Doublon-hole correlations and fluctuation thermometry in a Fermi-Hubbard gas

We report on the single atom and single site-resolved detection of the total density in a cold atom realization of the 2D Fermi-Hubbard model. Fluorescence imaging of doublons is achieved by splitting each lattice site into a double well, thereby separating atom pairs. Full density readout yields a direct measurement of the equation of state, including direct thermometry via the fluctuation-dissipation theorem. Site-resolved density correlations reveal the Pauli hole at low filling, and strong doublon-hole correlations near half filling. These are shown to account for the difference between local and non-local density fluctuations in the Mott insulator. Our technique enables the study of atom-resolved charge transport in the Fermi-Hubbard model, the site-resolved observation of molecules, and the creation of bilayer Fermi-Hubbard systems.Comment: 9 pages, 10 figure

Direct observation of non-local fermion pairing in an attractive Fermi-Hubbard gas

Pairing of fermions lies at the heart of superconductivity, the hierarchy of nuclear binding energies and superfluidity of neutron stars. The Hubbard model of attractively interacting fermions provides a paradigmatic setting for fermion pairing, featuring a crossover between Bose-Einstein condensation (BEC) of tightly bound pairs and Bardeen-Cooper-Schrieffer (BCS) superfluidity of long-range Cooper pairs, and a "pseudo-gap" region where pairs form already above the superfluid critical temperature. We here directly observe the non-local nature of fermion pairing in a Hubbard lattice gas, employing spin- and density-resolved imaging of $\sim$1000 fermionic ${}^{40}$K atoms under a bilayer microscope. Complete fermion pairing is revealed by the vanishing of global spin fluctuations with increasing attraction. In the strongly correlated regime, the fermion pair size is found to be on the order of the average interparticle spacing. We resolve polaronic correlations around individual spins, resulting from the interplay of non-local pair fluctuations and charge-density-wave order. Our techniques open the door toward in-situ observation of fermionic superfluids in a Hubbard lattice gas.Comment: 13 pages, 13 figure

Spin Transport in a Mott Insulator of Ultracold Fermions

Strongly correlated materials are expected to feature unconventional transport properties, such that charge, spin, and heat conduction are potentially independent probes of the dynamics. In contrast to charge transport, the measurement of spin transport in such materials is highly challenging. We observed spin conduction and diffusion in a system of ultracold fermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong interactions, spin diffusion is driven by super-exchange and doublon-hole-assisted tunneling, and strongly violates the quantum limit of charge diffusion. The technique developed in this work can be extended to finite doping, which can shed light on the complex interplay between spin and charge in the Hubbard model.Comment: 16 pages, 10 figure

Enterococcus faecalis MalR acts as a repressor of the maltose operons and additionally mediates their catabolite repression via direct interaction with seryl-phosphorylated-HPr

Enterococci are gram-positive pathogens and lead to cause hospital-acquired infections worldwide. Central carbon metabolism was shown as highly induced in Enterococcus faecalis during infection context. Metabolism of α-polysaccharides was previously described as an important factor for host colonisation and biofilm formation. A better characterisation of the adaptation of this bacterium to carbohydrate availabilities may lead to a better understanding of the link between carbohydrate metabolism and the infection process of E. faecalis. Here we show that MalR, a LacI/GalR transcriptional regulator, is the main factor in the regulation of the two divergent operons involved in maltose metabolism in this bacterium. The malR gene is transcribed from the malP promoter, but also from an internal promoter inside the gene located upstream of malR. In the absence of maltose, MalR acts as a repressor and in the presence of glucose, it exerts efficient CcpA-independent carbon catabolite repression. The central PTS protein P-Ser-HPr interacts directly with MalR and enhances its DNA binding capacity, which allows E. faecalis to adapt its metabolism to environmental conditions.Fil: Grand, Maxime. Universite de Caen Basse Normandie; FranciaFil: Blancato, Victor Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Espariz, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Deutscher, Josef. Université Paris-Saclay; Francia. Universite de Paris; FranciaFil: Pikis, Andreas. Center For Drug Evaluation And Research; Estados UnidosFil: Hartke, Axel. Universite de Caen Basse Normandie; FranciaFil: Magni, Christian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Biología Molecular y Celular de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario; ArgentinaFil: Sauvageot, Nicolas. Universite de Caen Basse Normandie; Franci

Performance characterization and near-realtime monitoring of MUSE adaptive optics modes at Paranal

The Multi Unit Spectroscopic Explorer (MUSE) is an integral field spectrograph on the Very Large Telescope Unit Telescope 4, capable of laser guide star assisted and tomographic adaptive optics using the GALACSI module. Its observing capabilities include a wide field (1 square arcmin), ground layer AO mode (WFM-AO) and a narrow field (7.5"x7.5"), laser tomography AO mode (NFM-AO). The latter has had several upgrades in the 4 years since commissioning, including an optimisation of the control matrices for the AO system and a new sub-electron noise detector for its infra-red low order wavefront sensor. We set out to quantify the NFM-AO system performance by analysing $\sim$230 spectrophotometric standard star observations taken over the last 3 years. To this end we expand upon previous work, designed to facilitate analysis of the WFM-AO system performance. We briefly describe the framework that will provide a user friendly, semi-automated way for system performance monitoring during science operations. We provide the results of our performance analysis, chiefly through the measured Strehl ratio and full width at half maximum (FWHM) of the core of the point spread function (PSF) using two PSF models, and correlations with atmospheric conditions. These results will feed into a range of applications, including providing a more accurate prediction of the system performance as implemented in the exposure time calculator, and the associated optimization of the scientific output for a given set of limiting atmospheric conditions.Comment: SPIE proceedings (2022), Observatory Operations: Strategies, Processes, and Systems I

Distinction between the Poole-Frenkel and tunneling models of electric field-stimulated carrier emission from deep levels in semiconductors

The enhancement of the emission rate of charge carriers from deep-level defects in electric field is routinely used to determine the charge state of the defects. However, only a limited number of defects can be satisfactorily described by the Poole-Frenkel theory. An electric field dependence different from that expected from the Poole-Frenkel theory has been repeatedly reported in the literature, and no unambiguous identification of the charge state of the defect could be made. In this article, the electric field dependencies of emission of carriers from DX centers in AlxGa1-xAs:Te, Cu pairs in silicon, and Ge:Hg have been studied applying static and terahertz electric fields, and analyzed by using the models of Poole-Frenkel and phonon assisted tunneling. It is shown that phonon assisted tunneling and Poole-Frenkel emission are two competitive mechanisms of enhancement of emission of carriers, and their relative contribution is determined by the charge state of the defect and by the electric-field strength. At high-electric field strengths carrier emission is dominated by tunneling independently of the charge state of the impurity. For neutral impurities, where Poole-Frenkel lowering of the emission barrier does not occur, the phonon assisted tunneling model describes well the experimental data also in the low-field region. For charged impurities the transition from phonon assisted tunneling at high fields to Poole-Frenkel effect at low fields can be traced back. It is suggested that the Poole-Frenkel and tunneling models can be distinguished by plotting logarithm of the emission rate against the square root or against the square of the electric field, respectively. This analysis enables one to unambiguously determine the charge state of a deep-level defect

Genome-Wide Identification of Small RNAs in the Opportunistic Pathogen Enterococcus faecalis V583

Small RNA molecules (sRNAs) are key mediators of virulence and stress inducible gene expressions in some pathogens. In this work we identify sRNAs in the Gram positive opportunistic pathogen Enterococcus faecalis. We characterized 11 sRNAs by tiling microarray analysis, 5′ and 3′ RACE-PCR, and Northern blot analysis. Six sRNAs were specifically expressed at exponential phase, two sRNAs were observed at stationary phase, and three were detected during both phases. Searches of putative functions revealed that three of them (EFA0080_EFA0081 and EFB0062_EFB0063 on pTF1 and pTF2 plasmids, respectively, and EF0408_EF04092 located on the chromosome) are similar to antisense RNA involved in plasmid addiction modules. Moreover, EF1097_EF1098 shares strong homologies with tmRNA (bi-functional RNA acting as both a tRNA and an mRNA) and EF2205_EF2206 appears homologous to 4.5S RNA member of the Signal Recognition Particle (SRP) ribonucleoprotein complex. In addition, proteomic analysis of the ΔEF3314_EF3315 sRNA mutant suggests that it may be involved in the turnover of some abundant proteins. The expression patterns of these transcripts were evaluated by tiling array hybridizations performed with samples from cells grown under eleven different conditions some of which may be encountered during infection. Finally, distribution of these sRNAs among genome sequences of 54 E. faecalis strains was assessed. This is the first experimental genome-wide identification of sRNAs in E. faecalis and provides impetus to the understanding of gene regulation in this important human pathogen

Bacterial Stressors in Minimally Processed Food

Stress responses are of particular importance to microorganisms, because their habitats are subjected to continual changes in temperature, osmotic pressure, and nutrients availability. Stressors (and stress factors), may be of chemical, physical, or biological nature. While stress to microorganisms is frequently caused by the surrounding environment, the growth of microbial cells on its own may also result in induction of some kinds of stress such as starvation and acidity. During production of fresh-cut produce, cumulative mild processing steps are employed, to control the growth of microorganisms. Pathogens on plant surfaces are already stressed and stress may be increased during the multiple mild processing steps, potentially leading to very hardy bacteria geared towards enhanced survival. Cross-protection can occur because the overlapping stress responses enable bacteria exposed to one stress to become resistant to another stress. A number of stresses have been shown to induce cross protection, including heat, cold, acid and osmotic stress. Among other factors, adaptation to heat stress appears to provide bacterial cells with more pronounced cross protection against several other stresses. Understanding how pathogens sense and respond to mild stresses is essential in order to design safe and effective minimal processing regimes