921 research outputs found
Chaotic spin-spin entanglement on a recursive lattice
We propose an exactly solvable multisite interaction spin-1/2
Ising-Heisenberg model on a triangulated Husimi lattice for the rigorous
studies of chaotic entanglement. By making use of the generalized star-triangle
transformation, we map the initial model onto an effective Ising one on a
Husimi lattice, which we solve then exactly by applying the recursive method.
Expressing the entanglement of the Heisenberg spins, that we quantify by means
of the concurrence, in terms of the magnetic quantities of the system, we
demonstrate its bifurcation and chaotic behavior. Furthermore, we show that the
underlying chaos may slightly enhance the amount of the entanglement, and
present on the phase diagram the transition lines from the uniform to periodic
and from the periodic to chaotic regimes.Comment: 12 pages, 7 figures. Updated version for publicatio
Generation of entanglement in systems of intercoupled qubits
We consider systems of two and three qubits, mutually coupled by
Heisenberg-type exchange interaction and interacting with external laser
fields. We show that these systems allow one to create maximally entangled Bell
states, as well as three qubit Greenberger-Horne-Zeilinger and W states. In
particular, we point out that some of the target states are the eigenstates of
the initial bare system. Due to this, one can create entangled states by means
of pulse area and adiabatic techniques, when starting from a separable
(non-entangled) ground state. On the other hand, for target states, not present
initially in the eigensystem of the model, we apply the robust stimulated Raman
adiabatic passage and pulse techniques, that create desired coherent
superpositions of non-entangled eigenstates.Comment: 9 pages, 7 figures. Updated version for publicatio
Magnetic field--induced modification of selection rules for Rb D line monitored by selective reflection from a vapor nanocell
Magnetic field-induced giant modification of the probabilities of five
transitions of of Rb and
three transitions of of Rb
forbidden by selection rules for zero magnetic field has been observed
experimentally and described theoretically for the first time. For the case of
excitation with circularly-polarized () laser radiation, the
probability of transition becomes
the largest among the seventeen transitions of Rb group, and the probability of transition becomes the largest among the nine transitions of
Rb group, in a wide range of magnetic
field 200 -- 1000 G. Complete frequency separation of individual Zeeman
components was obtained by implementation of derivative selective reflection
technique with a 300 nm-thick nanocell filled with Rb, allowing formation of
narrow optical resonances. Possible applications are addressed. The theoretical
model is perfectly consistent with the experimental results.Comment: 6 pages, 5 figure
The adiabatic invariant of any harmonic oscillator : an unexpected application of Glauber's formalism
In this theoretical paper, we propose a general derivation of the adiabatic invariant of the n-degree-of-freedom harmonic oscillator, available whichever the physical nature of the oscillator and of the parametrical excitation it undergoes. This derivation is founded on the use of the classical Glauber variables and ends up with this simplest result: the oscillator's adiabatic invariant is just the sum of all the semiclassical quanta numbers associated with its different eigenmodes
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