Abstract
Josephson junctions (JJs) and junction arrays are well-studied devices in superconductivity. With external magnetic fields one can modulate the phase in a long junction and create traveling, solitonic waves of magnetic flux, called fluxons. Today, it is also possible to devise two different types of junctions: depending on the sign of the critical current density , they are called 0- or π-junctions. In turn, a 0–π junction is formed by joining two of these junctions. As a result, one obtains a pinned Josephson vortex of fractional magnetic flux, at the 0–π boundary. Here, we analyze this arrangement of superconducting junctions in the context of an atomic bosonic quantum gas, where two-state atoms in a double well trap are coupled in an analogous fashion. There, an all-optical 0–π JJ is created by the phase of a complex valued Rabi frequency and we derive a discrete four-mode model for this situation, which qualitatively resembles a semifluxon.
Highlights
During the past two decades, the field of cold atomic gases has come a long way starting from almost lossless trapping and cooling techniques [1] to reaching quantum degeneracy of Bosons and Fermions [2]
In the present article we will report on such a transfer of concepts from a superconducting device [31], i.e., in various realizations of Josephson junction arrays and their unusual state properties of traveling and pinned magnetic flux quanta to an analogous set up for neutral bosonic atoms in a trap
In the present article we have briefly summarized the status of the fluxon and semifluxon physics in superconductivity
Summary
During the past two decades, the field of cold atomic gases has come a long way starting from almost lossless trapping and cooling techniques [1] to reaching quantum degeneracy of Bosons and Fermions [2]. The combination of optical lattices with ultracold gases [26, 27] has boosted the possibilities to investigate junction arrays experimentally. In the present article we will report on such a transfer of concepts from a superconducting device [31], i.e., in various realizations of Josephson junction arrays and their unusual state properties of traveling (fluxons) and pinned (semifluxons) magnetic flux quanta to an analogous set up for neutral bosonic atoms in a trap. We will refer to the most relevant publications in this thriving field of fluxon and semifluxon physics; in Sec. 3, we will discuss a similar setup, which allows to find a pinned semifluxon in an atomic 0-π Josephson junction and we compare the results. We will discuss further open questions in a Conclusion
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