Matter-wave interference, Josephson oscillation and its disruption in a Bose-Einstein condensate on an optical lattice

TL;DR

This paper models matter-wave interference and Josephson oscillations in a Bose-Einstein condensate within an optical lattice, revealing how trap displacement disrupts superfluidity, indicating a transition to an insulator state.

Contribution

It provides a theoretical analysis of Josephson oscillations and their disruption in BECs on optical lattices, aligning with experimental observations and identifying critical displacement for superfluid-insulator transition.

Findings

Josephson oscillations are observed in the BEC within the optical lattice.

Displacing the trap beyond a critical distance disrupts the Josephson current.

The disruption signals a transition from superfluid to insulator in the condensate.

Abstract

Using the axially-symmetric time-dependent mean-field Gross-Pitaevskii equation we study the Josephson oscillation in a repulsive Bose-Einstein condensate trapped by a harmonic plus an one-dimensional optical-lattice potential to describe the experiments by Cataliotti et. al. [Science 293 (2001) 843, New J. Phys. 5 (2003) 71.1]. After a study of the formation of matter-wave interference upon releasing the condensate from the optical trap, we directly investigate the alternating atomic superfluid Josephson current upon displacing the harmonic trap along the optical axis. The Josephson current is found to be disrupted upon displacing the harmonic trap through a distance greater than a critical distance signaling a superfluid to a classical insulator transition in the condensate.