Many-body quantum coherence and interaction blockade in Josephson-linked Bose-Einstein condensates

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 {\em symmetric} systems of large N, and reveal several peculiar phenomena that may occur in {\em asymmetric} systems and systems of small N. For asymmetric systems, we show that, due to an interplay between asymmetry and inter-particle interaction, the coherence fluctuations are suppressed dramatically when |E_C/E_J|ll 1, and both {\it resonant tunneling} and {\it interaction blockade} take place for large values of |E_C/E_J|, 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.