A comparison is made of various searching procedures, based upon different entanglement measures or entanglement indicators, for highly entangled multiqubits states. In particular, our present results are compared with those recently reported by Brown et al (J. Phys. A: Math. Gen. 2005 38 1119). The statistical distribution of entanglement values for the aforementioned multiqubit systems is also explored.

Entanglement is closely related to some fundamental features of the dynamics of composite quantum systems: quantum entanglement enhances the "speed" of evolution of certain quantum states, as measured by the time required to reach an orthogonal state. The concept of "speed" of quantum evolution constitutes an important ingredient in any attempt to determine the fundamental limits that basic physical laws impose on how fast a physical system can process or transmit information.Here we explore the relationship between entanglement and the speed of quantum evolution in the context of the quantum brachistochrone problem. Given an initial and a final state of a composite system we consider the amount of entanglement associated with the brachistochrone evolution between those states, showing that entanglement is an essential resource to achieve the alluded time-optimal quantum evolution.

There exists an interesting relationship between entanglement and the time evolution of composite quantum systems: quantum entanglement enhances the 'speed' of evolution of certain quantum states, as measured by the time needed to reach an orthogonal state. Previous research done on this subject has been focused upon comparing extreme cases (highly entangled states versus separable states) or upon bi-partite systems. In the present contribution we explore the aforementioned connection (between entanglement and time evolution) in the cases of two-qubits and N-qubits systems, taking into account states of intermediate entanglement. In particular, we investigate a family of energetically symmetric states of low entanglement that saturate the quantum speed bound. We show that, as the number of qubits increases, very little entanglement is needed to reach the quantum speed limit.

The violation of uncertainty relations is used as a signature of entanglement for both pure and mixed states of two identical fermions. In the case of fermions with a four dimensional single particle Hilbert space we obtain several different types of uncertainty-related entanglement criteria based on local uncertainty relations, on the sum of variances of projectors, and on various entropic measures. Within the latter approach we consider either entropic uncertainty relations involving a single observable or relations based upon the sum of entropies associated with more than one observable. We extend the projector based entanglement criterion to the case of two-fermion and three-fermion systems with a six dimensional single particle Hilbert space.

-We investigate the main features of a measure of fidelity between states in a general family of probabilistic theories admitting classical probability theory and standard quantum theory as particular instances. We apply the aforementioned measure to investigate informationtheoretical features of these theories related to the conservation of information during the evolution of closed physical systems. In particular, we derive a generalization of a fundamental result in quantum theory relevant for the measurement problem: Zurek's recent extension of the no-cloning theorem. Copyright c EPLA, 2009Introduction. -The physics of information and computation [1][2][3][4][5][6] has been the focus of an intense and increasing research activity in recent years [5][6][7][8][9][10][11][12][13]. Part of this research effort has been devoted to determine the ultimate limits imposed by the fundamental laws of physics on any device processing or transmitting information [6][7][8].On the other hand, a growing body of theoretical developments indicate that the concept of information constitutes an essential ingredient for a deep understanding of physical systems and processes [1][2][3][4][5][6][9][10][11][12]. Ideas, techniques, and models inspired by the theoretical analysis of information processing devices proved to be relevant for the study of a variegated range of physical scenarios, including applications to subjects as diverse as quantum thermodynamical machines [9] or the fundamental limits on the accuracy of spacetime measurements [10]. Interesting attempts have been recently made to derive the basic formalism of quantum theory from information-theoretical concepts [11]. The advent of quantum information science, and the concomitant discovery of the novel, subtle, and counter-intuitive ways of processing and transmitting information allowed by quantum mechanics [6,13] greatly stimulated the interest in these lines of enquiry. Work on quantum information