Rates of multi-partite entanglement transformations and applications in quantum networks

The theory of the asymptotic manipulation of pure bipartite quantum systems can be considered completely understood: The rates at which bipartite entangled states can be asymptotically transformed into each other are fully determined by a single number each, the respective entanglement entropy. In the multi-partite setting, similar questions of the optimally achievable rates of transforming one pure state into another are notoriously open. This seems particularly unfortunate in the light of the revived interest in such questions due to the perspective of experimentally realizing multi-partite quantum networks. In this work, we report substantial progress by deriving surprisingly simple upper and lower bounds on the rates that can be achieved in asymptotic multi-partite entanglement transformations. These bounds are based on ideas of entanglement combing and state merging. We identify cases where the bounds coincide and hence provide the exact rates. As an example, we bound rates at which resource states for the cryptographic scheme of quantum secret sharing can be distilled from arbitrary pure tripartite quantum states, providing further scope for quantum internet applications beyond point-to-point.Comment: 4+7 pages, 1 figure, v2 is significantly extended in its results and presents a general statement providing bounds for achievable asymptotic rates for an arbitrary number of partie

Rates of Multipartite Entanglement Transformations

The theory of the asymptotic manipulation of pure bipartite quantum systems can be considered completely understood: the rates at which bipartite entangled states can be asymptotically transformed into each other are fully determined by a single number each, the respective entanglement entropy. In the multipartite setting, similar questions of the optimally achievable rates of transforming one pure state into another are notoriously open. This seems particularly unfortunate in the light of the revived interest in such questions due to the perspective of experimentally realizing multipartite quantum networks. In this Letter, we report substantial progress by deriving simple upper and lower bounds on the rates that can be achieved in asymptotic multipartite entanglement transformations. These bounds are based on ideas of entanglement combing and state merging. We identify cases where the bounds coincide and hence provide the exact rates. As an example, we bound rates at which resource states for the cryptographic scheme of quantum secret sharing can be distilled from arbitrary pure tripartite quantum states. This result provides further scope for quantum internet applications, supplying tools to study the implementation of multipartite protocols over quantum networks

Super- and subradiance of clock atoms in multimode optical waveguides

The transversely confined propagating modes of an optical fiber mediate virtually infinite range energy exchanges among atoms placed within their field, which adds to the inherent free space dipole–dipole coupling. Typically, the single atom free space decay rate largely surpasses the emission rate into the guided fiber modes. However, scaling up the atom number as well as the system size amounts to entering a collective emission regime, where fiber-induced superradiant spontaneous emission dominates over free space decay. We numerically study this super- and subradiant decay of highly excited atomic states for one or several transverse fiber modes as present in hollow core fibers. As particular excitation scenarios we compare the decay of a totally inverted state to the case of π/2 pulses applied transversely or along the fiber axis as in standard Ramsey or Rabi interferometry. While a mean field approach fails to correctly describe the initiation of superradiance, a second-order approximation accounting for pairwise atom–atom quantum correlations generally proves sufficient to reliably describe superradiance of ensembles from two to a few hundred particles. In contrast, a full account of subradiance requires the inclusion of all higher order quantum correlations. Considering multiple guided modes introduces a natural effective cut-off for the interaction range emerging from the dephasing of different fiber contributions

GaAs low cost microwave monolithic circuits for high volume television applications.

Two MMICs have been designed and fabricated for television applications. To be compatible with the needs of the market, low cost approaches have been used to design these circuits. The first one, is an image rejection downconverter fabricated on a 2.4mm2 chip using a 0.5 micron MESFET low cost process. This circuit converts signals in the 10.95 to 12.75GHz band to a lower frequency band (1). The second one is a fully integrated 2GHz downconverter IC fabricated on a 0.9mm2 chip, using an enhancement mode GaAs process. It converts signals in the 0.95GHz to 2GHz band to the UHF band with its internal local oscillator (2). In both cases, original solutions have been used to reduce the cost of the packaged chips

The role of national context and HR strategy in shaping training and development practice in French and U.K. organizations

A comparative analysis of French and U.K. organizations is used to explore the impact of national context and formal human resources (HR) strategy on employee development systems. Survey data is drawn from 531 French and 879 U.K. organizations. The results indicate that national context is the strongest predictor of how employee development is organized above and beyond the impact of a formalized HR strategy. In contrast to French organizations, U.K. companies tend to be less restrictive in the range of management tools they use for monitoring, evaluating and delivering training and development. These differences are considered in the light of divergent national approaches to education and skill development. The use of a formalized HR strategy was correlated with the collection of workforce data on training and development need and effectiveness. It is suggested that the formalization of an HR strategy promotes HR planning mechanisms. The implications of these findings with respect to the ethnocentricity of the human resource management literature are considered

Conflicts and Negotiations in the Intergenerational Succession of Family Firms: A Literature Review

This chapter intends to stimulate a serious debate on the topic of conflict in family businesses and the theory of negotiation as a tool to resolve these conflicts. The methodology is based on the survey of the main literature on these topics. Despite the literature on conflict management is highly developed as well as the literature in family business, scholars and researchers have not yet deepened several areas of conflict management in family businesses, so the two fields of literature are yet not well integrated, showing a potential for future research avenues. We then propose a research agenda identifying the issues and research gaps that should be explored by researchers to reach a deeper understanding on conflict resolution in family businesses