1,265 research outputs found
Simulation of some quantum gates, with decoherence
Methods and results for numerical simulations of one and two interacting
rf-Squid systems suitable for adiabatic quantum gates are presented. These are
based on high accuracy numerical solutions to the static and time dependent
Schroedinger equation for the full Squid Hamiltonian in one and two variables.
Among the points examined in the static analysis is the range of validity of
the effective two-state or ``spin 1/2'' picture. A range of parameters is
determined where the picture holds to good accuracy as the energy levels
undergo gate manipulations. Some general points are presented concerning the
relations between device parameters and ``good'' quantum mechanical state
spaces.
The time dependent simulations allow the examination of suitable conditions
for adiabatic behavior, and permits the introduction of a random noise to
simulate the effects of decoherence. A formula is derived and tested relating
the random noise to the decoherence rate. Sensitivity to device and operating
parameters for the logical gates NOT and CNOT are examined, with particular
attention to values of the tunnel parameter beta slightly above one. It appears
that with values of beta close to one, a quantum CNOT gate is possible even
with rather short decoherence times.
Many of the methods and results will apply to coupled double-potential well
systems in general.Comment: 26 pages, 15 figures, Some clarification added on decoherence
treatment, many small errors corrected, symbols on some figures enlarged,
refs added. No change in conten
Il contributo degli Enti Locali alla riduzione dei gas serra
Le città occupano solo il 2% della superficie del pianeta, ma sono responsabili di circa tre quarti delle
emissioni globali di anidride carbonica di origine antropica. Si comprende dunque come sia fondamentale un
ruolo attivo degli enti locali e dei cittadini in una efficace strategia di riduzione delle emissioni. Da un lato una
politica intelligente e coraggiosa può portare in diverse aree (pensiamo innanzitutto alla mobilità urbana) alla
definizione di incisivi interventi di riduzione delle emissioni. In secondo luogo un’azione di sensibilizzazione
dei cittadini può orientare le scelte individuali verso comportamenti ambientalmente corretti.
Come si è visto nelle esperienze sviluppatesi finora, non si tratta di inventarsi niente di nuovo, ma di inserire
azioni che generalmente hanno una valenza positiva sull’ambiente e sulla qualità della vita a livello locale nel
contesto più ampio della lotta al riscaldamento del pianeta
Universal Unitarity Triangle and Physics Beyond the Standard Model
We make the simple observation that there exists a universal unitarity
triangle for all models, like the SM, the Two Higgs Doublet Models I and II and
the MSSM with minimal flavour violation, that do not have any new operators
beyond those present in the SM and in which all flavour changing transitions
are governed by the CKM matrix with no new phases beyond the CKM phase. This
universal triangle can be determined in the near future from the ratio (Delta
M)_d/(Delta M)_s and sin(2 beta) measured first through the CP asymmetry in
B_d^0 to psi K_S and later in K to pi nu nubar decays. Also suitable ratios of
the branching ratios for B to X_{d,s} nu nubar and B_{d,s} to mu^+ mu^- and the
angle gamma measured by means of CP asymmetries in B decays can be used for
this determination. Comparison of this universal triangle with the
non-universal triangles extracted in each model using epsilon, (Delta M)_d and
various branching ratios for rare decays will allow to find out in a
transparent manner which of these models, if any, is singled out by experiment.
A virtue of the universal triangle is that it allows to separate the
determination of the CKM parameters from the determination of new parameters
present in the extensions of the SM considered here.Comment: 12 pages, 1 figur
Inhomogeneous Superconductivity in Comb-Shaped Josephson Junction Networks
We show that some of the Josephson couplings of junctions arranged to form an
inhomogeneous network undergo a non-perturbative renormalization provided that
the network's connectivity is pertinently chosen. As a result, the zero-voltage
Josephson critical currents turn out to be enhanced along directions
selected by the network's topology. This renormalization effect is possible
only on graphs whose adjacency matrix admits an hidden spectrum (i.e. a set of
localized states disappearing in the thermodynamic limit). We provide a
theoretical and experimental study of this effect by comparing the
superconducting behavior of a comb-shaped Josephson junction network and a
linear chain made with the same junctions: we show that the Josephson critical
currents of the junctions located on the comb's backbone are bigger than the
ones of the junctions located on the chain. Our theoretical analysis, based on
a discrete version of the Bogoliubov-de Gennes equation, leads to results which
are in good quantitative agreement with experimental results.Comment: 4 pages, 2 figures, revte
Observation of breather-like states in a single Josephson cell
We present experimental observation of broken-symmetry states in a
superconducting loop with three Josephson junctions. These states are generic
for discrete breathers in Josephson ladders. The existence region of the
breather-like states is found to be in good accordance with the theoretical
expectations. We observed three different resonant states in the
current-voltage characteristics of the broken-symmetry state, as predicted by
theory. The experimental dependence of the resonances on the external magnetic
field is studied in detail.Comment: 7 pages, 8 figure
Expressão de genes de resistência em resposta à infecção por nematóides.
A identificação de genes relacionados com a resistência de plantas a pragas e doenças é de grande importância para o entendimento dos mecanismos de defesa envolvidos durante o ataque de patógenos. Atualmente, vários desses genes, identificados em diferentes espécies vegetais, já foram caracterizados ao nível molecular e suas seqüências estão disponíveis em Bancos de Dados. Atualmente, com a conclusão do sequenciamento do Genoma Café, homólogos de genes de defesa tiveram suas seqüências estabelecidas. No entanto, estudos de genômica funcional são necessários para que o papel destes genes no mecanismo de resistência aos patógenos do café seja conhecido. Este trabalho tem como objetivo inicial caracterizar os mecanismos de defesa em café, através da identificação e avaliação da expressão de genes relacionados com a resistência a nematóides. Foram realizadas buscas de seqüências homólogas a genes de defesa no Banco de Dados do Genoma Café através do programa BLAST e foram identificados genes pertencentes a 12 categorias de genes de defesa. Em experimentos de infecção controlada, raízes de cafeeiros suscetíveis e resistentes foram infectadas pelo nematóide Meloidogyne exigua. Amostras de RNA extraído destas raízes serviram como molde para amplificação de transcritos correspondentes a 6 genes de resistência. Os resultados mostram que os genes avaliados neste estudo apresentam uma expressão basal em raízes infectadas pelo nematóide, sugerindo que a ativação da resposta de defesa é controlada por outras famílias de genes não testadas neste estudo
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