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Josephson Tunnelling of a Phase-imprinted Bose-Einstein Condensate in a Time-dependent Double-Well Potential

E Sakellari, Nick P. Proukakis, M. Leadbeater, C. S. Adams

Published Dec 31, 2004• 0 citations
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Abstract

This paper discusses the feasibility of experimental control of the flow direction of atomic Bose-Einstein condensates in a double-well potential using phase imprinting. The flow is induced by the application of a time-dependent potential gradient, providing a clear signature of macroscopic quantum tunnelling in atomic condensates. By studying both initial-state preparation and subsequent tunnelling dynamics, we find the parameters to optimize the phase-induced Josephson current. We find that the effect is largest for condensates of up to a few thousand atoms, and is only weakly dependent on trap geometry.

DOI
10.25405/ncl.34578912

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This paper discusses the feasibility of experimental control of the flow direction of atomic Bose-Einstein condensates in a double-well potential using phase imprinting. The flow is induced by the application of a time-dependent potential gradient, providing a clear signature of macroscopic quantum tunnelling in atomic condensates. By studying both initial-state preparation and subsequent tunnelling dynamics, we find the parameters to optimize the phase-induced Josephson current. We find that the effect is largest for condensates of up to a few thousand atoms, and is only weakly dependent on trap geometry.
This paper discusses the feasibility of experimental control of the flow direction of atomic Bose–Einstein condensates in a double-well potential using phase imprinting. The flow is induced by the application of a time-dependent potential gradient, providing a clear signature of macroscopic quantum tunnelling in atomic condensates. By studying both initial-state preparation and subsequent tunnelling dynamics, we find the parameters to optimize the phase-induced Josephson current. We find that the effect is largest for condensates of up to a few thousand atoms, and is only weakly dependent on trap geometry.
We investigate the quantum dynamics of an experimentally realized spin-orbit-coupled Bose-Einstein condensate in a double-well potential. The spin-orbit coupling can significantly enhance the atomic interwell tunneling. We find the coexistence of internal and external Josephson effects in the system, which are moreover inherently coupled in a complicated form even in the absence of interatomic interactions. Moreover, we show that the spin-dependent tunneling between two wells can induce a net atomic spin current referred as spin Josephson effects. Such spin Josephson effects can be observable under realistic conditions.
Josephson weak links in superconductors can be engineered such that the phase difference across the junction is πππ (πππ-junction),leading to the reversal of the current. The conditions under which the analogous effect of supercurrent counterflow can be achieved in a double-well atomic Bose-Einstein condensate are investigated. It is shown that this effect is observable for condensates up to a few thousand atoms, which are initially prepared in an anti-symmetric 'πππ-state' and subsequently subjected to a uniformly increasing magnetic field gradient. This effect is found to be only weakly-dependent on trap geometry, and can be observed in both attractive and repulsive condensates.
The stability of a low-temperature Bose–Einstein condensate with attractive interactions in one- and three-dimensional double-well potentials is discussed. In particular, the tunnelling dynamics of a condensate under the influence of a time-dependent potential gradient is investigated. The condensate is shown to collapse at a critical potential gradient which corresponds to a critical number of atoms in one of the two wells. The sensitivity of this tunnelling-induced collapse could provide a useful tool in the study of condensates with attractive interactions.
In this thesis, I present the first experimental implementation of a Josephson junction for Bose-Einstein condensates. The weak link between two BECs constitutes the nonlinear generalization of the well known Josephson junction of weakly-coupled superconductors that are separated by a thin insulating barrier. In our experiment, the required overlap of two macroscopic wavefunctions is provided by loading a BEC into an optical double well potential. It is realized by a superposition of a one-dimensional optical lattice with a focused laser beam optical dipole trap. The tunneling dynamics between the two potential wells exhibits two distinct dynamical regimes. For small initial population imbalances of the two wells we observe nearly sinusoidal Josephson tunneling oscillations, which are characterized by an oscillating population and relative phase. The situation changes drastically, if the initial population imbalance is chosen above a critical value. In this case, resonant tunneling between the two wells is prohibited because the difference between the on-site particle interaction energies in the two wells exceeds the tunneling energy splitting. As a consequence, the atomic distribution becomes self-locked and the relative phase evolves unbound in time. This regime of prohibited tunneling, which has no analogon in superconducting Josephson junctions, is called “macroscopic quantum self-trapping”.
The stability of a low temperature Bose-Einstein condensate with attractive interactions in one and three dimensional double-well potentials is discussed. In particular, the tunnelling dynamics of a condensate under the influence of a time-dependent potential gradient is investigated. The condensate is shown to collapse at a critical potential gradient which corresponds to a critical number of atoms in one of the two wells. The sensitivity of this tunnelling induced collapse could provide a useful tool in the study of condensates with attractive interactions.