Robustness of bipartite Gaussian entangled beams propagating in lossy channels

Subtle quantum properties offer exciting new prospects in optical communications. Quantum entanglement enables the secure exchange of cryptographic keys and the distribution of quantum information by teleportation. Entangled bright beams of light attract increasing interest for such tasks, since they enable the employment of well-established classical communications techniques. However, quantum resources are fragile and undergo decoherence by interaction with the environment. The unavoidable losses in the communication channel can lead to a complete destruction of useful quantum properties -- the so-called "entanglement sudden death". We investigate the precise conditions under which this phenomenon takes place for the simplest case of two light beams and demonstrate how to produce states which are robust against losses. Our study sheds new light on the intriguing properties of quantum entanglement and how they may be tamed for future applications.Comment: To be published - Nature Photonic

Disentanglement in Bipartite Continuous-Variable Systems

Entanglement in bipartite continuous-variable systems is investigated in the presence of partial losses, such as those introduced by a realistic quantum communication channel, e.g. by propagation in an optical fiber. We find that entanglement can vanish completely for partial losses, in a situa- tion reminiscent of so-called entanglement sudden death. Even states with extreme squeezing may become separable after propagation in lossy channels. Having in mind the potential applications of such entangled light beams to optical communications, we investigate the conditions under which entanglement can survive for all partial losses. Different loss scenarios are examined and we derive criteria to test the robustness of entangled states. These criteria are necessary and sufficient for Gaussian states. Our study provides a framework to investigate the robustness of continuous-variable entanglement in more complex multipartite systems.Comment: Phys. Rev. A (in press

Properties of magnetic nanodots with perpendicular anisotropy

Nanodots with magnetic vortices have many potential applications, such as magnetic memories (VRAMs) and spin transfer nano-oscillators (STNOs). Adding a perpendicular anisotropy term to the magnetic energy of the nanodot it becomes possible to tune the vortex core properties. This can be obtained, e.g., in Co nanodots by varying the thickness of the Co layer in a Co/Pt stack. Here we discuss the spin configuration of circular and elliptical nanodots for different perpendicular anisotropies; we show for nanodisks that micromagnetic simulations and analytical results agree. Increasing the perpendicular anisotropy, the vortex core radii increase, the phase diagrams are modified and new configurations appear; the knowledge of these phase diagrams is relevant for the choice of optimum nanodot dimensions for applications. MFM measurements on Co/Pt multilayers confirm the trend of the vortex core diameters with varying Co layer thicknesses.Comment: 7 pages, 8 figure

From hysteria to somatic symptom disorders: Searching for a common psychopathological ground

After decades of manifold contributions aimed at defining hysteria, somatisation and conversion, such syndromes are still neglected and their nosographical definition is debated. The DSM and the ICD have undergone major changes, but their clinical utility with regards to these syndromes is still questionable. On the contrary, the Diagnostic Criteria for Psychosomatic Research represents a useful clinical instrument since it translates psychosocial variables derived from psychosomatic research into operational tools. The present paper offers an overview on the psychopathological description of syndromes such as alexithymia, hypochondriasis, health anxiety, thanatophobia, conversion symptoms, anniversary and reaction which are frequent in clinical practice, but often misdiagnosed due to their absence in the DSM and the ICD. In addition, the influence of culture and cultural changes on the modifications of psychopathological manifestations is described as a further possible source of misdiagnosing and underreporting. New psychopathologies (e.g., multiple chemical sensitivity, orthorexia/vigorexia) that resemble conversion and/or somatisation have been developed, but neither is included in nosography nor taught to clinicians. The aim of the present paper is thus to describe psychopathological manifestations of somatic symptoms and related disorders to help clinicians formulate their diagnosis on the presence of signs and symptoms that can be elicited during a clinical visit, rather than by way of exclusion of other organic or psychiatric disease only