Rate analysis for a hybrid quantum repeater

We present a detailed rate analysis for a hybrid quantum repeater assuming perfect memories and using optimal probabilistic entanglement generation and deterministic swapping routines. The hybrid quantum repeater protocol is based on atomic qubit-entanglement distribution through optical coherent-state communication. An exact, analytical formula for the rates of entanglement generation in quantum repeaters is derived, including a study on the impacts of entanglement purification and multiplexing strategies. More specifically, we consider scenarios with as little purification as possible and we show that for sufficiently low local losses, such purifications are still more powerful than multiplexing. In a possible experimental scenario, our hybrid system can create near-maximally entangled (F = 0.98) pairs over a distance of 1280 km at rates of the order of 100 Hz

A non-adiabatic approach to entanglement distribution over long distances

Entanglement distribution between trapped-atom quantum memories, viz. single atoms in optical cavities, is addressed. In most scenarios, the rate of entanglement distribution depends on the efficiency with which the state of traveling single photons can be transferred to trapped atoms. This loading efficiency is analytically studied for two-level, $V$-level, $\Lambda$-level, and double-$\Lambda$-level atomic configurations by means of a system-reservoir approach. An off-resonant non-adiabatic approach to loading $\Lambda$-level trapped-atom memories is proposed, and the ensuing trade-offs between the atom-light coupling rate and input photon bandwidth for achieving a high loading probability are identified. The non-adiabatic approach allows a broad class of optical sources to be used, and in some cases it provides a higher system throughput than what can be achieved by adiabatic loading mechanisms. The analysis is extended to the case of two double-$\Lambda$ trapped-atom memories illuminated by a polarization-entangled biphoton.Comment: 15 pages, 15 figure

The Rules of Human T Cell Fate in vivo.

The processes governing lymphocyte fate (division, differentiation, and death), are typically assumed to be independent of cell age. This assumption has been challenged by a series of elegant studies which clearly show that, for murine cells in vitro, lymphocyte fate is age-dependent and that younger cells (i.e., cells which have recently divided) are less likely to divide or die. Here we investigate whether the same rules determine human T cell fate in vivo. We combined data from in vivo stable isotope labeling in healthy humans with stochastic, agent-based mathematical modeling. We show firstly that the choice of model paradigm has a large impact on parameter estimates obtained using stable isotope labeling i.e., different models fitted to the same data can yield very different estimates of T cell lifespan. Secondly, we found no evidence in humans in vivo to support the model in which younger T cells are less likely to divide or die. This age-dependent model never provided the best description of isotope labeling; this was true for naïve and memory, CD4+ and CD8+ T cells. Furthermore, this age-dependent model also failed to predict an independent data set in which the link between division and death was explored using Annexin V and deuterated glucose. In contrast, the age-independent model provided the best description of both naïve and memory T cell dynamics and was also able to predict the independent dataset

Effect of Pressure on Superconducting Ca-intercalated Graphite CaC6_6

The pressure effect on the superconducting transition temperature ($T_c$) of the newly-discovered Ca-intercalated graphite compound CaC$_6$ has been investigated up to $\sim$ 16 kbar. $T_c$ is found to increase under pressure with a large relative ratio $\Delta$$T_c$/$T_c$ of $\approx$ +0.4 %/kbar. Using first-principles calculations, we show that the large and positive effect of pressure on $T_c$ can be explained in the scope of electron-phonon theory due to the presence of a soft phonon branch associated to in-plane vibrations of Ca atoms. Implications of the present findings on the current debate about the superconducting mechanism in graphite intercalation compounds are discussed.Comment: 6 pages, 5 figs, final PRB versio

the effect of residual stress on fatigue behavior of v notched components a review

Abstract: Fatigue strength of mechanical components in the high cycle regime depends on the intensity of the residual stress field induced by non-homogeneous plastic deformation or the solidification of a local portion of material due to welding operations. In presence of geometric variations modelled as sharp V-notch angle, the residual stress distribution near the notch tip is singular and follows the same solution obtained by Williams in 1952 where the intensity of the asymptotic stress field is quantified by the notch stress intensity factor (NSIF). However, the residual stress varies during fatigue loading until a stationary value is reached. Numerical models were developed for the calculation of the residual NSIFs and their variation under fatigue loading. Taking advantage from these models, new approaches were recently developed which are able to predict the fatigue strength of pre-stressed notched components. A review of such recent advances is described in this work