Coherent photon manipulation in interacting atomic ensembles

Coupling photons to Rydberg excitations in a cold atomic gas yields unprecedentedly large optical nonlinearities at the level of individual light quanta, where the formation of nearby dark-state polaritons is blocked by the strong interactions between Rydberg atoms. This blockade mechanism, however, realizes an inherently dissipative nonlinearity, which limits the performance of practical applications. In this work, we propose a new approach to strong photon interactions via a largely coherent mechanism at drastically suppressed photon losses. Rather than a polariton blockade, it is based on an interaction induced conversion between distinct types of dark-state polaritons with different propagation characteristics. We outline a specific implementation of this approach and show that it permits to turn a single photon into an effective mirror with a robust and continuously tuneable reflection phase. We describe potential applications, including a detailed discussion of achievable operational fidelities

Attitudes toward Birth Control in Bandung, Indonesia

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An Innovative Cold-formed Floor System

Optimizing the use of building materials has always been one of the primary goals of engineers. It is a constant challenge to seek innovative methods to build lighter weight structures. Sometimes this is achieved through the development of new building materials, other times it can be accomplished by creating entirely new types of structural systems. Often lightweight structures can be more asthetically pleasing because of their stream-lined appearance. However, in general the motivating factor in building lightweight structures is to reduce the overall cost. One portion of a structure which offers tremendous potential for weight reduction is the floor system. The floor system is one of the heaviest components in typical steel framed buildings. A reduction in the dead load of this component will result in a subsequent reduction in the total weight of the building structural system

Magnetomechanical performance and mechanical properties of Ni-Mn-Ga ferromagnetic shape memory alloys

A Ni-Mn-Ga ferromagnetic shape memory alloy was tested for strain versus applied field and strain versus stress. Field- induced strains up to 6 percent were measured with a hysteresis of about 160 kA/m. The results are compared with the predictions of modeling with a focus on hysteresis. The model is applied to the case in which the magnetic external field and external load are orthogonal to each other. It predicts the magneto-mechanical hysteresis as a function of the yield stress in a twinned martensite. Magnetization versus applied field was measured on a sample that was mechanically constrained in order to understand the magnetization behavior of the sample in the absence of twin motion. These measurements give the magnetic anisotropy and are used to estimate the demagnetization fields. The measured behavior of strain with stress at constant field is approximated by the model

6% magnetic-field-induced strain by twin-boundary motion in ferromagnetic Ni–Mn–Ga

Field-induced strains of 6% are reported in ferromagnetic Ni–Mn–Ga martensites at room temperature. The strains are the result of twin boundary motion driven largely by the Zeeman energy difference across the twin boundary. The strain measured parallel to the applied magnetic field is negative in the sample/field geometry used here. The strain saturates in fields of order 400 kA/m and is blocked by a compressive stress of order 2 MPa applied orthogonal to the magnetic field. The strain versus field curves exhibit appreciable hysteresis associated with the motion of the twin boundaries. A simple model accounts quantitatively for the dependence of strain on magnetic field and external stress using as input parameters only measured quantities

Photon Subtraction by Many-Body Decoherence

We experimentally and theoretically investigate the scattering of a photonic quantum field from another stored in a strongly interacting atomic Rydberg ensemble. Considering the many-body limit of this problem, we derive an exact solution to the scattering-induced spatial decoherence of multiple stored photons, allowing for a rigorous understanding of the underlying dissipative quantum dynamics. Combined with our experiments, this analysis reveals a correlated coherence-protection process in which the scattering from one excitation can shield all others from spatial decoherence. We discuss how this effect can be used to manipulate light at the quantum level, providing a robust mechanism for single-photon subtraction, and experimentally demonstrate this capability