Abstract
We study the complex quantum dynamics of a system of many interacting atoms in an elongated anharmonic trap. The system is initially in a Bose–Einstein condensed state, well described by Thomas–Fermi profile in the elongated direction and the ground state in the transverse directions. After a sudden quench to a coherent superposition of the ground and lowest energy transverse modes, quantum dynamics starts. We describe this process employing a three-mode many-body model. The experimental realization of this system displays decaying oscillations of the atomic density distribution. While a mean-field description predicts perpetual oscillations of the atomic density distribution, our quantum many-body model exhibits a decay of the oscillations for sufficiently strong atomic interactions. We associate this decay with the fragmentation of the condensate during the evolution. The decay and fragmentation are also linked with the approach of the many-body model to the chaotic regime. The approach to chaos lifts degeneracies and increases the complexity of the eigenstates, enabling the relaxation to equilibrium and the onset of thermalization. We verify that the damping time and quantum signatures of chaos show similar dependences on the interaction strength and on the number of atoms.
Highlights
The emergence of new quantum simulators have allowed for a better understanding, description, and control of quantum many-body systems out of equilibrium
We have shown that the three-mode quantum many-body model is a minimal model to qualitatively describe both the atomic density distribution oscillations and their damping
This behavior is qualitatively similar to the one observed experimentally with a quasi-1D Bose-Einstein condensate (BEC) prepared in a coherent superposition of its two lowest motional states [38, 39, 11]
Summary
The emergence of new quantum simulators have allowed for a better understanding, description, and control of quantum many-body systems out of equilibrium. Experiments with cold atoms have a prominent place in studies of relaxation and thermalization due to their high level of isolation [29, 12, 30, 31, 32, 33, 34, 35, 36, 16] Their access to precise coherence manipulation and to the preparation of desired initial states are essential for the investigation of quantum many-body dynamics [37]. In the scenario of isolated quantum systems, fragmentation, relaxation, and thermalization are caused by the interparticle interaction, rather than by couplings with an external thermal bath They reinforce the fact that the mean-field approximation is not valid for long times.
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