Effect of Loss on Multiplexed Single-Photon Sources

An on-demand single-photon source is a key requirement for scaling many optical quantum technologies. A promising approach to realize an on-demand single-photon source is to multiplex an array of heralded single-photon sources using an active optical switching network. However, the performance of multiplexed sources is degraded by photon loss in the optical components and the non-unit detection efficiency of the heralding detectors. We provide a theoretical description of a general multiplexed single-photon source with lossy components and derive expressions for the output probabilities of single-photon emission and multi-photon contamination. We apply these expressions to three specific multiplexing source architectures and consider their tradeoffs in design and performance. To assess the effect of lossy components on near- and long-term experimental goals, we simulate the multiplexed sources when used for many-photon state generation under various amounts of component loss. We find that with a multiplexed source composed of switches with ~0.2-0.4 dB loss and high efficiency number-resolving detectors, a single-photon source capable of efficiently producing 20-40 photon states with low multi-photon contamination is possible, offering the possibility of unlocking new classes of experiments and technologies.Comment: Journal versio

Towards a Molecular Inventory of Protostellar Discs

The chemical environment in circumstellar discs is a unique diagnostic of the thermal, physical and chemical environment. In this paper we examine the structure of star formation regions giving rise to low mass stars, and the chemical environment inside them, and the circumstellar discs around the developing stars.Comment: 9 page PDF, 550 kbyte

Managerial Attitutes Toward Industrial Relations : Public and Private Sectors

Le passage, en matière de fixation des traitements et des conditions de travail, des politiques de la Fonction publique à la négociation collective, s'est fait rapidement. Cependant, les décisions-clés à l'origine de ce changement furent l'oeuvre d'hommes politiques qui ont agi sans connaître les sentiments des cadres moyens sur la question. D'autres études ont montré que les vues des cadres fonctionnels sur le syndicalisme et la négociation collective pouvaient avoir une influence considérable sur la qualité des relations professionnelles. La proximité des cadres de la direction pouvait disposer ceux-ci en faveur des relations professionnelles, mais pas nécessairement davantage que dans le secteur privé. Par contre, la nouveauté de la négociation collective dans la fonction publique incline à première vue à penser que les cadres y auraient montré plus de résistance que leurs collègues de l'industrie privée, où la négociation collective y a une plus longue histoire.Une enquête antérieure concernant les attitudes patronales en matière de négociation collective était fondée sur un échantillonnage tiré du secteur privé. On y avaittrouvé un sectionnement entre deux facteurs, c'est-à-dire que les réactions étaient différentes selon qu'il était question des aspectsinstitutionnels ouopérationnels des relations du travail. Cet article reprend l'étude antérieure en comparant les attitudes des cadres du secteur privé et celles des cadres de la fonction publique. Les deux échantillonnages étaient autant que possible similaires, chacun comportant un questionnaire en sept points auquel on pouvait répondre en se déclarant d'accord ou en désaccord.On y retrouve le même fractionnement. Les réponses de l'un et de l'autre échantillonnage ne diffèrent pas sur les deux points où il était question de l'aspectinstitutionnel des relations professionnelles, mais les cadres de la fonction publique étaient plus enclins à accepter le rôle nécessaire et important de la négociation collective et du syndicalisme. Les cadres de la fonction publique se sont montrés plus favorables que leurs collègues du secteur privé au sujet de l'aspectopérationnel des relations de travail.Les cadres de la fonction publique semblent réagir d'une façon plus positive que les cadres du secteur privé à la négociation collective et ils montrent moins de scepticisme et de désenchantement envers les syndicats, envers leurs revendications et envers leurs tactiques. Le degré élevé d'acceptation des aspectsinstitutionnels des relations professionnelles est conforme au développement rapide de la négociation collective dans le secteur public. Cette constatation augure bien en ce qui a trait à l'établissement de relations professionnelles harmonieuses dans la fonction publique.Il n'existe pas d'explications toutes faites à l'attitude généralement plus favorable des cadres de la fonction publique. On peut y aller de quelques hypothèses: la tradition de consultation sous les anciens systèmes en vigueur dans la fonction publique et la stabilité des budgets.Cette étude est la troisième où l'on a découvert ce phénomène du fractionnement des attitudes des cadres au sujet des relations professionnelles, ce qui donne encore plus de poids à l'existence de conceptsinstitutionnels etopérationnels dans le domaine des relations de travail.The authors analyse possible differences in managerial attitudes toward unionism and collective bargaining in the public and private sectors in Canada. Distinct patterns of attitudes emerge showing more favorable views in the public se et or

To germinate or not to germinate: more than just a question of dormancy

Consider the following four quotations concerning the distinction between breaking dormancy and stimulating germination

Preservation of Garnet Growth Zoning and the Duration of Prograde Metamorphism

Chemically zoned garnet growth and coeval modification of this zoning through diffusion are calculated during prograde metamorphic heating to temperatures of up to 850°C. This permits quantification of how the preservation or elimination of zoning profiles in garnet crystals of a given size is sensitive to the specific burial and heating (P-T) path followed, and the integrated duration spent at high temperature (dT/dt). Slow major element diffusion in garnet at T 30 Myr at amphibolite-grade conditions, but small-scale (tens of micrometres) zoning features will be lost early in the prograde stage unless this is ‘rapid' (5 Myr for rocks reaching c. 600°C). Calculations indicate that preservation of unmodified growth compositions in even relatively large (up to 3 mm diameter) pelitic garnet crystals requires prograde and exhumational events to be <10 Myr for rocks reaching c. 600°C. This timescale can be 5 Myr for garnet in rocks reaching 650°C or hotter. It is likely, therefore, that most natural prograde-zoned crystals record compositions already partially re-equilibrated between the time of crystal growth and of reaching maximum temperature. However, a large T-t window exists within which crystals begin to lose their growth compositions but retain evidence of crystal-scale zoning trends that may still be useful for thermobarometry purposes. The upper limit of this window for 500 μm diameter crystals can be as much as several tens of millions of years of heating to c. 700°C. Absolute re-equilibration timescales can be significantly different for garnet growing in different rock compositions, with examples of a granodiorite and a pelite give

Characterizing precursors to stellar clusters with Herschel

Context. Despite their profound effect on the universe, the formation of massive stars and stellar clusters remains elusive. Recent advances in observing facilities and computing power have brought us closer to understanding this formation process. In the past decade, compelling evidence has emerged that suggests infrared dark clouds (IRDCs) may be precursors to stellar clusters. However, the usual method for identifying IRDCs is biased by the requirement that they are seen in absorption against background mid-IR emission, whereas dust continuum observations allow cold, dense pre-stellar-clusters to be identified anywhere. Aims: We aim to understand what dust temperatures and column densities characterize and distinguish IRDCs, to explore the population of dust continuum sources that are not IRDCs, and to roughly characterize the level of star formation activity in these dust continuum sources. Methods: We use Hi-GAL 70 to 500 $m data to identify dust continuum sources in the ell = 30deg and ell = 59deg Hi-GAL science demonstration phase (SDP) fields, to characterize and subtract the Galactic cirrus emission, and perform pixel-by-pixel modified blackbody fits on cirrus-subtracted Hi-GAL sources. We utilize archival Spitzer data to indicate the level of star-forming activity in each pixel, from mid-IR-dark to mid-IR-bright. Results: We present temperature and column density maps in the Hi-GAL ell = 30deg and ell = 59deg SDP fields, as well as a robust algorithm for cirrus subtraction and source identification using Hi-GAL data. We report on the fraction of Hi-GAL source pixels which are mid-IR-dark, mid-IR-neutral, or mid-IR-bright in both fields. We find significant trends in column density and temperature between mid-IR-dark and mid-IR-bright pixels; mid-IR-dark pixels are about 10 K colder and have a factor of 2 higher column density on average than mid-IR-bright pixels. We find that Hi-GAL dust continuum sources span a range of evolutionary states from pre- to star-forming, and that warmer sources are associated with more star formation tracers. Additionally, there is a trend of increasing temperature with tracer type from mid-IR-dark at the coldest, to outflow/maser sources in the middle, and finally to 8 and 24$m bright sources at the warmest. Finally, we identify five candidate IRDC-like sources on the far-side of the Galaxy. These are cold (20 K), high column density (N(H$_2$) gt 10$^22$ cm$^-2$) clouds identified with Hi-GAL which, despite bright surrounding mid-IR emission, show little to no absorption at 8 $m. These are the first inner Galaxy far-side candidate IRDCs of which the authors are aware. Herschel in an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation by NASA.The FITS files discussed in the paper would be released publicly WITH the Hi-GAL data (on the Hi-GAL website) when the Hi-GAL data is released publicly.Peer reviewe