Feasibility of approximating spatial and local entanglement in long-range interacting systems using the extended Hubbard model

We investigate the extended Hubbard model as an approximation to the local and spatial entanglement of a one-dimensional chain of nanostructures where the particles interact via a long range interaction represented by a `soft' Coulomb potential. In the process we design a protocol to calculate the particle-particle spatial entanglement for the Hubbard model and show that, in striking contrast with the loss of spatial degrees of freedom, the predictions are reasonably accurate. We also compare results for the local entanglement with previous results found using a contact interaction (PRA, 81 (2010) 052321) and show that while the extended Hubbard model recovers a better agreement with the entanglement of a long-range interacting system, there remain realistic parameter regions where it fails to predict the quantitative and qualitative behaviour of the entanglement in the nanostructure system.Comment: 6 pages, 5 figures and 1 table; added results with correlated hopping term; accepted by EP

Hubbard model as an approximation to the entanglement in nanostructures

We investigate how well the one-dimensional Hubbard model describes the entanglement of particles trapped in a string of quantum wells. We calculate the average single-site entanglement for two particles interacting via a contact interaction and consider the effect of varying the interaction strength and the interwell distance. We compare the results with the ones obtained within the one-dimensional Hubbard model with on-site interaction. We suggest an upper bound for the average single-site entanglement for two electrons in M wells and discuss analytical limits for very large repulsive and attractive interactions. We investigate how the interplay between interaction and potential shape in the quantum-well system dictates the position and size of the entanglement maxima and the agreement with the theoretical limits. Finally, we calculate the spatial entanglement for the quantum-well system and compare it to its average single-site entanglement

Direct measurement of finite-time disentanglement induced by a reservoir

We propose a method for directly probing the dynamics of disentanglement of an initial two-qubit entangled state, under the action of a reservoir. We show that it is possible to detect disentanglement, for experimentally realizable examples of decaying systems, through the measurement of a single observable, which is invariant throughout the decay. The systems under consideration may lead to either finite-time or asymptotic disentanglement. A general prescription for measuring this observable, which yields an operational meaning to entanglement measures, is proposed, and exemplified for cavity quantum electrodynamics and trapped ions.Comment: 4 pages, 2 figure

Controlling the dynamics of a coupled atom-cavity system by pure dephasing : basics and potential applications in nanophotonics

The influence of pure dephasing on the dynamics of the coupling between a two-level atom and a cavity mode is systematically addressed. We have derived an effective atom-cavity coupling rate that is shown to be a key parameter in the physics of the problem, allowing to generalize the known expression for the Purcell factor to the case of broad emitters, and to define strategies to optimize the performances of broad emitters-based single photon sources. Moreover, pure dephasing is shown to be able to restore lasing in presence of detuning, a further demonstration that decoherence can be seen as a fundamental resource in solid-state cavity quantum electrodynamics, offering appealing perspectives in the context of advanced nano-photonic devices.Comment: 10 pages, 7 figure

Abrupt Changes in the Dynamics of Quantum Disentanglement

Entanglement evolution in high dimensional bipartite systems under dissipation is studied. Discontinuities for the time derivative of the lower bound of entanglement of formation is found depending on the initial conditions for entangled states. This abrupt changes along the evolution appears as precursors of entanglement sudden death.Comment: 4 pages and 6 figures, submitted for publicatio

Crescimento de mudas de Schizolobium parahyba var. amazonicum (Huber ex Ducke) Barneby sob diferentes níveis de nitrogênio, fósforo e potássio.

O presente trabalho teve por objetivo avaliar os efeitos das dosagens de Nitrogênio, Fósforo, e Potássio sobre o crescimento de mudas do Schizolobium parahyba var. amazonicum. (Huber ex Ducke) Barneby. As doses utilizadas foram as seguintes: Nitrogênio (0, 25, 50 e 100 mg deN/kg de solo), Fósforo (0, 60, 120 e 180 mg de P2 O5/kg de solo ) e Potássio (0, 25, 50 e 100 mg de K2O/kg de solo), através dos adubos comerciais: uréia, superfosfato triplo e cloreto de potássio. Foi desenvolvido na Empresa Brasileira de Pesquisa Agropecuária Embrapa Rondônia. O experimento foi desenvolvido em campo, sob condições ambientais de 50% de sombreamento. Utilizou-se o delineamento experimental de blocos casualizados em esquema fatorial, com sessenta e quatro tratamentos e quatro repetições. As mudas foram plantadas em sacos de polietileno com 4,2 kg de solo previamente adubado. Aos 100 dias após o plantio, as mudas foram avaliadas individualmente, quanto à altura do caule e diâmetro do colo. Observou-se efeito significativo nos tratamentos (P<0,05), para todas as características analisadas. As mudas cultivadas em substratos cujos tratamentos continham doses de Nitrogênio elevadas apresentaram melhor crescimento nos parâmetros avaliados. No entanto, as piores médias foram observadas nas mudas cultivadas nos substratos sem adição de Nitrogênio e Fósforo. O Potássio mostrou-se menos limitante no desenvolvimento da cultura em comparação a exigência de Fósforo. O melhor rendimento das mudas em resposta ao N, P205 e K2O ocorreu nas dosagens de 100 mg N/kg de solo, 60 mg/kg de solo e 25 mg de solo, respectivamente.bitstream/item/24660/1/bpd31-schizolobium-parahyba.pd