92 research outputs found
Generation of long-living entanglement between two separate atoms
A scheme for non-conditional generation of long-living maximally entangled
states between two spatially well separated atoms is proposed. In the scheme,
-type atoms pass a resonator-like equipment of dispersing and
absorbing macroscopic bodies giving rise to body-assisted electromagnetic field
resonances of well-defined heights and widths. Strong atom-field coupling is
combined with weak atom-field coupling to realize entanglement transfer from
the dipole-allowed transitions to the dipole-forbidden transitions, thereby the
entanglement being preserved when the atoms depart from the bodies and from
each other. The theory is applied to the case of the atoms passing by a
microsphere.Comment: 13 pages, 5 figure
Detecting entanglement with non-hermitian operators
We derive several entanglement conditions employing non-hermitian operators.
We start with two conditions that were derived previously for field mode
operators, and use them to derive conditions that can be used to show the
existence of field-atom entanglement and entanglement between groups of atoms.
The original conditions can be strengthened by making them invariant under
certain sets of local unitary transformations, such as Gaussian operations. We
then apply these conditions to several examples, such as the Dicke model. We
conclude with a short discussion of how local uncertainty relations with
non-hermitian operators can be used to derive entanglement conditions.Comment: Typos correcte
Input-output relations at dispersing and absorbing planar multilayers for the quantized electromagnetic field containing evanescent components
By using the Green-function concept of quantization of the electromagnetic
field in dispersing and absorbing media, the quantized field in the presence of
a dispersing and absorbing dielectric multilayer plate is studied.
Three-dimensional input-output relations are derived for both amplitude
operators in the -space and the field operators in the coordinate
space. The conditions are discussed, under which the input-output relations can
be expressed in terms of bosonic operators. The theory applies to both
(effectively) free fields and fields, created by active atomic sources inside
and/or outside the plate, including also evanescent-field components.Comment: 14 pages, 1 figur
Spontaneous Decay in the Presence of Absorbing Media
After giving a summary of the basic-theoretical concept of quantization of
the electromagnetic field in the presence of dispersing and absorbing
(macroscopic) bodies, their effect on spontaneous decay of an excited atom is
studied. Various configurations such as bulk material, planar half space media,
spherical cavities, and microspheres are considered. In particular, the
influence of material absorption on the local-field correction, the decay rate,
the line shift, and the emission pattern are examined. Further, the interplay
between radiative losses and losses due to material absorption is analyzed.
Finally, the possibility of generating entangled states of two atoms coupled by
a microsphere-assisted field is discussed.Comment: 32 pages, 15 eps figures, contribution to Recent Research
Developments in Optics, to be published by Research Signpos
Conditions for entanglement in multipartite systems
We introduce two entanglement conditions that take the form of inequalities
involving expectation values of operators. These conditions are sufficient
conditions for entanglement, that is if they are satisfied the state is
entangled, but if they are not, one can say nothing about the entanglement of
the state. These conditions are quite flexible, because the operators in them
are not specified, and they are particularly useful in detecting multipartite
entanglement. We explore the range of utility of these conditions by
considering a number of examples of entangled states, and seeing under what
conditions entanglement in them can be detected by the inequalities presented
here.Comment: accepted for publication in Physical Review
Resonant dipole-dipole interaction in the presence of dispersing and absorbing surroundings
Within the framework of quantization of the macroscopic electromagnetic
field, equations of motion and an effective Hamiltonian for treating both the
resonant dipole-dipole interaction between two-level atoms and the resonant
atom-field interaction are derived, which can suitably be used for studying the
influence of arbitrary dispersing and absorbing material surroundings on these
interactions. The theory is applied to the study of the transient behavior of
two atoms that initially share a single excitation, with special emphasis on
the role of the two competing processes of virtual and real photon exchange in
the energy transfer between the atoms. In particular, it is shown that for weak
atom-field interaction there is a time window, where the energy transfer
follows a rate regime of the type obtained by ordinary second-order
perturbation theory. Finally, the resonant dipole-dipole interaction is shown
to give rise to a doublet spectrum of the emitted light for weak atom-field
interaction and a triplet spectrum for strong atom-field interaction.Comment: 15 pages, 1 figure, RevTE
Efficiency of tunable band-gap structures for single-photon emission
The efficiency of recently proposed single-photon emitting sources based on
tunable planar band-gap structures is examined. The analysis is based on the
study of the total and ``radiative'' decay rates, the expectation value of
emitted radiation energy and its collimating cone. It is shown that the scheme
operating in the frequency range near the defect resonance of a defect band-gap
structure is more efficient than the one operating near the band edge of a
perfect band-gap structure.Comment: 9 pages, 7 figure
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