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The nonequilibrium dynamics of a gas of cold atoms in which Rydberg states are off-resonantly excited is studied in the presence of noise. The interplay between interaction and off-resonant excitation leads to an initial dynamics where aggregates of excited Rydberg atoms slowly nucleate and grow, eventually reaching long-lived metastable arrangements which then relax further on much longer time scales. This growth dynamics is governed by an effective Master equation which permits a transparent and largely analytical understanding of the underlying physics. By means of extensive numerical simulations we study the many-body dynamics and the correlations of the resulting nonequilibrium states in various dimensions. Our results provide insight into the dynamical richness of strongly interacting Rydberg gases in noisy environments, and highlight the usefulness of these kinds of systems for the exploration of soft-matter-type collective behavior. [ABSTRACT FROM AUTHOR]

In a recent paper [Phys. Rev. A 92, 022309 (2015)], the authors proposed a quantum oblivious set-member decision protocol, which is designed to allow a server to check whether a private secret of a user is a member of his private set in an oblivious manner. Such protocols should protect the privacies of both the server and the user. However, we find that the user in their protocol can steal l-1 bits of information about the server's private set by sending the false decoy states. [ABSTRACT FROM AUTHOR]