1,393 research outputs found
Disordered Cellulose-based Nanostructures for Enhanced Light-scattering
Cellulose is the most abundant bio-polymer on earth. Cellulose fibres, such
as the one extracted form cotton or woodpulp, have been used by humankind for
hundreds of years to make textiles and paper. Here we show how, by engineering
light matter-interaction, we can optimise light scattering using exclusively
cellulose nanocrystals. The produced material is sustainable, biocompatible
and, when compared to ordinary microfibre-based paper, it shows enhanced
scattering strength (x4) yielding a transport mean free path as low as 3.5 um
in the visible light range. The experimental results are in a good agreement
with the theoretical predictions obtained with a diffusive model for light
propagation
Universal computation by multi-particle quantum walk
A quantum walk is a time-homogeneous quantum-mechanical process on a graph
defined by analogy to classical random walk. The quantum walker is a particle
that moves from a given vertex to adjacent vertices in quantum superposition.
Here we consider a generalization of quantum walk to systems with more than one
walker. A continuous-time multi-particle quantum walk is generated by a
time-independent Hamiltonian with a term corresponding to a single-particle
quantum walk for each particle, along with an interaction term. Multi-particle
quantum walk includes a broad class of interacting many-body systems such as
the Bose-Hubbard model and systems of fermions or distinguishable particles
with nearest-neighbor interactions. We show that multi-particle quantum walk is
capable of universal quantum computation. Since it is also possible to
efficiently simulate a multi-particle quantum walk of the type we consider
using a universal quantum computer, this model exactly captures the power of
quantum computation. In principle our construction could be used as an
architecture for building a scalable quantum computer with no need for
time-dependent control
Stationary Entangled Radiation from Micromechanical Motion
Mechanical systems facilitate the development of a new generation of hybrid
quantum technology comprising electrical, optical, atomic and acoustic degrees
of freedom. Entanglement is the essential resource that defines this new
paradigm of quantum enabled devices. Continuous variable (CV) entangled fields,
known as Einstein-Podolsky-Rosen (EPR) states, are spatially separated two-mode
squeezed states that can be used to implement quantum teleportation and quantum
communication. In the optical domain, EPR states are typically generated using
nondegenerate optical amplifiers and at microwave frequencies Josephson
circuits can serve as a nonlinear medium. It is an outstanding goal to
deterministically generate and distribute entangled states with a mechanical
oscillator. Here we observe stationary emission of path-entangled microwave
radiation from a parametrically driven 30 micrometer long silicon nanostring
oscillator, squeezing the joint field operators of two thermal modes by
3.40(37) dB below the vacuum level. This mechanical system correlates up to 50
photons/s/Hz giving rise to a quantum discord that is robust with respect to
microwave noise. Such generalized quantum correlations of separable states are
important for quantum enhanced detection and provide direct evidence for the
non-classical nature of the mechanical oscillator without directly measuring
its state. This noninvasive measurement scheme allows to infer information
about otherwise inaccessible objects with potential implications in sensing,
open system dynamics and fundamental tests of quantum gravity. In the near
future, similar on-chip devices can be used to entangle subsystems on vastly
different energy scales such as microwave and optical photons.Comment: 13 pages, 5 figure
Some remarks on the spectral functions of the Abelian Higgs Model
We consider the unitary Abelian Higgs model and investigate its spectral
functions at one-loop order. This analysis allows to disentangle what is
physical and what is not at the level of the elementary particle propagators,
in conjunction with the Nielsen identities. We highlight the role of the
tadpole graphs and the gauge choices to get sensible results. We also introduce
an Abelian Curci-Ferrari action coupled to a scalar field to model a massive
photon which, like the non-Abelian Curci-Ferarri model, is left invariant by a
modified non-nilpotent BRST symmetry. We clearly illustrate its non-unitary
nature directly from the spectral function viewpoint. This provides a
functional analogue of the Ojima observation in the canonical formalism: there
are ghost states with nonzero norm in the BRST-invariant states of the
Curci-Ferrari model.Comment: 32 pages, 12 figure
Atomically-thin quantum dots integrated with lithium niobate photonic chips
The electro-optic, acousto-optic and nonlinear properties of lithium niobate
make it a highly versatile material platform for integrated quantum photonic
circuits. A prerequisite for quantum technology applications is the ability to
efficiently integrate single photon sources, and to guide the generated photons
through ad-hoc circuits. Here we report the integration of quantum dots in
monolayer WSe2 into a Ti in-diffused lithium niobate directional coupler. We
investigate the coupling of individual quantum dots to the waveguide mode,
their spatial overlap, and the overall efficiency of the hybrid-integrated
photonic circuit
Evolução de brotação em cultivares de macieiras com variações de exigência de frio tratadas com cianamida hidrogenada ao longo do período de endodormência.
O estudo pretendeu responder as seguintes questões: 1) De modo empírico, sabe-se que as plantas precisam de um certo acúmulo de horas de frio (HF) para que o tratamento com cianamida hidrogenada (CH) seja eficaz, porém qual o somatório de frio mínimo para que esse produto tenha efeito pleno? 2) Existe diferença nesta quantidade de HF acumulada para que a CH tenha efeito quando utiliza-se genótipos contrastes de exigência de frio
Macieiras contrastantes em exigência de frio apresentam a mesma evolução de brotação quando tratadas com cianamida hidrogenada ao longo da endodormência?
A macieira, sendo uma espécie de clima temperado, apresenta a entrada em endodormência no outono e requer um acúmulo de horas de frio (HF, soma de temperatura < 7,2°C) durante o inverno para superar esse estado fisiológico. As exigências de HF variam entre genótipos e quando o somatório de frio local é menor são recomendados tratamentos químicos indutores, como a cianamida hidrogenada (CH). Para que o tratamento com CH seja eficaz, sabe-se que as plantas precisam de um certo acúmulo de HF, tornando-se necessário determinar o somatório de frio mínimo para que esse produto tenha efeito pleno. Outra questão importante é definir se existe diferença na quantidade de HF acumulada para que a CH tenha efeito, quando utiliza-se genótipos contrastantes de exigência de frio. Buscando responder a estas questões, em maio/2013 foram coletadas brindilas de Castel Gala (K, exigência de 300HF) e Imperial Gala (G, 600 HF), as quais foram esterilizadas em hipoclorito, embaladas em sacos plásticos e submetidas a um frio constante de 3°C (BODs), por seis tempos de frio para K (50 a 350HF) e G (50 a 600HF). Em cada ponto de frio, 80 brindilas de cada genótipo foram transferidas para uma condição de 25°C e 70% de umidade (fitotron) para estimular e avaliar a brotação, sendo 40 como controle e 40 tratadas no dia da transferência com CH (1% Dormex® + 3% Assist® ). Diariamente, todas as brindilas foram avaliadas quanto à ocorrência de brotação (ponta verde) das gemas apicais e laterais, sendo esses dados ajustados em um modelo assimétrico de evolução da brotação (curva de Gompertz) para obter os parâmetros de precocidade, uniformidade e máximo percentual de brotação. Para K, os tratamentos de CH não proporcionaram diferenças significativas em relação ao controle. Em contrapartida, para G o efeito de CH foi desde 300 HF, o que corresponde a 50% da exigência de frio desta cultivar. Portanto, observa-se um comportamento distinto entre genótipos em relação à resposta a CH, o que deve ser considerado no manejo fitotécnico da dormência em pomares
Novel Collective Effects in Integrated Photonics
Superradiance, the enhanced collective emission of energy from a coherent
ensemble of quantum systems, has been typically studied in atomic ensembles. In
this work we study theoretically the enhanced emission of energy from coherent
ensembles of harmonic oscillators. We show that it should be possible to
observe harmonic oscillator superradiance for the first time in waveguide
arrays in integrated photonics. Furthermore, we describe how pairwise
correlations within the ensemble can be measured with this architecture. These
pairwise correlations are an integral part of the phenomenon of superradiance
and have never been observed in experiments to date.Comment: 7 pages, 3 figure
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