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J Britton

Publications and source records attributed to J Britton.

At least 19 recordsLinked to original sources
PubMed2006

Experimental purification of two-atom entanglement.

Entanglement is a necessary resource for quantum applications--entanglement established between quantum systems at different locations enables private communication and quantum teleportation, and facilitates quantum information processing. Distributed entanglement is established by preparing an entangled pair of quantum particles in one location, and transporting one member of the pair to another location. However, decoherence during transport reduces the quality (fidelity) of the entanglement. A protocol to achieve entanglement 'purification' has been proposed to improve the fidelity after transport. This protocol uses separate quantum operations at each location and classical communication to distil high-fidelity entangled pairs from lower-fidelity pairs. Proof-of-principle experiments distilling entangled photon pairs have been carried out. However, these experiments obtained distilled pairs with a low probability of success and required destruction of the entangled pairs, rendering them unavailable for further processing. Here we report efficient and non-destructive entanglement purification with atomic quantum bits. Two noisy entangled pairs were created and distilled into one higher-fidelity pair available for further use. Success probabilities were above 35 per cent. The many applications of entanglement purification make it one of the most important techniques in quantum information processing.

Journal Article↗
PubMed2006

Prevalence, diagnosis and relation to tobacco dependence of chronic obstructive pulmonary disease in a nationally representative population sample.

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is the fourth most common cause of death worldwide. It is caused primarily by cigarette smoking. Given its importance, it is remarkable that reliable national prevalence data are lacking for most countries. This study provides estimates of the national prevalence of COPD in England, the extent of under-detection of the disorder, and patterns of cigarette smoking, dependence, and motivation to stop smoking in those with the disease. METHODS: Data from 8215 adults over the age of 35 who participated in the Health Survey for England were analysed. Information was obtained on self-reported and cotinine validated smoking status, cigarette dependence, motivation to stop smoking, COPD defined by spirometry using joint American Thoracic Society and European Respiratory Society criteria, and self-reports of diagnosis with respiratory disorders. RESULTS: Spirometry-defined COPD was present in 13.3% (95% CI 12.6 to 14.0) of participants, over 80% of whom reported no respiratory diagnosis. Even among people with severe or very severe COPD by spirometric assessment, only 46.8% (95% CI 39.1 to 54.6) reported any diagnosed respiratory disease. A total of 34.9% (95% CI 32.1 to 37.8) of people with spirometry-defined COPD were smokers compared with 22.4% (95% CI 21.4 to 23.4) of those without, and smoking prevalence increased with disease severity. Smokers with spirometry-defined COPD were more cigarette dependent but had no greater desire to quit than other smokers. CONCLUSION: COPD is common among adults in England and is predominantly undiagnosed. In smokers it is associated with higher degrees of cigarette dependence but not with a greater motivation to stop smoking.

Adult↗
PubMed2006

Microfabricated surface-electrode ion trap for scalable quantum information processing.

Individual laser-cooled 24Mg+ ions are confined in a linear Paul trap with a novel geometry where gold electrodes are located in a single plane and the ions are trapped 40 microm above this plane. The relatively simple trap design and fabrication procedure are important for large-scale quantum information processing (QIP) using ions. Measured ion motional frequencies are compared to simulations. Measurements of ion recooling after cooling is temporarily suspended yield a heating rate of approximately 5 motional quanta per millisecond for a trap frequency of 2.83 MHz, sufficiently low to be useful for QIP.

Journal Article↗
PubMed2006

Use and misuse of aspirin in rural Ethiopia.

OBJECTIVES: To investigate ability to distinguish simple analgesics, to document misconceptions about aspirin use, and to identify strategies to diminish potentially harmful aspirin use in Ethiopia. DESIGN: Qualitative study (eight focus group discussions) used to inform cross-sectional survey. SETTING: Butajira, a small town in southern Ethiopia, and surrounding rural areas. PARTICIPANTS: Purposively selected informants for focus groups; random sample of urban and rural residents for cross-sectional survey. MAIN OUTCOME MEASURES: Ability to distinguish aspirin from paracetamol; proportion using aspirin; proportion aware of common risks of aspirin. RESULTS: Questionnaires were completed by 204 of the 250 residents sampled (82% response). Three-quarters of survey participants knew the difference between aspirin and paracetamol. Aspirin was used by 7.3% of respondents, and was mainly taken for headache and fever. In focus group discussions there was a suggestion that aspirin was considered particularly useful for children. There was very low awareness of the risks of using aspirin in children (2.5% unprompted, 18.6% prompted) or in people with asthma (1% unprompted, 5.9% prompted). Aspirin is cheap and widely available in urban and rural areas. CONCLUSION: Awareness of the risks of aspirin use by children and in asthma is extremely low in this rural Ethiopian setting. Medications are purchased with minimal packaging by a population with low literacy. Drug dispensers and vendors must be trained to convey simple verbal warnings about aspirin use.

Acetaminophen↗
PubMed2005

Creation of a six-atom 'Schrödinger cat' state.

Among the classes of highly entangled states of multiple quantum systems, the so-called 'Schrödinger cat' states are particularly useful. Cat states are equal superpositions of two maximally different quantum states. They are a fundamental resource in fault-tolerant quantum computing and quantum communication, where they can enable protocols such as open-destination teleportation and secret sharing. They play a role in fundamental tests of quantum mechanics and enable improved signal-to-noise ratios in interferometry. Cat states are very sensitive to decoherence, and as a result their preparation is challenging and can serve as a demonstration of good quantum control. Here we report the creation of cat states of up to six atomic qubits. Each qubit's state space is defined by two hyperfine ground states of a beryllium ion; the cat state corresponds to an entangled equal superposition of all the atoms in one hyperfine state and all atoms in the other hyperfine state. In our experiments, the cat states are prepared in a three-step process, irrespective of the number of entangled atoms. Together with entangled states of a different class created in Innsbruck, this work represents the current state-of-the-art for large entangled states in any qubit system.

Journal Article↗
PubMed2005

Long-lived qubit memory using atomic ions.

We demonstrate experimentally a robust quantum memory using a magnetic-field-independent hyperfine transition in 9Be+ atomic ion qubits at a magnetic field B approximately = 0.01194 T. We observe that the single physical qubit memory coherence time is greater than 10 s, an improvement of approximately 5 orders of magnitude from previous experiments with 9Be+. We also observe long coherence times of decoherence-free subspace logical qubits comprising two entangled physical qubits and discuss the merits of each type of qubit.

Journal Article↗
PubMed2005

Bupropion and the risk of sudden death: a self-controlled case-series analysis using The Health Improvement Network.

BACKGROUND: Bupropion is an effective smoking cessation therapy but its use in the UK has been limited by concerns that it may increase the risk of sudden death. METHODS: Data for all patients prescribed bupropion within The Health Improvement Network (a computerised general practice database) were extracted and the self-controlled case-series method was used to estimate the relative incidence of death during the first 28 days of treatment. The incidence of seizures, a recognised adverse effect of bupropion, was also investigated during this period. RESULTS: A total of 9329 individuals had been prescribed bupropion (mean age 44 years, 48% male). The total person-time after the first prescription for bupropion was 17,586 years, and during this time 121 people died. Two people died within the first 28 days of treatment, which was less than expected in comparison with the remaining observation period by an incidence ratio of 0.50 (95% confidence interval (CI) 0.12 to 2.05). Twenty eight people were recorded as having a total of 45 seizures (23 before starting bupropion, two in the first 28 days of treatment, and 20 at a later point). The relative incidence of seizures during the first 28 days of treatment was 3.62 (95% CI 0.87 to 15.09), equivalent to one additional seizure per 6219 first time bupropion users. CONCLUSIONS: Bupropion use is probably associated with an increased risk of seizures, but no evidence was found to suggest that the drug is associated with an increased risk of sudden death.

Antidepressive Agents, Second-Generation↗
PubMed2005

Vagus nerve stimulation for epilepsy: randomized comparison of three stimulation paradigms.

Vagus nerve stimulation (VNS) is an effective adjunctive treatment for intractable epilepsy. However, the optimal range of device duty-cycles [on/(on + off times)] is poorly understood. The authors performed a multicenter, randomized trial of three unique modes of VNS, which varied primarily by duty-cycle. The results indicate that the three duty-cycles were equally effective. The data support the use of standard duty-cycles as initial therapy.

Cough↗
PubMed2005

Hyperfine coherence in the presence of spontaneous photon scattering.

The coherence of a hyperfine-state superposition of a trapped 9Be+ ion in the presence of off-resonant light is studied experimentally. It is shown that Rayleigh elastic scattering of photons that does not change state populations also does not affect coherence. We observe coherence times that exceed the average scattering time of 19 photons which is determined from measured Stark shifts. This result implies that, with sufficient control over its parameters, laser light can be used to manipulate hyperfine-state superpositions with very little decoherence.

Journal Article↗
PubMed2005

Implementation of the semiclassical quantum Fourier transform in a scalable system.

We report the implementation of the semiclassical quantum Fourier transform in a system of three beryllium ion qubits (two-level quantum systems) confined in a segmented multizone trap. The quantum Fourier transform is the crucial final step in Shor's algorithm, and it acts on a register of qubits to determine the periodicity of the quantum state's amplitudes. Because only probability amplitudes are required for this task, a more efficient semiclassical version can be used, for which only single-qubit operations conditioned on measurement outcomes are required. We apply the transform to several input states of different periodicities; the results enable the location of peaks corresponding to the original periods. This demonstration incorporates the key elements of a scalable ion-trap architecture, suggesting the future capability of applying the quantum Fourier transform to a large number of qubits as required for a useful quantum factoring algorithm.

Journal Article↗
PubMed2005

Secondhand smoke, dietary fruit intake, road traffic exposures, and the prevalence of asthma: a cross-sectional study in young children.

The authors have investigated the independent effects of exposure to secondhand smoke, road vehicle traffic, and dietary fruit intake in a cross-sectional study of asthma in young children. They surveyed all children aged 4-6 years in 235 schools in the East Midlands and East of England regions of the United Kingdom in 2003. Data on respiratory symptoms, diagnoses and treatment, smoking in the home, and dietary fruit intake were collected by parental questionnaire. A geographic information system was used to map postcodes and determine the distance of the home from the nearest main road. Responses were obtained from 11,562 children. Wheeze in the past year and physician-diagnosed asthma were reported by 14.1% and 18.2%, respectively. Both of these outcomes were more common in children who lived with a smoker, and the prevalence of asthma increased with the number of smokers in the home. Asthma prevalence was not associated with proximity of the home to a main road or with dietary fruit intake. The authors conclude that, of the potential risk factors considered in this study, preventing secondhand smoke exposure may be the most effective way of preventing asthma.

Asthma↗
PubMed2005

Enhanced quantum state detection efficiency through quantum information processing.

We investigate theoretically and experimentally how quantum state-detection efficiency is improved by the use of quantum information processing (QIP). Experimentally, we encode the state of one 9Be(+) ion qubit with one additional ancilla qubit. By measuring both qubits, we reduce the state-detection error in the presence of noise. The deviation from the theoretically allowed reduction is due to infidelities of the QIP operations. Applying this general scheme to more ancilla qubits suggests that error in the individual qubit measurements need not be a limit to scalable quantum computation.

Journal Article↗
PubMed2005

Lung function and blood levels of copper, selenium, vitamin C and vitamin E in the general population.

BACKGROUND: Increased dietary intake of antioxidants has been associated with higher lung function, but few studies have used biological markers of antioxidant intake. OBJECTIVE: This study aimed to determine if antioxidant status, as measured by blood levels, influences lung function. DESIGN: Using a random subsample of 479 participants, aged 18-65 y old, from a larger cross-sectional observational study, the association of forced expiratory volume in 1 s (FEV1) with plasma copper, vitamin C, vitamin E and serum selenium was assessed. RESULTS: An s.d. increase in blood copper level was associated with a difference in FEV1 of -48 ml (95% confidence intervals: -95, -2 ml, P = 0.04), vitamin C +49 ml (+4, +94, P = 0.03), vitamin E -15 ml (-62, +32, P = 0.53) and selenium +52 ml (+7, +96, P = 0.02). The sizes of association were not appreciably altered in a mutually adjusted model. CONCLUSIONS: Higher levels of serum vitamin C and selenium appear to be associated with higher FEV1. The association between higher serum copper and lower FEV1 requires further study in view of the ubiquitous exposure to this mineral.

Adult↗
PubMed2005

Validation of the International Study of Asthma and Allergies in Children (ISAAC) and U.K. criteria for atopic eczema in Ethiopian children.

BACKGROUND: Reliable diagnostic criteria for atopic eczema (AE) are essential in order to make international comparisons and to identify possible disease risk factors. Little is known about the prevalence of atopic eczema and validity of diagnostic criteria for AE in developing countries where English is not the first language. OBJECTIVES: We sought to determine the prevalence of AE in an area of urban and rural Ethiopia, and to compare the predictive values of different questionnaire and examination methods for diagnosing AE in this population. METHODS: We conducted a cross-sectional survey of 7915 children aged 1-5 years living in and around the town of Jimma in southwest Ethiopia. AE prevalence was assessed in two ways: (i) by using the International Study for Asthma and Allergies in Childhood (ISAAC) questionnaire, and (ii) using the U.K. refinement of Hanifin and Rajka's diagnostic criteria. All possible cases identified by screening questions and random samples of controls were then examined by an experienced local paediatrician, who acted as a reference standard to determine the predictive value of the criteria used to diagnose AE. RESULTS: The overall 1-year period prevalence of AE according to ISAAC and U.K. criteria was 4.4%[95% confidence interval (CI) 3.95-4.85] and 1.8% (95% CI 1.5-2.1), respectively. Corresponding point prevalence estimates (symptoms in the last week) were 1.8% for ISAAC and 1.3% for the U.K. criteria. The positive predictive values of the ISAAC and U.K. criteria questions for AE symptoms still reported to be present (in the last week) at the doctor's examination were 48.8% and 55.5%, respectively. Corresponding negative predictive values were 90.5% and 90.1%, respectively. The sign of visible flexural dermatitis (a component of the U.K. criteria) when used alone had positive and negative predictive values of 57% and 91%, respectively. CONCLUSIONS: Neither the ISAAC nor U.K. criteria performed especially well in predicting cases of AE in this survey. Possible reasons include problems with questionnaire translation, cultural conceptions of terminology, asking parents rather than the child about symptoms, the transient nature of AE signs, and differences in what a doctor perceives to constitute a typical case of AE. The results do not preclude the use of standardized diagnostic criteria alongside a doctor's examination in future surveys of Ethiopian children, and knowledge of the criteria's limited predictive value should help to interpret study findings that have employed such criteria. Consideration should be given to adopting the sign of visible flexural dermatitis as a standard for estimating the point prevalence of AE throughout the world because it is less susceptible to problems with translation and interpretation.

Age Distribution↗
PubMed2005

Wheeze, allergic sensitization and geohelminth infection in Butajira, Ethiopia.

BACKGROUND: The effect of geohelminth infection on wheeze and allergen sensitization is inconsistent across different epidemiological studies. OBJECTIVE: To investigate the association between self-reported wheeze, self-reported asthma, allergic sensitization and geohelminth infection in urban and rural areas of Butajira, southern Ethiopia. METHODS: Questionnaire data on wheeze, asthma and a range of confounding variables was gathered in a cross-sectional study of 7649 people aged 5 years or more from the Butajira Rural Health Project database. Allergic skin sensitization to Dermatophagoides pteronyssinus and cockroach was measured, and a stool sample collected for qualitative and quantitative geohelminth analysis. RESULTS: Wheeze was weakly associated with allergic sensitization to D. pteronyssinus and cockroach (odds ratios (OR) 1.21, 95% confidence interval (CI) 0.98-1.51, and 1.27, 95% CI 1.00-1.62, respectively). Self-reported asthma was related to sensitization to D. pteronyssinus only (OR 4.09, 95% CI 2.86-5.84). Geohelminths were present in 33.8% of participants, and the median egg load in infested individuals was 6 eggs/g. Overall, presence of any geohelminths was associated with a diminished risk of cockroach sensitization (adjusted OR 0.82, 95% CI 0.68-0.99) but there were no significant protective effects of any geohelminth infection against wheeze or asthma. CONCLUSION: In a developing country community with relatively low geohelminth prevalence and intensity, we found weak association between allergic sensitization and wheeze, but no evidence of a protective effect of geohelminths against wheeze or asthma.

Adolescent↗
PubMed2005

Proximity of the home to roads and the risk of wheeze in an Ethiopian population.

BACKGROUND: There is widespread public concern that exposure to road vehicle traffic pollution causes asthma, but epidemiological studies in developed countries have not generally confirmed a strong effect and may have underestimated the risk as a result of relatively high and widespread exposure to traffic in everyday life. AIMS: To investigate the effect of living close to a traffic bearing road on the risk of wheezing in Jimma, Ethiopia where road traffic is generally low and restricted to a limited network of roads. METHODS: Data have been previously collected on respiratory symptoms, allergic sensitisation, and numerous demographic and lifestyle factors in a systematic sample of inhabitants of Jimma town. In 2003 the homes of these people were retraced; the shortest distance to the nearest surfaced road, and traffic flows on these roads were measured. RESULTS: Distance measurements were collected for 7609 (80%) individuals. The overall prevalence of wheeze was similar in those living within 150 m of a road compared to those living further away (3.9% v 3.7%), but among the 3592 individuals living within 150 m, the risk of wheeze increased significantly in linear relation to proximity to the road (adjusted odds ratio = 1.17 per 30 m proximity, 95% CI 1.01 to 1.36). This relation was stronger, though not significantly so, for roads with above median traffic flows. CONCLUSION: These findings indicate that living in close proximity to road vehicle traffic is associated with an increased risk of wheeze, but that other environmental factors are also likely to be important.

Adolescent↗
PubMed2005

Smoking cessation treatment in primary care: prospective cohort study.

OBJECTIVE: To compare the characteristics of smokers who do and do not receive smoking cessation treatment in primary care. DESIGN: Prospective cohort study using practices registered with the pilot QRESEARCH database. SETTING: 156,550 patients aged 18 years and over from 39 general practices located within four strategic health authorities, representing the former Trent Region, UK. SUBJECTS: Patients registered with practices between 1 April 2001 and 31 March 2003 aged 18 years and over who were identified as smokers before the two year study period. OUTCOME: Prescription for smoking cessation treatment (nicotine replacement therapy (NRT) or bupropion) in the two year study period. VARIABLES: Age, sex, deprivation score, co-morbidity. RESULTS: Of the 29,492 patients recorded as current smokers at the start of the study period 1892 (6.4%) were given prescriptions for smoking cessation treatment during the subsequent two years. Of these, 1378 (72.8%) were given NRT alone, 406 (21.5%) bupropion alone, and 108 (5.7%) both treatments. Smokers were more likely to receive smoking cessation treatment if they lived in the most deprived areas (odds ratio (OR) for the most relative to the least deprived fifth, adjusted for sex, age, and co-morbidity, 1.50, 95% confidence interval (CI) 1.26 to 1.78), and if they were aged 25-74 years compared to 18-24 years or 75 and over. Smokers with co-morbidity were also more likely to receive smoking cessation treatment. Smokers were less likely to receive smoking cessation treatment if they were male (adjusted OR 0.68, 95% CI 0.62 to 0.75). CONCLUSION: The low proportion of smokers being prescribed these products strongly suggests that a major public health opportunity to prevent smoking related illness is being missed.

Adolescent↗