Quantum phases of interacting phonons in ion traps

The vibrations of a chain of trapped ions can be considered, under suitable experimental conditions, as an ensemble of interacting phonons, whose quantum dynamics is governed by a Bose--Hubbard Hamiltonian. In this work we study the quantum phases which appear in this system, and show that thermodynamical properties, such as critical parameters and critical exponents, can be measured in experiments with a limited number of ions. Besides that, interacting phonons in trapped ions offer us the possibility to access regimes which are difficult to study with ultracold bosons in optical lattices, like models with attractive or site--dependent phonon-phonon interactions.Comment: 10 page

Zeno dynamics in wave-packet diffraction spreading

We analyze a simple and feasible practical scheme displaying Zeno, anti-Zeno, and inverse-Zeno effects in the observation of wave-packet spreading caused by free evolution. The scheme is valid both in spatial diffraction of classical optical waves and in time diffraction of a quantum wave packet. In the optical realization, diffraction spreading is observed by placing slits between a light source and a light-power detector. We show that the occurrence of Zeno or anti-Zeno effects depends just on the frequency of observations between the source and detector. These effects are seen to be related to the diffraction mode theory in Fabry-Perot resonators.Comment: 7 pages, 8 figure

Rabi lattice models with discrete gauge symmetry: Phase diagram and implementation in trapped-ion quantum simulators

We study a spin-boson chain that exhibits a local Z2 symmetry. We investigate the quantum phase diagram of the model by means of perturbation theory, mean-field theory, and the density matrix renormalization group method. Our calculations show the existence of a first-order phase transition in the region where the boson quantum dynamics is slow compared to the spin-spin interactions. Our model can be implemented with trapped-ion quantum simulators, leading to a realization of minimal models showing local gauge invariance and first-order phase transitions

Credit Supply versus Demand: Bank and Firm Balance-Sheet Channels in Good and Crisis Times

Abstract: Banking crises involve periods of persistently low credit and economic growth. Banks’ balance sheets are then weak but so are those of non-financial corporate borrowers. Hence, a crucial question is whether credit growth is low due to supply or to demand factors. However convincing identification has been elusive due to a lack of detailed loan application-, bank-, and firm-level data. Access to a dataset of loan applications in Spain that is matched with complete bank and firm balance-sheet data covering the period from 2002 to 2010 allows us to identify bank and firm balancesheet channels. We find robust evidence showing that bank balance-sheet strength determines the success of loan applications and the granting of loans in crisis times. The heterogeneity in firm balance-sheet strength determines loan granting in both good and crisis times, although the potency of this firm balance-sheet channel is the largest in the latter period. Our findings therefore hold important implications for both theory and policy.bank lending channel;credit supply;business cycle;credit crunch;capital;liquidity

OH+ in Diffuse Molecular Clouds

Near ultraviolet observations of OH+ and OH in diffuse molecular clouds reveal a preference for different environments. The dominant absorption feature in OH+ arises from a main component seen in CH+ (that with the highest CH+/CH column density ratio), while OH follows CN absorption. This distinction provides new constraints on OH chemistry in these clouds. Since CH+ detections favor low-density gas with small fractions of molecular hydrogen, this must be true for OH+ as well, confirming OH+ and H2O+ observations with the Herschel Space Telescope. Our observed correspondence indicates that the cosmic ray ionization rate derived from these measurements pertains to mainly atomic gas. The association of OH absorption with gas rich in CN is attributed to the need for high enough density and molecular fraction before detectable amounts are seen. Thus, while OH+ leads to OH production, chemical arguments suggest that their abundances are controlled by different sets of conditions and that they coexist with different sets of observed species. Of particular note is that non-thermal chemistry appears to play a limited role in the synthesis of OH in diffuse molecular clouds.Comment: 15 pages, 4 figures, to appear in ApJ Letter

Renormalization algorithm for the calculation of spectra of interacting quantum systems

We present an algorithm for the calculation of eigenstates with definite linear momentum in quantum lattices. Our method is related to the Density Matrix Renormalization Group, and makes use of the distribution of multipartite entanglement to build variational wave--functions with translational symmetry. Its virtues are shown in the study of bilinear--biquadratic S=1 chains.Comment: Corrected version. We have added an appendix with an extended explanation of the implementation of our algorith

Using Eco-schemes in the new CAP: a guide for managing authorities

This guide has been developed primarily for policy makers and Member State officials involved in the national and regional programming processes of the CAP Strategic Plans (CSPs). This process might involve different administrative levels (national, regional, local), different political fields (agriculture, environmental, food and health ministries), different public bodies (paying agencies, environmental agencies, rural development offices) depending on the administrative setting of each MS. In addition, the guide provides support to other stakeholders and practitioners from the public and private sectors and civil society (including agricultural, environmental, food, health and consumer NGOs), with a direct or indirect involvement in the programming and evaluation process of the CSPs. Since these new plans will have a strong impact on MS environments, agricultural sectors, rural areas, etc., the engagement of all stakeholders will be an important asset for supporting an effective implementation of the CSP objectives. There are many others with potential interests in the contents of this guide. EU citizens have demonstrated their increasing interest in the contents of the CAP objectives and policy framework, as demonstrated both by civil society initiatives and consumption decisions. The contents of this guide may therefore also be of interest to other societal actors with interests in agricultural and environmental policies, such as researchers, journalists, trade unions, and civil society organizations. However, the guide is intentionally more focused on the technical needs of those involved in CSP development and implementation

Non-coding RNA regulatory networks

It is well established that the vast majority of human RNA transcripts do not encode for proteins and that non-coding RNAs regulate cell physiology and shape cellular functions. A subset of them is involved in gene regulation at different levels, from epigenetic gene silencing to post-transcriptional regulation of mRNA stability. Notably, the aberrant expression of many non-coding RNAs has been associated with aggressive pathologies. Rapid advances in network biology indicates that the robustness of cellular processes is the result of specific properties of biological networks such as scale-free degree distribution and hierarchical modularity, suggesting that regulatory network analyses could provide new insights on gene regulation and dysfunction mechanisms. In this study we present an overview of public repositories where non-coding RNA-regulatory interactions are collected and annotated, we discuss unresolved questions for data integration and we recall existing resources to build and analyse networks

Color Superconducting Phases of Cold Dense Quark Matter

We investigate color superconducting phases of cold quark matter at densities relevant for the interiors of compact stars. At these densities, electrically neutral and weak-equilibrated quark matter can have unequal numbers of up, down, and strange quarks. The QCD interaction favors Cooper pairs that are antisymmetric in color and in flavor, and a crystalline color superconducting phase can occur which accommodates pairing between flavors with unequal number densities. In the crystalline color superconductor, quarks of different flavor form Cooper pairs with nonzero total momentum, yielding a condensate that varies in space like a sum of plane waves. Rotational and translational symmetry are spontaneously broken. We use a Ginzburg-Landau method to evaluate candidate crystal structures and predict that the favored structure is face-centered-cubic. We predict a robust crystalline phase with gaps comparable in magnitude to those of the color-flavor-locked phase that occurs when the flavor number densities are equal. Crystalline color superconductivity will be a generic feature of the QCD phase diagram, occurring wherever quark matter that is not color-flavor locked is to be found. If a very large flavor asymmetry forbids even the crystalline state, single-flavor pairing will occur; we investigate this and other spin-one color superconductors in a survey of generic color, flavor, and spin pairing channels. Our predictions for the crystalline phase may be tested in an ultracold gas of fermionic atoms, where a similar crystalline superfluid state can occur. If a layer of crystalline quark matter occurs inside of a compact star, it could pin rotational vortices, leading to observable pulsar glitches.Comment: Ph.D. thesis, submitted to the MIT Department of Physics, May 2003. Five chapters and two appendices (180 pages, 30 figures). Chapters 1 and 5 are new: chapter 1 is a detailed review of previous work, and chapter 5 discusses applications of the crystalline phase for the physics of pulsar spin glitches and cold trapped atom