Photo-Induced Charge State Dynamics of the Neutral and Negatively Charged Silicon Vacancy Centers in Room-Temperature Diamond.

The silicon vacancy (SiV) center in diamond is drawing much attention due to its optical and spin properties, attractive for quantum information processing and sensing. Comparatively little is known, however, about the dynamics governing SiV charge state interconversion mainly due to challenges associated with generating, stabilizing, and characterizing all possible charge states, particularly at room temperature. Here, multi-color confocal microscopy and density functional theory are used to examine photo-induced SiV recombination - from neutral, to single-, to double-negatively charged - over a broad spectral window in chemical-vapor-deposition (CVD) diamond under ambient conditions. For the SiV0 to SiV- transition, a linear growth of the photo-recombination rate with laser power at all observed wavelengths is found, a hallmark of single photon dynamics. Laser excitation of SiV‒, on the other hand, yields only fractional recombination into SiV2‒, a finding that is interpreted in terms of a photo-activated electron tunneling process from proximal nitrogen atoms.

Phonon-induced population dynamics and intersystem crossing in nitrogen-vacancy centers.

We report direct measurement of population dynamics in the excited state manifold of a nitrogen-vacancy (NV) center in diamond. We quantify the phonon-induced mixing rate and demonstrate that it can be completely suppressed at low temperatures. Further, we measure the intersystem crossing (ISC) rate for different excited states and develop a theoretical model that unifies the phonon-induced mixing and ISC mechanisms. We find that our model is in excellent agreement with experiment and that it can be used to predict unknown elements of the NV center's electronic structure. We discuss the model's implications for enhancing the NV center's performance as a room-temperature sensor.

Precision measurement of electronic ion-ion interactions between neighboring Eu3+ optical centers.

We report measurements of discrete excitation-induced frequency shifts on the 7F0→5D0 transition of the Eu+ center in La:Lu:EuCl3·6D2O resulting from the optical excitation of neighboring Eu3+ ions. Shifts of up to 46.081±0.005 MHz were observed. The magnitude of the interaction between neighboring ions was found to be significantly larger than expected from the electric dipole-dipole mechanism often observed in rare earth systems. We show that a large network of interacting and individually addressable centers can be created by lightly doping crystals otherwise stoichiometric in the optically active rare earth ion, and that this network could be used to implement a quantum processor with more than ten qubits.

Optimum photoluminescence excitation and recharging cycle of single nitrogen-vacancy centers in ultrapure diamond.

Important features in the spectral and temporal photoluminescence excitation of single nitrogen-vacancy (NV) centers in diamond are reported at conditions relevant for quantum applications. Bidirectional switching occurs between the neutral (NV(0)) and negatively charged (NV(-)) states. Luminescence of NV(-) is most efficiently triggered at a wavelength of 575 nm which ensures optimum excitation and recharging of NV(0). The dark state of NV(-) is identified as NV(0). A narrow resonance is observed in the excitation spectra at 521 nm, which mediates efficient conversion to NV(0).

Low temperature studies of the excited-state structure of negatively charged nitrogen-vacancy color centers in diamond.

We report a study of the 3E excited-state structure of single negatively charged nitrogen-vacancy (NV) defects in diamond, combining resonant excitation at cryogenic temperatures and optically detected magnetic resonance. A theoretical model is developed and shows excellent agreement with experimental observations. In addition, we show that the two orbital branches associated with the 3E excited state are averaged when operating at room temperature. This study leads to an improved physical understanding of the NV defect electronic structure, which is invaluable for the development of diamond-based quantum information processing.

What factors influence the results of coronary artery bypass grafting in aged patients?

AIM: Early and late results were studied in order to improve the indication for coronary artery bypass grafting (CABG) and to enhance METHODS: A total of 1 973 patients aged 70 years and older who had undergone isolated CABG were studied. Elective operations (EL) were performed in 1 716 patients and 257 patients underwent urgent or emergency operations (UR/EM). Patients were divided into two groups; 104 patients aged 80 years and older (Oct. Group) and 1 869 patients of septuagenarians (Sept. Group). There were no differences between the groups in the number of diseased vessels. RESULTS: Total operative mortality rates in the Oct. and the Sept. groups were 7% and 4%, respectively. The operative mortality of elective surgery was 4% in both groups. The operative mortality of UR/EM CABG was significantly higher in the Oct. group than in the Sept. group (21% vs 6%). Operative mortality was significantly higher in patients with preoperative poor (<49%) left ventricular ejection fraction (LVEF) than in patients with higher (>50%) LVEF (6% vs 3%). Among preoperative risk factors, diabetes mellitus and peripheral vascular disease were significant contributory factors to operative death. In the follow-up study, 70% patients of the Oct. group and 72% patients of the Sept. group survived. Preoperative number of diseased vessels and number of CABG grafts did not influence the early and late CONCLUSION: Preoperative poor LVEF, diabetes mellitus and peripheral vascular disease were significant contributory factors to operative death. When feasible, CABG in octogenarians should be performed electively.

Photon echoes produced by switching electric fields.

We demonstrate photon echoes in Eu3+:Y2SiO5 by controlling the inhomogeneous broadening of the Eu3+ 7F0<-->5D0 optical transition. This transition has a linear Stark shift, and we induce inhomogeneous broadening by applying an external electric field gradient. After optical excitation, reversing the polarity of the field rephases the ensemble, resulting in a photon echo. This is the first demonstration of such a photon echo, and its application as a quantum memory is discussed.

Stopped light with storage times greater than one second using electromagnetically induced transparency in a solid.

We report on the demonstration of light storage for times greater than a second in praseodymium doped Y2SiO5 using electromagnetically induced transparency. The long storage times were enabled by the long coherence times possible for the hyperfine transitions in this material. The use of a solid-state system also enabled operation with the probe and coupling beam counter-propagating, allowing easy separation of the two beams. The efficiency of the storage was low because of the low optical thickness of the sample; as is discussed, this deficiency should be easy to rectify.

Presenting behavioural genetics: spin, ideology, and our narrative interests.

A short review is given of the Nuffield Council's report on behavioural genetics. This review is used as an entry point to a discussion of the factors that influence the presentation of behavioural genetics in the media and in the popular scientific press. It is argued that our interest in formulating narrative explanations of our individual lives puts pressure on publishers and editors to present behavioural genetics in a selective, misleading, way. Some other influences on presentation are discussed and it is suggested that the Nuffield report is particularly useful in so far as it lacks these distorting influences.

Demonstration of conditional quantum phase shift between ions in a solid.

Because of their long coherence times, dopant ions have been considered promising candidates for scalable solid state quantum computing. Here we demonstrate a conditional phase shift between two qubits based on an optical transition of europium ions. The demonstration uses ensembles that have been selected from a randomly doped sample using spectral hole burning techniques. The electron dipole-dipole interaction between the ions that usually causes instantaneous spectral diffusion is used to generate the conditional phase shift.

Efficacy of calcium sulfate plus decompression bone in lumbar and lumbosacral spinal fusion: preliminary results in 40 patients.

OBJECTIVE: To compare the efficacy of calcium sulfate pellets plus bone obtained from decompression with fresh autologous iliac crest bone in lumbar and lumbosacral spinal fusion with decompression. DESIGN: A prospective randomized clinical trial. SETTING: Four tertiary care centres in Halifax, NS. PATIENTS: All were consenting, skeletally mature and suffering from degenerative disc disease or spondylolisthesis. The first 40 patients from a single test centre are reported; 32 of these had completed 1-year follow-up. INTERVENTIONS: Posterolateral lumbar or lumbosacral spinal fusion with spinal canal decompression and randomized placement of test material (decompression bone plus an equal volume of calcium sulfate pellets) on one side and control material (autologous posterior iliac crest bone of equal volume to the test material) on the contralateral side, which allowed subjects to act as their own control. OUTCOME MEASURES: Assessment of bone formation by radiographic evaluation at 6 and 12 months after fusion by an independent musculoskeletal radiologist blinded to the placement of test material. RESULTS: At 6 and 12 months after fusion, 78% and 88% of patients, respectively, showed bone formation at the test site that was 75% to 100% of, equal to or more than that at the control site. Increases in bone formation at 6 and 12 months were almost identical at both sites. Smoking status, patient gender or age, instrumentation used and volume of graft used were not predictive of outcome. CONCLUSIONS: Calcium sulfate pellets plus decompression bone provided bone formation equivalent to autologous iliac crest bone in a majority of patients. Calcium sulfate pellets plus decompression bone may provide a viable alternative to autologous iliac crest as a graft material for spinal fusion.

Telemedicine and the New Children's Hospital (Royal Alexandra Hospital for Children).

Telemedicine is an important factor in the future strategy of the Royal Alexandra Hospital for Children. As a state, national and international centre of excellence, it is the hospital's role to assist in the development of the best child health services. An important aim is to provide easy access to a full range of paediatric services through the provision of a comprehensive telemedicine service, which encompasses videoconferencing and tele-imaging, and positions the child as the centre of service provision. Experience so far suggests that in Australia, as in other countries, the adoption of telemedicine may outstrip the ability of the legislative and administrative frameworks to keep pace. Thus, the enablers appear to be cultural and technological while the obstacles are rooted in the way in which health systems are financed and administered.

The effect of hypochlorous acid and hydrogen peroxide on coronary flow and arrhythmogenesis in myocardial ischemia and reperfusion.

The purpose of this study was to investigate the effect of the oxidants hypochlorous acid (HOCl) and hydrogen peroxide (H2O2) on the vulnerability of the myocardium to reperfusion-induced arrhythmias following global ischemia. After a 15 min equilibration period with or without experimental intervention, isolated perfused rat hearts in the Langendorff mode were made globally ischemic for 5 min by cross-clamping the aortic line. No dysrhythmias were evoked upon reperfusion at the 5 min global ischemia time period. HOCl or H2O2 were added to the perfusate 5 min into the equilibration period with a total exposure of 10 min. Global ischemia was then induced for 5 min followed by 10 min of reperfusion. A dose-response curve for HOCl (50-200 microM) indicated the development of idioventricular rhythms, in a concentration-dependent way. Furthermore, coronary flow of the hearts exposed to 100 and 200 microM HOCl, at 5 min post-reperfusion, was decreased; methionine (10 microM to 1 mM), an accepted scavenger for HOCl, prevented the responses to 200 microM HOCl, in a concentration-dependent manner. All hearts exposed to 200 microM H2O2 developed ventricular dysrhythmias during the reperfusion period. Coronary flow increased after 5 min of exposure to 200 microM H2O2 and remained elevated during reperfusion. It is concluded that toxic oxygen derived products are capable of increasing the susceptibility of the myocardium to reperfusion induced arrhythmias, and that although the electrical responses to exposure to those two oxidants were similar, the effects on the vasculature were not the same.

Raman heterodyne detection of electron paramagnetic resonance.

We report the detection of an electron paramagnetic resonance signal using Raman heterodyne spectroscopy, a rf -optical double-resonance technique. The signals are associated with the nitrogen-vacancy center in diamond, which has a spin-triplet ground state. A three-line spectrum associated with the nitrogen hyperfine structure is observed for various magnetic field strengths and crystal orientations.

Raman heterodyne detected electron-nuclear-double-resonance measurements of the nitrogen-vacancy center in diamond.

We report two new applications of the Raman heterodyne detection technique. Raman heterodyne detected electron-nuclear double resonance and a double rf resonance technique are used to obtain the hyperfine structure of the nitrogen-vacancy center in diamond.

Differential effect of global ischemia on the ryanodine-sensitive and ryanodine-insensitive calcium uptake of cardiac sarcoplasmic reticulum.

The effect of ischemia on the function of cardiac sarcoplasmic reticulum (SR) was assessed by the calcium uptake rate of rat whole-heart homogenates in the presence of 10 mM oxalate. Previous studies have shown that this uptake is restricted to the SR. The contribution of the ryanodine-sensitive fractions of the SR to the total homogenate uptake was assessed by using 20 microM ruthenium red and 625 microM ryanodine to close the SR calcium release channel under previously established optimal conditions. Global ischemia of 10, 15, 30, and 60 minutes depressed homogenate calcium uptake rate 19 +/- 2%, 50 +/- 6%, 65 +/- 3%, and 81 +/- 5%, respectively. This decrease was not observed when the uptake rates were measured after closure of the calcium channel with ryanodine or ruthenium red. Similar results were obtained with a Langendorff in vitro perfusion preparation, in which calcium uptake was decreased 35 +/- 5%, 37 +/- 8%, 58 +/- 7%, and 64 +/- 4% after 10, 15, 30, and 60 minutes of ischemia, but no significant decrease was observed when homogenate uptake rates were measured in the presence of ryanodine. Thus, ischemia caused a depression in the calcium uptake rate of cardiac SR only when this activity was measured in the absence of SR calcium channel blockers. Reperfusion of ischemic hearts in a Langendorff preparation resulted in recovery of homogenate calcium uptake activity that correlated well with the return to sinus rhythm of the reperfused hearts. These reperfused hearts showed no change in the calcium uptake rate measured in the presence of ryanodine. These results suggest that the decrease in homogenate calcium uptake caused by ischemia is not due to a defect in calcium pumping capabilities but is due to an increased efflux through the ryanodine-sensitive calcium release channel of cardiac SR.

The rate and capacity of calcium uptake by sarcoplasmic reticulum in fast, slow, and cardiac muscle: effects of ryanodine and ruthenium red.

The rate and capacity of oxalate-supported calcium uptake was measured in homogenates of rat fast, slow, and cardiac muscle. The contribution of the releasing fraction of the sarcoplasmic reticulum (SR) to the calcium uptake abilities was estimated using ruthenium red or ryanodine to block the release channel. A relatively small fraction (12-20%) of the calcium pumping activity was associated with the release channel in skeletal muscle compared to 50% or more in cardiac muscle. The total capacity of the SR in the muscle types was in the ratio 1:0.75:1.5 for cardiac, slow, and fast muscle, respectively, while the rates of uptake were in the ratio 1:3.8:14.4. The major difference in the muscle types appears to be the density of pumping activity in the SR rather than the volume of the SR. The difference in the density of pumping activity is due to intrinsic differences in the kinetics of the calcium pump units and in their surface density.

Reperfusion-induced arrhythmias: characterization studies with the globally ischemic rat heart.

It has previously been demonstrated in the rat heart, in vivo and in vitro, with regional ischemia, that an asymmetric bell-shaped curve defines the relationship between the vulnerability to reperfusion-induced arrhythmias and the duration of the preceding period of ischemia. The present study sought to establish whether a similar relationship occurred with global ischemia and reperfusion. Using rats from three different sources (two British, one North American) it was observed that, when an appropriate duration of ischemia was selected, reperfusion was capable of eliciting a very high incidence (up to 100%) of ventricular fibrillation and ventricular tachycardia. In the first series of studies an asymmetric bell-shaped relationship was observed such that with reperfusion after 5, 10, 20, 25, 28, 30, 33, 37 and 45 mins 0, 8, 8, 8, 50, 58, 83, 33, 33 and 25% of hearts fibrillated, respectively (12 hearts per group). However, upon repeating the studies with groups of rats from other suppliers or different batches from the same supplier, different results were obtained. Thus, in some study groups a very high incidence of arrhythmia was observed with reperfusion after very short (7.5 mins) durations of ischemia and low incidences were sometimes obtained with reperfusion after 30 mins, a time which, in some study groups, elicited a very high (100%) incidence of severe arrhythmias. These results contrast strikingly with those obtained with regional ischemia where a highly reproducible profile for the incidence of arrhythmias is consistently observed.(ABSTRACT TRUNCATED AT 250 WORDS)