Analysis of the three-dimensional segmented Poincaré plot for complex coupling analyses of the autonomic regulation

Pregnancy is still one of the most delicate stages in a woman’s life, especially in the third world countries. In this project, we propose to characterize and analyse the respiratory and cardiovascular systems using the Poincaré plot. 112 pregnant women that suffered different pregnancy illnesses and 10 Non-pregnant women were analysed. In this project we implement a new algorithm to an already established method of analysis, the 3 dimension Segmented Poincaré Plot Analysis (3DSPPA). RR, SYS, DIA and TRESP time series were extracted from the ECG, blood pressure and respiratory flow signals, respectively. Parameters that describe the importance of the concentrations of the scatterplot of the Poincaré method along their relative positions, related to a series of levels described by the user, were extracted. An analysis of those extracted parameters lead to our results. These results show a difference between the studied parameters from every health condition analysed leading us to be able to discern between them with our algorithm

Perfect Sampling with Unitary Tensor Networks

Tensor network states are powerful variational ans\"atze for many-body ground states of quantum lattice models. The use of Monte Carlo sampling techniques in tensor network approaches significantly reduces the cost of tensor contractions, potentially leading to a substantial increase in computational efficiency. Previous proposals are based on a Markov chain Monte Carlo scheme generated by locally updating configurations and, as such, must deal with equilibration and autocorrelation times, which result in a reduction of efficiency. Here we propose a perfect sampling scheme, with vanishing equilibration and autocorrelation times, for unitary tensor networks -- namely tensor networks based on efficiently contractible, unitary quantum circuits, such as unitary versions of the matrix product state (MPS) and tree tensor network (TTN), and the multi-scale entanglement renormalization ansatz (MERA). Configurations are directly sampled according to their probabilities in the wavefunction, without resorting to a Markov chain process. We also describe a partial sampling scheme that can result in a dramatic (basis-dependent) reduction of sampling error.Comment: 11 pages, 9 figures, renamed partial sampling to incomplete sampling for clarity, extra references, plus a variety of minor change

Extraordinary exciton conductance induced by strong coupling

We demonstrate that exciton conductance in organic materials can be enhanced by several orders of magnitude when the molecules are strongly coupled to an electromagnetic mode. Using a 1D model system, we show how the formation of a collective polaritonic mode allows excitons to bypass the disordered array of molecules and jump directly from one end of the structure to the other. This finding could have important implications in the fields of exciton transistors, heat transport, photosynthesis, and biological systems in which exciton transport plays a key role.Comment: Main text: 5 pages, 4 figures; Supplemental: 2 pages, 1 figure. Version 2: Updated reference to related work arXiv:1409.2550. Version 3: Updated to version accepted for publication in Physical Review Letter

Tensor network states and algorithms in the presence of a global SU(2) symmetry

The benefits of exploiting the presence of symmetries in tensor network algorithms have been extensively demonstrated in the context of matrix product states (MPSs). These include the ability to select a specific symmetry sector (e.g. with a given particle number or spin), to ensure the exact preservation of total charge, and to significantly reduce computational costs. Compared to the case of a generic tensor network, the practical implementation of symmetries in the MPS is simplified by the fact that tensors only have three indices (they are trivalent, just as the Clebsch-Gordan coefficients of the symmetry group) and are organized as a one-dimensional array of tensors, without closed loops. Instead, a more complex tensor network, one where tensors have a larger number of indices and/or a more elaborate network structure, requires a more general treatment. In two recent papers, namely (i) [Phys. Rev. A 82, 050301 (2010)] and (ii) [Phys. Rev. B 83, 115125 (2011)], we described how to incorporate a global internal symmetry into a generic tensor network algorithm based on decomposing and manipulating tensors that are invariant under the symmetry. In (i) we considered a generic symmetry group G that is compact, completely reducible and multiplicity free, acting as a global internal symmetry. Then in (ii) we described the practical implementation of Abelian group symmetries. In this paper we describe the implementation of non-Abelian group symmetries in great detail and for concreteness consider an SU(2) symmetry. Our formalism can be readily extended to more exotic symmetries associated with conservation of total fermionic or anyonic charge. As a practical demonstration, we describe the SU(2)-invariant version of the multi-scale entanglement renormalization ansatz and apply it to study the low energy spectrum of a quantum spin chain with a global SU(2) symmetry.Comment: 32 pages, 37 figure

Optical absorption and energy-loss spectra of aligned carbon nanotubes

Optical-absorption cross-sections and energy-loss spectra of aligned multishell carbon nanotubes are investigated, on the basis of photonic band-structure calculations. A local graphite-like dielectric tensor is assigned to every point of the tubules, and the effective transverse dielectric function of the composite is computed by solving Maxwell's equations in media with tensor-like dielectric functions. A Maxwell-Garnett-like approach appropriate to the case of infinitely long anisotropic tubules is also developed. Our full calculations indicate that the experimentally measured macroscopic dielectric function of carbon nanotube materials is the result of a strong electromagnetic coupling between the tubes. An analysis of the electric-field pattern associated with this coupling is presented, showing that in the close-packed regime the incident radiation excites a very localized tangential surface plasmon.Comment: 7 pages, 12 figures, to appear in Eur. Phys. J.

Single-atom control of the optoelectronic response in sub-nanometric cavities

By means of ab-initio time dependent density functional theory calculations carried out on an prototypical hybrid plasmonic device (two metallic nanoparticles bridged by a one-atom junction), we demonstrate the strong interplay between photoinduced excitation of localized surface plasmons and electron transport through the single atom. Such an interplay is remarkably sensitive to the atomic orbitals of the junction. Therefore, we show the possibility of a twofold tuning (plasmonic response and photoinduced current across the juntion) just by changing a single atom in the device.Comment: 5 pages, 5 figure

Cavity-induced modifications of molecular structure in the strong coupling regime

In most theoretical descriptions of collective strong coupling of organic molecules to a cavity mode, the molecules are modeled as simple two-level systems. This picture fails to describe the rich structure provided by their internal rovibrational (nuclear) degrees of freedom. We investigate a first-principles model that fully takes into account both electronic and nuclear degrees of freedom, allowing an exploration of the phenomenon of strong coupling from an entirely new perspective. First, we demonstrate the limitations of applicability of the Born-Oppenheimer approximation in strongly coupled molecule-cavity structures. For the case of two molecules, we also show how dark states, which within the two-level picture are effectively decoupled from the cavity, are indeed affected by the formation of collective strong coupling. Finally, we discuss ground-state modifications in the ultra-strong coupling regime and show that some molecular observables are affected by the collective coupling strength, while others only depend on the single-molecule coupling constant.Comment: 12 pages, 8 figure