Narrowband Photon Pair Source for Quantum Networks

We demonstrate a compact photon pair source based on a periodically poled lithium niobate nonlinear crystal in a cavity. The cavity parameters are chosen such that the emitted photon pair modes can be matched in the region of telecom ultra dense wavelength division multiplexing (U-DWDM) channel spacings. This approach provides efficient, low-loss, mode selection that is compatible with standard telecommunication networks. Photons with a coherence time of 8.6 ns (116 MHz) are produced and their purity is demonstrated. A source brightness of 134 pairs(s.mW.MHz)$^{-1}$ is reported. The high level of purity and compatibility with standard telecom networks is of great importance for complex quantum communication networks

CONTROL OF END-TIDAL HALOTHANE CONCENTRATION: Part B: Verification in Dogs

Conventional anaesthetic techniques do not allow for the automatic control of end-tidal halothane concentration and, therefore, brain concentration cannot be predicted. In this study, eight dogs were ventilated with halothane in oxygen using a new closed-loop anaesthetic breathing system which provided a constant end-tidal concentration. During the first 60 min the end-tidal concentration was maintained at 0.87 vol% (1 MAC). Then followed 60 min of halothane wash-out and a further 120-min period of halothane at 1.74 vol% (2 MAC). Halothane concentrations were measured in the inspired and expired air, and in the arterial, cerebral venous and mixed venous blood. Haemodynamic and respiratory variables were measured. The system reached 95% of the target end-tidal concentration within 6 min without over-shooting. After 2 h of wash-in, significant gradients still persisted between end-tidal, arterial and cerebral venous blood concentrations. Measured uptake differed from theoretically calculated uptake by 18.3-57.6%, depending on the model used. Measured arterial and cerebral venous concentrations differed from theoretically calculated values by 7% and 17.5%, respectively. It was shown that the required end-tidal concentrations can be obtained rapidly and accurately, and that brain tissue concentrations can be predicted within certain limit

Detector imperfections in photon-pair source characterization

We analyze how imperfections in single-photon detectors impact the characterization of photon-pair sources. We perform exact calculations to reveal the effects of multi-pair emissions and of noisy, non-unit efficiency, non photon-number resolving detections on the Cauchy-Schwarz parameter, on the second order auto-correlation and cross-correlation functions, and on the visibilities of both Hong-Ou-Mandel and Bell-like interferences. We consider sources producing either two-mode squeezed states or states with a Poissonian photon distribution. The proposed formulas are useful in practice to determine the impacts of multi-pair emissions and dark counts in standard tests used in quantum optics.Comment: 9 pages, 11 figure

IS THE END-TIDAL PARTIAL PRESSURE OF ISOFLURANE A GOOD PREDICTOR OF ITS ARTERIAL PARTIAL PRESSURE?

End-tidal partial pressure of isoflurane (PE′iso) may be used as a measure of anaesthetic depth. During uptake, an arterial partial pressure (Paiso) which is considerably less than PE′iso(Paiso/PE′iso<<1) leads to underestimation of depth of anaesthesia and, during elimination, PE′iso/Paiso<<1 will lead to an overestimation of anaesthetic depth. We measured Paiso/PE′iso during a 60-min uptake period of 1% isoflurane and PE′iso/Paiso during the subsequent 60-min elimination period in 26 patients (age 13-88 yr, ASA I-III) undergoing various surgical procedures. After 15 min of isoflurane uptake, Paiso/PE′iso of 26 patients was mean 0.78 (SD 0.10) and this increased only marginally at 60 min (0.79 (0.09)), whereas during elimination, PE′iso/Paiso was in the range 0.79 (0.14)-0.83 (0.11). Predictability of Paiso in a given patient is hindered by the high SD of Paiso/PE′iso and PE′iso/Paiso, but it may be improved by taking into account age, ASA physical status category, vital capacity, inspired minus end-tidal isoflurane partial pressure and arterial minus end-tidal carbon dioxide partial pressure during uptake; and obesity, end-tidal isoflurane partial pressure and arterial minus end-tidal carbon dioxide partial pressure during elimination. However, even with multiple regression analysis (to account for the various possible variables), clinically useful prediction of Paiso/PE′iso and PE′iso/Paiso in a particular patient is not possible (residual SD 0.084 and 0.113, respectively

Two independent photon pairs versus four-photon entangled states in parametric down conversion

We study the physics of four-photon states generated in spontaneous parametric down-conversion with a pulsed pump field. In the limit where the coherence time of the photons t_c is much shorter than the duration of the pump pulse Delta t, the four photons can be described as two independent pairs. In the opposite limit, the four photons are in a four-particle entangled state. Any intermediate case can be characterized by a single parameter chi, which is a function of t_c/Delta t. We present a direct measurement of chi through a simple experimental setup. The full theoretical analysis is also provided.Comment: 10 pages, 3 figures, submitte

DETERMINATION OF THE PARTIAL PRESSURE OF HALOTHANE (OR ISOFLURANE) IN BLOOD

A gas chromatographic method is described for the direct quantitative determination of the partial pressure of halothane {or isoflurane) in blood as well as the blood-gas partition coefficient. A head space technique and a flame ionization detector were used. Standard blood was obtained by equilibrating patients' blood with known gas concentrations in a tonometer. Using an infra-red analyser to measure the halothane gas concentration in the tonometer and within the anaesthetic system allowed for the direct comparison of the partial pressure in blood to the partial pressure in the inspired gas. Technical problems associated with this procedure, and with comparable methods, are discusse

Prediction of the haemodynamic response to tracheal intubation: comparison of laser-Doppler skin vasomotor reflex and pulse wave reflex

Background. The laser-Doppler skin vasomotor reflex (SVmR) caused by tetanic stimulation of the ulnar nerve may be a test that can predict the haemodynamic response to tracheal intubation. A decrease in pulse wave amplitude (pulse wave reflex, PWR) may be an alternative index of this response. We compared the abilities of PWR and SVmR to predict the haemodynamic response to tracheal intubation and studied how alfentanil, muscle relaxation, stimulation site and stimulation pattern affected the two reflexes. Methods. Anaesthesia was induced and maintained with 2% sevoflurane and 50% nitrous oxide in two groups of 10 ASA status I patients. Tetanic stimuli were applied to the flexor muscles of the forearm and the ulnar nerve before and after administration of vecuronium. The change in skin blood flow (laser-Doppler) and pulse wave amplitude (pulse oximetry) after a 5 and 10 s stimulation was measured on the opposite hand. If skin blood flow (laser-Doppler) decreased by more than 10%, a computer-controlled infusion of alfentanil was started and the target plasma concentration was increased in steps until this response was suppressed (<10%). The trachea was intubated and arterial pressure and heart rate responses were recorded. Plasma alfentanil concentration was measured. Results. When PWR and SVmR were suppressed, the haemodynamic response to tracheal intubation was reduced in 100 and 53% of patients respectively. PWR and SVmR responses decreased with increasing plasma alfentanil concentration. The SVmR response to muscle stimulation was reduced by muscle relaxants. The pulse wave response to both muscle and neural stimulation was reduced by relaxants. The responses to 5 and 10 s stimulations were similar. Conclusion. An absent SVmR does not predict a blunted arterial pressure or heart rate response to tracheal intubation. The PWR may be a better predicto

An indicator of sudden cardiac death during brief coronary occlusion: electrocardiogram QT time and the role of collaterals

Aims The coronary collateral circulation has a beneficial role regarding all-cause and cardiac mortality. Hitherto, the underlying mechanism has not been clarified. The aim of this prospective study was to assess the effect of the coronary collateral circulation on electrocardiogram (ECG) QTc time change during short-term myocardial ischaemia. Methods and results A total of 150 patients (mean age 63 ± 11 years, 38 women) were prospectively included in this study. An ECG was recorded at baseline and during a standardized 1 min coronary balloon occlusion. QT interval was measured before, during, and after balloon occlusion and was corrected for heart rate (QTc). Simultaneously obtained collateral flow index (CFI), expressing collateral flow relative to normal anterograde flow, was determined based on intracoronary pressure measurements. During occlusion of the left anterior descending coronary artery mean QTc interval increased from 422 ± 33 to 439 ± 36 ms (P < 0.001), left circumflex occlusion led to an increase from 414 ± 32 to 427 ± 27 ms (P < 0.001). QTc was not influenced by occlusion of the right coronary artery (RCA) (417 ± 35 and 415 ± 34 ms, respectively; P = 0.863). QTc change during occlusion of the left coronary artery was inversely correlated with CFI (R2 = 0.122, P = 0.0002). Conclusion Myocardial ischaemia leads to QT prolongation during a controlled 1 min occlusion of the left, but not the RCA. QT prolongation is inversely related to collateral function indicating a protective mechanism of human coronary collaterals against cardiac deat