318 research outputs found
De Broglie Wavelength of a Nonlocal Four-Photon
Superposition is one of the most distinct features of quantum theory and has
been demonstrated in numerous realizations of Young's classical double-slit
interference experiment and its analogues. However, quantum entanglement - a
significant coherent superposition in multiparticle systems - yields phenomena
that are much richer and more interesting than anything that can be seen in a
one-particle system. Among them, one important type of multi-particle
experiments uses path-entangled number-states, which exhibit pure higher-order
interference and allow novel applications in metrology and imaging such as
quantum interferometry and spectroscopy with phase sensitivity at the
Heisenberg limit or quantum lithography beyond the classical diffraction limit.
Up to now, in optical implementations of such schemes lower-order interference
effects would always decrease the overall performance at higher particle
numbers. They have thus been limited to two photons. We overcome this
limitation and demonstrate a linear-optics-based four-photon interferometer.
Observation of a four-particle mode-entangled state is confirmed by
interference fringes with a periodicity of one quarter of the single-photon
wavelength. This scheme can readily be extended to arbitrary photon numbers and
thus represents an important step towards realizable applications with
entanglement-enhanced performance.Comment: 19 pages, 4 figures, submitted on November 18, 200
Reduced Deadtime and Higher Rate Photon-Counting Detection using a Multiplexed Detector Array
We present a scheme for a photon-counting detection system that can be
operated at incident photon rates higher than otherwise possible by suppressing
the effects of detector deadtime. The method uses an array of N detectors and a
1-by-N optical switch with a control circuit to direct input light to live
detectors. Our calculations and models highlight the advantages of the
technique. In particular, using this scheme, a group of N detectors provides an
improvement in operation rate that can exceed the improvement that would be
obtained by a single detector with deadtime reduced by 1/N, even if it were
feasible to produce a single detector with such a large improvement in
deadtime. We model the system for continuous and pulsed light sources, both of
which are important for quantum metrology and quantum key distribution
applications.Comment: 6 figure
Super-resolving phase measurements with a multi-photon entangled state
Using a linear optical elements and post-selection, we construct an entangled
polarization state of three photons in the same spatial mode. This state is
analogous to a ``photon-number path entangled state'' and can be used for
super-resolving interferometry. Measuring a birefringent phase shift, we
demonstrate two- and three-fold improvements in phase resolution.Comment: 4 pages, 3 figure
Experimental demonstration of a hyper-entangled ten-qubit Schr\"odinger cat state
Coherent manipulation of an increasing number of qubits for the generation of
entangled states has been an important goal and benchmark in the emerging field
of quantum information science. The multiparticle entangled states serve as
physical resources for measurement-based quantum computing and high-precision
quantum metrology. However, their experimental preparation has proved extremely
challenging. To date, entangled states up to six, eight atoms, or six photonic
qubits have been demonstrated. Here, by exploiting both the photons'
polarization and momentum degrees of freedom, we report the creation of
hyper-entangled six-, eight-, and ten-qubit Schr\"odinger cat states. We
characterize the cat states by evaluating their fidelities and detecting the
presence of genuine multi-partite entanglement. Small modifications of the
experimental setup will allow the generation of various graph states up to ten
qubits. Our method provides a shortcut to expand the effective Hilbert space,
opening up interesting applications such as quantum-enhanced super-resolving
phase measurement, graph-state generation for anyonic simulation and
topological error correction, and novel tests of nonlocality with
hyper-entanglement.Comment: 11 pages, 5 figures, comments welcom
Exoplanet Atmosphere Measurements from Transmission Spectroscopy and other Planet-Star Combined Light Observations
It is possible to learn a great deal about exoplanet atmospheres even when we
cannot spatially resolve the planets from their host stars. In this chapter, we
overview the basic techniques used to characterize transiting exoplanets -
transmission spectroscopy, emission and reflection spectroscopy, and full-orbit
phase curve observations. We discuss practical considerations, including
current and future observing facilities and best practices for measuring
precise spectra. We also highlight major observational results on the
chemistry, climate, and cloud properties of exoplanets.Comment: Accepted review chapter; Handbook of Exoplanets, eds. Hans J. Deeg
and Juan Antonio Belmonte (Springer-Verlag). 22 pages, 6 figure
Reasons for compliance or noncompliance with advice to test for hepatitis C via an internet-mediated blood screening service: a qualitative study
<p>Abstract</p> <p>Background</p> <p>Hepatitis C virus (HCV) is mainly transmitted by exposure to infected blood, and can lead to liver cirrhosis and liver cancer. Since the onset of HCV and the development of liver cirrhosis usually are asymptomatic, many HCV-infected individuals are still undiagnosed. To identify individuals infected with HCV in the general population, a low threshold, internet-mediated blood testing service was set up. We performed a qualitative study examining reasons for compliance and noncompliance with advice to test for HCV via the online blood testing service.</p> <p>Methods</p> <p>Semistructured telephone interviews were conducted with 33 website visitors who had been advised to test for HCV (18 testers, 15 non-testers). Transcribed interviews were analyzed qualitatively and interpreted using psychosocial theories of health behavior.</p> <p>Results</p> <p>Reasons for testing pertaining to the online service were: the testing procedure is autonomous, personalized test advice is provided online, reminder emails are sent, and there is an online planning tool. Reasons for testing not specific to the online service were: knowing one's status can prevent liver disease and further transmission of HCV, HCV is curable, testing can provide reassurance, physical complaints are present, and there is liver disease in one's social environment. Service-related reasons for not testing pertained to inconvenient testing facilities, a lack of commitment due to the low threshold character of the service, computer/printing problems, and incorrectly interpreting an online planning tool. The reasons for not testing that are not specific to the online service were: the belief that personal risk is low, the absence of symptoms, low perceived urgency for testing and treatment, fear of the consequences of a positive test result, avoiding threatening information, and a discouraging social environment.</p> <p>Conclusions</p> <p>Features specific to the online service played a significant role in motivation to test for HCV above and beyond the more conventional perceived health benefits of HCV testing. However, some online specific features were considered problematic and need to be adapted. Methods and strategies for dealing with these impeding factors and for improving compliance with testing via the online service are outlined.</p
Cost-effectiveness of external cephalic version for term breech presentation
<p>Abstract</p> <p>Background</p> <p>External cephalic version (ECV) is recommended by the American College of Obstetricians and Gynecologists to convert a breech fetus to vertex position and reduce the need for cesarean delivery. The goal of this study was to determine the incremental cost-effectiveness ratio, from society's perspective, of ECV compared to scheduled cesarean for term breech presentation.</p> <p>Methods</p> <p>A computer-based decision model (TreeAge Pro 2008, Tree Age Software, Inc.) was developed for a hypothetical base case parturient presenting with a term singleton breech fetus with no contraindications for vaginal delivery. The model incorporated actual hospital costs (e.g., 5,581 for vaginal delivery), utilities to quantify health-related quality of life, and probabilities based on analysis of published literature of successful ECV trial, spontaneous reversion, mode of delivery, and need for unanticipated emergency cesarean delivery. The primary endpoint was the incremental cost-effectiveness ratio in dollars per quality-adjusted year of life gained. A threshold of 7,900/QALY. If the estimated probability of successful ECV is less than 32%, then ECV costs more to society and has poorer QALYs for the patient. However, as the probability of successful ECV was between 32% and 63%, ECV cost more than cesarean delivery but with greater associated QALY such that the cost-effectiveness ratio was less than $50,000/QALY. If the probability of successful ECV was greater than 63%, the computer modeling indicated that a trial of ECV is less costly and with better QALYs than a scheduled cesarean. The cost-effectiveness of a trial of ECV is most sensitive to its probability of success, and not to the probabilities of a cesarean after ECV, spontaneous reversion to breech, successful second ECV trial, or adverse outcome from emergency cesarean.</p> <p>Conclusions</p> <p>From society's perspective, ECV trial is cost-effective when compared to a scheduled cesarean for breech presentation provided the probability of successful ECV is > 32%. Improved algorithms are needed to more precisely estimate the likelihood that a patient will have a successful ECV.</p
Body mass index is not a predictor of biochemical recurrence after radical prostatectomy in Dutch men diagnosed with prostate cancer
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95677.pdf (publisher's version ) (Closed access)PURPOSE: To determine the effect of body mass index (BMI) on clinical and pathological characteristics at time of diagnosis and on risk of biochemical recurrence after radical prostatectomy among Dutch men diagnosed with prostate cancer. METHODS: In total, 1,116 prostate cancer patients with known BMI, diagnosed between 2003 and 2006, were identified from the population-based cancer registry held by the Comprehensive Cancer Centre East, The Netherlands. Of these, 504 patients underwent a radical prostatectomy. Patients were categorized as normal weight (BMI /= 30 kg/m(2)). Multivariable proportional hazards regression models, adjusted for age, prediagnostic PSA levels, and pathological characteristics were used to evaluate BMI as a prognostic factor for biochemical recurrence after radical prostatectomy. RESULTS: Overall, clinical and biopsy characteristics did not significantly differ among BMI groups. Pathological characteristics after radical prostatectomy did not significantly differ among BMI groups, except for tumor stage, which was highest in obese patients (P = 0.017). For patients treated with radical prostatectomy, 5-year risk (95% Confidence Intervals) of biochemical recurrence was 30% (23-37%) for normal weight, 32% (25-39%) for overweight, and 25% (9-41%) for obese patients (log rank P = 0.810). BMI was not an independent prognostic factor for biochemical recurrence in multivariable proportional hazards regression analyses (HR 0.99 per kg/m(2), 95% CI: 0.93-1.06). CONCLUSIONS: Compared with non-obese men, pathological tumor stage tended to be higher in obese men. Clinical relevance of this finding is unclear, because BMI was not an independent predictor of biochemical recurrence after radical prostatectomy
Cerebrospinal fluid fistula as the presenting manifestation of pituitary adenoma: case report with a 4-year follow-up
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