Many-body echo
Yang-Yang Chen, Pengfei Zhang, Wei Zheng, Zhigang Wu, Hui Zhai
Abstract
In this Rapid Communication, we propose a protocol to reverse a quantum many-body dynamic process. We name it ``many-body echo'' because the underlying physics is closely related to the spin echo effect in nuclear magnetic resonance systems. We consider a periodical modulation of the interaction strength in a weakly interacting Bose condensate, which resonantly excites quasiparticles 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 quasiparticles in the resonance modes will be absorbed back into the condensate. During the intermediate half-period, the free evolution introduces a $\ensuremath{\pi}$ phase, which plays a role reminiscent of that played by the $\ensuremath{\pi}$ pulse in the spin echo. Comparing our protocol with another one implemented by the Chicago group in a recent experiment, we find that ours is more effective at reversing the many-body process. The difference between these two schemes manifests the physical effect of the micromotion in the Floquet theory.