Delayed (sudden) birth of entanglement

The concept of time delayed creation of entanglement by the dissipative process of spontaneous emission is investigated. A threshold effect for the creation of entanglement is found that the initially unentangled qubits can be entangled after a finite time despite the fact that the coherence between the qubits exists for all times. This delayed creation of entanglement, that we call sudden birth of entanglement, is opposite to the currently extensively discussed sudden death of entanglement and is characteristic for transient dynamics of one-photon entangled states of the system. We determine the threshold time for the creation of entanglement and find that it is related to time at which the antisymmetric state remains the only excited state being populated. It is shown that the threshold time can be controlled by the distance between the qubits and the direction of initial excitation relative to the interatomic axis. This effect suggests a new alternative for the study of entanglement and provides an interesting resource for creation on demand of entanglement between two qubits.Comment: References added, version accepted for publication in PR

Entanglement induced by spontaneous emission in spatially extended two-atom systems

We investigate the role of the collective antisymmetric state in entanglement creation by spontaneous emission in a system of two non-overlapping two-level atoms. We calculate and illustrate graphically populations of the collective atomic states and the Wootters entanglement measure (concurrence) for two sets of initial atomic conditions. Our calculations include the dipole-dipole interaction and a spatial separation between the atoms that the antisymmetric state of the system is included throughout even for small interatomic separations. It is shown that spontaneous emission can lead to a transient entanglement between the atoms even if the atoms were prepared initially in an unentangled state. We find that the ability of spontaneous emission to create the transient entanglement relies on the absence of population in the collective symmetric state of the system. For the initial state of only one atom excited, the entanglement builds up rapidly in time and reaches a maximum for the parameter values corresponding roughly to zero population in the symmetric state. On the other hand, for the initial condition of both atoms excited, the atoms remain unentangled until the symmetric state is depopulated. A simple physical interpretation of these results is given in terms of the diagonal states of the density matrix of the system. We also study entanglement creation in a system of two non-identical atoms of different transition frequencies. It is found that the entanglement between the atoms can be enhanced compared to that for identical atoms, and can decay with two different time scales resulting from the coherent transfer of the population from the symmetric to the antisymmetric state. In addition, we find that a decaying initial entanglement between the atoms can display a revival behaviour.Comment: 14 pages, 6 figure

Entangling two atoms via spontaneous emission

We discuss the creation of entanglement between two two-level atoms in the dissipative process of spontaneous emission. It is shown that spontaneous emission can lead to a transient entanglement between the atoms even if the atoms were prepared initially in an unentangled state. The amount of entanglement created in the system is quantified by using two different measures: concurrence and negativity. We find analytical formulas for the evolution of concurrence and negativity in the system. We also find the analytical relation between the two measures of entanglement. The system consists of two two-level atoms which are separated by an arbitrary distance $r_{12}$ and interact with each other via the dipole-dipole interaction, and the antisymmetric state of the system is included throughout, even for small inter-atomic separations, in contrast to the small sample model. It is shown that for sufficiently large values of the dipole-dipole interaction initially the entanglement exhibits oscillatory behaviour with considerable entanglement in the peaks. For longer times the amount of entanglement is directly related to the population of the slowly decaying antisymmetric state.Comment: 13 pages, 5 figure

Tratamento das fraturas condilares e subcondilares

A traumatologia é uma das patologias mais frequentes da área maxilo e crânio facial. Este trabalho tem como objecto o estudo das fracturas condilares, a classificação delas e o tratamento conservador e médico-cirurgico, através da utilização de vários tipos de placas de fixação (rétas, trapezoidais, a lambda ou y, e a grelha). Para a realização desta revisão foram consultados vários textos e artigos científicos sobre o argumento, utilizando as seguintes palavras-chave: “fraturas condilares”, “fraturas subcondilares”, “tratamento cirurgico das fraturas condilares”, “placas de titânio”, “osteosíntese”, “placa lambda”, “placa trapezoidal”, “placas 3D”.Condyle’s trauma in the last few years has been the subject of numerous studies and clinical tries. This job has, as its goal, the study of condylar fractures, their classification and its medical and surgical treatment, through the most current techniques. To do this research many texts and scientific articles concerning this topic have been consulted, using these keywords: “condylar fractures”, “subcondylar fractures”, “surgical treatment of condylar fractures”, “titanium plates”, “bone synthesis”, “lambda plate”, “trapezoidal plate”, “3D plates”

Alien Registration- Tanas, Anna (Waterville, Kennebec County)

https://digitalmaine.com/alien_docs/14995/thumbnail.jp

Number-Phase Uncertainty Relations for Optical Fields

The Hermitian phase formalism of Pegg and Barnett allows for direct calculations of the phase variance and, consequently, the number-phase uncertainty product. This gives us a unique opportunity, inaccessible before, to study the number-phase uncertainty relations for optical fields in a direct way within a consistent quantum formalism. A few examples of fields generated in nonlinear optical processes are studied from the point of view of their number-phase uncertainty relations

Wehrl information entropy and phase distributions of Schrodinger cat and cat-like states

The Wehrl information entropy and its phase density, the so-called Wehrl phase distribution, are applied to describe Schr\"odinger cat and cat-like (kitten) states. The advantages of the Wehrl phase distribution over the Wehrl entropy in a description of the superposition principle are presented. The entropic measures are compared with a conventional phase distribution from the Husimi Q-function. Compact-form formulae for the entropic measures are found for superpositions of well-separated states. Examples of Schr\"odinger cats (including even, odd and Yurke-Stoler coherent states), as well as the cat-like states generated in Kerr medium are analyzed in detail. It is shown that, in contrast to the Wehrl entropy, the Wehrl phase distribution properly distinguishes between different superpositions of unequally-weighted states in respect to their number and phase-space configuration.Comment: 10 pages, 4 figure