Optically mediated nonlinear quantum optomechanics

We consider theoretically the optomechanical interaction of several mechanical modes with a single quantized cavity field mode for linear and quadratic coupling. We focus specifically on situations where the optical dissipation is the dominant source of damping, in which case the optical field can be adiabatically eliminated, resulting in effective multimode interactions between the mechanical modes. In the case of linear coupling, the coherent contribution to the interaction can be exploited e.g. in quantum state swapping protocols, while the incoherent part leads to significant modifications of cold damping or amplification from the single-mode situation. Quadratic coupling can result in a wealth of possible effective interactions including the analogs of second-harmonic generation and four-wave mixing in nonlinear optics, with specific forms depending sensitively on the sign of the coupling. The cavity-mediated mechanical interaction of two modes is investigated in two limiting cases, the resolved sideband and the Doppler regime. As an illustrative application of the formal analysis we discuss in some detail a two-mode system where a Bose-Einstein condensate is optomechanically linearly coupled to the moving end mirror of a Fabry-P\'erot cavity.Comment: 11 pages, 8 figure

Passage-time statistics of superradiant light pulses from Bose-Einstein condensates

We discuss the passage-time statistics of superradiant light pulses generated during the scattering of laser light from an elongated atomic Bose-Einstein condensate. Focusing on the early-stage of the phenomenon, we analyze the corresponding probability distributions and their scaling behaviour with respect to the threshold photon number and the coupling strength. With respect to these parameters, we find quantities which only vary significantly during the transition between the Kapitza Dirac and the Bragg regimes. A possible connection of the present observations to Brownian motion is also discussed.Comment: Close to the version published in J. Phys.

Infection levels and species diversity of ascaridoid nematodes in Atlantic cod, Gadus morhua, are correlated with geographic area and fish size

Atlantic cod (Gadus morhua) is among the most important commercial fish species on the world market. Its infection by ascaridoid nematodes has long been known, Pseudoterranova even being named cod worm. In the present study, 755 individuals were sampled in the Barents, Baltic and North Seas during 2012–2014. Prevalences for Anisakis in whole fish and in fillets in the different fishing areas varied from 16 to 100% and from 12 to 90% respectively. Abundance was also greatly influenced by the sampling area. Generalized additive model results indicate higher numbers of Anisakis in the North Sea, even after the larger body size was accounted for. Numbers and prevalence of Anisakis were positively related to fish length or weight. The prevalence of parasites in whole fish and in fillets was also influenced by the season, with the spring displaying a peak for the prevalence in whole fish and, at the same time, a drop for the prevalence in fillets. Whereas 46% of cod had Anisakis larvae in their fillets, the majority (39%) had parasites mainly in the ventral part of the fillet and only 12% had parasites in their dorsal part. This observation is of importance for the processing of the fish. Indeed, the trimming of the ventral part of the cod fillet would allow the almost total elimination of ascaridoids except for cod from the Baltic Sea where there was no difference between the dorsal and the ventral part. The presence of other ascaridoid genera was also noticeable in some areas. For Pseudoterranova, the highest prevalence (45%) in whole fish was observed in the Northern North Sea, whereas the other areas had prevalences between 3 and 16%. Contracaecum was present in every commercial size cod sampled in the Baltic Sea with an intensity of up to 96 worms but no Contracaecum was isolated from the Central North Sea. Non-zoonotic Hysterothylacium was absent from the Baltic Sea but with a prevalence of 83% in the Barents and the Northern North Sea. A subsample of worms was identified with genetic-molecular tools and assigned to the species A. simplex (s.s.), A. pegreffii, P. decipiens (s.s.), P. krabbei, C. osculatum and H. aduncum. In addition to high prevalence and abundance values, the cod sampled in this study presented a diversity of ascaridoid nematodes with a majority of fish displaying a co-infection. Out of 295 whole infected fish, 269 were co-infected by at least 2 genera

Radiative decays of decuplet hyperons

We calculate the radiative decay widths of decuplet hyperons in a chiral constituent quark model including electromagnetic exchange currents between quarks. Exchange currents contribute significantly to the E2 transition amplitude, while they largely cancel for the M1 transition amplitude. Strangeness suppression of the radiative hyperon decays is found to be weakened by exchange currents. Differences and similarities between our results and other recent model predictions are discussed.Comment: 11 pages, 1 eps figure, revtex, accepted for publication in Phys. Rev.

Generation of mechanical squeezing via magnetic dipoles on cantilevers

A scheme to squeeze the center-of-mass motional quadratures of a quantum mechanical oscillator below its standard quantum limit is proposed and analyzed theoretically. It relies on the dipole-dipole coupling between a magnetic dipole mounted on the tip of a cantilever to equally oriented dipoles located on a mesoscopic tuning fork. We also investigate the influence of several sources of noise on the achievable squeezing, including classical noise in the driving fork and the clamping noise in the oscillator. A detection of the state of the cantilever based on state transfer to a light field is considered. We investigate possible limitations of that scheme.Comment: 11 pages, 11 figures, submitted to PR

Fasting plasma glucose and risk factor assessment: Comparing sensitivity and specificity in identifying gestational diabetes in urban black African women

Background. Identifying women with gestational diabetes mellitus (GDM) allows interventions to improve perinatal outcomes. A fasting plasma glucose (FPG) level ≥5.1 mmol/L is 100% specific for a diagnosis of GDM. The International Association of Diabetes and Pregnancy Study Groups acknowledges that FPG <4.5 mmol/L is associated with a low probability of GDM.Objectives. The validity of selective screening based on the presence of risk factors was compared with the universal application of FPG ≥4.5 mmol/L to identify women with GDM. FPG ≥4.5 mmol/L or the presence of one or more risk factors was assumed to indicate an intermediate to high risk of GDM and therefore the need for an oral glucose tolerance test (OGTT).Methods. Consecutive black South African (SA) women were recruited to a 2-hour 75 g OGTT at 24 - 28 weeks’ gestation in an urban community health clinic. Of 969 women recruited, 666 underwent an OGTT, and of these 589 were eligible for analysis. The glucose oxidase laboratory method was used to measure plasma glucose concentrations. The World Health Organization GDM diagnostic criteria were applied. All participants underwent a risk factor assessment. The χ2 test was used to determine associations between risk factors and a positive diagnosis of GDM. The sensitivity and specificity of a positive diagnosis of GDM were calculated for FPG ≥4.5 mmol/L, FPG ≥5.1 mmol/L, and the presence of one or more risk factors.Results. The prevalence of overt diabetes mellitus and GDM was 0.5% and 7.0%, respectively. Risk factor-based selective screening indicated that 204/589 (34.6%) of participants needed an OGTT, but 18/41 (43.9%) of positive GDM diagnoses were missed. Universal screening using the FPG threshold of ≥4.5 mmol/L indicated that 152/589 (25.8%) of participants needed an OGTT, and 1/41 (2.4%) of positive diagnoses were missed. An FPG of ≥5.1 mmol/L identified 36/41 (87.8%) of GDM-positive participants. The sensitivity and specificity of the presence of one or more risk factors were 56% and 67%, respectively. The sensitivity and specificity of FPG ≥4.5 mmol/L were 98% and 80%, respectively.Conclusions. Universal screening using FPG ≥4.5 mmol/L had greater sensitivity and specificity in identifying GDM-affected women and required fewer women to undergo a resource-intensive diagnostic OGTT than risk factor-based selective screening. A universal screening strategy using FPG ≥4.5 mmol/L may be more efficient and cost-effective than risk factor-based selective screening for GDM in black SA women.

Continuous isotopic composition measurements of tropospheric CO₂ at Jungfraujoch (3580 m a.s.l.), Switzerland: real-time observation of regional pollution events

A quantum cascade laser based absorption spectrometer (QCLAS) is applied for the first time to perform in situ, continuous and high precision isotope ratio measurements of CO₂ in the free troposphere. Time series of the three main CO₂ isotopologue mixing ratios (¹²C¹⁶CO₂, ¹³C¹⁶CO₂ and ¹²C¹⁸O¹⁶O) have simultaneously been measured at one second time resolution over two years (from August 2008 to present) at the High Altitude Research Station Jungfraujoch (3580 m a.s.l., Switzerland). This work focuses on periods in February 2009 only, when sudden and pronounced enhancements in the tropospheric CO₂ were observed. These short-term changes were closely correlated with variations in CO mixing ratios measured at the same site, indicating combustion related emissions as potential source. The analytical precision of 0.046‰ (at 50 s integration time) for both δ¹³C and δ¹⁸O and the high temporal resolution allowed the application of the Keeling plot method for source signature identification. The spatial origin of these CO₂ emission sources was then determined by backward Lagrangian particle dispersion simulations