Abstract: We study many-body quantum coherence and interaction blockade in two Josephson-linked Bose-Einstein condensates. We introduce universal operators for characterizing many-body coherence without limitations on the system symmetry and total particle number N. We reproduce the results for both coherence fluctuations and number squeezing in symmetric systems of large N, and reveal several peculiar phenomena that may occur in asymmetric systems and systems of small N. For asymmetric systems, we show that, due to an interplay between asymmetry and interparticle interaction, the coherence fluctuations are suppressed dramatically when vertical bar E-C/E-J vertical bar << 1, and both resonant tunneling and interaction blockade take place for large values of vertical bar E-C/E-J vertical bar, where E-C and E-J are the interaction and tunneling energies, respectively. We emphasize that the resonant tunneling and interaction blockade may allow creating single- atom devices with promising technology applications. We demonstrate that for the systems at finite temperatures the formation of self-trapped states causes an anomalous behavior.

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