An adaptive inelastic magnetic mirror for Bose-Einstein condensates

We report the reflection and focussing of a Bose-Einstein condensate by a new pulsed magnetic mirror. The mirror is adaptive, inelastic, and of extremely high optical quality. The deviations from specularity are less than 0.5 mrad rms, making this the best atomic mirror demonstrated to date. We have also used the mirror to realize the analog of a beam-expander, producing an ultra-cold collimated fountain of matter wavesComment: 4 pages, 4 figure

Matter-wave cavity gravimeter

We propose a gravimeter based on a matter-wave resonant cavity loaded with a Bose-Einstein condensate and closed with a sequence of periodic Raman pulses. The gravimeter sensitivity increases quickly with the number of cycles experienced by the condensate inside the cavity. The matter wave is refocused thanks to a spherical wave-front of the Raman pulses. This provides a transverse confinement of the condensate which is discussed in terms of a stability analysis. We develop the analogy of this device with a resonator in momentum space for matter waves.Comment: 15 pages, 6 Figures. The expression for the atomic mirror focal length has been corrected. Other minor corrections and actualizations to the previously published versio

New insights into the genetic etiology of Alzheimer's disease and related dementias

Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele

Reconstruction of a cold atom cloud by magnetic focusing

Over the passed 15 years advances in laser cooling techniques have made it routinely possible to prepare cold clouds of atoms exhibiting temperatures of the order of several micro-Kelvin or less. Such low temperatures correspond to average atomic velocities of a few centimetres per second. Therefore, according to the de Broglie relationship p = h/#lambda#, the atoms increasingly exhibit wave-like behaviour and can no longer be treated solely as particles. These advances in atom manipulation have renewed interest in the field of atom optics. One of the concerns of atom optics is the manipulation of atoms with optical elements analogous to those used in photon optics. The most basic of such elements is the mirror. This thesis presents a curved mirror for paramagnetic atoms fabricated from commercial video tape. It is the smoothest magnetic mirror to date and is the third generation of mirrors fabricated by our group using magnetic recording media. Previous designs used audio tape and 5 1/4 inch floppy disk. Using fluorescence imaging we have directly imaged atoms bouncing above the mirror and, owing to its smoothness, have observed the first ever reconstruction of a cold atom cloud above a curved reflector. The atoms were collected in a magneto optical trap (MOT), cooled to a temperature of 18 #mu#K and then dropped onto the mirror. When released from a height of 13.5 mm we observed the collimation and refocusing of the cloud on consecutive bounces. Furthermore, we observed up to 14 bounces of the cloud, which corresponds to a time of #approx#1.5 s. One of the factors that limited the number of observable bounces was the presence of some finite roughness in the reflecting surface. Using images of the focused cloud at the peak of even bounces we were able to measure this roughness and found it to be 5.9 mrads. By analysing magnetic force microscope (MFM) scans of the fields above the mirror we attributed this residual roughness to the spatial inhomogeneity of magnetic particles in the tape. (author)Available from British Library Document Supply Centre-DSC:DXN031546 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Manipulation of cold atoms by an adaptable magnetic reflector

Adaptive optics for cold atoms has been experimentally realized by applying a bias magnetic field to a static magnetic mirror. The mirror consist of a 12-mm-diameter piece of commercial videotape, having a sine wave of wavelength 25.4 μm recorded in a single track across its width, curved to form a concave reflector with radius of curvature R D 54 mm. We have studied the performance of the mirror by monitoring the evolution of a 24 μK cloud of 85Rb atoms bouncing on it. A uniform static external magnetic field was added to the mirror field causing a corrugated potential from which the atoms bounce with increased angular spread. The characteristic angular distribution of the surface normal is mapped at the peak of the bounce for atoms dropped from a height of R=2 and at the peak of the second bounce for a drop height of R=4. In a second experiment a timedependent magnetic field was applied and the angular distribution of the cloud was measured as a function of field frequency. In this scheme we demonstrate a corrugated potential whose time-dependent magnitude behaves like a diffraction grating of variable depth. Finally a rotating field was added to generate a corrugated potential that moves with a velocity given by the product of the external field rotation frequency and the videotape wavelength. This travelling grating provides a new method of manipulation as cold atoms are transported across the surface by surfing along the moving wave. Two theoretical methods have been developed to predict the behaviour of atoms reflecting from these stationary, variable magnitude and moving corrugated potentials. A simple analytic theory provides excellent agreement for reflection from a stationary corrugated potential and gives good agreementwhen extended to the case of a travelling grating. A Monte Carlo simulation was also performed by brute force numeric integration of the equations of motion for atoms reflecting from all three corrugated potential cases

Manipulation of cold atoms using a corrugated magnetic reflector

A corrugated magnetic reflector is realized by adding a bias field to a static magnetic mirror. This permits real-time manipulation of a cold-atom cloud on time scales down to 10