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EN
A continuous variable-quantum key distribution system prototype that uses weak coherent states with a diffused phase, commercial off-the-shelf devices, complete free space 90-degrees hybrid and simplified quantum protocol is proposed in this paper. In general, the quantum transmitter-receiver shows an experimental average quantum bit error rate of 30% using auto-homodyne detection with 0.25 photons per pulse in locking phase mode. The emulated final secret key rate measurements were 20 and 40 Kbps for minimum (30 Mbps) and maximum (90 Mbps) throughput, respectively, in a real traffic network using databases for the quantum keys generated by two true random number generators.
EN
We investigate the entanglement between two atoms in an overdamped cavity injected with squeezed vacuum when these two atoms are initially prepared in coherent states. It is shown that the stationary entanglement exhibits a strong dependence on the initial state of the two atoms when the spontaneous emission rate of each atom is equal to the collective spontaneous emission rate, corresponding to the case where the two atoms are close together. It is found that the stationary entanglement of two atoms increases with decreasing effective atomic cooperativity parameter. The squeezed vacuum can enhance the entanglement of two atoms when the atoms are initially in coherent states. Valuably, this provides us with a feasible way to manipulate and control the entanglement, by changing the relative phases and the amplitudes of the polarized atoms and by varying the effective atomic cooperativity parameter of the system, even though the cavity is a bad one. When the spontaneous emission rate of each atom is not equal to the collective spontaneous emission rate, the steady-state entanglement of two atoms always maintains the same value, as the amplitudes of the polarized atoms varies. Moreover, the larger the degree of two-photon correlation, the stronger the steady-state entanglement between the atoms.
3
Content available remote Coherent states for Smorodinsky-Winternitz potentials
100%
Open Physics
|
2009
|
tom 7
|
nr 4
774-785
EN
In this study, we construct the coherent states for a particle in the Smorodinsky-Winternitz potentials, which are the generalizations of the two-dimensional harmonic oscillator problem. In the first case, we find the non-spreading wave packets by transforming the system into four oscillators in Cartesian, and also polar, coordinates. In the second case, the coherent states are constructed in Cartesian coordinates by transforming the system into three non-isotropic harmonic oscillators. All of these states evolve in physical-time. We also show that in parametric-time, the second case can be transformed to the first one with vanishing eigenvalues.
4
Content available remote On the deformed squeezed states on noncommutative plane
88%
Open Physics
|
2011
|
tom 9
|
nr 5
1261-1266
EN
A new kind of deformed boson operators is proposed to be consistent with the large noncommutativity parameters on noncommutative plane when noncommutativity of momentum spaces is considered. Using this kind of deformed boson operators, the coherent states and squeezed states are constructed, and their properties are discussed in detail.
5
Content available remote Informationally incomplete quantum tomography
51%
EN
In quantum-state tomography on sources with quantum degrees of freedom of large Hilbert spaces, inference of quantum states of light for instance, a complete characterization of the quantum states for these sources is often not feasible owing to limited resources. As such, the concepts of informationally incomplete state estimation becomes important. These concepts are ideal for applications to quantum channel/ process tomography, which typically requires a much larger number of measurement settings for a full characterization of a quantum channel. Some key aspects of both quantumstate and quantum-process tomography are arranged together in the form of a tutorial review article that is catered to students and researchers who are new to the field of quantum tomography, with focus on maximum-likelihood related techniques as instructive examples to illustrate these ideas.
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