609 research outputs found
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
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