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.Comment: 6 pages, 5 figures, accepted for publication in EPL (Europhysics Letters

Interaction induced mergence of Dirac points in Non-Abelian optical lattices

We study the properties of an ultracold Fermi gas loaded in a square optical lattice and subjected to an external and classical non-Abelian gauge field. We calculate the energy spectrum of the system and show that the Dirac points in the energy spectrum will remain quite stable under onsite interaction of certain strength. Once the on-site interaction grows stronger than a critical value, the Dirac points will no longer be stable and merge into a single hybrid point. This mergence implies a quantum phase transition from a semimetallic phase to a band insulator. The on-site interaction between ultracold fermions could be conveniently controlled by Feshbach resonances in current experiments. We proposed that this remarkable interaction induced mergence of Dirac points may be observed in the ultracold fermi gas experiments