41,378 research outputs found

    Manipulation of the dynamics of many-body systems via quantum control methods

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    We investigate how dynamical decoupling methods may be used to manipulate the time evolution of quantum many-body systems. These methods consist of sequences of external control operations designed to induce a desired dynamics. The systems considered for the analysis are one-dimensional spin-1/2 models, which, according to the parameters of the Hamiltonian, may be in the integrable or non-integrable limits, and in the gapped or gapless phases. We show that an appropriate control sequence may lead a chaotic chain to evolve as an integrable chain and a system in the gapless phase to behave as a system in the gapped phase. A key ingredient for the control schemes developed here is the possibility to use, in the same sequence, different time intervals between control operations.Comment: 10 pages, 3 figure

    Interface States in Carbon Nanotube Junctions: Rolling up graphene

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    We study the origin of interface states in carbon nanotube intramolecular junctions between achiral tubes. By applying the Born-von Karman boundary condition to an interface between armchair- and zigzag-terminated graphene layers, we are able to explain their number and energies. We show that these interface states, costumarily attributed to the presence of topological defects, are actually related to zigzag edge states, as those of graphene zigzag nanoribbons. Spatial localization of interface states is seen to vary greatly, and may extend appreciably into either side of the junction. Our results give an alternative explanation to the unusual decay length measured for interface states of semiconductor nanotube junctions, and could be further tested by local probe spectroscopies

    Atomic quantum gases in Kagom\'e lattices

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    We demonstrate the possibility of creating and controlling an ideal and \textit{trimerized} optical Kagom\'e lattice, and study the low temperature physics of various atomic gases in such lattices. In the trimerized Kagom\'e lattice, a Bose gas exhibits a Mott transition with fractional filling factors, whereas a spinless interacting Fermi gas at 2/3 filling behaves as a quantum magnet on a triangular lattice. Finally, a Fermi-Fermi mixture at half filling for both components represents a frustrated quantum antiferromagnet with a resonating-valence-bond ground state and quantum spin liquid behavior dominated by continuous spectrum of singlet and triplet excitations. We discuss the method of preparing and observing such quantum spin liquid employing molecular Bose condensates.Comment: 4 pages, 1 figure. Missing affiliations adde

    Sympathetic cooling of trapped fermions by bosons in the presence of particle losses

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    We study the sympathetic cooling of a trapped Fermi gas interacting with an ideal Bose gas below the critical temperature of the Bose-Einstein condensation. We derive the quantum master equation, which describes the dynamics of the fermionic component, and postulating the thermal distribution for both gases we calculate analytically the rate at which fermions are cooled by the bosonic atoms. The particle losses constitute an important source of heating of the degenerate Fermi gas. We evaluate the rate of loss-induced heating and derive analytical results for the final temperature of fermions, which is limited in the presence of particle losses.Comment: 7 pages, 2 figures, EPL style; final versio

    Gender equality and modernity in Portugal. An analysis on the obstacles to gender equality in highly qualified professions

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    In this review article, we argue that the transformations related to the modernisation of Portuguese society triggered by the implementation of democracy did not fully accommodate gender equality. In particular, when we consider the areas where the most progress has been made in keeping with a broadly shared urge for modernisation, education and science; whereas women have contributed to boosting the Portuguese population’s level of education, thus inverting the worst legacy of the dictatorship and developing scientific research, gender inequalities are still visible in highly qualified professions. Reviewing the results of studies from different professions, science, medicine and engineering, our analysis illustrates several factors that hinder not only the recognition of women’s competences and merit at work but also their career opportunities. Some of these factors are rooted in the type of gender ideology that was central to the propaganda of the dictatorship, thereby establishing continuity with the previous regime that seems particularly difficult to break in the absence of women’s voices to raise awareness on gender equality.info:eu-repo/semantics/publishedVersio

    Gender inequalities in highly qualified professions: a social psychological analysis

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    Research in social and political psychology contributes towards understanding the persistence of job market gender segregation prevailing in recent decades, the consequences for those involved and their reactions when having to cope with gender inequality. Within the framework of the literature on shared ideologies that justify and legitimize discrimination against women, this article focuses on Portugal and analyses the particular case of women in two highly qualified professions traditionally carried out by men – politics and medicine. Drawing on the results of quantitative and qualitative studies, our analytical approach demonstrates how while a majority of participants show awareness of the existence of gender inequality in these markedly masculine professions, meritocratic individualism and personal attributions to discrimination are the recurring explanations rather than any gender-based account. These results allow us to highlight the relevance of gender-based analysis as an ideology and furthermore to argue that ignoring this perspective not only diminishes individual responsibility for social change but also perpetuates gender asymmetries.info:eu-repo/semantics/publishedVersio

    Gender dynamics in elementary school teaching: the advantages of men

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    This article presents a study that identifies the gender dynamics prevailing in a specific context of tokenism – elementary school teaching – in which the members of an otherwise socially dominant group are proportionally scarce – men. The results contradict Kanter’s (1977) theory by showing that male elementary school teachers do not experience the tokenism dynamics. In line with Williams’ gender perspective and Amâncio’s gender symbolic asymmetry, the article finds that although men constitute a small minority in elementary education, they do not lose the social advantages they generally have: on the contrary, they seem rather to gain several privileges. Indeed, the results show strong links between the tokenism dynamics and gender asymmetry, putting the token men at an advantage. Thus, tokenism seems to be limited to maintaining the gender social order.info:eu-repo/semantics/acceptedVersio
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