Effective generation of cat and kitten states

We present an effective method of coherent state superposition (cat state) generation using single trapped ion in a Paul trap. The method is experimentally feasible for coherent states with amplitude $\alpha \le 2$ using available technology. It works both in and beyond the Lamb-Dicke regime.Comment: 11 pages, 8 figure

Dark periods and revivals of entanglement in a two qubit system

In a recent paper Yu and Eberly [Phys. Rev. Lett. {\bf 93}, 140404 (2004)] have shown that two initially entangled and afterwards not interacting qubits can become completely disentangled in a finite time. We study transient entanglement between two qubits coupled collectively to a multimode vacuum field and find an unusual feature that the irreversible spontaneous decay can lead to a revival of the entanglement that has already been destroyed. The results show that this feature is independent of the coherent dipole-dipole interaction between the atoms but it depends critically on whether or not the collective damping is present. We show that the ability of the system to revival entanglement via spontaneous emission relies on the presence of very different timescales for the evolution of the populations of the collective states and coherence between them.Comment: 4 pages, 3 figure

Generation of Werner-like stationary states of two qubits in a thermal reservoir

The dynamics of entanglement between two-level atoms immersed in a common photon reservoir at finite temperature is investigated. It is shown that in the regime of strong correlations there are nontrivial asymptotic states which can be interpreted in terms of thermal generalization of Werner states.Comment: Published versio

Local aspects of disentanglement induced by spontaneous emission

We consider spontaneous emission of two two-level atoms interacting with vacuum fluctuations. We study the process of disentanglement in this system and show the possibility of changing disentanglement time by local operations.Comment: 7 pages, 2 figure

Generation of Kerr non-Gaussian motional states of trapped ions

Non-Gaussian states represent a powerful resource for quantum information protocols in the continuous variables regime. Cat states, in particular, have been produced in the motional degree of freedom of trapped ions by controlled displacements dependent on the ionic internal state. An alternative method harnesses the Kerr nonlinearity naturally existent in this kind of system. We present detailed calculations confirming its feasibility for typical experimental conditions. Additionally, this method permits the generation of complex non-Gaussian states with negative Wigner functions. Especially, superpositions of many coherent states are achieved at a fraction of the time necessary to produce the cat state.Comment: 6 pages, 5 figure

Vacuum - induced stationary entanglement in radiatively coupled three - level atoms

We consider a pair of three - level atoms interacting with a common vacuum and analyze the process of entanglement production due to spontaneous emission. We show that in the case of closely separated atoms, collective damping can generate robust entanglement of the asymptotic states.Comment: published versio

Role of Bell Singlet State in the Suppression of Disentanglement

The stability of entanglement of two atoms in a cavity is analyzed in this work. By studying the general Werner states we clarify the role of Bell-singlet state in the problem of suppression of disentanglement due to spontaneous emission. It is also shown explicitly that the final amount of entanglement depends on the initial ingredients of the Bell-singlet state.Comment: 5 pages, 2 figures, accepted by Phys. Rev.

Atomic Squeezing under Collective Emission

Atomic squeezing is studied for the case of large systems of radiating atoms, when collective effects are well developed. All temporal stages are analyzed, starting with the quantum stage of spontaneous emission, passing through the coherent stage of superradiant emission, and going to the relaxation stage ending with stationary solutions. A method of governing the temporal behaviour of the squeezing factor is suggested. The influence of a squeezed effective vacuum on the characteristics of collective emission is also investigated.Comment: Latex file, 21 page, 9 figure

Міждисциплінарні зв'язки як дидактична основа професійної підготовки майбутніх учителів

In the article, the authors consider interdisciplinary links as an important factor in training students of higher pedagogical educational establishments for their future professional activities. As a result of the study and analysis of pedagogical experience, the researchers found that interdisciplinary links are the didactic principle and the basis for the formation of methodological knowledge. These connections are also considered as conditions for the formation of the outlook and the improvement of professional training of future specialists; they are means of increasing the efficiency of knowledge acquisition, activating cognitive activity, forming cognitive needs and developing a system type of thinking, etc. The attention is paid to the technology of implementation of interdisciplinary links in higher pedagogical education, which makes it possible to make the learning process of future teachers efficient. In the pedagogical practice, it became clear that the systematic nature of vocational and pedagogical knowledge involves an interdisciplinary synthesis of these knowledge. Students need to master the concepts, necessary skills and abilities within this knowledge system (system of philosophical knowledge, system of psychological knowledge, system of pedagogical knowledge, system of historical knowledge, system of knowledge in subjects that are profiling in the department, etc.). An analysis of the content of curricula, textbooks, manuals on a number of subjects enabled the authors to find out that interdisciplinary orientation in teaching philosophy, political science, sociology, economic theories, psychology, pedagogy and teaching methods of a particular discipline in the context of interdisciplinarity offers some extra opportunities for the formation of the system of professional and pedagogical knowledge of the future teachers, provides opportunities for mastering the methods of cognition, which prompts for a scientific understanding of the tasks of pedagogy, the issue of education and upbringing of the younger generation, understanding the state policy in the education area. As a result of the analysis and comparison of the contents of the curriculum, the sections, the topics and the separate questions that were adjacent to the indicated disciplines were identified. It allowed determining the content of interdisciplinary knowledge. Implementation of multifunctional interdisciplinary connections in the educational process affects the ideological orientation of a future teacher, the mastery of the dialectical method of cognition, the formation of a professional type of thinking and methodological culture.Міждисциплінарні зв’язки є важливим інструментом у процесі формування світогляду та вдосконалення фахової підготовки студентів вищих педагогічних навчальних закладів. Ці зв’язки розглядаються як засіб підвищення ефективності засвоєння знань, формування пізнавальних потреб. Вони розвивають системне мислення, активізують пізнавальну діяльність студентів. Автор з погляду дидактики окреслює шляхи реалізації міждисциплінарних зв’язків у процесі фахової підготовки студентів вищих педагогічних навчальних закладів. У статті приділяється увага технології реалізації міждисциплінарних зв’язків у вищій педагогічній освіті, що дає змогу зробити процес навчання майбутніх учителів результативним

Robust stationary entanglement of two coupled qubits in independent environments

The dissipative dynamics of two interacting qubits coupled to independent reservoirs at nonzero temperatures is investigated, paying special attention to the entanglement evolution. The counter-rotating terms in the qubit-qubit interaction give rise to stationary entanglement, traceable back to the ground state structure. The robustness of this entanglement against thermal noise is thoroughly analyzed, establishing that it can be detected at reasonable experimental temperatures. Some effects linked to a possible reservoir asymmetry are brought to light.Comment: 8 pages, 6 figures; version accepted for publication on Eur. Phys. J.