6,002 research outputs found
The pomeron in closed bosonic string theory
We review the features of the pomeron in the S-matrix theory and in quantum
field theory. We extend those general properties to the pomeron of closed
bosonic string theory in a Minkowskian background. We compute the couplings of
the pomeron to the lowest mass levels of closed bosonic string states in flat
space. We recognize the deviation from the linearity of the Regge trajectories
in a five dimensional anti De Sitter background.Comment: 13 page
Influence of the pair coherence on the charge tunneling through a quantum dot connected to a superconducting lead
We analyze the charge transport through a single level quantum dot coupled to
a normal (N) and superconducting (S) leads where the electron pairs exist
either as the coherent (for temperatures below T_c) or incoherent objects (in a
region T_c < T < T*). This situation can be achieved in practice if one uses
the high T_c superconducting material where various precursor effects have been
observed upon approaching from above. Without restricting to any
particular microscopic mechanism we investigate some qualitative changes of the
nonequilibrium charge current caused by the electron pair coherence.Comment: 7 pages, 9 figure
Quantum relative positioning in Hilbert space
A new class of state transformations that are quantum mechanically prohibited
is introduced. These can be seen as the generalization of the universal-NOT
transformation which, for all pure inputs state of a given Hilbert space
produces pure outputs whose projection on the original state is fixed to a
value smaller than one. The case of not pure output states is also addressed.
We give an application of these transformations in the context of separability
criteria.Comment: 5 pages, 1 figure; new material added: in particular we present an
application of quantum movers in the context of separability criteria. Typos
corrected. Phys. Rev. A, accepted for publicatio
Staying adiabatic with unknown energy gap
We introduce an algorithm to perform an optimal adiabatic evolution that
operates without an apriori knowledge of the system spectrum. By probing the
system gap locally, the algorithm maximizes the evolution speed, thus
minimizing the total evolution time. We test the algorithm on the Landau-Zener
transition and then apply it on the quantum adiabatic computation of 3-SAT: The
result is compatible with an exponential speed-up for up to twenty qubits with
respect to classical algorithms. We finally study a possible algorithm
improvement by combining it with the quantum Zeno effect.Comment: 4 pages, 4 figure
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