Coherent control of steady state entanglement

We show that coherent control of the steady state entanglement between pairs of cavity-atom systems in an array of lossy and driven coupled cavities is possible. The cavities are doped with atoms and are connected through waveguides, other cavities or fibers depending the implementation. We find that the steady state entanglement can be coherently controlled through the tuning of the phase difference between the driving fields. It can also be surprisingly high in spite of the pumps being classical fields. Furthermore, the maximal of entanglement for any pair is achieved when their corresponding direct coupling is much smaller than their individual couplings to the third party. This effect is reminiscent of coherent population transfer through a third level between otherwise uncoupled atomic levels using classical coherent fields. The above results are analyzed for a range of values of the system parameters and different network geometries. Click here for the paper.

Many-body entanglement

We establish a relation between entanglement of a many-body system and its diffractive properties, where the link is given by structure factors. Based on these, we provide a general analytical construction of multiqubit entanglement witnesses. The proposed witnesses contain two-point correlations. They could be either measured in a scattering experiment or via local measurements, depending on the underlying physical system. For some explicit examples of witnesses we analyze the properties of the states that are detected by them. We further study the robustness of these witnesses with respect to noise. Work done in collaboration with: Philipp Krammer and Reinhold A. Bertlmann (Vienna), Hermann Kampermann and Dagmar Bruss(Dusseldorf); Chiara Macchiavello (Pavia) To appear in Phys. Rev. Lett. (2009)





18 Aug 2009

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