitating the decision making of managers.
For the development of this work were determined from a competitive analysis of the country's major cities and ports, making an inventory of machinery and equipment and logistics infrastructure; framed challenges established in public policy
Exploring personal interests of physicians in hospitals and specialty clinics
Physicians' interests substantially influence intra-organizational dynamics in hospitals, though little is known about the actual content and structure of these interests. The objective of this study was to both identify and build a structured model of physicians' interests. Based on literature and 27 semi-structured interviews with physicians, a questionnaire containing 10 interests was developed. Next, 1475 physicians in the Netherlands filled out an online survey. Analyses of the data revealed a distinction between the primary interest of ‘helping patients as well as possible’ and nine secondary interests. Factor analysis identified the main secondary interest dimensions as work-related, setting-related, and life-related. Value attached to interests differs between specialties and types of hospitals. The influence of hospital type on the value attached to interests is stronger than the influence of specialty group on the value attached to interests. Insight in the relative importance of different interests may help policy-makers make decisions that foster shared interests
The evolution of representation in simple cognitive networks
Representations are internal models of the environment that can provide
guidance to a behaving agent, even in the absence of sensory information. It is
not clear how representations are developed and whether or not they are
necessary or even essential for intelligent behavior. We argue here that the
ability to represent relevant features of the environment is the expected
consequence of an adaptive process, give a formal definition of representation
based on information theory, and quantify it with a measure R. To measure how R
changes over time, we evolve two types of networks---an artificial neural
network and a network of hidden Markov gates---to solve a categorization task
using a genetic algorithm. We find that the capacity to represent increases
during evolutionary adaptation, and that agents form representations of their
environment during their lifetime. This ability allows the agents to act on
sensorial inputs in the context of their acquired representations and enables
complex and context-dependent behavior. We examine which concepts (features of
the environment) our networks are representing, how the representations are
logically encoded in the networks, and how they form as an agent behaves to
solve a task. We conclude that R should be able to quantify the representations
within any cognitive system, and should be predictive of an agent's long-term
adaptive success.Comment: 36 pages, 10 figures, one Tabl
Energy transfer in structured and unstructured environments: Master equations beyond the Born-Markov approximations
We explore excitonic energy transfer dynamics in a molecular dimer system coupled to both structured and unstructured oscillator environments. By extending the reaction coordinate master equation technique developed by Iles-Smith et al. [Phys. Rev. A 90, 032114 (2014)], we go beyond the commonly used Born-Markov approximations to incorporate system-environment correlations and the resultant non-Markovian dynamical effects. We obtain energy transfer dynamics for both underdamped and overdamped oscillator environments that are in perfect agreement with the numerical hierarchical equations of motion over a wide range of parameters. Furthermore, we show that the Zusman equations, which may be obtained in a semiclassical limit of the reaction coordinate model, are often incapable of describing the correct dynamical behaviour. This demonstrates the necessity of properly accounting for quantum correlations generated between the system and its environment when the Born-Markov approximations no longer hold. Finally, we apply the reaction coordinate formalism to the case of a structured environment comprising of both underdamped (i.e., sharply peaked) and overdamped (broad) components simultaneously. We find that though an enhancement of the dimer energy transfer rate can be obtained when compared to an unstructured environment, its magnitude is rather sensitive to both the dimer-peak resonance conditions and the relative strengths of the underdamped and overdamped contributions
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