98,685 research outputs found
Wave packet transmission of Bloch electron manipulated by magnetic field
We study the phenomenon of wave packet revivals of Bloch electrons and
explore how to control them by a magnetic field for quantum information
transfer. It is showed that the single electron system can be modulated into a
linear dispersion regime by the "quantized" flux and then an electronic wave
packet with the components localized in this regime can be transferred without
spreading. This feature can be utilized to perform the high-fidelity transfer
of quantum information encoded in the polarization of the spin. Beyond the
linear approximation, the re-localization and self-interference occur as the
novel phenomena of quantum coherence.Comment: 6 pages, 5 figures, new content adde
Inconsistences in Interacting Agegraphic Dark Energy Models
It is found that the origin agegraphic dark energy tracks the matter in the
matter-dominated epoch and then the subsequent dark-energy-dominated epoch
becomes impossible. It is argued that the difficulty can be removed when the
interaction between the agegraphic dark energy and dark matter is considered.
In the note, by discussing three different interacting models, we find that the
difficulty still stands even in the interacting models. Furthermore, we find
that in the interacting models, there exists the other serious inconsistence
that the existence of the radiation/matter-dominated epoch contradicts the
ability of agegraphic dark energy in driving the accelerated expansion. The
contradiction can be avoided in one of the three models if some constraints on
the parameters hold.Comment: 12 pages, no figure; analysis is added; conclusion is unchange
Quantum state swapping via qubit network with Hubbard interaction
We study the quantum state transfer (QST) in a class of qubit network with
on-site interaction, which is described by the generalized Hubbard model with
engineered couplings. It is proved that the system of two electrons with
opposite spins in this quantum network of sites can be rigorously reduced
into one dimensional engineered single Bloch electron models with central
potential barrier. With this observation we find that such system can perform a
perfect QST, the quantum swapping between two distant electrons with opposite
spins. Numerical results show such QST and the resonant-tunnelling for the
optimal on-site interaction strengths.Comment: 4 pages, 3 figure
On the performance of densified DVB-H single frequency networks
The broadcasting of TV programmes to mobile phones can be enabled by the newly developed technology called Digital Video Broadcasting-Handheld (DVB-H). Because of the scarcity and cost of frequency resources, frequency reuse needs to be considered when rolling out DVB-H networks. By simulcasting the same content from several transmitters, a Single Frequency Network (SFN) can provide good coverage and good frequency efficiency. In this paper, the performance of densified DVB-H SFN networks is analysed in terms of the coverage probability under different coverage requirements with and without frequency reuse. A dichotomy searching approach is used to determine the optimal cell radius for a cell in a densified DVB-H SFN for a given network topology. Based on the optimal cell radius map and a SFN gain map generated from the simulation results, guidelines are proposed on how to avoid the potential pitfalls in configuring the parameters of a densified DVB-H SFN network and optimise its parameters in terms of minimising the cost of the network for a range of predefined network parameters
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