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Echoes and revival echoes in systems of anharmonically confined atoms

We study echoes and what we call 'revival echoes' for a collection of atoms that are described by a single quantum wavefunction and are confined in a weakly anharmonic trap. The echoes and revival echoes are induced by applying two, successive temporally localized potential perturbations to the confining potential, one at time $t=0$, and a smaller one at time $t=τ$. Pulse-like responses in the expectation value of position $<x(t)>$ are predicted at $t \approx nτ$ ($n=2,3,...$) and are particularly evident at $t \approx 2τ$. A novel result of our study is the finding of 'revival echoes'. Revivals (but not echoes) occur even if the second perturbation is absent. In particular, in the absence of the second perturbation, the response to the first perturbation dies away, but then reassembles, producing a response at revival times $mT_x$ ($m=1,2,...$). Including the second perturbation at $t=τ$, we find temporally localized responses, revival echoes, both before and after $t\approx mT_x$, e.g., at $t\approx m T_x-n τ$ (pre-revival echoes) and at $t\approx mT_x+nτ$, (post-revival echoes), where $m$ and $n$ are $1,2,...$ . Depending on the form of the perturbations, the 'principal' revival echoes at $t \approx T_x \pm τ$ can be much larger than the echo at $t \approx 2τ$. We develop a perturbative model for these phenomena, and compare its predictions to the numerical solutions of the time-dependent Schrödinger Equation. The scaling of the size of the various echoes and revival echoes as a function of the symmetry and size of the perturbations applied at $t=0$ and $t=τ$ is investigated. We also study the presence of revivals and revival echoes in higher moments of position, $<x^p (t)>$, $p>1$, and the effect of atom-atom interactions on these phenomena.