Quantum ergodicity and entanglement in kicked coupled-tops

We study the dynamical generation of entanglement as a signature of chaos in a system of periodically kicked coupled-tops, where chaos and entanglement arise from the same physical mechanism. The long-time averaged entanglement as a function of the position of an initially localized wave packet very closely correlates with the classical phase space surface of section -- it is nearly uniform in the chaotic sea, and reproduces the detailed structure of the regular islands. The uniform value in the chaotic sea is explained by the random state conjecture. As classically chaotic dynamics take localized distributions in phase space to random distributions, quantized versions take localized coherent states to pseudo-random states in Hilbert space. Such random states are highly entangled, with an average value near that of the maximally entangled state. For a map with global chaos, we derive that value based on new analytic results for the typical entanglement in a subspace defined by the symmetries of the system. For a mixed phase space, we use the Percival conjecture to identify a "chaotic subspace" of the Hilbert space. The typical entanglement, averaged over the unitarily invariant Haar measure in this subspace, agrees with the long-time averaged entanglement for initial states in the chaotic sea. In all cases the dynamically generated entanglement is predicted by a unitary ensemble of random states, even though the system is time-reversal invariant, and the Floquet operator is a member of the circular orthogonal ensemble.Comment: 12 pages with 8 figure

Foliicolous lichens and their lichenicolous fungi collected during the Smithsonian International Cryptogamic Expedition to Guyana 1996

A total of 233 foliicolous lichen species and 18 lichenicolous fungi are reported from Guyana as a result of the Smithsonian „International Cryptogamic Expedition to Guyana“ 1996. Three lichens and two lichenicolous fungi are new to science: Arthonia grubei sp.n., Badimia subelegans sp.n., Calopadia pauciseptata sp.n., Opegrapha matzeri sp.n. (lichenicolous on Amazonomyces sprucei), and Pyrenidium santessonii sp.n. (lichenicolous on Bacidia psychotriae). The new combination Strigula janeirensis (Bas.: Phylloporina janeirensis; syn.: Raciborskiella janeirensis) is proposed. Apart from Amazonomyces sprucei and Bacidia psychotriae, Arthonia lecythidicola (with the lichenicolous A. pseudopegraphina) and Byssolecania deplanata (with the lichenicolous Opegrapha cf. kalbii) are reported as new hosts for lichenicolous fungi. Arthonia pseudopegraphina growing on A. lecythidicola is the first known case of adelphoparasitism at generic level in foliicolous Arthonia. Arthonia flavoverrucosa, Badimia polillensis, and Byssoloma vezdanum are new records for the Neotropics, and 115 species are new for Guyana, resulting in a total of c. 280 genuine foliicolous species reported for that country, while Porina applanata and P. verruculosa are excluded from its flora. The foliicolous lichen flora of Guyana is representative for the Guianas (Guyana, Suriname, French Guiana) and has great affinities with the Amazon region, while the degree of endemism is low. A characteristic species for this area is Amazonomyces sprucei. Species composition is typical of Neotropical lowland to submontane humid forests, with a dominance of the genera Porina, Strigula, and Mazosia. The table mountain vegetation supports elements of the upper montane forest, such as Echinoplaca fusconitida and Logilvia gilva. Foliicolous lichen diversity is highest in undisturbed lowland to submontane humid forest, much lower in the table mountain vegetation and drastically decreased in semi-open secondary vegetation and the coastal savanna. Species composition in semi-open, disturbed vegetation is similar to that found in the undisturbed forest canopy. Site preferences of foliicolous lichens follow those established by studies in other Neotropical regions like Costa Rica