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Abstract

Ultracold atoms provide a versatile platform for quantum simulation, offering a great deal of control on system parameters. The potential landscape experienced by the atoms can be precisely controlled with the optical dipole force, especially with the help of a digital micromirror device (DMD). The kinetic property of the atoms can be altered with optical lattices that create band structures with tunable dispersion. The interatomic interaction can also be controlled by magnetic field through Feshbach resonances. One popular method to leverage this high degree of tunability is Floquet engineering, where one periodically drives the system to realize Hamiltonians inaccessible to static systems. On the other hand, Bose-Einstein condensates provide a scalable and clean venue to study many-body physics, where tens of thousands of atoms share the same quantum state while interacting with each other. With driven Bose-Einstein condensates, we study two novel many-body phenomena. First, we create domain walls in the condensate, which are stable topological defects that behave as emergent particle-like excitations. The domain walls are found to display emergent dynamical properties drastically different from the constituent atoms. Second, we study the time reversal of a many-body system coupled to a continuum. The dynamics of such systems typically exhibit rapidly growing subsystem entropy, which according to classical thermodynamics appears irreversible. We are able to achieve significant reversal of the complex many-body dynamics by devising a technique inspired by the famous ‘spin echo’, which we call the ‘many-body echo’. Our work addresses two major standing questions in quantum many-body physics: emergence and thermalization.

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