A Monte Carlo Method for Modeling Thermal Damping: Beyond the Brownian-Motion Master Equation

The "standard" Brownian motion master equation, used to describe thermal damping, is not completely positive, and does not admit a Monte Carlo method, important in numerical simulations. To eliminate both these problems one must add a term that generates additional position diffusion. He we show that one can obtain a completely positive simple quantum Brownian motion, efficiently solvable, without any extra diffusion. This is achieved by using a stochastic Schroedinger equation (SSE), closely analogous to Langevin's equation, that has no equivalent Markovian master equation. Considering a specific example, we show that this SSE is sensitive to nonlinearities in situations in which the master equation is not, and may therefore be a better model of damping for nonlinear systems.Comment: 6 pages, revtex4. v2: numerical results for a nonlinear syste

Instantaneous Bethe-Salpeter equation: utmost analytic approach

The Bethe-Salpeter formalism in the instantaneous approximation for the interaction kernel entering into the Bethe-Salpeter equation represents a reasonable framework for the description of bound states within relativistic quantum field theory. In contrast to its further simplifications (like, for instance, the so-called reduced Salpeter equation), it allows also the consideration of bound states composed of "light" constituents. Every eigenvalue equation with solutions in some linear space may be (approximately) solved by conversion into an equivalent matrix eigenvalue problem. We demonstrate that the matrices arising in these representations of the instantaneous Bethe-Salpeter equation may be found, at least for a wide class of interactions, in an entirely algebraic manner. The advantages of having the involved matrices explicitly, i.e., not "contaminated" by errors induced by numerical computations, at one's disposal are obvious: problems like, for instance, questions of the stability of eigenvalues may be analyzed more rigorously; furthermore, for small matrix sizes the eigenvalues may even be calculated analytically.Comment: LaTeX, 23 pages, 2 figures, version to appear in Phys. Rev.

Fiber-Cavity-Based Optomechanical Device

We describe an optomechanical device consisting of a fiber-based optical cavity containing a silicon nitiride membrane. In comparison with typical free-space cavities, the fiber-cavity's small mode size (10 {\mu}m waist, 80 {\mu}m length) allows the use of smaller, lighter membranes and increases the cavity-membrane linear coupling to 3 GHz/nm and quadratic coupling to 20 GHz/nm^2. This device is also intrinsically fiber-coupled and uses glass ferrules for passive alignment. These improvements will greatly simplify the use of optomechanical systems, particularly in cryogenic settings. At room temperature, we expect these devices to be able to detect the shot noise of radiation pressure.Comment: 4 pages, 3 figures; the following article has been submitted to Applied Physics Letter

Trained immunity or tolerance : opposing functional programs induced in human monocytes after engagement of various pattern recognition receptors

Article Accepted Date: 29 January 2014. ACKNOWLEDGMENTS D.C.I. received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement HEALTH-2010-260338 (“Fungi in the setting of inflammation, allergy and autoimmune diseases: translating basic science into clinical practices” [ALLFUN]) (awarded to M.G.N.). M.G.N. and J.Q. were supported by a Vici grant of the Netherlands Organization of Scientific Research (awarded to M.G.N.). This work was supported, in part, by National Institutes of Health grant GM53522 to D.L.W. N.A.R.G. was supported by the Wellcome Trust.Peer reviewedPublisher PD

Holocene Environmental Change in the Frobisher Bay Area, Baffin Island, N.W.T.: Deglaciation, Emergence, and the Sequence of Vegetation and Climate

The late-glacial and Holocene paleoenvironmental sequence for the Frobisher Bay area is outlined using glacial, sea level, and palynological evidence. A rapid retreat of ice from the late Foxe glacial maximum in the lower part of the bay after 11,000 BP was followed by a series of stillstands or minor readvances between ca. 8500 and 7000 BP and possibly later, before the final disappearance of the inland ice centred near Amadjuak Lake. Lithostratigraphy of three buried organic sections which together represent deposition occurring over the period from 5500 to 400 BP indicates a change from a relatively warm, moist environment before 5500 BP to neoglacial conditions, with the coldest phases centred around 5000, 2700, 1200 BP and probably sometime after 400 radiocarbon years BP. As evidenced by peat growth and pollen data, milder, wetter conditions prevailed from 4500 to 3000 BP and again from ca. 2600 to 1800 BP. Peat growth and soil organic fractions point to lesser mild intervals ca. 900 BP and 400 BP, but these are not apparent in the pollen assemblage. The pollen record does not extend to the last four centuries; however, lichenometric studies of neoglacial moraines by DOWDESWELL (1984) show that the maximum late Holocene advance of glaciers in the area occurred within the last century. Modern pollen samples indicate that the present vegetation of the inner Frobisher Bay area is comparable to that of the milder intervals of the late Holocene.La présente étude porte sur l'évolution paléoenvironnementale fini-glaciaire et holocène de la région de la baie de Frobisher et se fonde sur les niveaux marins ainsi que sur des témoins polliniques et glaciaires. Le retrait rapide des glaciers dans la partie intérieure de la baie depuis 11 000 BP a été suivi d'épisodes de stabilité et de récurrences mineures entre 8500 et 7000 ans BP. et peut-être plus tard, avant la disparition définitive des glaces continentales dont le centre se trouvait près du lac Amadjuak. L'analyse a porté sur trois sections de sol enfoui qui représentent les dépôts accumulés entre 5500 et 400 ans BP. La lithostratigraphie révèle le passage d'un climat relativement humide et chaud, il y a plus de 5500 ans, à un climat néoglaciaire dont les périodes les plus froides se situent vers 5000, 2700 et 1200 ans BP et probablement après 400 ans BP. La tourbe et les données polliniques témoignent de conditions climatiques plus douces et plus humides pour les périodes allant de 4500 à 3000 ans BP et d'environ 2600 à 1800 ans BP. Mais, contrairement aux associations polliniques, la tourbe et certaines portions organiques de sol font penser qu'ont existé des intervalles plus frais environ de 900 à 400 ans BP. Les données pollinique ne donnent aucun renseignement sur les quatre derniers siècles. Cependant, les études Ii-chénométriques que DOWDESWELL (1984) a faites sur les moraines néoglaciaires révèlent que, dans la région pendant l'Holocène supérieur, l'avancée maximale des glaces s'est produite au siècle dernier. Des échantillons polliniques récents démontrent que la végétation actuelle de l'intérieur de la baie de Frobisher ressemble à celle qu'on trouvait pendant les intervalles tempérés de l'Holocène supérieur.Die spàtglaziale und holozàne Abfolge des Palâomilieus im Gebiete der Frobisher Bucht wird durch glaziale, Meeresspiegel- und palynologische Beweise umrissen. Ein rasches Zurùckweichen des Eises aus dem niederen Teil der Bucht hat sich nach 11 000 BP ereignet. gefolgt von mehreren Stillstânden oder kleinerem Wiedervorrùcken zwischen etwa 8500 und 7000 BP oder evtl. spater, bevor das Inlandeis schliesslich verschwunden ist. Drei verdeckte Bodenprofile sind analysiert worden, die zu-sammen die Ablagerung der Zeit von 5500 bis 400 BP darstellen. Die Lithostratigraphie hat eine relativ warme, feuchte Umgebung vor 5500 BP ergeben, die sich alsdann zu neoglazialen Zustânden geàndert hat, mit dem Mittel der kâltesten Phasen um etwa 5000, 2700, und wahrscheinlich auch irgandwann nach 400 Radiokohlenstoffjahren BP. Torfwuchs sowie auch palynologische Daten zeigen, dass milde, feuchte Zustânde von 4500 bis 3000 BP und dann nochmals von etwa 2600 bis 1800 BP vorgeherrscht haben. Der Torfwuchs und der organische Anteil des Bodens deuten auch auf kleinere milde Zeitspannen um etwa 900 und 400 BP, aber dièse sind nicht aus der Pollenvergesellschaftung ersichtlich. Fur die jùngsten vier Jahrhunderte fehlen Pollenunterlagen; aber durch Untersuchung der Flechten auf neoglazialen Morânen hat DOWDESWELL (1984) fur dieses Gebiet ein spatholozànes Gletschervorrùcken wahrend des letzten Jahrhunderts belegen konnen. Pollenmuster beweisen. dass sich im Gebiet der inneren Frobisher Bucht die heutige Pflanzendecke gut mit der Vegetation mlldererer Spâtholozànintervalle vergleichen làsst

Optimal control of entanglement via quantum feedback

It has recently been shown that finding the optimal measurement on the environment for stationary Linear Quadratic Gaussian control problems is a semi-definite program. We apply this technique to the control of the EPR-correlations between two bosonic modes interacting via a parametric Hamiltonian at steady state. The optimal measurement turns out to be nonlocal homodyne measurement -- the outputs of the two modes must be combined before measurement. We also find the optimal local measurement and control technique. This gives the same degree of entanglement but a higher degree of purity than the local technique previously considered [S. Mancini, Phys. Rev. A {\bf 73}, 010304(R) (2006)].Comment: 10 pages, 5 figure

Practical free-space quantum key distribution over 1 km

A working free-space quantum key distribution (QKD) system has been developed and tested over an outdoor optical path of ~1 km at Los Alamos National Laboratory under nighttime conditions. Results show that QKD can provide secure real-time key distribution between parties who have a need to communicate secretly. Finally, we examine the feasibility of surface to satellite QKD.Comment: 5 pages, 2 figures, 2 tables. Submitted to Physics Review Letters, May 199

Standard Quantum Limits for broadband position measurement

I utilize the Caves-Milburn model for continuous position measurements to formulate a broadband version of the Standard Quantum Limit (SQL) for monitoring the position of a free mass, and illustrate the use of Kalman filtering to recover the SQL for estimating a weak classical force that acts on a quantum-mechanical test particle under continuous observation. These derivations are intended to clarify the interpretation of SQL's in the context of continuous quantum measurement.Comment: Replaced version: changed title, fixed algebra error at the very end, conclusions modified accordingly. Four pages, one eps figur

Information Tradeoff Relations for Finite-Strength Quantum Measurements

In this paper we give a new way to quantify the folklore notion that quantum measurements bring a disturbance to the system being measured. We consider two observers who initially assign identical mixed-state density operators to a two-state quantum system. The question we address is to what extent one observer can, by measurement, increase the purity of his density operator without affecting the purity of the other observer's. If there were no restrictions on the first observer's measurements, then he could carry this out trivially by measuring the initial density operator's eigenbasis. If, however, the allowed measurements are those of finite strength---i.e., those measurements strictly within the interior of the convex set of all measurements---then the issue becomes significantly more complex. We find that for a large class of such measurements the first observer's purity increases the most precisely when there is some loss of purity for the second observer. More generally the tradeoff between the two purities, when it exists, forms a monotonic relation. This tradeoff has potential application to quantum state control and feedback.Comment: 15 pages, revtex3, 3 eps figure