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Biomedical subjects

W P Bowen

Publications and source records attributed to W P Bowen.

10 recordsLinked to original sources
PubMed2006

Observation of strong coupling between one atom and a monolithic microresonator.

Over the past decade, strong interactions of light and matter at the single-photon level have enabled a wide set of scientific advances in quantum optics and quantum information science. This work has been performed principally within the setting of cavity quantum electrodynamics with diverse physical systems, including single atoms in Fabry-Perot resonators, quantum dots coupled to micropillars and photonic bandgap cavities and Cooper pairs interacting with superconducting resonators. Experiments with single, localized atoms have been at the forefront of these advances with the use of optical resonators in high-finesse Fabry-Perot configurations. As a result of the extreme technical challenges involved in further improving the multilayer dielectric mirror coatings of these resonators and in scaling to large numbers of devices, there has been increased interest in the development of alternative microcavity systems. Here we show strong coupling between individual caesium atoms and the fields of a high-quality toroidal microresonator. From observations of transit events for single atoms falling through the resonator's evanescent field, we determine the coherent coupling rate for interactions near the surface of the resonator. We develop a theoretical model to quantify our observations, demonstrating that strong coupling is achieved, with the rate of coherent coupling exceeding the dissipative rates of the atom and the cavity. Our work opens the way for investigations of optical processes with single atoms and photons in lithographically fabricated microresonators. Applications include the implementation of quantum networks, scalable quantum logic with photons, and quantum information processing on atom chips.

Journal Article↗
PubMed2006

Squeezed-state purification with linear optics and feedforward.

A scheme for optimal and deterministic linear optical purification of mixed squeezed Gaussian states is proposed and experimentally demonstrated. The scheme requires only linear optical elements and homodyne detectors, and allows the balance between purification efficacy and squeezing degradation to be controlled. One particular choice of parameters gave a tenfold reduction of the thermal noise with a corresponding squeezing degradation of only 11%. We prove optimality of the protocol, and show that it can be used to enhance the performance of quantum informational protocols such as dense coding and entanglement generation.

Journal Article↗
PubMed2003

Generation of nonclassical photon pairs for scalable quantum communication with atomic ensembles.

Quantum information science attempts to exploit capabilities from the quantum realm to accomplish tasks that are otherwise impossible in the classical domain. Although sufficient conditions have been formulated for the physical resources required to achieve quantum computation and communication, there is a growing understanding of the power of quantum measurement combined with the conditional evolution of quantum states for accomplishing diverse tasks in quantum information science. For example, a protocol has recently been developed for the realization of scalable long-distance quantum communication and the distribution of entanglement over quantum networks. Here we report the first enabling step in the realization of this protocol, namely the observation of quantum correlations for photon pairs generated in the collective emission from an atomic ensemble. The nonclassical character of the fields is demonstrated by the violation of an inequality involving their normalized correlation functions. Compared to previous investigations of non-classical correlations for photon pairs produced in atomic cascades and in parametric down-conversion, our experiment is distinct in that the correlated photons are separated by a programmable time interval (of about 400 nanoseconds in our initial experiments).

Journal Article↗
PubMed2003

Experimental investigation of criteria for continuous variable entanglement.

We generate a pair of entangled beams from the interference of two amplitude squeezed beams. The entanglement is quantified in terms of EPR paradox and inseparability criteria, with both results clearly beating the standard quantum limit. We experimentally analyze the effect of decoherence on each criterion and demonstrate qualitative differences. We also characterize the number of required and excess photons present in the entangled beams and provide contour plots of the efficacy of quantum information protocols in terms of these variables.

Journal Article↗
PubMed2000

Measurement of cytochrome P450 gene induction in human hepatocytes using quantitative real-time reverse transcriptase-polymerase chain reaction.

Drug-induced changes in expression of cytochrome (CYP) P450 genes are a key cause of drug-drug interactions. Consequently, preclinical prediction of these changes by novel compounds is an integral component of drug development. To date, in vitro models of CYP induction have used mRNA measurement, immunodetection, and substrate metabolism as reporters. Here, we describe the application of quantitative real-time reverse transcriptase polymerase chain reaction to study CYP1A1 and CYP3A4 gene induction in 5-day-old cultures of human hepatocytes by known CYP inducers. After 5 days in culture, CYP1A1 expression was significantly elevated (5.1- to 26-fold; P <.01) in all four livers studied. In direct contrast, CYP3A4 mRNA levels consistently decreased during culture (80- to 300-fold; P <.001). In three independent experiments, a 48-h exposure to 3-methylcholanthrene, omeprazole, and lansoprazole significantly induced CYP1A1 expression in comparison to untreated cultures (P <.05). Rifampicin and solvent were without effect on CYP1A1 expression. Under identical experimental conditions, rifampicin and lansoprazole significantly elevated CYP3A4 mRNA expression (P <.05), whereas 3-methylcholanthrene, omeprazole, and dimethyl sulfoxide were without significant effect. These data demonstrate the applicability of quantitative reverse transcriptase polymerase chain reaction to the determination of gene dynamics in human hepatocytes. This offers a highly specific alternative to quantification of drug effects on CYP expression using immunodetection and substrate metabolism.

Base Sequence↗
PubMed1998

Identification of the L-menthol binding site in guinea-pig lung membranes.

1. L-Menthol inhibits both neurokinin A and capsaicin-induced bronchoconstriction in the guinea-pig and relaxes pre-constricted guinea-pig isolated bronchi. Structure-activity relationships have been defined for the action of (-)-menthol and related compounds on cold receptors, suggesting an action of L-menthol at a pharmacological receptor. We have performed radioligand binding studies to characterize the binding sites for [3H]-L-menthol in whole cell membranes prepared from guinea-pig lung tissue. 2. In kinetic studies. [3H]-L-menthol was found to bind rapidly and reversibly. Binding of [3H]-L-menthol to lung membranes was found to be time-dependent becoming fully associated to its site within 40 min, and half-maximum association occurred within 8 min (t1/2=8 min). [3H]-L-menthol was fully dissociated from its binding site within 8 min, (t1/2=2 min). 3. Inhibition studies presented a pharmacological profile of the 'L-menthol site'. Capsaicin, capsazepine, D-menthol, eugenol, SCH23390 and camphor were all found to displace [3H]-L-menthol binding. In contrast WS3, noradrenaline, 5-hydroxytryptamine, spiperone, flunarazine, bepridil and nicardipine were without effect. 4. We have identified a L-menthol binding site in the guinea-pig, which may represent a site common to a variety of compounds.

Animals↗
PubMed1995

Nonlinear regression using spreadsheets.

Pharmacologists are often required to analyse nonlinear experimental effects by fitting the data to defined theoretical models. This may require a specialized computer program capable of performing nonlinear regression analysis, which can prove costly given the variety of pharmacological research. Here, Wayne Bowen and Jeff Jerman describe a generic method of performing nonlinear regression using spreadsheet applications, and demonstrate how this approach can be used to create automated systems of data analysis.

Algorithms↗
PubMed1992

Regional and interspecific differences in the ligand binding properties of beta-adrenergic receptors of individual white adipose tissue depots in the sheep and rat.

The ligand binding of beta-adrenergic receptors was characterized in the omental, subcutaneous and popliteal adipose tissue depots in the sheep, and the lumbar and parametrial depots in the rat. Displacement of [125I]iodocyanopindolol ([125I]ICYP) binding to sheep adipose tissue membranes by the beta-adrenergic antagonists CGP 20712A and ICI 118,551 (beta 1- and beta 2-antagonists, respectively) suggested only a single ligand binding site predominantly beta 2 in character in all three depots, but revealed differences in affinity for these ligands between depots. Lactation increased beta-receptor ligand binding in subcutaneous and omental but not popliteal sheep adipose tissue depots, but had no effect on beta-adrenergic receptor affinities for CGP 20712A and ICI 118,551 in the three sheep adipose tissue depots studied. In rat adipocyte membranes, displacement of [125I]ICYP by CGP 20712A and ICI 118,551 was biphasic, indicating high and low affinity sites; displacement profiles differed markedly between lumbar and parametrial depots, the former having a preponderance of beta 1-like receptors and the latter a preponderance of beta 2-like receptors. The properties of the beta-adrenergic receptor binding site thus show species and depot specific differences.

Adipose Tissue↗