Current production in ring condensates with a weak link

TL;DR

This paper investigates the behavior of condensates in a ring trap with a weak link, analyzing solitonic trains, current dynamics, and methods to control state transitions, including adiabatic tuning and phase imprinting.

Contribution

It provides analytical solutions for wave functions, energies, and currents, and introduces two novel methods for coupling excited states to the ground state in ring condensates.

Findings

Excited states can be coupled to the ground state via adiabatic tuning or phase imprinting.

Current production and destruction are linked to defect formation and stirring parameters.

Hysteresis cycles in energy and current spectra are characterized.

Abstract

We consider attractive and repulsive condensates in a ring trap stirred by a weak link, and analyze the spectrum of solitonic trains dragged by the link, by means of analytical expressions for the wave functions, energies and currents. The precise evolution of current production and destruction in terms of defect formation in the ring and in terms of stirring is studied. We find that any excited state can be coupled to the ground state through two proposed methods: either by adiabatically tuning the link's strength and velocity through precise cycles which avoid the critical velocities and thus unstable regions, or by keeping the link still while setting an auxiliary potential and imprinting a nonlinear phase as the potential is turned off. We also analyze hysteresis cycles through the spectrum of energies and currents.