234 research outputs found
Bright and Dark periods in the Entanglement Dynamics of Interacting Qubits in Contact with the Environment
Interaction among the qubits are basis to many quantum logic operations. We
report how such inter-qubit interactions can lead to new features, in the form
of bright and dark periods in the entanglement dynamics of two qubits subject
to environmental perturbations. These features are seen to be precursors to the
well known phenomenon of sudden death of entanglement [Yu & Eberly, Phys.
Rev. Lett. {\bf 93}, 140404 (2004)] for noninteracting qubits. Further we find
that the generation of bright and dark periods are generic and occur for wide
varieties of the models of environment. We present explicit results for two
popular models.Comment: New published version, corrected figure
Strong Topological Rigidity of Non-Compact Orientable Surfaces
We show that if a homotopy equivalence between two non-compact orientable
(finite or infinite-type) surfaces is proper, then it is properly homotopic to
a homeomorphism, provided surfaces are neither the plane nor the punctured
plane. Thus all non-compact orientable surfaces, except the plane and the
punctured plane, are topologically rigid in a strong sense.Comment: 22 pages, 8 figures. Everything has been revised drastically. The
current version contains a much stronger statement than the previous one: The
non-zero degree assumption of the main theorem of the earlier version follows
from the main theorem of the current version, provided the punctured plane is
also omitted from the hypothesis. Comments Welcome
Quantum interference effects in an ensemble of Th nuclei interacting with coherent light
As a unique feature, the Th nucleus has an isomeric transition in the
vacuum ultraviolet that can be accessed by optical lasers. The interference
effects occurring in the interaction between coherent optical light and an
ensemble of Th nuclei are investigated theoretically. We consider the
scenario of nuclei doped in vacuum ultraviolet-vacuum ultraviolet transparent
crystals and take into account the effect of different doping sites and
therefore different lattice fields that broaden the nuclear transition width.
This effect is shown to come in interplay with interference effects due to the
hyperfine splitting of the ground and isomeric nuclear states. We investigate
possible experimentally available situations involving two-, three- and
four-level schemes of quadrupole sublevels of the ground and isomeric nuclear
states coupling to one or two coherent fields. Specific configurations which
offer clear signatures of the isomer excitation advantageous for the more
precise experimental determination of the transition energy are identified.
Furthermore, it is shown that population trapping into the isomeric state can
be achieved. This paves the way for further nuclear quantum optics applications
with Th such as nuclear coherent control.Comment: 14 papes, 13 figure
Quantum correlations and violation of Bell inequality induced by External Field in a two photon radiative cascade
We study the polarization dependent second order correlation of a pair of
photons emitted in a four level radiative cascade driven by an external field.
It is found that the quantum correlations of the emitted photons, degraded by
the energy splitting of the intermediate levels in the radiative cascade can be
efficiently revived by a far detuned external field. The physics of this
revival is linked to an induced stark shift and the formation of dressed states
in the system by the non-resonant external field. Further, we investigated the
competition between the effect of the coherent external field and incoherent
dephasing of the intermediate levels. We found that the degradation of quantum
correlations due to the incoherent dephasing can be content for small dephasing
with the external field. We also studied the non-locality of the correlations
by evaluating the Bell's inequality in the linear polarization basis for the
radiative cascade. We find that the Bell parameter decreases rapidly with
increase in the intermediate level energy splitting or incoherent dephasing
rate to the extent that there is no violation. However, the presence of an
external field leads to control over the degrading mechanisms and preservation
of nonlocal correlation among the photons. This in turn can induce, violation
of Bell's inequality in the radiative cascade for arbitrary intermediate level
splitting and small incoherent dephasing
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