Atomic Josephson junction with two bosonic species

TL;DR

This paper investigates the dynamics of a two-species Bose-Einstein condensate in a double well, deriving coupled equations, analyzing stability, and identifying conditions for macroscopic quantum self-trapping, with potential applications in measuring inter-species interactions.

Contribution

It introduces a coupled pendula model for two interacting BECs in a double well and derives analytical formulas for oscillation frequencies and MQST onset.

Findings

Analytical formula for oscillation frequency around stable points.

Good agreement between GPE and pendula models under certain conditions.

Identification of the crossover value for inter-species interaction leading to MQST.

Abstract

We study an atomic Josephson junction (AJJ) in presence of two interacting Bose-Einstein condensates (BECs) confined in a double well trap. We assume that bosons of different species interact with each other. The macroscopic wave functions of the two components obey to a system of two 3D coupled Gross-Pitaevskii equations (GPE). We write the Lagrangian of the system, and from this we derive a system of coupled ordinary differential equations (ODE), for which the coupled pendula represent the mechanic analogous. These differential equations control the dynamical behavior of the fractional imbalance and of the relative phase of each bosonic component. We perform the stability analysis around the points which preserve the symmetry and get an analytical formula for the oscillation frequency around the stable points. Such a formula could be used as an indirect measure of the inter-species s-wave scattering length. We also study the oscillations of each fractional imbalance around zero and non zero - the macroscopic quantum self-trapping (MQST) - time averaged values. For different values of the inter-species interaction amplitude, we carry out this study both by directly solving the two GPE and by solving the corresponding coupled pendula equations. We show that, under certain conditions, the predictions of these two approaches are in good agreement. Moreover, we calculate the crossover value of the inter-species interaction amplitude which signs the onset of MQST.