Non-Gaussian distribution of collective operators in quantum spin chains

We numerically analyse the behavior of the full distribution of collective observables in quantum spin chains. While most of previous studies of quantum critical phenomena are limited to the first moments, here we demonstrate how quantum fluctuations at criticality lead to highly non-Gaussian distributions thus violating the central limit theorem. Interestingly, we show that the distributions for different system sizes collapse after scaling on the same curve for a wide range of transitions: first and second order quantum transitions and transitions of the Berezinskii-Kosterlitz-Thouless type. We propose and carefully analyse the feasibility of an experimental reconstruction of the distribution using light-matter interfaces for atoms in optical lattices or in optical resonators.Comment: 15 pages, 5 figures; last version close to published versio

Characterization of Bose-Hubbard Models with Quantum Non-demolition Measurements

We propose a scheme for the detection of quantum phase transitions in the 1D Bose-Hubbard (BH) and 1D Extended Bose-Hubbard (EBH) models, using the non-demolition measurement technique of quantum polarization spectroscopy. We use collective measurements of the effective total angular momentum of a particular spatial mode to characterise the Mott insulator to superfluid phase transition in the BH model, and the transition to a density wave state in the EBH model. We extend the application of collective measurements to the ground states at various deformations of a super-lattice potential.Comment: 8 pages, 9 figures; published version in PRA, Editors' Suggestio

Entanglement detection in hybrid optomechanical systems

We study a device formed by a Bose Einstein condensate (BEC) coupled to the field of a cavity with a moving end-mirror and find a working point such that the mirror-light entanglement is reproduced by the BEC-light quantum correlations. This provides an experimentally viable tool for inferring mirror-light entanglement with only a limited set of assumptions. We prove the existence of tripartite entanglement in the hybrid device, persisting up to temperatures of a few milli-Kelvin, and discuss a scheme to detect it.Comment: 6 pages, 7 figures, published versio

Cavity-aided quantum parameter estimation in a bosonic double-well Josephson junction

We describe an apparatus designed to make non-demolition measurements on a Bose-Einstein condensate (BEC) trapped in a double-well optical cavity. This apparatus contains, as well as the bosonic gas and the trap, an optical cavity. We show how the interaction between the light and the atoms, under appropriate conditions, can allow for a weakly disturbing yet highly precise measurement of the population imbalance between the two wells and its variance. We show that the setting is well suited for the implementation of quantum-limited estimation strategies for the inference of the key parameters defining the evolution of the atomic system and based on measurements performed on the cavity field. This would enable {\it de facto} Hamiltonian diagnosis via a highly controllable quantum probe.Comment: 8 pages, 5 figures, RevTeX4; Accepted for publication in Phys. Rev.

From perfect to fractal transmission in spin chains

Perfect state transfer is possible in modulated spin chains, imperfections however are likely to corrupt the state transfer. We study the robustness of this quantum communication protocol in the presence of disorder both in the exchange couplings between the spins and in the local magnetic field. The degradation of the fidelity can be suitably expressed, as a function of the level of imperfection and the length of the chain, in a scaling form. In addition the time signal of fidelity becomes fractal. We further characterize the state transfer by analyzing the spectral properties of the Hamiltonian of the spin chain.Comment: 8 pages, 10 figures, published versio

Is efficiency of classical simulations of quantum dynamics related to integrability?

Efficiency of time-evolution of quantum observables, and thermal states of quenched hamiltonians, is studied using time-dependent density matrix renormalization group method in a family of generic quantum spin chains which undergo a transition from integrable to non-integrable - quantum chaotic case as control parameters are varied. Quantum states (observables) are represented in terms of matrix-product-operators with rank D_\epsilon(t), such that evolution of a long chain is accurate within fidelity error \epsilon up to time t. We find that rank generally increases exponentially, D_\epsilon(t) \propto \exp(const t), unless the system is integrable in which case we find polynomial increase.Comment: 4 pages; v2. added paragraph discussing pure state

Recent trends and climatic perspectives of hailstorms frequency and intensity in Tuscany and Central Italy

International audienceThe damages from climatic extremes have dramatically increased in the last decades in Europe, as likely outcomes of climate change: floods, droughts, heat waves and hailstorms have brought local as well as widespread damages to farmers, industry, infrastructures and society, to insurance and reinsurance companies; in this work we deal with the hailstorm hazard. The NCEP-NCAR Reanalysis (2.5 by 2.5° lat-lon) over the Italian area and the hailstorm reports at several sites are used to identify few forcings for hailstorms; statistical relationships linking forcings and hailstorm frequencies are derived. Such relationships are applied to the same forcings derived from the CGCM2-A2 climate scenario provided by the Canadian Centre for Climate modeling and analysis (CCCma; resolution approximately 3.75 by 3.75° lat-lon), to evaluate the expected changes of the frequency of hailstorms. The time series of the forcings from the NCEP-NCAR Reanalysis and the CCCma climate scenario in the past decades are compared in order to assess the reliability and accuracy of the predictions of the future hailstorm hazard. It is shown that the climate scenario provides a fairly faithful representation of the past trends of the forcings relevant to the hailstorms frequency and that such quantity, hence the hailstorm hazard, is growing and will likely grow in the future over the limited area taken into consideration in this study

Increasing of entanglement entropy from pure to random quantum critical chains

It is known that the entropy of a block of spins of size $L$ embedded in an infinite pure critical spin chain diverges as the logarithm of $L$ with a prefactor fixed by the central charge of the corresponding conformal field theory. For a class of strongly random spin chains, it has been shown that the correspondent block entropy still remains universal and diverges logarithmically with an "effective" central charge. By computing the entanglement entropy for a family of models which includes the $N$-states random Potts chain and the $Z_N$ clock model, we give some definitive answer to some recent conjectures about the behaviour of the effective central charge. In particular, we show that the ratio between the entanglement entropy in the pure and in the disordered system is model dependent and we provide a series of critical models where the entanglement entropy grows from the pure to the random case.Comment: 4 pages, 2 eps figures, added reference

23-valent pneumococcal polysaccharide vaccine (PPV23) for the prevention of invasive pneumococcal diseases (IPDs) in the elderly: is it really effective?

Introduction. Incidence of invasive pneumococcal diseases (IPDs) in Italy is constantly increasing and that is particularly true among the elderly. 23-valent polysaccharide pneumococcal vac- cine (PPV23) is recommended to this age group and offered in all Italian regions. However, efficacy of PPV23 on preventing IPDs is debated. We therefore performed a review of the most recent avail- able meta-analyses in order to assess the efficacy of PPVs. Methods. The literature search was conducted using PubMed and Scopus search engines. We used the following keywords: ?pneu- mococcal?, ?polysaccharide?, ?vaccine?, ?efficacy?, ?elderly?, ?meta analysis?. Only meta-analyses published in the last 7 years were selected. We examined the results of the selected meta-anal- yses and assessed their quality according to the PRISMA recom- mendations. Results. The search returned 16 results in PubMed and 12 in Scopus: among them we selected 3 meta-analyses. According to our quality assessment, all meta-analyses showed generally posi- tive results and almost all items of the PRISMA checklist were respected. However, the research protocol and the registration number were absent in all the 3 revisions and the flow-chart was not shown in Moberley?s and Melegaro?s works. In the study by Huss et al. the relative risk of developing IPDs among vaccinated subjects was 0.90 (95%CI: 0.46-1.77, I2 4.9%), indicating a very slight benefit after vaccination. This contrasts with the results of the Cochrane Review by Moberley et al., in which the PPVs showed a protective efficacy in reducing the risk of IPDs of 74% (OR 0.26, 95%CI: 0.15-0.46) with no statistical heterogeneity (I2 0%). Melegaro et al. found a reduction not statistically signifi- cant of the incidence of IPD of 65% (OR 0.35; 95%CI 0.08-1.49) among healthy elderly, while the global estimate of vaccine efficacy among high risk elderly was minimal (OR 0.80; 95%CI 0.22-2.88). Conclusions. Most of the studies suggest that the PPVs confer low protection against IPDs. Anyhow, their methodological het- erogeneity does not allow definitive conclusions. While waiting to see the results of new trials about the efficacy of PPVs, in particular of PPV23, and the extension of the use of conjugate vaccine among the population over 65, stakeholders should be aware of the results of the meta-analyses discussed in this paper during the implementation of the vaccination programs for the elderly in Public Health. The full article is free available on www.jpmh.or