The emergence of a diverging length scale in many-body systems at a quantum phase transition implies that total entanglement has to reach its maximum there. In order to fully characterize this, one has to consider multipartite entanglement as, for instance, bipartite entanglement between individual particles fails to signal this effect. However, quantification of multipartite entanglement is ve...

Given a unitary operator, in the context of quantum information 1 , one may ask how much entanglement capability the operator has. The entangling unitary operator can be considered as a resource for quantum-information processing, and it becomes important to quantitatively describe unitary operators. Recently, there is increasing interest in the entanglement capabilities of quantum evolution an...

We study the computational complexity of quantum discord (a measure of quantum correlation beyond entanglement), and prove that computing quantum discord is NP-complete. Therefore, quantum discord is computationally intractable: the running time of any algorithm for computing quantum discord is believed to grow exponentially with the dimension of the Hilbert space so that computing quantum disc...

In the framework of the theory of open systems based on completely positive quantum dynamical semigroups, we give a description of the continuous-variable quantum entanglement and quantum discord for a system consisting of two non-interacting modes embedded in a thermal environment. Entanglement and discord are used to quantify the quantum correlations of the system. For all values of the tempe...

This is an expanded version of the short report arXiv:1401.0539, where we studied the time evolution of (Renyi) entanglement entropies for the excited state defined by acting a given local operator on the ground state. In the present paper, we introduce (Renyi) entanglement entropies of given local operators which are defined by late time values of excesses of (Renyi) entanglement entropies. Th...

We study the possibility of using guided photons to generate, control, and measure the entanglement of two qubits that is mediated by a one-dimensional waveguide. We show how entanglement can be generated both with single-photon and with two-photon wave packets. The introduction of a second photon allows for a manipulation of the entanglement between the qubits, and phenomena such as sudden dea...

The coin-position entanglement generated by the evolution operator of a discrete–time quantum walk is quantified, using the von Neumann entropy of the reduced density operator (entropy of entanglement). In the case of a single walker, the entropy of entanglement converges, in the long time limit, to a well defined value which depends on the initial state. Exact expressions are obtained for loca...

Many previous works on quantum photolithography are based on maximally-entangled states (MES). In this paper, we generalize the MES quantum photolithography to the case where two light beams share a N-photon nonmaximally-entangled state. we investigate the correlations between quantum entanglement and quantum photolithography. It is shown that for nonlocal entanglement between the two light bea...

We study the role of entanglement in quantum computation. We consider the case of a pure state contaminated by "white noise." This framework arises, for example, in pseudopure state implementations of quantum computing using NMR. We analyze quantum computational protocols which aim to solve exponential classical problems with polynomial resources and ask whether or not entanglement of the pseud...

We discuss the semiclassical limit of the entanglement for the class of closed pure systems. By means of analytical and numerical calculations we obtain two main results: (i) the short-time entanglement does not depend on Planck’s constant and (ii) the long-time entanglement increases as more semiclassical regimes are attained. This result is in contrast with the common belief that the entangle...