Quantum key distribution with higher-order alphabets using spatially-encoded qudits

We propose and demonstrate a quantum key distribution scheme in higher-order $d$-dimensional alphabets using spatial degrees of freedom of photons. Our implementation allows for the transmission of 4.56 bits per sifted photon, while providing improved security: an intercept-resend attack on all photons would induce an error rate of 0.47. Using our system, it should be possible to send more than a byte of information per sifted photon.Comment: 4 pages, 5 figures. Replaced with published versio

Observation of Image Transfer and Phase Conjugation in Stimulated Down-Conversion

We observe experimentally the transfer of angular spectrum and image formation in the process of stimulated parametric down-conversion. Images and interference patterns can be transferred from either the pump or the auxiliary laser beams to the stimulated down-converted one. The stimulated field propagates as the complex conjugate of the auxiliary laser. The phase conjugation is observed through intensity pattern measurements

Propagation of transverse intensity correlations of a two-photon state

The propagation of transverse spatial correlations of photon pairs through arbitrary first-order linear optical systems is studied experimentally and theoretically using the fractional Fourier transform. Highly-correlated photon pairs in an EPR-like state are produced by spontaneous parametric down-conversion and subject to optical fractional Fourier transform systems. It is shown that the joint detection probability can display either correlation, anti-correlation, or no correlation, depending on the sum of the orders $\alpha$ and $\beta$ of the transforms of the down-converted photons. We present analytical results for the propagation of the perfectly correlated EPR state, and numerical results for the propagation of the two-photon state produced from parametric down-conversion. We find good agreement between theory and experiment.Comment: 9 pages, 7 figures, to appear PR

Experimental investigation of the dynamics of entanglement: Sudden death, complementarity, and continuous monitoring of the environment

We report on an experimental investigation of the dynamics of entanglement between a single qubit and its environment, as well as for pairs of qubits interacting independently with individual environments, using photons obtained from parametric down-conversion. The qubits are encoded in the polarizations of single photons, while the interaction with the environment is implemented by coupling the polarization of each photon with its momentum. A convenient Sagnac interferometer allows for the implementation of several decoherence channels and for the continuous monitoring of the environment. For an initially-entangled photon pair, one observes the vanishing of entanglement before coherence disappears. For a single qubit interacting with an environment, the dynamics of complementarity relations connecting single-qubit properties and its entanglement with the environment is experimentally determined. The evolution of a single qubit under continuous monitoring of the environment is investigated, demonstrating that a qubit may decay even when the environment is found in the unexcited state. This implies that entanglement can be increased by local continuous monitoring, which is equivalent to entanglement distillation. We also present a detailed analysis of the transfer of entanglement from the two-qubit system to the two corresponding environments, between which entanglement may suddenly appear, and show instances for which no entanglement is created between dephasing environments, nor between each of them and the corresponding qubit: the initial two-qubit entanglement gets transformed into legitimate multiqubit entanglement of the Greenberger-Horne-Zeilinger (GHZ) type.Comment: 15 pages, 14 figures; only .ps was working, now .pdf is also availabl

Control of quantum transverse correlations on a four-photon system

Control of spatial quantum correlations in bi-photons is one of the fundamental principles of Quantum Imaging. Up to now, experiments have been restricted to controlling the state of a single bi-photon, by using linear optical elements. In this work we demonstrate experimental control of quantum correlations in a four-photon state comprised of two pairs of photons. Our scheme is based on a high-efficiency parametric downconversion source coupled to a double slit by a variable linear optical setup, in order to obtain spatially encoded qubits. Both entangled and separable pairs have been obtained, by altering experimental parameters. We show how the correlations influence both the interference and diffraction on the double slit.Comment: 14 pages, 6 figure

Uso de funções discriminantes para comparação de cultivares dos gêneros Cynodon e Digitaria quanto à produção de matéria seca e teores de macronutrientes.

Foi realizado um experirnento no Centro Nacional de Pesquisa de Agrobiologia, Seropédica-RJ, com objetivo de comparar as gramineas Coast cross e Tifton 85, do gênero Cynodon, e as gramíneas Suazi (Digitaria swazilandensis) e Transvala (D. decumbens), do gênero Digitaria, quanto a produção de matéria seca (MS) e teores de macronutrientes da parte aérea e sistema radicular, em 15 amostras de cada cultivar, coletadas no período das chuvas (primavera/verão). A análise discriminante demonstrou que as variáveis Mg, Ca e MS na parte aérea e P e N na raiz foram importantes no processo de discriminação dos cultivares estudados. O cultivar Suázi foi diferente dos dernais avaliados quanto a produção de MS e aos teores de Mg e Ca na parte aérea, além do P e N na raiz. Os cultivares Tifton 85 e Coast cross, apesar de serem do mesmo gênero, diferem quanto a produção de MS e aos teores de Mg e Ca na parte aérea, alem do P e N na raiz. Algumas amostras dos cultivares Tifton 85 e Coast cross apresentaram semelhança com O capim Transvala, com relação a produção de MS e aos teores de Mg e Ca na parte aérea, alem de P e N na raiz. An experiment was carried out at the National Center of Research of Agrobiology, Seropedica--RJ, with objective of evaluating the grasses Coast cross (Cynodon spp.) and Tifton 85 (Cynodon dactylon (L.)), of the Cynodon genus, and the grasses Suazi (Digitaria swazilandensis) and Transvala (Digitaria decumbens), of the Digitaria genus, through the discriminant analysis. The evaluated variables were: dry matter production (DMP) and contents of nitrogen (N), phosphorus (P), magnesium (Mg) and calcium (Ca) in the shoot and root on 15 samples of each grasses, accomplished in the period of the rains (spring/ summer). The discriminant analysis demonstrated that the variables Mg, Ca and dry matter production (DMP) in shoot, and P and N root are important in the discrimination process of the Coast cross, Tifton 85, Suazi and Transvala cultivars. Suazi cultivar is clearly different from the others cultivars, in relationship to Mg and Ca contents and DMP at the shoot, P and N at the root. O Tifton 85 and Coast cross cultivars, in spite of being of the same genus, differ in relationship to Mg and Ca contents and DMP at the shoot, match and N at the root. Some samples of the Tifton 85 and Coast cross cultivars can be similar to the grass Transvala, in relation to the Mg, Ca and DMP contents in shoot, P and N root.Parceria: UFV; PESAGRO-Rio/ESS; UFRRJ; ESALQ

Stress shielding and bone resorption of press-fit polyether-ether-ketone (PEEK) hip prosthesis: a sawbone model study

Stress shielding secondary to bone resorption is one of the main causes of aseptic loosening, which limits the lifespan of the hip prostheses and increases the rates of revision surgery. This study proposes a low stiffness polyether-ether-ketone (PEEK) hip prostheses, produced by fused deposition modelling to minimize the stress difference after the hip replacement. The stress shielding effect and the potential bone resorption of the PEEK implant was investigated through both experimental tests and FE simulation. A generic Ti6Al4V implant was incorporated in this study to allow fair comparison as control group. Attributed to the low stiffness, the proposed PEEK implant showed a more natural stress distribution, less stress shielding (by 104%), and loss in bone mass (by 72%) compared with the Ti6Al4V implant. The stiffness of the Ti6Al4V and the PEEK implant were measured through compression tests to be 2.76 kN/mm and 0.276 kN/mm. The factor of safety for the PEEK implant in both static and dynamic loading scenarios were obtained through simulation. Most of the regions in the PEEK implant were tested to be safe (FoS larger than 1) in terms of representing daily activities (2300 N), while the medial neck and distal restriction point of the implant attracts large von Mises stress 82 MPa and 76 MPa, respectively, and, thus, may possibly fail during intensive activities by yield and fatigue. Overall, considering the reduction in stress shielding and bone resorption in cortical bone, PEEK could be a promising material for the patient-specific femoral implants

Resonance of Vector Vortex Beams in a Triangular Optical Cavity

We experimentally demonstrate resonance of first-order vector vortex beams (VVB) with a triangular optical cavity. We also show that, due to their symmetry properties, the so-called radial and azimuthal VVBs do not resonate at the same cavity length, which could be explored to use the triangular resonator as a mode sorter. In addition, an intracavity Pancharatnam phase shifter (PPS) is implemented in order to compensate for any birefringent phase that the cavity mirrors may introduce

Double membrane based on lidocaine-coated polymyxin-alginate nanoparticles for wound healing: in vitro characterization and in vivo tissue repair

The aim of this study was to develop and characterize a double layer biomembrane for dual drug delivery to be used for the treatment of wounds. The membrane was composed of chitosan, hydroxypropyl methylcellulose and lidocaine chloride (anesthetic drug) in the first layer, and of sodium alginate-polymyxin B sulphate (antibiotic) nanoparticles as the second layer. A product with excellent thickness (0.01-0.02 mm), adequate mechanical properties with respect to elasticity, stiffness, tension, and compatible pH for lesion application has been successfully obtained. The incorporation of the drugs was confirmed analysing the membrane cross-sections by scanning electron microscopy. A strong interaction between the drugs and the functional groups of respective polymers was confirmed by Fourier-Transform Infrared Spectroscopy, thermal analysis and X-ray diffraction. Microbiological assays showed a high antimicrobial activity when polymyxin B was present to act against the Staphylococcus aureus and Pseudomonas aeruginosa strains. Low cytotoxicity observed in a cell viability colorimetric assay and SEM analysis suggest biocompatibility between the developed biomembrane and the cell culture. The in vivo assay allowed visualizing the healing potential by calculating the wound retraction index and by histological analysis. Our results confirm the effectiveness of the developed innovative biomaterial for tissue repair and regeneration in an animal model.The authors acknowledge the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES/Brazil), Fundação de Amparo a Pesquisa do Estado de Sergipe (FAPITEC, MS/CNPq/FAPITEC/SE/SES N◦06/2018) e do Conselho Nacional de Pesquisas (CNPq, Apoio a Projetos de Pesquisa/MCTI/CNPQ/Universal 14/2014) for supporting funds. EBS acknowledges the Portuguese Science and Technology Foundation (FCT) for the funded projects M-ERA-NET/0004/2015 (PAIRED) and UIDB/04469/2020 (strategic fund) financed from national funds, and co-financed Education (FCT/MEC) from national funds and FEDER, under the Partnership Agreement PT2020.info:eu-repo/semantics/publishedVersio