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

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

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

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

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

Coherent Time Evolution and Boundary Conditions of Two-Photon Quantum Walks

Multi-photon quantum walks in integrated optics are an attractive controlled quantum system, that can mimic less readily accessible quantum systems and exhibit behavior that cannot in general be accurately replicated by classical light without an exponential overhead in resources. The ability to observe time evolution of such systems is important for characterising multi-particle quantum dynamics---notably this includes the effects of boundary conditions for walks in spaces of finite size. Here we demonstrate the coherent evolution of quantum walks of two indistinguishable photons using planar arrays of 21 evanescently coupled waveguides fabricated in silicon oxynitride technology. We compare three time evolutions, that follow closely a model assuming unitary evolution, corresponding to three different lengths of the array---in each case we observe quantum interference features that violate classical predictions. The longest array includes reflecting boundary conditions.Comment: 7 pages,7 figure

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

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

On a renormalizable class of gauge fixings for the gauge invariant operator Amin⁡2A_{\min }^{2}

The dimension two gauge invariant non-local operator $A_{\min }^{2}$, obtained through the minimization of $\int d^4x A^2$ along the gauge orbit, allows to introduce a non-local gauge invariant configuration $A^h_\mu$ which can be employed to built up a class of Euclidean massive Yang-Mills models useful to investigate non-perturbative infrared effects of confining theories. A fully local setup for both $A_{\min }^{2}$ and $A^{h}_\mu$ can be achieved, resulting in a local and BRST invariant action which shares similarities with the Stueckelberg formalism. Though, unlike the case of the Stueckelberg action, the use of $A_{\min }^{2}$ gives rise to an all orders renormalizable action, a feature which will be illustrated by means of a class of covariant gauge fixings which, as much as 't Hooft's $R_\zeta$-gauge of spontaneously broken gauge theories, provide a mass for the Stueckelberg field