Ancilla-Driven Universal Quantum Computation

We propose a method of manipulating a quantum register remotely with the help of a single ancilla that steers the evolution of the register. The fully controlled ancilla qubit is coupled to the computational register solely via a fixed unitary two-qubit interaction, E, and then measured in suitable bases. We characterize all interactions E that induce a unitary, step-wise deterministic measurement back-action on the register sufficient to implement any arbitrary quantum channel. Our scheme offers significant experimental advantages for implementing computations, preparing states and performing generalized measurements as no direct control of the register is required.Comment: 4 pages, 3 figure

Quantum Criticality and Incipient Phase Separation in the Thermodynamic Properties of the Hubbard Model

Transport measurements on the cuprates suggest the presence of a quantum critical point hiding underneath the superconducting dome near optimal hole doping. We provide numerical evidence in support of this scenario via a dynamical cluster quantum Monte Carlo study of the extended two-dimensional Hubbard model. Single particle quantities, such as the spectral function, the quasiparticle weight and the entropy, display a crossover between two distinct ground states: a Fermi liquid at low filling and a non-Fermi liquid with a pseudogap at high filling. Both states are found to cross over to a marginal Fermi-liquid state at higher temperatures. For finite next-nearest-neighbor hopping t' we find a classical critical point at temperature T_c. This classical critical point is found to be associated with a phase separation transition between a compressible Mott gas and an incompressible Mott liquid corresponding to the Fermi liquid and the pseudogap state, respectively. Since the critical temperature T_c extrapolates to zero as t' vanishes, we conclude that a quantum critical point connects the Fermi-liquid to the pseudogap region, and that the marginal-Fermi-liquid behavior in its vicinity is the analogous of the supercritical region in the liquid-gas transition.Comment: 18 pages, 9 figure

Differentiating patterns of violence in the family

The feasibility and prevalence of Reciprocal, Hierarchical and Paternal patterns of family aggression hypothesised by Dixon and Browne (2003) were explored within a sample of maltreating families. The psychological reports of 67 families referred to services for alleged child maltreatment that evidenced concurrent physical intimate partner violence and child maltreatment were investigated. Of these, 29 (43.3%) cases were characterised by hierarchical; 28 (41.8%) Reciprocal and 10 (14.9%) Paternal patterns. Significant differences in the form of child maltreatment perpetrated by mothers and fathers and parent dyads living in different patterns were found. In Hierarchical sub-patterns, fathers were significantly more likely to have been convicted for a violent and/or sexual offence than mothers and were significantly less likely to be biologically related to the child. The findings demonstrate the existence of the different patterns in a sample of families involved in the Child Care Protection process in England and Wales, supporting the utility of a holistic approach to understanding aggression in the family

The Físchlár digital video system: a digital library of broadcast TV programmes

Físchlár is a system for recording, indexing, browsing and playback of broadcast TV programmes which has been operational on our University campus for almost 18 months. In this paper we give a brief overview of how the system operates, how TV programmes are organised for browse/playback and a short report on the system usage by over 900 users in our University

Determinants of Under-Five Mortality in Builsa District, Upper East Region, Ghana

Under-five mortality rate is an important indicator of a community’s social development. The Upper East region, one of the most poverty-stricken regions in Ghana, has however recorded a dramatic decline in its under-five mortality rate since 1993; from 180 per 1000 live births to 79 per 1000 live births in 2003. The aim was to identify the determinants of under-five mortality in Builsa district. A case-control study was used to collect data from mothers of 60 cases and 120 controls matched for age, sex and place of residence. Even though 70% of mothers were illiter-ate, the educational level of mothers did not influence the child’s risk of death (OR 1.1). Chil-dren of mothers who had had previous child deaths were about 8 times more likely to die (OR 7.45,) while those who had not had vitamin A supplementation were about 10 times more likely to die (OR 9.57). Over 90% of mothers had an insecticide-treated bednet and more than 50% of them exclusively breastfed their children for the first 6 months of life. Protective risk factors identified included: exclusive breastfeeding (OR 0.72), use of an insecticide-treated bednet (OR 0.12), the number of live children a mother had (OR 0.54) and immunization (OR 0.53). Even in poverty, it is possible to improve the child health status of communities. Health staff should be equipped to pay special attention to mothers with previous child deaths in order to assist them to prevent further deaths.Keywords: Under-five mortality, determinants, case-control study, Builsa distric