Quantum computing with nearest neighbor interactions and error rates over 1%

Large-scale quantum computation will only be achieved if experimentally implementable quantum error correction procedures are devised that can tolerate experimentally achievable error rates. We describe a quantum error correction procedure that requires only a 2-D square lattice of qubits that can interact with their nearest neighbors, yet can tolerate quantum gate error rates over 1%. The precise maximum tolerable error rate depends on the error model, and we calculate values in the range 1.1--1.4% for various physically reasonable models. Even the lowest value represents the highest threshold error rate calculated to date in a geometrically constrained setting, and a 50% improvement over the previous record.Comment: 4 pages, 8 figure

DOES TECHNIQUE CHANGE AFFECT MUSCULAR SUPPORT AT THE KNEE IN SIDESTEP CUTTING?

Technique modification can reduce knee loads during sidestepping but its effect on muscular support has yet to be identified. Electromyography data was collected from ten muscles during sidestepping under planned and unplanned conditions, prior to and following training. Flexion/Extension and Medial/Lateral co-contraction ratios and total activation were calculated for pre-contact and weight acceptance phases. The only observed change due to training was unplanned tasks becoming more laterally dominated and planned tasks more medially. While significant these changes are nonfunctional as the ratios still represent high levels of co-contraction. Technique modification training should lower anterior cruciate ligament loads as it results in reduced knee moments but similar levels of muscular support, thus lowering the risk of injury

Bird Monitoring at Herbert Hoover National Historic Site, Iowa, Status Report 2005–2017

Executive Summary In 2005, the Heartland Inventory & Monitoring Network initiated breeding bird surveys on Herbert Hoover National Historic Site, Iowa, to address two objectives: (1) to monitor changes in bird community composition and abundance, and (2) to improve our understanding of relationships between breeding birds and habitat, and the effects of management actions on those relationships. This report evaluates trends in the park’s breeding bird populations in the context of trends observed within the North American Bird Conservation Initiative’s (NABCI) Eastern Tallgrass Prairie Bird Conservation Region , the region in which the park is located. By doing so, we can assess the influence of park habitat management on bird populations with an understanding of regional population trends that are outside the influence of natural resource management activities at Herbert Hoover National Historic Site. Sixty-eight species of birds were recorded during May and June site visits in the twelve years since initiating monitoring. Sixty-seven of the species are considered breeding species because they are permanent or summer residents. Seven of the breeding species recorded on Herbert Hoover National Historic Site are species of concern for the Eastern Tallgrass Prairie Bird Conservation Region. Eight species were observed during the survey period in sufficient numbers to calculate annual abundances and trends with some degree of confidence. The American Robin (Turdus migratorius) and Red-winged Blackbird (Agelaius phoeniceus) were the most abundant and widespread species on Herbert Hoover National Historic Site. Comparing population trends on the park with regional trends suggest that populations of the most common species on the park were similar to those of the region, especially for American Goldfinch (Spinus tristis), Common Grackle (Quiscalus quiscula), Common Yellowthroat (Geothlypis trichas), Dickcissel (Spiza americana), and Mourning Dove (Zenaida macroura). The population of Eastern Meadowlark (Sturnella magna) on the park was doing slightly better than the population region-wide. One of the species that was common and widespread on the park, American Robin, had an uncertain park population trend, but a region-wide trend that was increasing. The other common and widespread species, Red-winged Blackbird, had a population trend that was declining both on the park and across the region. This report provides current regional and local trends for breeding birds for future comparisons with bird data collected as part of the long-term monitoring efforts at Herbert Hoover National Historic Site. This information will help park staff plan management objectives and assess the effectiveness of management alternatives. These monitoring data also provide park staff with additional information for interpreting natural resources

Quantum Process Tomography of the Quantum Fourier Transform

The results of quantum process tomography on a three-qubit nuclear magnetic resonance quantum information processor are presented, and shown to be consistent with a detailed model of the system-plus-apparatus used for the experiments. The quantum operation studied was the quantum Fourier transform, which is important in several quantum algorithms and poses a rigorous test for the precision of our recently-developed strongly modulating control fields. The results were analyzed in an attempt to decompose the implementation errors into coherent (overall systematic), incoherent (microscopically deterministic), and decoherent (microscopically random) components. This analysis yielded a superoperator consisting of a unitary part that was strongly correlated with the theoretically expected unitary superoperator of the quantum Fourier transform, an overall attenuation consistent with decoherence, and a residual portion that was not completely positive - although complete positivity is required for any quantum operation. By comparison with the results of computer simulations, the lack of complete positivity was shown to be largely a consequence of the incoherent errors during the quantum process tomography procedure. These simulations further showed that coherent, incoherent, and decoherent errors can often be identified by their distinctive effects on the spectrum of the overall superoperator. The gate fidelity of the experimentally determined superoperator was 0.64, while the correlation coefficient between experimentally determined superoperator and the simulated superoperator was 0.79; most of the discrepancies with the simulations could be explained by the cummulative effect of small errors in the single qubit gates.Comment: 26 pages, 17 figures, four tables; in press, Journal of Chemical Physic