1,345 research outputs found
Comment on 'Quantum inversion of cold atoms in a microcavity: spatial dependence'
In a recent work, Abdel-Aty and Obada [2002 J. Phys. B 35 807-813] analyzed
the quantum inversion of cold atoms in a microcavity, the motion of the atoms
being described quantum mechanically. Two-level atoms were assumed to interact
with a single mode of the cavity, and the off-resonance case was considered
(namely the atomic transition frequency is detuned from the single mode cavity
frequency). We demonstrate in this paper that this case is incorrectly treated
by these authors and we question therefore their conclusions.Comment: 4 pages, no figure
Isotope shifts and hyperfine structure of the laser cooling Fe I 358-nm line
We report on the measurement of the isotope shifts of the Fe~I line at 358~nm between all four
stable isotopes Fe, Fe, Fe and Fe, as well
as the hyperfine structure of that line for Fe, the only stable
isotope having a nonzero nuclear spin. This line is of primary importance for
laser cooling applications. In addition, an experimental value of the field and
specific mass shift coefficients of the transition is reported as well as the
hyperfine structure magnetic dipole coupling constant of the transition
excited state in Fe, namely
MHz. The measurements were carried out by means of laser-induced fluorescence
spectroscopy performed on an isotope-enriched iron atomic beam. All measured
frequency shifts are reported with uncertainties below the third percent level.Comment: 5 pages, 5 figure
Tunable Entanglement, Antibunching and Saturation effects in Dipole Blockade
We report a model that makes it possible to analyze quantitatively the dipole
blockade effect on the dynamical evolution of a two two-level atom system
driven by an external laser field. The multiple excitations of the atomic
sample are taken into account. We find very large concurrence in the dipole
blockade regime. We further find that entanglement can be tuned by changing the
intensity of the exciting laser. We also report a way to lift the dipole
blockade paving the way to manipulate in a controllable way the blockade
effects. We finally report how a continuous monitoring of the dipole blockade
would be possible using photon-photon correlations of the scattered light in a
regime where the spontaneous emission would dominate dissipation in the sample.Comment: 5 pages, 5 figure
Operational Entanglement Families of Symmetric Mixed N-Qubit States
We introduce an operational entanglement classification of symmetric mixed
states for an arbitrary number of qubits based on stochastic local operations
assisted with classical communication (SLOCC operations). We define families of
SLOCC entanglement classes successively embedded into each other, we prove that
they are of non-zero measure, and we construct witness operators to distinguish
them. Moreover, we discuss how arbitrary symmetric mixed states can be realized
in the lab via a one-to-one correspondence between well-defined sets of
controllable parameters and the corresponding entanglement families.Comment: 6 pages, 2 figures, published version, Phys. Rev. A, in pres
Tensor Representation of Spin States
We propose a generalization of the Bloch sphere representation for arbitrary
spin states. It provides a compact and elegant representation of spin density
matrices in terms of tensors that share the most important properties of Bloch
vectors. Our representation, based on covariant matrices introduced by Weinberg
in the context of quantum field theory, allows for a simple parametrization of
coherent spin states, and a straightforward transformation of density matrices
under local unitary and partial tracing operations. It enables us to provide a
criterion for anticoherence, relevant in a broader context such as quantum
polarization of light.Comment: 5 pages + 7 pages of supplementary informatio
Heralded Entanglement of Arbitrary Degree in Remote Qubits
Incoherent scattering of photons off two remote atoms with a Lambda-level
structure is used as a basic Young-type interferometer to herald long-lived
entanglement of an arbitrary degree. The degree of entanglement, as measured by
the concurrence, is found to be tunable by two easily accessible experimental
parameters. Fixing one of them to certain values unveils an analog to the
Malus' law. An estimate of the variation in the degree of entanglement due to
uncertainties in an experimental realization is given.Comment: published version, 4 pages and 2 figure
Operational multipartite entanglement classes for symmetric photonic qubit states
We present experimental schemes that allow to study the entanglement classes
of all symmetric states in multiqubit photonic systems. In addition to
comparing the presented schemes in efficiency, we will highlight the relation
between the entanglement properties of symmetric Dicke states and a recently
proposed entanglement scheme for atoms. In analogy to the latter, we obtain a
one-to-one correspondence between well-defined sets of experimental parameters
and multiqubit entanglement classes inside the symmetric subspace of the
photonic system.Comment: 5 pages, 1 figur
Operational determination of multi-qubit entanglement classes via tuning of local operations
We present a physical setup with which it is possible to produce arbitrary
symmetric long-lived multiqubit entangled states in the internal ground levels
of photon emitters, including the paradigmatic GHZ and W states. In the case of
three emitters, where each tripartite entangled state belongs to one of two
well-defined entanglement classes, we prove a one-to-one correspondence between
well-defined sets of experimental parameters, i.e., locally tunable polarizer
orientations, and multiqubit entanglement classes inside the symmetric
subspace.Comment: Improved version. Accepted in Physical Review Letter
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