Optical lattices with large scattering length: Using few-body physics to simulate an electron-phonon system

We propose to go beyond the usual Hubbard model description of atoms in optical lattices and show how few-body physics can be used to simulate many-body phenomena, e.g., an electron-phonon system. We take one atomic species to be trapped in a deep optical lattice at full filling and another to be untrapped spin-polarized fermions (which do not see the optical lattice) but has an s-wave contact interaction with the first species. For large positive scattering length on the order of lattice spacing, the usual two-body bound (dimer) states overlap forming giant orbitals extending over the entire lattice, which can be viewed as an "electronic" band for the untrapped species while the trapped atoms become the "ions" with their own on-site dynamics, thereby simulating an electron-phonon system with renormalization of the phonon frequencies and Peierls transitions. This setup requires large scattering lengths but minimises losses, does not need higher bands and adds new degrees of freedom which cannot easily be described in terms of lattice variables, thus opening up intriguing possibilities to explore interesting physics at the interface between few-body and many-body systems.Comment: published version; title change

A single impurity in an ideal atomic Fermi gas: current understanding and some open problems

We briefly review some current theoretical and experimental aspects of the problem of a single spinless impurity in a 3D polarised atomic Fermi gas at zero temperature where the interactions can be tuned using a wide Feshbach resonance. We show that various few-body states in vacuum composed of the impurity and background gas atoms (single impurity, dimer, trimer, tetramer) give rise to corresponding dressed states ({\em polaron}, {\em dimeron}, {\em trimeron}, {\em tetrameron}) in the gas and inherit many of their characteristics. We study the ground state focussing on the choice of wave function and its properties. We raise a few unsolved problems: whether the polaron and dimeron are really separate branches, what other few-body states might exist, the nature of the groundstate for large numbers of particle-hole pairs and why is the polaron ansatz so good. We then turn to the excited states, and to the calculation of the effective mass. We examine the bounds on the effective mass and raise a conjecture about that of composite quasiparticle states.Comment: Review asked by Journal of the Indian Institute of Science, to appear in Vol. 94 No. 2 (Apr. - Jun. 2014) Cold Atom Quantum Emulators: From Condensed Matter to Filed Theory to Optical Clock

Excitonic states of an impurity in a Fermi gas

We study excitonic states of an atomic impurity in a Fermi gas, i.e., bound states consisting of the impurity and a hole. Previous studies considered bound states of the impurity with particles from the Fermi sea where the holes only formed part of the particle-hole dressing. Within a two-channel model, we find that, for a wide range of parameters, excitonic states are not ground but metastable states. We further calculate the decay rates of the excitonic states to polaronic and dimeronic states and find they are long lived, scaling as $\Gamma^{\rm{Exc}}_ {\rm{Pol}} \propto ( \Delta\omega)^{5.5}$ and $\Gamma^{\rm{Exc}}_ {\rm{Dim}} \propto (\Delta\omega)^{4}$. We also find that a new continuum of exciton-particle states should be considered alongside the previously known dimeron-hole continuum in spectroscopic measurements. Excitons must therefore be considered as a new ingredient in the study of metastable physics currently being explored experimentally.Comment: published versio

Artificial Intelligence and medicine

Ao mesmo tempo em que se discutem problemas na relação médico-paciente e a deficiência do exame clínico na atenção médica, que torna o diagnóstico clínico mais dependente de exames complementares, enfatiza-se cada vez mais a importância do computador em medicina e na saúde pública. Isto se dá seja pela adoção de sistemas de apoio à decisão clínica, seja pelo uso integrado de novas tecnologias, incluindo as tecnologias vestíveis/corporais (wearable devices), seja pelo armazenamento de grandes volumes de dados de saúde de pacientes e da população. A capacidade de armazenamento e processamento de dados aumentou exponencialmente ao longo dos recentes anos, criando o conceito de big data. A Inteligência Artificial processa esses dados por meio de algoritmos, que tendem a se aperfeiçoar pelo seu próprio funcionamento (self learning) e a propor hipóteses diagnósticas cada vez mais precisas. Sistemas computadorizados de apoio à decisão clínica, processando dados de pacientes, têm indicado diagnósticos com elevado nível de acurácia. O supercomputador da IBM, denominado Watson, armazenou um volume extraordinário de informações em saúde, criando redes neurais de processamento de dados em vários campos, como a oncologia e a genética. Watson assimilou dezenas de livros-textos em medicina, toda a informação do PubMed e Medline, e milhares de prontuários de pacientes do Sloan Kettering Memorial Cancer Hospital. Sua rede de oncologia é hoje consultada por especialistas de um grande número de hospitais em todo o mundo. O supercomputador inglês Deep Mind, da Google, registrou informações de 1,6 milhão de pacientes atendidos no National Health Service (NHS), permitindo desenvolver novos sistemas de apoio à decisão clínica, analisando dados desses pacientes, permitindo gerar alertas sobre a sua evolução, evitando medicações contraindicadas ou conflitantes e informando tempestivamente os profissionais de saúde sobre seus pacientes. O Deep Mind, ao avaliar um conjunto de imagens dermatológicas na pesquisa de melanoma, mostrou um desempenho melhor do que o de especialistas (76% versus 70,5%), com uma especificidade de 62% versus 59% e uma sensibilidade de 82%. Mas se o computador fornece o know-what, caberá ao médico discutir o problema de saúde e suas possíveis soluções com o paciente, indicando o know-why do seu caso. Isto requer uma contínua preocupação com a qualidade da educação médica, enfatizando o conhecimento da fisiopatologia dos processos orgânicos e o desenvolvimento das habilidades de ouvir, examinar e orientar um paciente e, consequentemente, propor um diagnóstico e um tratamento de seu problema de saúde, acompanhando sua evolução.While discussions develop regarding problems in the doctor-patient relationship and the deficiency of the clinical examination in medical practice, which leaves diagnoses more dependent of complementary tests, the importance of the computer in medicine and public health is highlighted. This is happening, either through the adoption of clinical decision support systems, the use of new technologies, such as wearable devices, or the storage and processing of large volumes of patient and population data. Data storage and processing capacity has increased exponentially over recent years, creating the concept of “big data”. Artificial Intelligence processes such data using algorithms that continually improve through intrinsic self-learning, thus proposing increasingly precise diagnostic hypotheses. Computerized clinical decision support systems, analyzing patient data, have achieved a high degree of accuracy in their diagnoses. IBM’s supercomputer, named “Watson”, has stored an extraordinary volume of health information, creating a neural network of data processing in several fields, such as oncology and genetics. Watson has assimilated dozens of medical textbooks, all the information from PubMed and Medline, and thousands of medical records from the Sloan Kettering Cancer Memorial Hospital. Its oncology network is now consulted by numerous specialists from all over the world. The English supercomputer Deep-Mind, by Google, has stored data from 1.6 million National Health Service patients, enabling the development of new clinical decision support systems, analysis of these patient data and generating alerts on their evolution in order to avoid contraindicated or conflicting medications, whilst also sending timely updates to the physicians about the health of their patients. Analyzing a set of dermatological images in a melanoma study, Deep-Mind showed a higher level of performance than that of specialists (76% versus 70.5%), with a specificity of 62% versus 59% and a sensitivity of 82%. Nevertheless, whereas the computer provides the know-what, it is the physician that will discuss the medical problem and the possible solutions with the patient, indicating the know-why of his or her case. This area requires continuous focus on the quality of medical training, emphasizing knowledge of the physiopathology of the organic processes and the development of the abilities to listen to, examine and advise a patient and, consequently, propose a diagnosis and treatment, accompanying his or her evolution

Spanish unemployment: Normative versus analytical regionalisation procedures

In applied regional analysis, statistical information is usually published at different territorial levels with the aim of providing information of interest for different potential users. When using this information, there are two different choices: first, to use normative regions (towns, provinces, etc.), or, second, to design analytical regions directly related with the analysed phenomena. In this paper, provincial time series of unemployment rates in Spain are used in order to compare the results obtained by applying two analytical regionalisation models (a two stages procedure based on cluster analysis and a procedure based on mathematical programming) with the normative regions available at two different scales: NUTS II and NUTS I. The results have shown that more homogeneous regions were designed when applying both analytical regionalisation tools. Two other obtained interesting results are related with the fact that analytical regions were also more stable along time and with the effects of scale in the regionalisation process.unemployment, regionalisation, analytical region, normative region

Design of Homogeneous Territorial Units: A Methodological Proposal

One of the main questions to solve when analysing geographically added information consists of the design of territorial units adjusted to the objectives of the study. This is related with the reduction of the effects of the Modifiable Areal Unit Problem (MAUP). In this paper an optimisation model to solve regionalisation problems is proposed. This model seeks to reduce some disadvantages found in previous works about automated regionalisation tools.contiguity constraint, zone design, optimisation, modifiable areal unit problem

La Seguridad Social y la Sanidad Pública

Este artículo pretende ofrecer una panorámica sintética y breve de la situación y principales transformaciones experimentadas en los últimos años por la Seguridad Social y la Sanidad Pública en España. Se describen sus características más notables y sus datos fundamentales y se enuncian los problemas más importantes desde las perspectivas de la financiación y del gasto

Introduction: Post-Photographic Truths: Poetics vs Politics

Devoted to contemporary photography artistic practices, under the motto “Post­-Photographic Truths: Poetics vs Politics”, this text aims to question and discuss the drifts of contemporary photographic practices in our post-truth era. Rooted in the historiography of the medium, the poetics and the political are hypothetical boundaries that prevail in current photographic artistic practices. If the reoccurrence of the poetics beautiful image could be understood as a counter-reaction to the vulnerability of the myth of representation. Hence, the exhaustion of the mechanisms of representation and the political stance could be correlated with the photographic endeavour to represent the complexity of the outer world. The invited authors’ essays, reviewed papers and visual essays published on this issue aim to contribute to the critical discussion of this hypothetical quarrel, merging the notions of poetics and politics, while reaffirming the polysemy of photographs.  &nbsp

Measuring Chern numbers in Hofstadter strips

Topologically non-trivial Hamiltonians with periodic boundary conditions are characterized by strictly quantized invariants. Open questions and fundamental challenges concern their existence, and the possibility of measuring them in systems with open boundary conditions and limited spatial extension. Here, we consider transport in Hofstadter strips, that is, two-dimensional lattices pierced by a uniform magnetic flux which extend over few sites in one of the spatial dimensions. As we show, an atomic wavepacket exhibits a transverse displacement under the action of a weak constant force. After one Bloch oscillation, this displacement approaches the quantized Chern number of the periodic system in the limit of vanishing tunneling along the transverse direction. We further demonstrate that this scheme is able to map out the Chern number of ground and excited bands, and we investigate the robustness of the method in presence of both disorder and harmonic trapping. Our results prove that topological invariants can be measured in Hofstadter strips with open boundary conditions and as few as three sites along one direction.Comment: v1: 17 pages, 10 figures; v2: minor changes, reference added, SciPost style, 26 pages, 10 figures; v3: published versio