Analytic treatment of controlled reversible inhomogeneous broadening quantum memories for light using two-level atoms

It has recently been discovered that the optical analog of a gradient echo, in an optically thick material, could form the basis of an optical memory that is both completely efficient and noise-free. Here we present analytical calculations showing that this is the case. There is close analogy between the operation of the memory and an optical system with two beam splitters. We can use this analogy to calculate efficiencies as a function of optical depth for a number of quantum memory schemes based on controlled inhomogeneous broadening. In particular, we show that multiple switching leads to a net 100% retrieval efficiency for the optical gradient echo even in the optically thin case

Characterization of electromagnetically-induced-transparency-based continuous-variable quantum memories

We present a quantum multimodal treatment describing electromagnetically induced transparency EIT as a mechanism for storing continuous-variable quantum information in light fields. Taking into account the atomic noise and decoherences of realistic experiments, we numerically model the propagation, storage, and readout of signals contained in the sideband amplitude and phase quadratures of a light pulse using phase space methods. An analytical treatment of the effects predicted by this model is then presented. Finally, we use quantum information benchmarks to examine the properties of the EIT-based memory and show the parameters needed to operate beyond the quantum limit

Transferrin receptor 1 mRNA is downregulated in placenta of hepcidin transgenic embryos

AbstractWe have previously shown that hepcidin transgenic embryos are severely anemic and die around birth. Here, we report that embryonic hepcidin transgene expression decreases transferrin receptor 1 (TfR1) mRNA level in placenta, as shown by cDNA microarray analysis and quantitative RT-PCR, by a mechanism which is independent of placenta iron content and iron responsive element/iron regulatory protein (IRE/IRP) activity. On the contrary, iron injections into pregnant mothers result in increased placenta iron and ferritin content, and reduced IRE binding activity of IRP1 leading to decreased TfR1 mRNA level. Taken together, these results suggest that hepcidin action on placenta is mostly through transcriptional downregulation of the iron uptake machinery

Segmentation automatique d'images sonar à antenne synthétique pour la détection d'échos de mines sous-marines

Cet article présente une méthode de segmentation des images obtenues au moyen d'un sonar à antenne synthétique (SAS), afin de mettre en évidence certaines caractéristiques des échos (nombre, position, forme, ... ) des mines sous-marines, posées au fond de la mer. Cette méthode de segmentation est basée sur les caractéristiques statistiques de l'image sonar, mises en évidence par la représentation moyenne / écart-type. Elle est automatisée en utilisant un critère d'entropie

Vacuum squeezed light for atomic memories at the D2 cesium line

We report the experimental generation of squeezed light at 852 nm, locked on the Cesium D2 line. 50% of noise reduction down to 50 kHz has been obtained with a doubly resonant optical parametric oscillator operating below threshold, using a periodically-polled KTP crystal. This light is directly utilizable with Cesium atomic ensembles for quantum networking application

Can optical squeezing be generated via polarization self-rotation in a thermal vapour cell?

The traversal of an elliptically polarized optical field through a thermal vapour cell can give rise to a rotation of its polarization axis. This process, known as polarization self-rotation (PSR), has been suggested as a mechanism for producing squeezed light at atomic transition wavelengths. In this paper, we show results of the characterization of PSR in isotopically enhanced Rubidium-87 cells, performed in two independent laboratories. We observed that, contrary to earlier work, the presence of atomic noise in the thermal vapour overwhelms the observation of squeezing. We present a theory that contains atomic noise terms and show that a null result in squeezing is consistent with this theory.Comment: 10 pages, 11 figures, submitted to PRA. Please email author for a PDF file if the article does not appear properl

Application de l'algorithme Principal Component Inverse 3D pour la détection de mines enfouies

- Cet article s'intéresse à la réduction de fausses alarmes dans le cadre de la détection de mines sous marines enfouies. Nous proposons d'utiliser un algorithme algèbrique. le Principal Component Inverse 3D, pour réduire l'influence de la réverbération et séparer les échos de mines entre eux. Cette méthode est testée sur des données réelles fournies par le GESMA et les résultats sont comparés à ceux donnés par des algorithmes algébriques 2D

Highly non-Gaussian states created via cross-Kerr nonlinearity

We propose a feasible scheme for generation of strongly non-Gaussian states using the cross-Kerr nonlinearity. The resultant states are highly non-classical states of electromagnetic field and exhibit negativity of their Wigner function, sub-Poissonian photon statistics, and amplitude squeezing. Furthermore, the Wigner function has a distinctly pronounced ``banana'' or ``crescent'' shape specific for the Kerr-type interactions, which so far was not demonstrated experimentally. We show that creating and detecting such states should be possible with the present technology using electromagnetically induced transparency in a four-level atomic system in N-configuration.Comment: 12 pages, 7 figure