Anyonic interferometry and protected memories in atomic spin lattices

Strongly correlated quantum systems can exhibit exotic behavior called topological order which is characterized by non-local correlations that depend on the system topology. Such systems can exhibit remarkable phenomena such as quasi-particles with anyonic statistics and have been proposed as candidates for naturally fault-tolerant quantum computation. Despite these remarkable properties, anyons have never been observed in nature directly. Here we describe how to unambiguously detect and characterize such states in recently proposed spin lattice realizations using ultra-cold atoms or molecules trapped in an optical lattice. We propose an experimentally feasible technique to access non-local degrees of freedom by performing global operations on trapped spins mediated by an optical cavity mode. We show how to reliably read and write topologically protected quantum memory using an atomic or photonic qubit. Furthermore, our technique can be used to probe statistics and dynamics of anyonic excitations.Comment: 14 pages, 6 figure

Two chemically similar stellar overdensities on opposite sides of the plane of the Galaxy

Our Galaxy is thought to have undergone an active evolutionary history dominated by star formation, the accretion of cold gas, and, in particular, mergers up to 10 gigayear ago. The stellar halo reveals rich fossil evidence of these interactions in the form of stellar streams, substructures, and chemically distinct stellar components. The impact of dwarf galaxy mergers on the content and morphology of the Galactic disk is still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups, which may have extragalactic origin. However, there is mounting evidence that stellar overdensities at the outer disk/halo interface could have been caused by the interaction of a dwarf galaxy with the disk. Here we report detailed spectroscopic analysis of 14 stars drawn from two stellar overdensities, each lying about 5 kiloparsecs above and below the Galactic plane - locations suggestive of association with the stellar halo. However, we find that the chemical compositions of these stars are almost identical, both within and between these groups, and closely match the abundance patterns of the Milky Way disk stars. This study hence provides compelling evidence that these stars originate from the disk and the overdensities they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.Comment: accepted for publication in Natur

Experimental simulation of quantum tunneling in small systems

It is well known that quantum computers are superior to classical computers in efficiently simulating quantum systems. Here we report the first experimental simulation of quantum tunneling through potential barriers, a widespread phenomenon of a unique quantum nature, via NMR techniques. Our experiment is based on a digital particle simulation algorithm and requires very few spin-1/2 nuclei without the need of ancillary qubits. The occurrence of quantum tunneling through a barrier, together with the oscillation of the state in potential wells, are clearly observed through the experimental results. This experiment has clearly demonstrated the possibility to observe and study profound physical phenomena within even the reach of small quantum computers.Comment: 17 pages and 8 figure

The Distribution of Dark Matter in Galaxies: the Core Radius Issue

I review the up-to-date status on the properties of the Dark Matter density distribution around Galaxies. The rotation curves of spirals all conform to a same Universal profile which can be uniquely decomposed as the sum of an exponential thin stellar disk and a dark halo with a flat density core. From dwarfs to giants galaxies, the halos embedding the stellar component feature a constant density region of size $r_0$ and value $\rho_0$, which are inversely correlated. The fine structure of dark halos in the region of the stellar disk has been derived for a number of low--luminosity disk galaxies: the halo circular velocity increases almost linearly with radius out to the edge of the stellar disk, implying, up there, an almost constant dark matter density. This sets a serious discrepancy between the cuspy density distribution predicted by N-body simulations of $\Lambda$CDM cosmology, and those actually detected around galaxies. The small scatter around the Fundamental Plane (FP) of elliptical galaxies constraints the distribution of dark and luminous matter in these systems. The measured central velocity dispersion $\sigma_0$ in the FP is linked to both photometric and dynamical properties of luminous and dark matter. As a consequence, the well-known features of the FP imply that, inside the effective radius $R_e$, the stellar spheroid must dominate over the dark matter, in contrast with $\Lambda$CDM predictions.Comment: 14 pages, 10 figures, invited talk given at Beyond the Desert '03, Ringberg, 11-15 July 200

The role of the smartphone in the transition from medical student to foundation trainee: a qualitative interview and focus group study

Background The transition from medical student to junior doctor is one of the most challenging in medicine, affecting both doctor and patient health. Opportunities to support this transition have arisen from advances in mobile technology and increased smartphone ownership. Methods This qualitative study consisted of six in-depth interviews and two focus groups with Foundation Year 1 Trainees (intern doctors) and final year medical students within the same NHS Trust. A convenience sample of 14 participants was recruited using chain sampling. Interviews and focus groups were recorded, transcribed verbatim, analysed in accordance with thematic analysis and presented below in keeping with the standards for reporting qualitative research. Results Participants represented both high and low intensity users. They used their smartphones to support their prescribing practices, especially antimicrobials through the MicroGuide™ app. Instant messaging, via WhatsApp, contributed to the existing bleep system, allowing coordination of both work and learning opportunities across place and time. Clinical photographs were recognised as being against regulations but there had still been occasions of use despite this. Concerns about public and colleague perceptions were important to both students and doctors, with participants describing various tactics employed to successfully integrate phone use into their practices. Conclusion This study suggests that both final year medical students and foundation trainees use smartphones in everyday practice. Medical schools and healthcare institutions should seek to integrate such use into core curricula/training to enable safe and effective use and further ease the transition to foundation training. We recommend juniors are reminded of the potential risks to patient confidentiality associated with smartphone use