Sub-Doppler laser cooling of 40K with Raman gray molasses on the D2 line

Gray molasses is a powerful tool for sub-Doppler laser cooling of atoms to low temperatures. For alkaline atoms, this technique is commonly implemented with cooling lasers which are blue-detuned from either the D1 or D2 line. Here we show that efficient gray molasses can be implemented on the D2 line of 40K with red-detuned lasers. We obtained temperatures of 48(2)µK, which enables direct loading of 9.2(3)x106 atoms from a magneto-optical trap into an optical dipole trap. We support our findings by a one-dimensional model and three-dimensional numerical simulations of the optical Bloch equations which qualitatively reproduce the experimentally observed cooling effects.PreprintPublisher PDFPeer reviewe

Single-atom imaging of fermions in a quantum-gas microscope

Single-atom-resolved detection in optical lattices using quantum-gas microscopes has enabled a new generation of experiments in the field of quantum simulation. Fluorescence imaging of individual atoms has so far been achieved for bosonic species with optical molasses cooling, whereas detection of fermionic alkaline atoms in optical lattices by this method has proven more challenging. Here we demonstrate single-site- and single-atom-resolved fluorescence imaging of fermionic potassium-40 atoms in a quantum-gas microscope setup using electromagnetically-induced-transparency cooling. We detected on average 1000 fluorescence photons from a single atom within 1.5s, while keeping it close to the vibrational ground state of the optical lattice. Our results will enable the study of strongly correlated fermionic quantum systems in optical lattices with resolution at the single-atom level, and give access to observables such as the local entropy distribution and individual defects in fermionic Mott insulators or anti-ferromagnetically ordered phases.Comment: 7 pages, 5 figures; Nature Physics, published online 13 July 201

A single-site resolution fermionic quantum-gas microscope

Quantum-gas microscopes have become an important tool in quantum simulation as they enable direct probing of local quantities by single-atom-resolved detection in optical lattices. Recent years have seen many fascinating results from the bosonic quantum-gas microscopes using 87Rb. However, no such device existed for fermionic species.;The goal of this thesis work was to develop and build a quantum-gas microscope setup for fermionic potassium-40. Single-atom-resolved imaging of 40K has proven very challenging due to its smaller mass and smaller excited-state hyperfine splitting compared to 87Rb. In addition, the inverted excited state trapping potential required us to employ electromagnetically induced transparency (EIT) cooling instead of sub-Doppler molasses cooling.;EIT cooling occurs when a coherent driving of a three-level system generates a spectrally narrow Fano-like resonance which can be set to favour red-sideband transitions over blue ones of the quantised vibrational levels in the optical lattice potential. During the cooling process, the fluorescence light is collected by a high-NA objective to image the atomic distribution in a two-dimentional square lattice potential.;Due to the physical constraints of our apparatus, EIT cooling had to be combined with coupling between different motional axes via Raman transitions to achieve cooling of all degrees of freedom. Our imaging method allowed us to collect about 1,000 fluorescence photons per atom within a 1.5 s exposure time. From the analysis of two distinct subsequent fluorescence images, we found that less than 5% of the atoms hopped or were lost during 1s of EIT cooling. Such fidelity will allow fermionic quantum-gas microscopes to investigate fermionic quantum phases, spin-spin correlations, and out of-equilibrium dynamics of correlated fermionic many-body quantum systems.Quantum-gas microscopes have become an important tool in quantum simulation as they enable direct probing of local quantities by single-atom-resolved detection in optical lattices. Recent years have seen many fascinating results from the bosonic quantum-gas microscopes using 87Rb. However, no such device existed for fermionic species.;The goal of this thesis work was to develop and build a quantum-gas microscope setup for fermionic potassium-40. Single-atom-resolved imaging of 40K has proven very challenging due to its smaller mass and smaller excited-state hyperfine splitting compared to 87Rb. In addition, the inverted excited state trapping potential required us to employ electromagnetically induced transparency (EIT) cooling instead of sub-Doppler molasses cooling.;EIT cooling occurs when a coherent driving of a three-level system generates a spectrally narrow Fano-like resonance which can be set to favour red-sideband transitions over blue ones of the quantised vibrational levels in the optical lattice potential. During the cooling process, the fluorescence light is collected by a high-NA objective to image the atomic distribution in a two-dimentional square lattice potential.;Due to the physical constraints of our apparatus, EIT cooling had to be combined with coupling between different motional axes via Raman transitions to achieve cooling of all degrees of freedom. Our imaging method allowed us to collect about 1,000 fluorescence photons per atom within a 1.5 s exposure time. From the analysis of two distinct subsequent fluorescence images, we found that less than 5% of the atoms hopped or were lost during 1s of EIT cooling. Such fidelity will allow fermionic quantum-gas microscopes to investigate fermionic quantum phases, spin-spin correlations, and out of-equilibrium dynamics of correlated fermionic many-body quantum systems

Formation of ultracold fermionic NaLi Feshbach molecules

We describe the formation of fermionic NaLi Feshbach molecules from an ultracold mixture of bosonic [superscript 23]Na and fermionic [superscript 6]Li. Precise magnetic field sweeps across a narrow Feshbach resonance at 745 G result in a molecule conversion fraction of 5% for our experimental densities and temperatures, corresponding to a molecule number of 5×10[superscript 4]. The observed molecular decay lifetime is 1.3 ms after removing free Li and Na atoms from the trap. Due to its extremely low reactivity, NaLi molecules in the ground state will have a much longer lifetime than KRb.United States. Air Force Office of Scientific Research. Multidisciplinary University Research InitiativeNational Science Foundation (U.S.)United States. Office of Naval ResearchUnited States. Army Research Office (Grant W911NF-07-1-0493)United States. Defense Advanced Research Projects Agency. Optical Lattice Emulator ProgramNatural Sciences and Engineering Research Council of Canada (NSERC

Antimicrobial de-escalation in the critically ill patient and assessment of clinical cure: the DIANA study

Purpose: The DIANA study aimed to evaluate how often antimicrobial de-escalation (ADE) of empirical treatment is performed in the intensive care unit (ICU) and to estimate the effect of ADE on clinical cure on day 7 following treatment initiation. Methods: Adult ICU patients receiving empirical antimicrobial therapy for bacterial infection were studied in a prospective observational study from October 2016 until May 2018. ADE was defined as (1) discontinuation of an antimicrobial in case of empirical combination therapy or (2) replacement of an antimicrobial with the intention to narrow the antimicrobial spectrum, within the first 3 days of therapy. Inverse probability (IP) weighting was used to account for time-varying confounding when estimating the effect of ADE on clinical cure. Results: Overall, 1495 patients from 152 ICUs in 28 countries were studied. Combination therapy was prescribed in 50%, and carbapenems were prescribed in 26% of patients. Empirical therapy underwent ADE, no change and change other than ADE within the first 3 days in 16%, 63% and 22%, respectively. Unadjusted mortality at day 28 was 15.8% in the ADE cohort and 19.4% in patients with no change [p = 0.27; RR 0.83 (95% CI 0.60-1.14)]. The IP-weighted relative risk estimate for clinical cure comparing ADE with no-ADE patients (no change or change other than ADE) was 1.37 (95% CI 1.14-1.64). Conclusion: ADE was infrequently applied in critically ill-infected patients. The observational effect estimate on clinical cure suggested no deleterious impact of ADE compared to no-ADE. However, residual confounding is likely

The LHCb upgrade I

International audienceThe LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software