7,845 research outputs found
Quantum Key Distribution using Continuous-variable non-Gaussian States
In this work we present a quantum key distribution protocol using
continuous-variable non-Gaussian states, homodyne detection and post-selection.
The employed signal states are the Photon Added then Subtracted Coherent States
(PASCS) in which one photon is added and subsequently one photon is subtracted.
We analyze the performance of our protocol, compared to a coherent state based
protocol, for two different attacks that could be carried out by the
eavesdropper (Eve). We calculate the secret key rate transmission in a lossy
line for a superior channel (beam-splitter) attack, and we show that we may
increase the secret key generation rate by using the non-Gaussian PASCS rather
than coherent states. We also consider the simultaneous quadrature measurement
(intercept-resend) attack and we show that the efficiency of Eve's attack is
substantially reduced if PASCS are used as signal states.Comment: We have included an analysis of the simultaneous quadrature
measurement attack plus 2 figures; we have also clarified some point
Chaotic and deterministic switching in a two-person game
We study robust long-term complex behaviour in the Rock-Scissors-Paper game with two players, played using reinforcement learning. The complex behaviour is connected to the existence of a heteroclinic network for the dynamics. This network is made of three heteroclinic cycles consisting of nine equilibria and the trajectories connecting them. We provide analytical proof both for the existence of chaotic switching near the heteroclinic network and for the relative asymptotic stability of at least one cycle in the network, leading to behaviour ranging from almost deterministic actions to chaotic-like dynamics. Our results are obtained by making use of the symmetry of the original problem, a new approach in the context of learning.learning process, dynamics, switching, chaos
Semiclassical Tunneling of Wavepackets with Real Trajectories
Semiclassical approximations for tunneling processes usually involve complex
trajectories or complex times. In this paper we use a previously derived
approximation involving only real trajectories propagating in real time to
describe the scattering of a Gaussian wavepacket by a finite square potential
barrier. We show that the approximation describes both tunneling and
interferences very accurately in the limit of small Plank's constant. We use
these results to estimate the tunneling time of the wavepacket and find that,
for high energies, the barrier slows down the wavepacket but that it speeds it
up at energies comparable to the barrier height.Comment: 23 pages, 7 figures Revised text and figure
Chaos in one-dimensional lattices under intense laser fields
A model is investigated where a monochromatic, spatially homogeneous laser
field interacts with an electron in a one-dimensional periodic lattice. The
classical Hamiltonian is presented and the technique of stroboscopic maps is
used to study the dynamical behavior of the model. The electron motion is found
to be completely regular only for small field amplitudes, developing a larger
chaotic region as the amplitude increases. The quantum counterpart of the
classical Hamiltonian is derived. Exact numerical diagonalizations show the
existence of universal, random-matrix fluctuations in the electronic energy
bands dressed by the laser field. A detailed analysis of the classical phase
space is compatible with the statistical spectral analysis of the quantum
model. The application of this model to describe transport and optical
absorption in semiconductor superlattices submitted to intense infrared laser
radiation is proposed.Comment: 9 pages, RevTex 3.0, EPSF (6 figures), to appear in Europhys. J.
State sum construction of two-dimensional open-closed Topological Quantum Field Theories
We present a state sum construction of two-dimensional extended Topological
Quantum Field Theories (TQFTs), so-called open-closed TQFTs, which generalizes
the state sum of Fukuma--Hosono--Kawai from triangulations of conventional
two-dimensional cobordisms to those of open-closed cobordisms, i.e. smooth
compact oriented 2-manifolds with corners that have a particular global
structure. This construction reveals the topological interpretation of the
associative algebra on which the state sum is based, as the vector space that
the TQFT assigns to the unit interval. Extending the notion of a
two-dimensional TQFT from cobordisms to suitable manifolds with corners
therefore makes the relationship between the global description of the TQFT in
terms of a functor into the category of vector spaces and the local description
in terms of a state sum fully transparent. We also illustrate the state sum
construction of an open-closed TQFT with a finite set of D-branes using the
example of the groupoid algebra of a finite groupoid.Comment: 33 pages; LaTeX2e with xypic and pstricks macros; v2: typos correcte
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