Photon echo without a free induction decay in a double-Lambda system

We have characterized a novel photon-echo pulse sequence for a double-$\Lambda$ type energy level system where the input and rephasing transitions are different to the applied $\pi$-pulses. We show that despite having imperfect $\pi$-pulses (associated with large coherent emission due to free induction decay), the noise added is only 0.019$\pm$0.001 relative to the shot noise in the spectral mode of the echo. Using this echo pulse sequence in the `rephased amplified spontaneous emission' (RASE) scheme \cite{Ledingham2010} will allow for generation of entangled photon pairs that are in different frequency, temporal, and potentially spatial modes to any bright driving fields. The coherence and efficiency properties of this sequence were characterized in a Pr:YSO crystal

Non-classical photon streams using rephased amplified spontaneous emission

We present a fully quantum mechanical treatment of optically rephased photon echoes. These echoes exhibit noise due to amplified spontaneous emission, however this noise can be seen as a consequence of the entanglement between the atoms and the output light. With a rephasing pulse one can get an "echo" of the amplified spontaneous emission, leading to light with nonclassical correlations at points separated in time, which is of interest in the context of building wide bandwidth quantum repeaters. We also suggest a wideband version of DLCZ protocol based on the same ideas.Comment: 5 pages, 4 figures. Added section

Photon echo quantum memories in inhomogeneously broadened two level atoms

Here we propose a solid-state quantum memory that does not require spectral holeburning, instead using strong rephasing pulses like traditional photon echo techniques. The memory uses external broadening fields to reduce the optical depth and so switch off the collective atom-light interaction when desired. The proposed memory should allow operation with reasonable efficiency in a much broader range of material systems, for instance Er3+ doped crystals which have a transition at 1.5 um. We present analytic theory supported by numerical calculations and initial experiments.Comment: 7 pages, 8 figure

Experimental realization of light with time separated correlations by rephasing amplified spontaneous emission

Amplified spontaneous emission is a common noise source in active optical systems, it is generally seen as being an incoherent process. Here we excite an ensemble of rare earth ion dopants in a solid with a {\pi}-pulse, resulting in amplified spontaneous emission. The application of a second {\pi}-pulse leads to a coherent echo of the amplified spontaneous emission that is correlated in both amplitude and phase. For small optical thicknesses, we see evidence that the amplified spontaneous emission and its echo are entangled.Comment: 6 pages, 5 figures, the supplementary information pdf was uploaded with latex source files. This version accepted for publication in PR

Parkinson disease-linked GBA mutation effects reversed by molecular chaperones in human cell and fly models

GBA gene mutations are the greatest cause of Parkinson disease (PD). GBA encodes the lysosomal enzyme glucocerebrosidase (GCase) but the mechanisms by which loss of GCase contributes to PD remain unclear. Inhibition of autophagy and the generation of endoplasmic reticulum (ER) stress are both implicated. Mutant GCase can unfold in the ER and be degraded via the unfolded protein response, activating ER stress and reducing lysosomal GCase. Small molecule chaperones that cross the blood brain barrier help mutant GCase refold and traffic correctly to lysosomes are putative treatments for PD. We treated fibroblast cells from PD patients with heterozygous GBA mutations and Drosophila expressing human wild-type, N370S and L444P GBA with the molecular chaperones ambroxol and isofagomine. Both chaperones increased GCase levels and activity, but also GBA mRNA, in control and mutant GBA fibroblasts. Expression of mutated GBA in Drosophila resulted in dopaminergic neuronal loss, a progressive locomotor defect, abnormal aggregates in the ER and increased levels of the ER stress reporter Xbp1-EGFP. Treatment with both chaperones lowered ER stress and prevented the loss of motor function, providing proof of principle that small molecule chaperones can reverse mutant GBA-mediated ER stress in vivo and might prove effective for treating PD

Rapid microplate rotations and backarc rifting at the transition between collision and subduction

ABSTRACT Using global positioning system velocities from convergent plate boundaries in Papua New Guinea, New Zealand, Tonga, Vanuatu, and the Marianas, we note a spatial correlation between rapid tectonic block rotations and the transition from subduction to collision. We present a mechanism for the block rotations, in which the change from collision of a buoyant indentor to normal subduction exerts a torque on the upper-plate microplate. This work improves our understanding of the causes of rapid vertical axis rotations, often observed in paleomagnetic studies. We also show how collision-induced rotations may lead to backarc rifting

Viewing speech in action: speech articulation videos in the public domain that demonstrate the sounds of the International Phonetic Alphabet (IPA)

In this article, we introduce recently released, publicly available resources, which allow users to watch videos of hidden articulators (e.g. the tongue) during the production of various types of sounds found in the world’s languages. The articulation videos on these resources are linked to a clickable International Phonetic Alphabet chart ([International Phonetic Association. 1999. Handbook of the International Phonetic Association: A Guide to the Use of the International Phonetic Alphabet. Cambridge: Cambridge University Press]), so that the user can study the articulations of different types of speech sounds systematically. We discuss the utility of these resources for teaching the pronunciation of contrastive sounds in a foreign language that are absent in the learner’s native language