Synthesis and Analysis of Entangled Photonic Qubits in Spatial-Parity Space

We present the novel embodiment of a photonic qubit that makes use of one continuous spatial degree of freedom of a single photon and relies on the the parity of the photon's transverse spatial distribution. Using optical spontaneous parametric downconversion to produce photon pairs, we demonstrate the controlled generation of entangled-photon states in this new space. Specifically, two Bell states, and a continuum of their superpositions, are generated by simple manipulation of a classical parameter, the optical-pump spatial parity, and not by manipulation of the entangled photons themselves. An interferometric device, isomorphic in action to a polarizing beam splitter, projects the spatial-parity states onto an even--odd basis. This new physical realization of photonic qubits could be used as a foundation for future experiments in quantum information processing.Comment: 6 pages, 5 figures, submitted to PR

Phase-unlocked Hong-Ou-Mandel interferometry

There is a fundamental dimensional mismatch between the Hong-Ou-Mandel (HOM) interferometer and two-photon (2P) states: while the latter are represented using two temporal (or spectral) dimensions, the HOM interferometer allows access to only one temporal dimension. We introduce a linear 2P interferometer containing two independent delays spanning the 2P state. By unlocking the fixed phase relationship between the interfering 2P probability amplitudes in a HOM interferometer, one of these probability amplitudes now serves as a delay-free 2P reference against which the other beats, thereby resolving ambiguities in 2P state identification typical of HOM interferometry and extending its utility to a large family of 2P states

Experimental demonstration of multi-aperture digital coherent combining over a 3.2-km free-space link

The next generation free-space optical communications infrastructure will need to support a wide variety of space-to-ground links. As a result of the limited size, weight, and power on space-borne assets, the ground terminals need to scale efficiently to large collection areas to support extremely long link distances or high data rates. Recent advances in integrated digital coherent receivers enable the coherent combining (i.e., full-field addition) of signals from several small apertures to synthesize an effective single large aperture. In this work, we experimentally demonstrate the coherent combining of signals received by four independent receive chains after propagation through a 3:2-km atmospheric channel. Measured results show the practicality of coherently combining the four received signals via digital signal processing after transmission through a turbulent atmosphere. In particular, near-lossless combining is demonstrated using the technique of maximal ratio combining

Experimental demonstration of photon efficient coherent temporal combining for data rate scaling

The next generation free-space optical (FSO) communications infrastructure will need to support a wide range of links from space-based terminals at LEO, GEO, and deep space to the ground. Efficiently enabling such a diverse mission set requires a common ground station architecture capable of providing excellent sensitivity (i.e., few photons-per-bit) while supporting a wide range of data rates. One method for achieving excellent sensitivity performance is to use integrated digital coherent receivers. Additionally, coherent receivers provide full-field information, which enables efficient temporal coherent combining of block repeated signals. This method allows system designers to trade excess link margin for increased data rate without requiring hardware modifications. We present experimental results that show a 45-dB scaling in data rate over a 41-dB range of input powers by block-repeating and combining a PRBS sequence up to 36,017 times. Keywords: digital signal processing, optical receivers, phase shift keying, coherent combiningUnited States. Dept. of Defense. Assistant Secretary of Defense for Research & Engineering (Contract FA8721-05-C-0002

Sins of Omission

Little is known about the relative incidence of serious errors of omission versus errors of commission. Objective : To identify the most common substantive medical errors identified by medical record review. Design : Retrospective cohort study. Setting : Twelve Veterans Affairs health care systems in 2 regions. Participants : Stratified random sample of 621 patients receiving care over a 2-year period. Main Outcome Measure : Classification of reported quality problems. Methods : Trained physicians reviewed the full inpatient and outpatient record and described quality problems, which were then classified as errors of omission versus commission. Results : Eighty-two percent of patients had at least 1 error reported over a 13-month period. The average number of errors reported per case was 4.7 (95% confidence intervals [CI]: 4.4, 5.0). Overall, 95.7% (95% CI: 94.9%, 96.4%) of errors were identified as being problems with underuse. Inadequate care for people with chronic illnesses was particularly common. Among errors of omission, obtaining insufficient information from histories and physicals (25.3%), inadequacies in diagnostic testing (33.9%), and patients not receiving needed medications (20.7%) were all common. Out of the 2,917 errors identified, only 27 were rated as being highly serious, and 26 (96%) of these were errors of omission. Conclusions : While preventing iatrogenic injury resulting from medical errors is a critically important part of quality improvement, we found that the overwhelming majority of substantive medical errors identifiable from the medical record were related to people getting too little medical care, especially for those with chronic medical conditions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74567/1/j.1525-1497.2005.0152.x.pd

Eligibility for interventions, co-occurrence and risk factors for unhealthy behaviours in patients consulting for routine primary care: results from the Pre-Empt study

Smoking, excessive drinking, lack of exercise and a poor diet remain key causes of premature morbidity and mortality globally, yet it is not clear what proportion of patients attending for routine primary care are eligible for interventions about these behaviours, the extent to which they co-occur within individuals, and which individuals are at greatest risk for multiple unhealthy behaviours. The aim of the trial was to examine 'intervention eligibility' and co-occurrence of the 'big four' risky health behaviours - lack of exercise, smoking, an unhealthy diet and excessive drinking - in a primary care population. Data were collected from adult patients consulting routinely in general practice across South Wales as part of the Pre-Empt study; a cluster randomised controlled trial. After giving consent, participants completed screening instruments, which included the following to assess eligibility for an intervention based on set thresholds: AUDIT-C (for alcohol), HSI (for smoking), IPAQ (for exercise) and a subset of DINE (for diet). The intervention following screening was based on which combination of risky behaviours the patient had. Descriptive statistics, χ2 tests for association and ordinal regressions were undertaken. Two thousand sixty seven patients were screened: mean age of 48.6 years, 61.9 % female and 42.8 % in a managerial or professional occupation. In terms of numbers of risky behaviours screened eligible for, two was the most common (43.6 %), with diet and exercise (27.2 %) being the most common combination. Insufficient exercise was the most common single risky behaviour (12.0 %). 21.8 % of patients would have been eligible for an intervention for three behaviours and 5.9 % for all four behaviours. Just 4.5 % of patients did not identify any risky behaviours. Women, older age groups and those in managerial or professional occupations were more likely to exhibit all four risky behaviours. Very few patients consulting for routine primary care screen ineligible for interventions about common unhealthy behaviours, and most engage in more than one of the major common unhealthy behaviours. Clinicians should be particularly alert to opportunities to engaging younger, non professional men and those with multi-morbidity about risky health behaviour. ISRCTN22495456. BACKGROUND METHODS RESULTS CONCLUSION TRIAL REGISTRATIO

Atomoxetine Enhances Connectivity of Prefrontal Networks in Parkinson's Disease.

Cognitive impairment is common in Parkinson's disease (PD), but often not improved by dopaminergic treatment. New treatment strategies targeting other neurotransmitter deficits are therefore of growing interest. Imaging the brain at rest ('task-free') provides the opportunity to examine the impact of a candidate drug on many of the brain networks that underpin cognition, while minimizing task-related performance confounds. We test this approach using atomoxetine, a selective noradrenaline reuptake inhibitor that modulates the prefrontal cortical activity and can facilitate some executive functions and response inhibition. Thirty-three patients with idiopathic PD underwent task-free fMRI. Patients were scanned twice in a double-blind, placebo-controlled crossover design, following either placebo or 40-mg oral atomoxetine. Seventy-six controls were scanned once without medication to provide normative data. Seed-based correlation analyses were used to measure changes in functional connectivity, with the right inferior frontal gyrus (IFG) a critical region for executive function. Patients on placebo had reduced connectivity relative to controls from right IFG to dorsal anterior cingulate cortex and to left IFG and dorsolateral prefrontal cortex. Atomoxetine increased connectivity from the right IFG to the dorsal anterior cingulate. In addition, the atomoxetine-induced change in connectivity from right IFG to dorsolateral prefrontal cortex was proportional to the change in verbal fluency, a simple index of executive function. The results support the hypothesis that atomoxetine may restore prefrontal networks related to executive functions. We suggest that task-free imaging can support translational pharmacological studies of new drug therapies and provide evidence for engagement of the relevant neurocognitive systems.This work was funded by the Wellcome trust (103838), Parkinson’s UK, National Institute for Health Research’s Cambridge Biomedical Research Centre and the Medical Research Council (MC_US_A060_0016 and RG62761) and the James F McDonnell Foundation (21st century science initiative on Understanding Human Cognition). The BCNI is supported by a joint award from the Wellcome Trust and Medical Research Council.This is the final version of the article. It first appeared from Nature Publishing Group via http://dx.doi.org/10.1038/npp.2016.1

A Phase-Unlocked Hong-Ou-Mandel Interferometer

There exists a fundamental dimensional mismatch between the Hong-Ou-Mandel (HOM) interferometer and two-photon states: while the latter are represented using two temporal (or spectral) dimensions, the HOM interferometer allows access to only one temporal dimension owing to its single delay element. We introduce a linear two-photon interferometer containing two independent delays spanning the two-photon state. By unlocking the fixed phase relationship between the interfering two-photon probability amplitudes in a HOM interferometer, one of these probability amplitudes now serves as a delay-free two-photon reference against which the other beats, thereby resolving ambiguities in two-photon state identification typical of HOM interferometry. We discuss the operation of this phase-unlocked HOM on a variety of input states focusing on instances where this new interferometer outperforms a traditional HOM interferometer: frequency-correlated states and states produced by a pulse doublet pump. Additionally, this interferometer affords the opportunity to synchronize two-photon states in a manner analogous to an HOM interferometer; moreover, it extends that capability to the aforementioned class of states. © 2013 SPIE

Angular And Radial Mode Analyzer For Optical Beams

We describe an approach to determining both the angular and the radial modal content of a scalar optical beam in terms of optical angular momentum modes. A modified Mach - Zehnder interferometer that incorporates a spatial rotator to determine the angular modes and an optical realization of the fractional Hankel transform (fHT) to determine the radial modes is analyzed. Varying the rotation angle and the order of the fHT produces a two-dimensional (2D) interferogram from which we extract the modal coefficients by simple 2D Fourier analysis. © 2011 Optical Society of America

Generalized Optical Interferometry For Modal Analysis In Arbitrary Degrees Of Freedom

We generalize the traditional concept of temporal optical interferometry to any degree of freedom of a coherent optical field. By identifying the structure of a unitary optical transformation that we designate the generalized phase operator, we enable optical interferometry to be carried out in any modal basis describing a degree of freedom. The structure of the generalized phase operator is that of a fractional optical transform, thus establishing the connection between fractional transforms, optical interferometry, and modal analysis. © 2012 Optical Society of America