27,176 research outputs found
Effects of non-local initial conditions in the Quantum Walk on the line
We report an enhancement of the decay rate of the survival probability when
non-local initial conditions in position space are considered in the Quantum
Walk on the line. It is shown how this interference effect can be understood
analytically by using previously derived results. Within a restricted position
subspace, the enhanced decay is correlated with a maximum asymptotic
entanglement level while the normal decay rate corresponds to initial relative
phases associated to a minimum entanglement level.Comment: 5 pages, 1 figure, Elsevier style, to appear in Physica
Quantum walk on the line: entanglement and non-local initial conditions
The conditional shift in the evolution operator of a quantum walk generates
entanglement between the coin and position degrees of freedom. This
entanglement can be quantified by the von Neumann entropy of the reduced
density operator (entropy of entanglement). In the long time limit, it
converges to a well defined value which depends on the initial state. Exact
expressions for the asymptotic (long-time) entanglement are obtained for (i)
localized initial conditions and (ii) initial conditions in the position
subspace spanned by the +1 and -1 position eigenstates.Comment: A few mistakes where corrected. One of them leads to a factor of 2 in
eq. (49), the other results remain unchanged. In this version, several
figures where replaced by color version
Rediscovering Lutra lutra from Grotta Romanelli (southern Italy) in the framework of the puzzling evolutionary history of Eurasian otter
A river otter hemimandible has been rediscovered during the revision of the historical collections of G.A. Blanc from Grotta
Romanelli, complementing the ongoing multidisciplinary research fieldwork on the site. The specimen, recovered from the
level G (“terre rosse”; early Late Pleistocene or late Middle Pleistocene), is here assigned to Lutra lutra. Indeed, morphological
and morphometric comparisons with other Quaternary Lutrinae fossils from Europe allow to exclude an attribution
to the relatively widespread and older Lutra simplicidens, characterized by distinctive carnassial proportions. Differences
with Cyrnaonyx antiqua, which possessed a more robust, shellfish-feeding dentition, support the view of a successful niche
repartition between the two species during the late Middle to Late Pleistocene of Europe. The occurrence of Lutra lutra from
the “terre rosse” of Grotta Romanelli suggests deep modifications of the landscapes due to the ecological adaptation of the
taxon, and indicates that the Eurasian otter spread into Europe at the Middle–Late Pleistocene transition
Grotta Romanelli (Southern Italy, Apulia). Legacies and issues in excavating a key site for the Pleistocene of the Mediterranean
Grotta Romanelli, located on the Adriatic coast of southern Apulia (Italy), is considered a key site for the Mediterranean Pleistocene for its archaeological and palaeontological contents. The site, discovered in 1874, was re-evaluated only in 1900, when P. E. Stasi realised that it contained the first evidence of the Palaeolithic in Italy. Starting in 1914, G. A. Blanc led a pioneering excavation campaign, for the first-time using scientific methods applied to systematic palaeontological and stratigraphical studies. Blanc proposed a stratigraphic framework for the cave. Different dating methods (C-14 and U/Th) were used to temporally constrain the deposits. The extensive studies of the cave and its contents were mostly published in journals with limited distribution and access, until the end of the 1970s, when the site became forgotten. In 2015, with the permission of the authorities, a new excavation campaign began, led by a team from Sapienza University of Rome in collaboration with IGAG CNR and other research institutions. The research team had to deal with the consequences of more than 40 years of inactivity in the field and the combined effect of erosion and legal, as well as illegal, excavations. In this paper, we provide a database of all the information published during the first 70 years of excavations and highlight the outstanding problems and contradictions between the chronological and geomorphological evidence, the features of the faunal assemblages and the limestone artefacts
An introduction to the early Holocene eolian deposits of Grotta Romanelli, Apulia, Southern Italy
Due to its geographic position and geomorphological configuration, Grotta Romanelli acted as a sediment trap since at least MIS 5. The so-called 'terre brune' sequence is a deposit mainly of eolian origin bearing upper Palaeolithic artefacts and fossil re-mains of vertebrate fauna; it was deposited during the Glacial-Interglacial transition and the Holocene. Sedimentology and mineralogy of this deposit are investigated. The stratigraphic sequence provides a promising archive within which both human and climatic impacts can be studied
Quantum walks: decoherence and coin-flipping games
We investigate the global chirality distribution of the quantum walk on the
line when decoherence is introduced either through simultaneous measurements of
the chirality and particle position, or as a result of broken links. The first
mechanism drives the system towards a classical diffusive behavior. This is
used to build new quantum games, similar to the spin-flip game. The second
mechanism involves two different possibilities: (a) All the quantum walk links
have the same probability of being broken. (b) Only the quantum walk links on a
half-line are affected by random breakage. In case (a) the decoherence drives
the system to a classical Markov process, whose master equation is equivalent
to the dynamical equation of the quantum density matrix. This is not the case
in (b) where the asymptotic global chirality distribution unexpectedly
maintains some dependence with the initial condition. Explicit analytical
equations are obtained for all cases.Comment: 9 pages, 7 figure
Anomalous diffusion in the resonant quantum kicked rotor
We study the resonances of the quantum kicked rotor subjected to an
excitation that follows a deterministic time-dependent prescription. For the
primary resonances we find an analytical relation between the long-time
behavior of the standard deviation and the external kick strength. For the
secondary resonances we obtain essentially the same result numerically.
Selecting the time sequence of the kick allows to obtain a variety of
asymptotic wave-function spreadings: super-ballistic, ballistic, sub-ballistic,
diffusive, sub-diffusive and localized.Comment: 5 pages, 3 figures To appear in Physica A
Frequency-locked chaotic opto-RF oscillator
A driven opto-RF oscillator, consisting of a dual-frequency laser (DFL)
submitted to frequency-shifted feedback, is studied experimentally and
numerically in a chaotic regime. Precise control of the reinjection strength
and detuning permits to isolate a parameter region of bounded-phase chaos,
where the opto-RF oscillator is frequency-locked to the master oscillator, in
spite of chaotic phase and intensity oscillations. Robust experimental evidence
of this synchronization regime is found and phase noise spectra allows to
compare phase-locking and bounded-phase chaos regimes. In particular, it is
found that the long-term phase stability of the master oscillator is well
transferred to the opto-RF oscillator even in the chaotic regime
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