120 research outputs found
Hot-electron noise suppression in n-Si via the Hall effect
We investigate how hot-electron fluctuations in n-type Si are affected by the
presence of an intense (static) magnetic field in a Hall geometry. By using the
Monte Carlo method, we find that the known Hall-effect-induced redistribution
of electrons among valleys can suppress electron fluctuations with a
simultaneous enhancement of the drift velocity
Non-Markovianity of a quantum emitter in front of a mirror
We consider a quantum emitter ("atom") radiating in a one-dimensional (1D)
photonic waveguide in the presence of a single mirror, resulting in a delay
differential equation for the atomic amplitude. We carry out a systematic
analysis of the non-Markovian (NM) character of the atomic dynamics in terms of
refined, recently developed notions of quantum non-Markovianity such as
indivisibility and information back-flow. NM effects are quantified as a
function of the round-trip time and phase shift associated with the atom-mirror
optical path. We find, in particular, that unless an atom-photon bound state is
formed a finite time delay is always required in order for NM effects to be
exhibited. This identifies a finite threshold in the parameter space, which
separates the Markovian and non-Markovian regimes.Comment: 7 pages, 4 figures. Fig. 3 featured in Phys. Rev. A Kaleidoscope
Images: July 201
Landauer's principle in multipartite open quantum system dynamics
We investigate the link between information and thermodynamics embodied by
Landauer's principle in the open dynamics of a multipartite quantum system.
Such irreversible dynamics is described in terms of a collisional model with a
finite temperature reservoir. We demonstrate that Landauer's principle holds,
for such a configuration, in a form that involves the flow of heat dissipated
into the environment and the rate of change of the entropy of the system. Quite
remarkably, such a principle for {\it heat and entropy power} can be explicitly
linked to the rate of creation of correlations among the elements of the
multipartite system and, in turn, the non-Markovian nature of their reduced
evolution. Such features are illustrated in two exemplary cases.Comment: 5 pages, 3 figures, RevTeX4-1; Accepted for publication in Phys. Rev.
Let
Extraction of Singlet States from Noninteracting High-Dimensional Spins
We present a scheme for the extraction of singlet states of two remote
particles of arbitrary quantum spin number. The goal is achieved through
post-selection of the state of interaction mediators sent in succession. A
small number of iterations is sufficient to make the scheme effective. We
propose two suitable experimental setups where the protocol can be implemented.Comment: 4 pages, 2 figure
Non-Markovian dynamics from band edge effects and static disorder
It was recently shown [S. Lorenzo, F. Lombardo, F. Ciccarello and M. Palma, Sci. Rep. 7 (2017) 42729] that the presence of static disorder in a bosonic bath \ue2\u80\u94 whose normal modes thus become all Anderson-localized \ue2\u80\u94 leads to non-Markovianity in the emission of an atom weakly coupled to it (a process which in absence of disorder is fully Markovian). Here, we extend the above analysis beyond the weak-coupling regime for a finite-band bath so as to account for band edge effects. We study the interplay of these with static disorder in the emergence of non-Markovian behavior in terms of a suitable non-Markovianity measure
Entanglement-induced electron coherence in a mesoscopic ring with two magnetic impurities
We investigate the Aharonov-Bohm (AB) interference pattern in the electron
transmission through a mesoscopic ring in which two identical non-interacting
magnetic impurities are embedded. Adopting a quantum waveguide theory, we
derive the exact transmission probability amplitudes and study the influence of
maximally entangled states of the impurity spins on the electron transmittivity
interference pattern. For suitable electron wave vectors, we show that the
amplitude of AB oscillations in the absence of impurities is in fact not
reduced within a wide range of the electron-impurity coupling constant when the
maximally entangled singlet state is prepared. Such state is thus able to
inhibit the usual electron decoherence due to scattering by magnetic
impurities. We also show how this maximally entangled state of the impurity
spins can be generated via electron scattering.Comment: 8 page
Taxonomic remarks and distribution of Smyrnium dimartinoi (Apiaceae)
Smyrnium L., an Eurasian genus of the family Apiaceae, includes about 20 taxa of which only 7 are accepted at specific rank; among these, 5 are native to Europe (Tutin & al. 1968; Gomez 2003). In the Italian flora, the genus is represented by 3 taxa also occurring in Sicily (Pignatti 1982; Giardina & al. 2007); these are Smyrnium olusatrum L., S. perfoliatum L. and S. rotundifolium Mill. The last one has also been treated at the rank of subspecies under S. perfoliatum [S. perfoliatum subsp. rotundifolium (Mill.) Hartvig] (Strid 1986; Conti & al. 2005), or as a variety [S. perfoliatum var. rotundifolium (Mill.)Fiori (Fiori 1925)]. In Sicily, same populations related to S. perfoliatum differ from this taxon for both morphological and ecological characteristics, especially on the Madonie Mountains and the Mountains around Palermo.
The study of the morphological characteristics \u2013 namely of the root, stem, and leaf \u2013 allowed to clearly distinguish these populations that, therefore, represented a taxonomically and perhaps even chorologically critical case, since similar plants occurring in Greece were described as S. rotundifolium var. ovatifolium Hal\ue1csy (Hal\ue1csy 1901). In Sicily the same population was finally described as a new species named Smyrnium dimartinoi (Raimondo et al., 2015) to commemorate Andrea Di Martino (1926-2009), professor of botany and director of the Botanical Garden and Herbarium Mediterraneum in the Palermo University.
The occurrence of the new taxon related to S. perfoliatum \u2013 ascertained only in Central-Western Sicily and in Crete \u2013 has also been supposed in other countries of the Mediterranean Europe; this, owing to some critical specimens observed in PAL and PAL-Gr.
In this contribution, the analytical key of S. perfoliatum group is presented. Furthermore, the geographical distribution of S. dimartinoi is specified after the study of selected exsiccata from other Italian and foreign herbaria. The results found in this research show that S. dimartinoi belongs to the Eurimediterranean element, spread in various countries of the Southern Europe, from Greece to Italy and Spain
Quantum non-Markovianity induced by Anderson localization
As discovered by P. W. Anderson, excitations do not propagate freely in a disordered lattice, but, due to destructive interference, they localise. As a consequence, when an atom interacts with a disordered lattice, one indeed observes a non-trivial excitation exchange between atom and lattice. Such non-trivial atomic dynamics will in general be characterised also by a non-trivial quantum information backflow, a clear signature of non-Markovian dynamics. To investigate the above scenario, we consider a quantum emitter, or atom, weakly coupled to a uniform coupled-cavity array (CCA). If initially excited, in the absence of disorder, the emitter undergoes a Markovian spontaneous emission by releasing all its excitation into the CCA (initially in its vacuum state). By introducing static disorder in the CCA the field normal modes become Anderson-localized, giving rise to a non-Markovian atomic dynamics. We show the existence of a functional relationship between a rigorous measure of quantum non-Markovianity and the CCA localization. We furthermore show that the average non-Markovianity of the atomic dynamics is well-described by a phenomenological model in which the atom is coupled, at the same time, to a single mode and to a standard - Markovian - dissipative bath
Study of the alien flora of the urban area of Palermo (Sicily)
Alien plants are an integral part of the Mediterranean agricultural and urban landscape.
Taking into account that man is an active voluntary or involuntary carrier of plant diasporas, cities and
areas where human activity is predominant represent preferential targets for the study of new plant
introductions.
In addition, some species as Pennisetum setaceum (Forssk.) Chiov. and Opuntia ficus-indica (L.) Mill.,
initially exclusive to high disturbed habitats, succeeded in penetrating in cliffs, degraded maquis and
garrigues characterizing them. Thus the importance of studying these areas to predict future colonization
of more natural habitats.
Starting from literature and integrating it with field observations we prepared a list of alien species
occurring in the urban area of Palermo. This list includes a categorization of the non native species
occurring in the city according to their origin, their behaviour and the habitat where these plants were
recorded.
The starting points were the contributions about the flora of Sicily (1, 2, 3), the alien flora of Italy (4) and the
flora living on trees of the city of Palermo (5). Literature sources were followed by intense field work from
September 2013 to May 2016, that allowed to include new species that only recently showed their
tendency to naturalization and to exclude species reported more than 100 years ago that have not be
found anymore or taxa occurring in different parts of Sicily but not in the perimeter that defines the study
area.
About the categories, relevant literature gives different categorization depending on whether the point of
view adopted is anthropocentric, biological, ecological or biogeographic.
Here we adopted the categories suggested by Raimondo & al. (1) dividing the studied taxa in Adventive
or Cultivated depending on whether the introduction was accidental or voluntary, and subdividing them
further in casual, naturalized and invasive depending on whether their permanence and development
into the new territory.
On the whole, 145 specific and infraspecific taxa have been recorded. Neophytes are 133: 43 adventive
and 90 coming from cultivation; 42 are casual, 94 naturalized and 9 invasive. Archaeophytes (cfr. 6, 7) are
12: 6 casual, 5 naturalized and 1 invasive.
This study allowed to record recent changes in the alien flora of the city. These are mainly due to:
- the popularity of the plants that are grown for ornament (e.g. Nephrolepis cordifolia (L.) K. Presl widely
cultivated until 30 years ago now its cultivation is almost entirely disappeared inside the city);
- the variation of construction techniques and materials with the rarefaction of roof tiles and rough walls in
limestone in favour of more modern covers that do not allow the establishment of plants (comporting an
evident reduction of Crassulaceae observable on the roofs);
- the arrival of new pollinators that allowed the production of fertile fruits e.g. in Ficus microcarpa L. and F.
watkinsiana F. M. Bailey.
An example of the spreading of new taxa is Sesamum indicum L., reported as only cultivated plant without
tendency to naturalize (8) in the last year, several individuals inside the city of Palermo have been
recorded in ruderal habitat. This could have been due to the presence of an increasing number of not
Italian of birth citizens who grow this plant for food purposes
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