Abstract
We present the properties of the ground state and low-energy excitations of Bose–Hubbard chains with a geometry that varies from open to closed and with a tunable twisted link. In the vicinity of the symmetric π-flux case the system behaves as an interacting gas of discrete semifluxons for finite chains and interactions in the Josephson regime. The energy spectrum of the system is studied by direct diagonalization and by solving the corresponding Bogoliubov–de Gennes equations. The atom–atom interactions are found to enhance the presence of strongly correlated macroscopic superpositions of semifluxons.
Highlights
One-dimensional chains have attracted a great deal of interest in the past due to their simple analytical treatment both for bosons [1] and fermions [2]
Instead, condensate dragging can lead to a persistent current, experimentally observed in [7,8,9,10]
In this paper we have studied the role of a tunable link in a BH chain of arbitrary size
Summary
One-dimensional chains have attracted a great deal of interest in the past due to their simple analytical treatment both for bosons [1] and fermions [2]. Persistent currents may be produced in ultracold atoms trapped in a few sites of an optical lattice [26,27,28,29], such that one can profit from the nice properties of ultracold atomic experiments, namely the isolation from the environment and the control over the interactions and geometry [30, 31] In this way we have previously shown how topological defects can be produced by manipulating the phase-dependence of a single link [32]. Forcing one of the links to flip the quantum phase, macroscopic superpositions of discrete semifluxon states are found to form the degenerate set of ground states of the system for small but finite atom– atom interactions This feature makes this setup appealing in contrast to the fully symmetric chains considered before [27], where persistent currents in closed BH configurations were studied for excited states.
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