146 research outputs found
Quantum phase transitions of light
Recently, condensed matter and atomic experiments have reached a length-scale
and temperature regime where new quantum collective phenomena emerge. Finding
such physics in systems of photons, however, is problematic, as photons
typically do not interact with each other and can be created or destroyed at
will. Here, we introduce a physical system of photons that exhibits strongly
correlated dynamics on a meso-scale. By adding photons to a two-dimensional
array of coupled optical cavities each containing a single two-level atom in
the photon-blockade regime, we form dressed states, or polaritons, that are
both long-lived and strongly interacting. Our zero temperature results predict
that this photonic system will undergo a characteristic Mott insulator
(excitations localised on each site) to superfluid (excitations delocalised
across the lattice) quantum phase transition. Each cavity's impressive photon
out-coupling potential may lead to actual devices based on these quantum
many-body effects, as well as observable, tunable quantum simulators. We
explicitly show that such phenomena may be observable in micro-machined diamond
containing nitrogen-vacancy colour centres and superconducting microwave
strip-line resonators.Comment: 11 pages, 5 figures (2 in colour
A single-atom quantum memory in silicon
Long coherence times and fast gate operations are desirable but often conflicting requirements for physical qubits. This conflict can be resolved by resorting to fast qubits for operations, and by storing their state in a 'quantum memory' while idle. The 31 P donor in silicon comes naturally equipped with a fast qubit (the electron spin) and a long-lived qubit (the 31 P nuclear spin), coexisting in a bound state at cryogenic temperatures. Here, we demonstrate storage and retrieval of quantum information from a single donor electron spin to its host phosphorus nucleus in isotopically enriched 28 Si. The fidelity of the memory process is characterised via both state and process tomography. We report an overall process fidelity %, and memory storage times up to 80 ms. These values are limited by a transient shift of the electron spin resonance frequency following high-power radiofrequency pulses
Development of sentinel node localization and ROLL in breast cancer in Europe
The concept of a precise region in which to find the lymph nodes that drain the lymph directly from the primary tumor site can be traced back to a century ago to the observations of Jamieson and Dobson who described how cancer cells spread from cancer of the stomach in a single lymph node, which they called the â\u80\u9cprimary glandâ\u80\u9d. However, Cabanas was the first in 1977 to realize the importance of this concept in clinical studies following lymphography performed in patients with penile cancer. Thanks to Mortonâ\u80\u99s studies on melanoma in 1992, we began to understand the potential impact of the sentinel lymph node (SN) on the surgical treatment of this type of cancer. The use of a vital dye (blue dye) administered subdermally in the region surrounding the melanoma lesion led to the identification of the sentinel node, and the vital dye technique was subsequently applied to other types of solid tumors, e.g. breast, vulva. However, difficulties in using this technique in anatomical regions with deep lymphatic vessels, e.g. axilla, led to the development of lymphoscintigraphy, started by Alex and Krag in 1993 on melanoma and breast cancer and optimized by our group at European Institute of Oncology (IEO) in Milan in 1996. Today, lymphoscintigraphy is still considered as the most reliable method for the detection of the SN. In 1996, a new method for the localization of non-palpable breast lesion called radioguided occult lesion localization (ROLL) was also developed at IEO. Retrospective and prospective studies have since shown that the ROLL procedure permits the easy and accurate surgical removal of non-palpable breast lesions, overcoming the limitations of previous techniques such as the wire-guided localization. The purpose of this paper is to describe the evolution of SN biopsy and radioguided surgery in the management of breast cancer. We also include a review of the literature on the clinical scenarios in which SN biopsy in breast cancer is currently used, with particular reference to controversies and future prospects
Two-electron spin correlations in precision placed donors in silicon
Substitutional donor atoms in silicon are promising qubits for quantum computation with extremely long relaxation and dephasing times demonstrated. One of the critical challenges of scaling these systems is determining inter-donor distances to achieve controllable wavefunction overlap while at the same time performing high fidelity spin readout on each qubit. Here we achieve such a device by means of scanning tunnelling microscopy lithography. We measure anti-correlated spin states between two donor-based spin qubits in silicon separated by 16 ± 1 nm. By utilising an asymmetric system with two phosphorus donors at one qubit site and one on the other (2P−1P), we demonstrate that the exchange interaction can be turned on and off via electrical control of two in-plane phosphorus doped detuning gates. We determine the tunnel coupling between the 2P−1P system to be 200 MHz and provide a roadmap for the observation of two-electron coherent exchange oscillations
Stress analysis in a layered aortic arch model under pulsatile blood flow
BACKGROUND: Many cardiovascular diseases, such as aortic dissection, frequently occur on the aortic arch and fluid-structure interactions play an important role in the cardiovascular system. Mechanical stress is crucial in the functioning of the cardiovascular system; therefore, stress analysis is a useful tool for understanding vascular pathophysiology. The present study is concerned with the stress distribution in a layered aortic arch model with interaction between pulsatile flow and the wall of the blood vessel. METHODS: A three-dimensional (3D) layered aortic arch model was constructed based on the aortic wall structure and arch shape. The complex mechanical interaction between pulsatile blood flow and wall dynamics in the aortic arch model was simulated by means of computational loose coupling fluid-structure interaction analyses. RESULTS: The results showed the variations of mechanical stress along the outer wall of the arch during the cardiac cycle. Variations of circumferential stress are very similar to variations of pressure. Composite stress in the aortic wall plane is high at the ascending portion of the arch and along the top of the arch, and is higher in the media than in the intima and adventitia across the wall thickness. CONCLUSION: Our analysis indicates that circumferential stress in the aortic wall is directly associated with blood pressure, supporting the clinical importance of blood pressure control. High stress in the aortic wall could be a risk factor in aortic dissections. Our numerical layered aortic model may prove useful for biomechanical analyses and for studying the pathogeneses of aortic dissection
Respiratory Virus Infection and Risk of Invasive Meningococcal Disease in Central Ontario, Canada
BACKGROUND: In temperate climates, invasive meningococcal disease (IMD) incidence tends to coincide with or closely follow peak incidence of influenza virus infection; at a seasonal level, increased influenza activity frequently correlates with increased seasonal risk of IMD. METHODS: We evaluated 240 cases of IMD reported in central Ontario, Canada, from 2000 to 2006. Associations between environmental and virological (influenza A, influenza B and respiratory syncytial virus (RSV)) exposures and IMD incidence were evaluated using negative binomial regression models controlling for seasonal oscillation. Acute effects of weekly respiratory virus activity on IMD risk were evaluated using a matched-period case-crossover design with random directionality of control selection. Effects were estimated using conditional logistic regression. RESULTS: Multivariable negative binomial regression identified elevated IMD risk with increasing influenza A activity (per 100 case increase, incidence rate ratio = 1.18, 95% confidence interval (CI): 1.06, 1.31). In case-crossover models, increasing weekly influenza A activity was associated with an acute increase in the risk of IMD (per 100 case increase, odds ratio (OR)  = 2.03, 95% CI: 1.28 to 3.23). Increasing weekly RSV activity was associated with increased risk of IMD after adjusting for RSV activity in the previous 3 weeks (per 100 case increase, OR = 4.31, 95% CI: 1.14, 16.32). No change in disease risk was seen with increasing influenza B activity. CONCLUSIONS: We have identified an acute effect of influenza A and RSV activity on IMD risk. If confirmed, these finding suggest that influenza vaccination may have the indirect benefit of reducing IMD risk
Laboratory-based evaluation of legionellosis epidemiology in Ontario, Canada, 1978 to 2006
BACKGROUND: Legionellosis is a common cause of severe community acquired pneumonia and
respiratory disease outbreaks. The Ontario Public Health Laboratory (OPHL) has conducted most
testing for Legionella species in the Canadian province of Ontario since 1978, and represents a
multi-decade repository of population-based data on legionellosis epidemiology. We sought to
provide a laboratory-based review of the epidemiology of legionellosis in Ontario over the past 3
decades, with a focus on changing rates of disease and species associated with legionellosis during
that time period.
METHODS: We analyzed cases that were submitted and tested positive for legionellosis from 1978
to 2006 using Poisson regression models incorporating temporal, spatial, and demographic
covariates. Predictors of infection with culture-confirmed L. pneumophila serogroup 1 (LP1) were
evaluated with logistic regression models.
Results: 1,401 cases of legionellosis tested positive from 1978 to 2006. As in other studies, we
found a late summer to early autumn seasonality in disease occurrence with disease risk increasing
with age and in males. In contrast to other studies, we found a decreasing trend in cases in the
recent decade (IRR 0.93, 95% CI 0.91 to 0.95, P-value = 0.001); only 66% of culture-confirmed
isolates were found to be LP1.
CONCLUSION: Despite similarities with disease epidemiology in other regions, legionellosis appears
to have declined in the past decade in Ontario, in contrast to trends observed in the United States
and parts of Europe. Furthermore, a different range of Legionella species is responsible for illness,
suggesting a distinctive legionellosis epidemiology in this North American region
Investigating off-Hugoniot states using multi-layer ring-up targets
Laser compression has long been used as a method to study solids at high pressure. This is commonly achieved by sandwiching a sample between two diamond anvils and using a ramped laser pulse to slowly compress the sample, while keeping it cool enough to stay below the melt curve. We demonstrate a different approach, using a multilayer ‘ring up’ target whereby laser-ablation pressure compresses Pb up to 150 GPa while keeping it solid, over two times as high in pressure than where it would shock melt on the Hugoniot. We find that the efficiency of this approach compares favourably with the commonly used diamond sandwich technique and could be important for new facilities located at XFELs and synchrotrons which often have higher repetition rate, lower energy lasers which limits the achievable pressures that can be reached
Room temperature coherent control of coupled single spins in solid
Coherent coupling between single quantum objects is at the heart of modern
quantum physics. When coupling is strong enough to prevail over decoherence, it
can be used for the engineering of correlated quantum states. Especially for
solid-state systems, control of quantum correlations has attracted widespread
attention because of applications in quantum computing. Such coherent coupling
has been demonstrated in a variety of systems at low temperature1, 2. Of all
quantum systems, spins are potentially the most important, because they offer
very long phase memories, sometimes even at room temperature. Although precise
control of spins is well established in conventional magnetic resonance3, 4,
existing techniques usually do not allow the readout of single spins because of
limited sensitivity. In this paper, we explore dipolar magnetic coupling
between two single defects in diamond (nitrogen-vacancy and nitrogen) using
optical readout of the single nitrogen-vacancy spin states. Long phase memory
combined with a defect separation of a few lattice spacings allow us to explore
the strong magnetic coupling regime. As the two-defect system was well-isolated
from other defects, the long phase memory times of the single spins was not
diminished, despite the fact that dipolar interactions are usually seen as
undesirable sources of decoherence. A coherent superposition of spin pair
quantum states was achieved. The dipolar coupling was used to transfer spin
polarisation from a nitrogen-vacancy centre spin to a nitrogen spin, with
optical pumping of a nitrogen-vacancy centre leading to efficient
initialisation. At the level anticrossing efficient nuclear spin polarisation
was achieved. Our results demonstrate an important step towards controlled spin
coupling and multi-particle entanglement in the solid state
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