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

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.