How fast can a quantum system evolve? We answer this question focusing on the role of entanglement and interactions among subsystems. In particular, we analyze how the order of the interactions shapes the dynamics .
Any method for estimating the ensemble average of arbitrary operator (observables or not, including the density matrix) relates the quantity of interest to a complete set of observables, i.e. a quorum. This corresponds to an expansion on an irreducible set of operators in the Liouville space. We give two general characterizations of these sets. All the… (More)
Bell's theorem is a fundamental result in quantum mechanics: it discriminates between quantum mechanics and all theories where probabilities in measurement results arise from the ignorance of pre-existing local properties. We give an extremely simple proof of Bell's inequality; a single figure suffices. This simplicity may be useful in the unending debate… (More)
Clock synchronization procedures are analyzed in the presence of imperfect communications. In this context we show that there are physical limitations, which prevent one from synchronizing distant clocks when the intervening medium is completely dephasing, as in the case of a rapidly varying dispersive medium.
Quantum entanglement is the ability of joint quantum systems to possess global properties (correlation among systems) even when subsystems have no definite individual property. Whilst the 2-dimensional (qubit) case is well-understood, currently, tools to characterise entanglement in high dimensions are limited. We experimentally demonstrate a new procedure… (More)