Quantum metrology with nonclassical states of atomic ensembles

Quantum technologies exploit entanglement to revolutionize computing, measurements, and communications. This has stimulated the research in different areas of physics to engineer and manipulate fragile many-particle entangled states. Progress has been particularly rapid for atoms. Thanks to the large and tunable nonlinearities and the well developed techniques for trapping, controlling and counting, many groundbreaking experiments have demonstrated the generation of entangled states of trapped ions, cold and ultracold gases of neutral atoms. Moreover, atoms can couple strongly to external forces and light fields, which makes them ideal for ultra-precise sensing and time keeping. All these factors call for generating non-classical atomic states designed for phase estimation in atomic clocks and atom interferometers, exploiting many-body entanglement to increase the sensitivity of precision measurements. The goal of this article is to review and illustrate the theory and the experiments with atomic ensembles that have demonstrated many-particle entanglement and quantum-enhanced metrology.Comment: 76 pages, 40 figures, 1 table, 603 references. Some figures bitmapped at 300 dpi to reduce file siz

Modified spin-wave theory with ordering vector optimization I: frustrated bosons on the spatially anisotropic triangular lattice

We investigate a system of frustrated hardcore bosons, modeled by an XY antiferromagnet on the spatially anisotropic triangular lattice, using Takahashi's modified spin-wave (MSW) theory. In particular we implement ordering vector optimization on the ordered reference state of MSW theory, which leads to significant improvement of the theory and accounts for quantum corrections to the classically ordered state. The MSW results at zero temperature compare favorably to exact diagonalization (ED) and projected entangled-pair state (PEPS) calculations. The resulting zero-temperature phase diagram includes a 1D quasi-ordered phase, a 2D Neel ordered phase, and a 2D spiraling ordered phase. We have strong indications that the various ordered or quasi-ordered phases are separated by spin-liquid phases with short-range correlations, in analogy to what has been predicted for the Heisenberg model on the same lattice. Within MSW theory we also explore the finite-temperature phase diagram. We find that the zero-temperature long-range-ordered phases turn into quasi-ordered phases (up to a Berezinskii-Kosterlitz-Thouless temperature), while zero-temperature quasi-ordered phases become short-range correlated at finite temperature. These results show that modified spin-wave theory is very well suited for describing ordered and quasi-ordered phases of frustrated XY spins (or, equivalently, of frustrated lattice bosons) both at zero and finite temperatures. While MSW theory, just as other theoretical methods, cannot describe spin-liquid phases, its breakdown provides a fast method for singling out Hamiltonians which may feature these intriguing quantum phases. We thus suggest a tool for guiding our search for interesting systems whose properties are necessarily studied with a physical quantum simulator.Comment: 40 pages, 16 figure

‘Being the bridge and the beacon’: a qualitative study of the characteristics and functions of the liaison role in child and family health services in Australia

© 2016 John Wiley & Sons Ltd Aims and objectives: This article explores the characteristics and functions of the liaison role in child and family health services in Australia. Background: Liaison roles are increasingly being used to improve communication between health services and professionals and to facilitate access to support for individuals and families in need. Nurses are commonly, although not always, the professionals who undertake these roles. Research on the role and outcomes of liaison positions in child and family health services is limited in Australia and internationally. Design: A qualitative interpretive design informed this study. Interviews and focus groups were conducted with 40 liaison and other health professionals, primarily nurses, working with families with newborn and young children in two Australian States. Data were analysed thematically. Results: Three major themes were identified reflecting the importance of defining the role and tasks which included building bridges between services and professionals, supporting families during transition between services and supporting clinicians. Several facilitators and barriers were identified, including concerns about sustainability of the roles. Conclusions: Professionals working in a liaison role in child and family health services emphasise that these positions have the potential to link services and professionals, thereby providing more effective care pathways for children and families especially for those with complex and multiple vulnerabilities. While a few children and family health services in Australia provide liaison services, the extent of liaison support and the outcomes for families in Australia is unknown. Relevance to clinical practice: Nurses working with children and families are the most likely health professionals to undertake a liaison role. In many nursing contexts, liaison roles are relatively new and those in the role have the responsibility to define the key purpose of their role. Liaison roles are multifaceted requiring the nurse to have excellent communication and negotiation skills to effectively link diverse professionals and services, while simultaneously engaging with and supporting vulnerable families and children. Nurses in these roles also support and educate clinical colleagues

Phase Space Tomography of Matter-Wave Diffraction in the Talbot Regime

We report on the theoretical investigation of Wigner distribution function (WDF) reconstruction of the motional quantum state of large molecules in de Broglie interference. De Broglie interference of fullerenes and as the like already proves the wavelike behaviour of these heavy particles, while we aim to extract more quantitative information about the superposition quantum state in motion. We simulate the reconstruction of the WDF numerically based on an analytic probability distribution and investigate its properties by variation of parameters, which are relevant for the experiment. Even though the WDF described in the near-field experiment cannot be reconstructed completely, we observe negativity even in the partially reconstructed WDF. We further consider incoherent factors to simulate the experimental situation such as a finite number of slits, collimation, and particle-slit van der Waals interaction. From this we find experimental conditions to reconstruct the WDF from Talbot interference fringes in molecule Talbot-Lau interferometry.Comment: 16 pages, 9 figures, accepted at New Journal of Physic