25,816 research outputs found
Entanglement in atomic resonance fluorescence
The resonance fluorescence from regular atomic systems is shown to represent
a continuous source of non-Gaussian entangled radiation propagating in two
different directions. For a single atom entanglement occurs under the same
conditions as squeezing. For more atoms, the entanglement can be more robust
against dephasing than squeezing, hence providing a useful continuous source
for various applications of entangled radiation.Comment: 4 pages, 1 figur
Optimal Squeezing in Resonance Fluorescence via Atomic-State Purification
Squeezing of atomic resonance fluorescence is shown to be optimized by a
properly designed environment, which can be realized by a quasi-resonant
cavity. Optimal squeezing is achieved if the atomic coherence is maximized,
corresponding to a pure atomic quantum state. The atomic-state purification is
achieved by the backaction of the cavity field on the atom, which increases the
atomic coherence and decreases the atomic excitation. For realistic cavities,
the coupling of the atom to the cavity field yields a purity of the atomic
state of more than 99%. The fragility of squeezing against dephasing is
substantially reduced in this scenario, which may be important for various
applications.Comment: 6 pages including supplemental information, 3 figures. Accepted for
PR
Inseparability criteria for bipartite quantum states
We provide necessary and sufficient conditions for the partial transposition
of bipartite harmonic quantum states to be nonnegative. The conditions are
formulated as an infinite series of inequalities for the moments of the state
under study. The violation of any inequality of this series is a sufficient
condition for entanglement. Previously known entanglement conditions are shown
to be special cases of our approach.Comment: 4 pages, no figures. Small misprints were correcte
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