The tunneling process in a many-body system is a phenomenon which lies at thevery heart of quantum mechanics. It appears in nature in the form ofalpha-decay, fusion and fission in nuclear physics, photoassociation andphotodissociation in biology and chemistry. A detailed theoretical descriptionof the decay process in these systems is a very cumbersome problem, eitherbecause of very complicated or even unknown interparticle interactions or dueto a large number of constitutent particles. In this work, we theoreticallystudy the phenomenon of quantum many-body tunneling in a more transparent andcontrollable physical system, in an ultracold atomic gas. We analyze a full,numerically exact many-body solution of the Schr\"odinger equation of aone-dimensional system with repulsive interactions tunneling to open space. Weshow how the emitted particles dissociate or fragment from the trapped andcoherent source of bosons: the overall many-particle decay process is a quantuminterference of single-particle tunneling processes emerging from sources withdifferent particle numbers taking place simultaneously. The close relation toatom lasers and ionization processes allows us to unveil the great relevance ofmany-body correlations between the emitted and trapped fractions of thewavefunction in the respective processes.
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