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Many-body echo phenomenon in a periodically driven Bose condensate


In this talk I will discuss a recent protocol we proposed to reverse a quantum many-body dynamical process. We name it "many-body echo" because the underlying physics is closely related to the spin echo effect in nuclear magnetic resonance systems. The dynamic problem we consider is a periodical modulation of the interaction strength in a weakly interacting Bose condensate, which resonantly excites quasi-particles from the condensate. A dramatic phenomenon is that, after pausing the interaction modulation for half a period and then continuing on with the same modulation, nearly all the excited quasi-particles in the resonance modes will be absorbed back into the condensate. During the intermediate half period, the free evolution introduces a π  phase, which plays a role reminiscent of that played by the π-pulse in the spin echo. Comparing our protocol with another implemented by the Chicago group in a recent experiment (J. Hu et al, Nat. Phys. 15, 785 (2019)), we find that ours is more effective at reversing the many-body dynamic process. The difference between these two schemes manifests the physical effect of the micro-motion in the Floquet theory.