Lower Bounds of Concurrence for Multipartite States

We study the entanglement of multipartite quantum states. Some lower bounds of the multipartite concurrence are reviewed. We further present more effective lower bounds for detecting and qualifying entanglement, by establishing functional relations between the concurrence and the generalized partial transpositions of the multipartite systems.Comment: 13 page

A lower bound of concurrence for multipartite quantum systems

We present a lower bound of concurrence for four-partite systems in terms of the concurrence for $M\, (2\leq M\leq 3)$ part quantum systems and give an analytical lower bound for $2\otimes2\otimes2\otimes2$ mixed quantum sates. It is shown that these lower bounds are able to improve the existing bounds and detect entanglement better. Furthermore, our approach can be generalized to multipartite quantum systems.Comment: 9 pages,2 figure

Analytical Expression of Quantum Discord for Rank-2 Two-qubit States

Quantum correlations characterized by quantum entanglement and quantum discord play important roles in many quantum information processing. We study the relations among the entanglement of formation, concurrence, tangle, linear entropy based classical correlation and von Neumann entropy based classical correlation. We present analytical formulae of linear entropy based classical correlation for arbitrary $d\otimes 2$ quantum states and von Neumann entropy based classical correlation for arbitrary $2\otimes 2$ rank-2 quantum states. From the von Neumann entropy based classical correlation, we derive an explicit formula of quantum discord for arbitrary rank-2 two-qubit quantum states.Comment: 9 pages,2 figure

State-independent geometric quantum gates via nonadiabatic and noncyclic evolution

Geometric phases are robust to local noises and the nonadiabatic ones can reduce the evolution time, thus nonadiabatic geometric gates have strong robustness and can approach high fidelity. However, the advantage of geometric phase has not being fully explored in previous investigations. Here, we propose a scheme for universal quantum gates with pure nonadiabatic and noncyclic geometric phases from smooth evolution paths. In our scheme, only geometric phase can be accumulated in a fast way, and thus it not only fully utilizes the local noise resistant property of geometric phase but also reduces the difficulty in experimental realization. Numerical results show that the implemented geometric gates have stronger robustness than dynamical gates and the geometric scheme with cyclic path. Furthermore, we propose to construct universal quantum gate on superconducting circuits, and the gate fidelity can be $99.97\%$ and $99.87\%$, respectively. Therefore, these high-fidelity quantum gates are promising for large-scale fault-tolerant quantum computation

A comparative study of the proventricular structure in twenty Chinese Tettigoniidae (Orthoptera) species

This study focuses on the proventriculus and the alimentary canal of twenty Tettigoniidae species among three subfamilies, Tettigoniinae, Phaneropterinae and Conocephalinae. Each part of the alimentary canal and the inner structure of proventriculus were examined under optic microscope and scanning electron microscopy. As a result, the length of each part of the alimentary canal and the inner structure of proventriculus were highly associated with feeding habits. Carnivorous species always had a short foregut and long cilia on the base of the sclerotized appendix in proventriculus, whereas herbivorous species always had a longer foregut and a highly sclerotized proventriculus. These results increase understanding of the alimentary canal in Tettigoniidae and will be useful in future studies of their feeding habits