Coherent back and forward scattering peaks in the quantum kicked rotor

We propose and analyze an experimental scheme using the quantum kicked rotor to observe the newly-predicted coherent forward scattering peak together with its long-known twin brother, the coherent backscattering peak. Contrary to coherent backscattering, which arises already under weak-localization conditions, coherent forward scattering is only triggered by Anderson or strong localization. So far, coherent forward scattering has not been observed in conservative systems with elastic scattering by spatial disorder. We propose to turn to the quantum kicked rotor, which has a long and succesful history as an accurate experimental platform to observe dynamical localization, i.e., Anderson localization in momentum space. We analyze the coherent forward scattering effect for the quantum kicked rotor by extensive numerical simulations, both in the orthogonal and unitary class of disordered quantum systems, and show that an experimental realization involving phase-space rotation techniques is within reach of state-of-the-art cold-atom experiments.Comment: 26 pages, 11 figure

Mesures en ligne du champ magnétique du GANIL

La mesure en ligne du champ magnétique des électroaimants du Grand Accélérateur National d'Ions Lourds (GANIL) a été étudiée et mise au point. Elle permet le réglage et la surveillance des paramètres de conduite du faisceau, de l'accélérateur aux salles d'expériences. Les développements ont été menés autour de magnétomètres à Résonnance Magnétique Nucléaire (RMN) et de magnétomètres à effet Hall. Les limitations de fonctionnement des sondes RMN en zone de champ inhomogène ont nécessité des solutions particulières. Des techniques de positionnement et de compensation de gradient adaptées ont été mises en œuvre. Les sondes RMN et à effet Hall sont intégrées dans une électronique d'acquisition et de traitement définie selon les standards du GANIL. L'ensemble constitue une instrumentation qui répond parfaitement aux besoins, en particulier du point de vue de la mesure et de la surveillance des paramètres magnétiques

Universality of the Anderson transition with the quasiperiodic kicked rotor

We report a numerical analysis of the Anderson transition in a quantum-chaotic system, the quasiperiodic kicked rotor with three incommensurate frequencies. It is shown that this dynamical system exhibits the same critical phenomena as the truly random 3D-Anderson model. By taking proper account of systematic corrections to one-parameter scaling, the universality of the critical exponent is demonstrated. Our result $\nu = 1.59 \pm 0.01$ is in perfect agreement with the value found for the Anderson model.Comment: 4 figures, 3 tables (published version

Universal scaling of the order-parameter distribution in strongly disordered superconductors

We investigate theoretically and experimentally the statistical properties of the inhomogeneous order-parameter distribution (OPD) at the verge of the superconductor-insulator transition (SIT). We find within two prototype fermionic and bosonic models for disordered superconductors that one can identify a universal rescaling of the OPD. By performing scanning-tunneling microscopy experiments in three samples of NbN with increasing disorder we show that such a rescaling describes also with an excellent accuracy the experimental data. These results can provide a breakthrough in our understanding of the SIT.Comment: 11 pages, 8 figures, revised version submitted to PR

Symmetry Violation of Quantum Multifractality: Gaussian fluctuations versus Algebraic Localization

Quantum multifractality is a fundamental property of systems such as non-interacting disordered systems at an Anderson transition and many-body systems in Hilbert space. Here we discuss the origin of the presence or absence of a fundamental symmetry related to this property. The anomalous multifractal dimension $\Delta_q$ is used to characterize the structure of quantum states in such systems. Although the multifractal symmetry relation \mbox{$\Delta_q=\Delta_{1-q}$} is universally fulfilled in many known systems, recently some important examples have emerged where it does not hold. We show that this is the result of two different mechanisms. The first one was already known and is related to Gaussian fluctuations well described by random matrix theory. The second one, not previously explored, is related to the presence of an algebraically localized envelope. While the effect of Gaussian fluctuations can be removed by coarse graining, the second mechanism is robust to such a procedure. We illustrate the violation of the symmetry due to algebraic localization on two systems of very different nature, a 1D Floquet critical system and a model corresponding to Anderson localization on random graphs.Comment: Closest to published versio

Factors affecting compliance with glove removal after contact with a patient or environment in four intensive care units

International audienc

Impact of screening and identifying methicillin-resistant Staphylococcus aureus carriers on hand hygiene compliance in 4 intensive care units

BackgroundOur objective was to assess the impact of screening and identifying methicillin-resistant Staphylococcus aureus (MRSA) carriers as a single measure in 4 intensive care units (ICUs). Methods An evaluative study including two 6-month periods was conducted prospectively. The evaluation concerned the hand hygiene compliance (HHC) for contacts with MRSA carriers versus contacts with noncarriers (comparison C1, main objective) and for a period of absence of identification (P1) versus a period of identification (P2) (comparison C2) and MRSA cross transmission (P1 vs P2) (comparison C3) measured with 2 indicators. Results Overall, 1326 opportunities of hand hygiene were observed. Concerning C1, the HHC for contacts with MRSA carriers was 42.5% versus 43.1% for contacts with noncarriers (not significant). This absence of difference was recorded whatever the ICU specialty, the category of personnel, and the nature of contacts. Concerning C2, the HHC in P1 was 44.8% versus 48.5% in P2 (not significant). Concerning C3, no significant difference was identified between the 2 periods. Conclusion We did not identify any advantage by using screening and identifying MRSA carriers in those 4 ICUs in which no specific strategy of additional contact measures was implemented for MRSA carriers

A process very similar to multifractional Brownian motion

In Ayache and Taqqu (2005), the multifractional Brownian (mBm) motion is obtained by replacing the constant parameter $H$ of the fractional Brownian motion (fBm) by a smooth enough functional parameter $H(.)$ depending on the time $t$. Here, we consider the process $Z$ obtained by replacing in the wavelet expansion of the fBm the index $H$ by a function $H(.)$ depending on the dyadic point $k/2^j$. This process was introduced in Benassi et al (2000) to model fBm with piece-wise constant Hurst index and continuous paths. In this work, we investigate the case where the functional parameter satisfies an uniform H\"older condition of order \beta>\sup_{t\in \rit} H(t) and ones shows that, in this case, the process $Z$ is very similar to the mBm in the following senses: i) the difference between $Z$ and a mBm satisfies an uniform H\"older condition of order $d>\sup_{t\in \R} H(t)$; ii) as a by product, one deduces that at each point $t\in \R$ the pointwise H\"older exponent of $Z$ is $H(t)$ and that $Z$ is tangent to a fBm with Hurst parameter $H(t)$.Comment: 18 page

Discordance in the minimal inhibitory concentrations of ertapenem for Enterobacter cloacae: Vitek 2 system versus Etest and agar dilution methods

Our objective was to compare the ertapenem minimal inhibitory concentrations (MICs) for Enterobacter cloacae isolates categorized intermediate or resistant to ertapenem when measured with the Vitek 2 system, with the MICs for these isolates when measured by two methods performed in agar medium: the Etest and agar plate dilution method (APDM). Overall, 50 E. cloacae isolates were included in the study. The mean MIC of ertapenem was 2.92±1.77μg/ml according to the Vitek 2 system, 0.94±0.84μg/ml according to the Etest strips, and 0.93±0.62μg/ml according to the APDM. Furthermore, the MICs determined by the Vitek 2 system were higher than the MICs determined by the two other methods for 96% of strains. Lastly, according to the Etest strips and APDM, 42% of E. cloacae were susceptible to ertapenem. No carbapenemase was identified by the screening method used. Using the Vitek 2 system to determine ertapenem MICs for E. cloacae can have potential consequences in terms of additional carbapenemase-detecting tests and antimicrobial therapy. It would be interesting to determine if the Vitek 2 system is more effective for the detection of carbapenemase producers with low-level carbapenem resistance than the two methods performed in agar medium