138 research outputs found

    Revealing correlations between a system and an inaccessible environment

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    How can we detect that our local, controllable quantum system is correlated with some other inaccessible environmental system? The local detection method developed in recent years allows to realize a dynamical witness for correlations without requiring knowledge of or access to the environment that is correlated with the local accessible quantum system. Here, we provide a brief summary of the theoretical method and recent experimental studies with single photons and trapped ions coupled to increasingly complex environments.Comment: 12 pages, 3 figure

    Entanglement and squeezing in continuous-variable systems

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    We introduce a multi-mode squeezing coefficient to characterize entanglement in NN-partite continuous-variable systems. The coefficient relates to the squeezing of collective observables in the 2N2N-dimensional phase space and can be readily extracted from the covariance matrix. Simple extensions further permit to reveal entanglement within specific partitions of a multipartite system. Applications with nonlinear observables allow for the detection of non-Gaussian entanglement.Comment: 11 pages, 2 figure