Optimal quantum repeaters for qubits and qudits

A class of optimal quantum repeaters for qubits is suggested. The schemes are minimal, i.e. involve a single additional probe qubit, and optimal, i.e. provide the maximum information adding the minimum amount of noise. Information gain and state disturbance are quantified by fidelities which, for our schemes, saturate the ultimate bound imposed by quantum mechanics for randomly distributed signals. Special classes of signals are also investigated, in order to improve the information-disturbance trade-off. Extension to higher dimensional signals (qudits) is straightforward.Comment: Revised version. To appear in PR

A measure of the non-Gaussian character of a quantum state

We address the issue of quantifying the non-Gaussian character of a bosonic quantum state and introduce a non-Gaussianity measure based on the Hilbert-Schmidt distance between the state under examination and a reference Gaussian state. We analyze in details the properties of the proposed measure and exploit it to evaluate the non-Gaussianity of some relevant single- and multi-mode quantum states. The evolution of non-Gaussianity is also analyzed for quantum states undergoing the processes of Gaussification by loss and de-Gaussification by photon-subtraction. The suggested measure is easily computable for any state of a bosonic system and allows to define a corresponding measure for the non-Gaussian character of a quantum operation.Comment: revised and enlarged version, 7 pages, 4 figure

Group Mentoring and Professionalism: A Programme Evaluation

This evaluative research represents the first report in the literature to date in which a group mentoring programme has been evaluated using a quasi-experimental research design. Results indicated that the programme was effective in one domain of professionalism, the main outcome variable; and that career-development outcomes were significantly higher in programme participants. In addition to the previously established functions of mentoring (career and psychosocial development), the research suggests that the conceptual basis of mentoring should be expanded to include the function of professionalism. This has implications for both the practical aspects of mentoring programme development and for future evaluative research. Data were collected by means of pre- and post-test questionnaires and analysed by multiple regression analysis

Quantifying the nonlinearity of a quantum oscillator

We address the quantification of nonlinearity for quantum oscillators and introduce two measures based on the properties of the ground state rather than on the form of the potential itself. The first measure is a fidelity-based one, and corresponds to the renormalized Bures distance between the ground state of the considered oscillator and the ground state of a reference harmonic oscillator. Then, in order to avoid the introduction of this auxiliary oscillator, we introduce a different measure based on the non-Gaussianity (nG) of the ground state. The two measures are evaluated for a sample of significant nonlinear potentials and their properties are discussed in some detail. We show that the two measures are monotone functions of each other in most cases, and this suggests that the nG-based measure is a suitable choice to capture the anharmonic nature of a quantum oscillator, and to quantify its nonlinearity independently on the specific features of the potential. We also provide examples of potentials where the Bures measure cannot be defined, due to the lack of a proper reference harmonic potential, while the nG-based measure properly quantify their nonlinear features. Our results may have implications in experimental applications where access to the effective potential is limited, e.g., in quantum control, and protocols rely on information about the ground or thermal state.Comment: 8 pages, 5 figures, published versio

Reliable source of conditional non-Gaussian states from single-mode thermal fields

We address both theoretically and experimentally the generation of pulsed non-Gaussian states from classical Gaussian ones by means of conditional measurements. The setup relies on a beam splitter and a pair of linear photodetectors able to resolve up to tens of photons in the two outputs. We show the reliability of the setup and the good agreement with the theory for a single-mode thermal field entering the beam splitter and present a thorough characterization of the photon statistics of the conditional states.Comment: 18 pages, 12 figure

An investigation of digital scholarship and disciplinary culture in Oman

The purpose of this study is to investigate disciplinary differences in the use of networked information for research and scholarly communication at Sultan Qaboos University, Oman. The study produced quantitative data on how and why academics within different disciplines utilise networked information either made available internally through the university library, or externally through services accessed by the Internet. A questionnaire survey was conducted with academic staff at Sultan Qaboos University. Statistical analysis found a number of significant differences between respondents in the science disciplines and those in the social sciences and humanities with regard to their use of, and attitudes towards, digital information services. While respondents from science disciplines show overall longer and more frequent use of networked information, respondents from humanities and social sciences indicated more positive attitudes toward library networked services.The Arab country context presents a challenge in determining the degree to which results can be extrapolated to other environments, in that disciplines are also divided by language. Science disciplines teach in English, and the social science and humanities in Arabic.While similar studies have been undertaken in developed countries, this study is an attempt to establish some data for a developing Arab country

Conditional measurements on multimode pairwise entangled states from spontaneous parametric downconversion

We address the intrinsic multimode nature of the quantum state of light obtained by pulsed spontaneous parametric downconversion and develop a theoretical model based only on experimentally accessible quantities. We exploit the pairwise entanglement as a resource for conditional multimode measurements and derive closed formulas for the detection probability and the density matrix of the conditional states. We present a set of experiments performed to validate our model in different conditions that are in excellent agreement with experimental data. Finally, we evaluate nonGaussianity of the conditional states obtained from our source with the aim of discussing the effects of the different experimental parameters on the efficacy of this type of conditional state preparation