171 research outputs found
Delayed birth of distillable entanglement in the evolution of bound entangled states
The dynamical creation of entanglement between three-level atoms coupled to
the common vacuum is investigated. For the class of bound entangled initial
states we show that the dynamics of closely separated atoms generates
stationary distillable entanglement of asymptotic states. We also find that the
effect of delayed sudden birth of distillable entanglement occurs in the case
of atoms separated by a distance comparable with the radiation wavelength.Comment: published versio
Stationary two-atom entanglement induced by nonclassical two-photon correlations
A system of two two-level atoms interacting with a squeezed vacuum field can
exhibit stationary entanglement associated with nonclassical two-photon
correlations characteristic of the squeezed vacuum field. The amount of
entanglement present in the system is quantified by the well known measure of
entanglement called concurrence. We find analytical formulas describing the
concurrence for two identical and nonidentical atoms and show that it is
possible to obtain a large degree of steady-state entanglement in the system.
Necessary conditions for the entanglement are nonclassical two-photon
correlations and nonzero collective decay. It is shown that nonidentical atoms
are a better source of stationary entanglement than identical atoms. We discuss
the optimal physical conditions for creating entanglement in the system, in
particular, it is shown that there is an optimal and rather small value of the
mean photon number required for creating entanglement.Comment: 17 pages, 5 figure
66. Late effects of CNS prophylactic irradiation in childhood due to LLA using Magnetic Resonance Spectro-skopy. (preliminary report)
PurposeThe aim of this study was to evaluate changes in magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) of the brain in survivars with Acute Lymphoblastic Leukemia to assess neurotixicity follow profilactic brain irradiation.MethodsTen from 100 patients with LLA treated in Department of Pediatric Hematology from 1990 to 1995 and irradiated in Centre of Oncology were icluded in MRI and MRS studies. The study group included 6 male and 4 female. All patients had been irradiated for brain using fraction dose of 1,8 Gy up to total dose of 18 Gy and had recived MTX based chemotherapy in doses depending on level of risk. Two of them were included in low risk and eight in intermediate risk.ResultsMRI of brain was abnormal in 5 cases. There were mild white matter changes.The changes were Been in H- MRS metabolite ratios. In one of these cases we observed a impair of verbal functions.ConclusionsThe MRS could be valuable method to access brain tissue metabolism after radiotherapy. That noninvasive method may be recomended for children with LLA to observe neurotoxicity of profilactic irradiation
Entanglement and spin squeezing in the two-atom Dicke model
We analyze the relation between the entanglement and spin-squeezing parameter
in the two-atom Dicke model and identify the source of the discrepancy recently
reported by Banerjee and Zhou et al that one can observe entanglement without
spin squeezing. Our calculations demonstrate that there are two criteria for
entanglement, one associated with the two-photon coherences that create
two-photon entangled states, and the other associated with populations of the
collective states. We find that the spin-squeezing parameter correctly predicts
entanglement in the two-atom Dicke system only if it is associated with
two-photon entangled states, but fails to predict entanglement when it is
associated with the entangled symmetric state. This explicitly identifies the
source of the discrepancy and explains why the system can be entangled without
spin-squeezing. We illustrate these findings in three examples of the
interaction of the system with thermal, classical squeezed vacuum and quantum
squeezed vacuum fields.Comment: 7 pages, 1 figur
A Study on the Sudden Death of Entanglement
The dynamics of entanglement and the phenomenon of entanglement sudden death
(ESD) \cite{yu} are discussed in bipartite systems, measured by Wootters
Concurrence. Our calculation shows that ESD appears whenever the system is open
or closed and is dependent on the initial condition. The relation of the
evolution of entanglement and energy transfer between the system and its
surroundings is also studied.Comment: Comments and criticism are welcome. Accepted by Phys. Lett.
27 Przypadek skojarzenia leczenia promieniami (brachyterapia i teleterapia) mięsaka prążkowokomórkowego oczodołu u dziecka
W pracy przedstawiono przykład leczenia promieniami mięsaka prążkowo-komórkowego oczodołu u 9 ietniego dziecka w stopniu zaawansowania klinicznego T1- po nieradykalnym zabiegu operacyjnym. W pierwszym etapie przeprowadzono brachyterapię HDR Ir-192. Podano 21 Gy w punkcie referencyjnym w 3 frakcjach w ciągu 3 dni. Następnie chorego napromieniano w warunkach terapii megawoltowej na obszar części przyśrodkowej oczodołu strony lewej, dawka frakcyjna 1,5 Gy/g do dawki całkowitej 25,5 Gy/g. Całkowita dawka fizyczna wyniosła 46 Gy. Celem skojarzenia brachterapii z teleterapią była ochrona soczewki i zmniejszenie ryzyka zaćmy popromiennej. W pracy przedstawiono rozkłady dawek w brachyterapii wykonane na podstawie tomografii komputerowej oraz technikę konformalnej teleterapii
Transition from antibunching to bunching for two dipole-interacting atoms
It is known that there is a transition from photon antibunching to bunching
in the resonance fluorescence of a driven system of two two-level atoms with
dipole-dipole interaction when the atomic distance decreases and the other
parameters are kept fixed. We give a simple explanation for the underlying
mechanism which in principle can also be applied to other systems. PACS numbers
42.50.Ar, 42.50FxComment: Submitted to Phys. Rev. A; 15 pages Latex + 4 figure
66. Late effects of CNS prophylactic irradiation in childhood due to LLA using Magnetic Resonance Spectro-skopy. (preliminary report)
PurposeThe aim of this study was to evaluate changes in magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) of the brain in survivars with Acute Lymphoblastic Leukemia to assess neurotixicity follow profilactic brain irradiation.MethodsTen from 100 patients with LLA treated in Department of Pediatric Hematology from 1990 to 1995 and irradiated in Centre of Oncology were icluded in MRI and MRS studies. The study group included 6 male and 4 female. All patients had been irradiated for brain using fraction dose of 1,8 Gy up to total dose of 18 Gy and had recived MTX based chemotherapy in doses depending on level of risk. Two of them were included in low risk and eight in intermediate risk.ResultsMRI of brain was abnormal in 5 cases. There were mild white matter changes.The changes were Been in H- MRS metabolite ratios. In one of these cases we observed a impair of verbal functions.ConclusionsThe MRS could be valuable method to access brain tissue metabolism after radiotherapy. That noninvasive method may be recomended for children with LLA to observe neurotoxicity of profilactic irradiation
Cascaded two-photon nonlinearity in a one-dimensional waveguide with multiple two-level emitters
We propose and theoretically investigate a model to realize cascaded optical
nonlinearity with few atoms and photons in one-dimension (1D). The optical
nonlinearity in our system is mediated by resonant interactions of photons with
two-level emitters, such as atoms or quantum dots in a 1D photonic waveguide.
Multi-photon transmission in the waveguide is nonreciprocal when the emitters
have different transition energies. Our theory provides a clear physical
understanding of the origin of nonreciprocity in the presence of cascaded
nonlinearity. We show how various two-photon nonlinear effects including
spatial attraction and repulsion between photons, background fluorescence can
be tuned by changing the number of emitters and the coupling between emitters
(controlled by the separation).Comment: 6 pages, 4 figure
Quantum entanglement and disentanglement of multi-atom systems
We present a review of recent research on quantum entanglement, with special
emphasis on entanglement between single atoms, processing of an encoded
entanglement and its temporary evolution. Analysis based on the density matrix
formalism are described. We give a simple description of the entangling
procedure and explore the role of the environment in creation of entanglement
and in disentanglement of atomic systems. A particular process we will focus on
is spontaneous emission, usually recognized as an irreversible loss of
information and entanglement encoded in the internal states of the system. We
illustrate some certain circumstances where this irreversible process can in
fact induce entanglement between separated systems. We also show how
spontaneous emission reveals a competition between the Bell states of a two
qubit system that leads to the recently discovered "sudden" features in the
temporal evolution of entanglement. An another problem illustrated in details
is a deterministic preparation of atoms and atomic ensembles in long-lived
stationary squeezed states and entangled cluster states. We then determine how
to trigger the evolution of the stable entanglement and also address the issue
of a steered evolution of entanglement between desired pairs of qubits that can
be achieved simply by varying the parameters of a given system.Comment: Review articl
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