13,176 research outputs found
Effects of two-site composite excitations in the Hubbard model
The electronic states of the Hubbard model are investigated by use of the
Composite Operator Method. In addition to the Hubbard operators, two other
operators related with two-site composite excitations are included in the
basis. Within the present formulation, higher-order composite excitations are
reduced to the chosen operatorial basis by means of a procedure preserving the
particle-hole symmetry. The positive comparison with numerical simulations for
the double occupancy indicates that such approximation improves over the
two-pole approximation.Comment: 2 pages, 1 figur
Different realizations of tomographic principle in quantum state measurement
We establish a general principle for the tomographic approach to quantum
state reconstruction, till now based on a simple rotation transformation in the
phase space, which allows us to consider other types of transformations. Then,
we will present different realizations of the principle in specific examples.Comment: 17 pages, Latex file, no figures, accepted by J. of Mod. Op
Quantum dynamics of a damped deformed oscillator
The interaction of a quantum deformed oscillator with the environment is
studied deriving a master equation whose form strongly depends on the type of
deformation.Comment: LaTeX file, 6 page
Stochastic control of quantum dynamics for a single trapped system
A stochastic control of the vibrational motion for a single trapped ion/atom
is proposed. It is based on the possibility to continously monitor the motion
through a light field meter. The output from the measurement process should be
then used to modify the system's dynamics.Comment: LaTeX file, 7 pages, contribution to proceedings of 6th
central-european workshop on quantum optic
Efficiency of Entanglement Concentration by Photon Subtraction
We introduce a measure of efficiency for the photon subtraction protocol
aimed at entanglement concentration on a single copy of bipartite continuous
variable state. We then show that iterating the protocol does not lead to
higher efficiency than a single application. In order to overcome this limit we
present an adaptive version of the protocol able to greatly enhance its
efficiency.Comment: 6 pages, 3 figures, accepted by Physica Script
Quantum channels from reflections on moving mirrors
Light reflection on a mirror can be thought as a simple physical effect.
However if this happens when the mirror moves a rich scenario opens up. Here we
aim at analyzing it from a quantum communication perspective. In particular, we
study the kind of quantum channel that arises from (Gaussian) light reflection
upon an accelerating mirror. Two competing mechanisms emerge in such a context,
namely photons production by the mirror's motion and {\blu interference between
modes}. As consequence we find out a quantum amplifier channel and quantum
lossy channel respectively below and above a threshold frequency (that depends
on parameters determining mirror's acceleration). Exactly at the threshold
frequency the channel behaves like a purely classical additive channel, while
it becomes purely erasure for large frequencies. In addition the time behavior
of the channel is analyzed by employing wave packets expansion of the light
field.Comment: 12 pages, 3 figure
Towards feedback control of entanglement
We provide a model to investigate feedback control of entanglement. It
consists of two distant (two-level) atoms which interact through a radiation
field and becomes entangled. We then show the possibility to stabilize such
entanglement against atomic decay by means of a feedback action.Comment: 6 pages, 4 figure
Privacy of a lossy bosonic memory channel
We study the security of the information transmission between two honest
parties realized through a lossy bosonic memory channel when losses are
captured by a dishonest party. We then show that entangled inputs can enhance
the private information of such a channel, which however does never overcome
that of unentangled inputs in absence of memory.Comment: RevTex file, 4 pages, 2 figure
Cosmological dark energy effects from entanglement
The thorny issue of relating information theory to cosmology is here
addressed by assuming a possible connection between quantum entanglement
measures and observable universe. In particular, we propose a cosmological toy
model, where the equation of state of the cosmological fluid, which drives the
today observed cosmic acceleration, can be inferred from quantum entanglement
between different cosmological epochs. In such a way the dynamical dark energy
results as byproduct of quantum entanglement.Comment: 5 pages, to be published in Phys. Lett.
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