A complete characterisation of the heralded noiseless amplification of photons

Heralded noiseless amplifcation of photons has recently been shown to provide a means to overcome losses in complex quantum communication tasks. In particular, to overcome transmission losses that could allow for the violation of a Bell inequality free from the detection loophole, for Device Independent Quantum Key Distribution (DI-QKD). Several implementations of a heralded photon amplifier have been proposed and the first proof of principle experiments realised. Here we present the first full characterisation of such a device to test its functional limits and potential for DI-QKD. This device is tested at telecom wavelengths and is shown to be capable of overcoming losses corresponding to a transmission through $20\, \rm km$ of single mode telecom fibre. We demonstrate heralded photon amplifier with a gain $>100$ and a heralding probability $>83$, required by DI-QKD protocols that use the Clauser-Horne-Shimony-Holt (CHSH) inequality. The heralded photon amplifier clearly represents a key technology for the realisation of DI-QKD in the real world and over typical network distances.Comment: 9 pages, 4 figure

Quantifying solute spreading and mixing in reservoir rocks using 3-D PET imaging

We report results of an experimental investigation into the effects of small-scale (mm-cm) heterogeneities on solute spreading and mixing in a Berea sandstone core. Pulse-tracer tests have been carried out in the Péclet number regime Pe = 6-40 and are supplemented by a unique combination of two imaging techniques. X-ray computed tomography (CT) is used to quantify subcore-scale heterogeneities in terms of permeability contrasts at a spatial resolution of approximately 10 mm3, while [11C] positron emission tomography (PET) is applied to image the spatial and temporal evolution of the full tracer plume non-invasively. To account for both advective spreading and local (Fickian) mixing as driving mechanisms for solute transport, a streamtube model is applied that is based on the one-dimensional advection-dispersion equation. We refer to our modelling approach as semideterministic, because the spatial arrangement of the streamtubes and the corresponding solute travel times are known from the measured rock's permeability map, which required only small adjustments to match the measured tracer breakthrough curve. The model reproduces the three-dimensional PET measurements accurately by capturing the larger-scale tracer plume deformation as well as subcore-scale mixing, while confirming negligible transverse dispersion over the scale of the experiment. We suggest that the obtained longitudinal dispersivity (0.10±0.02 cm) is rock rather than sample specific, because of the ability of the model to decouple subcore-scale permeability heterogeneity effects from those of local dispersion. As such, the approach presented here proves to be very valuable, if not necessary, in the context of reservoir core analyses, because rock samples can rarely be regarded as 'uniformly heterogeneous'

Sexuelle Zufriedenheit von Frauen mit vaginaler Aplasie nach operativer Neovagina-Bildung

Obwohl kein sehr seltenes Phänomen, stellt der Befund einer Aplasie von Uterus und Vagina (Mayer-Rokitansky-Küster-Hauser-Syndrom) ein im Allgemeinen wenig bekanntes Thema dar. In der Literatur wird es mit einer Häufigkeit von 1:4000 weiblichen Neugeborenen beschrieben. Die Ursache ist eine Hemmung der Entwicklung, der Ausdifferenzierung und Vereinigung der Müller’schen Gänge, sowie eine fehlende Epithelausknospung aus dem Sinus urogenitalis, wodurch keine Vaginalplatte angelegt und der Anschluss an die Müller’schen Gänge nicht erreicht wird. Die Aplasie von Uterus und Vagina wird in der Regel bei der Abklärung wegen primärer Amenorrhoe diagnostiziert. Frauen mit dieser Fehlbildung sind in zweifacher Weise betroffen: Einerseits beim Fehlen der Vagina durch die Unmöglichkeit, vaginalen Geschlechtsverkehr haben zu können und andererseits beim Fehlen des Uterus durch die Unmöglichkeit, eine Schwangerschaft erleben zu können. Zur Bildung einer Neovagina stehen für diese Frauen verschiedene operative Möglichkeiten oder unblutige, bougierende Verfahren zur Verfügung. An der Klinik für Gynäkologie des Departements für Frauenheilkunde des Universitätsspitals Zürich wird zur Neovagina-Bildung die laparoskopisch modifizierte Operationsmethode nach Vecchietti gewählt. Ziel dieser Arbeit war es zu erfahren, ob Frauen nach diesem operativen Eingriff zur Neovagina-Bildung ein für sie normales Sexualleben führen konnten. Dazu wurden von den Patientinnen, die im Zeitraum von 1993 bis 2000 an der Klinik für Gynäkologie im USZ im Sinne einer Neovagina-Bildung nach Vecchietti operiert worden waren, die Krankengeschichten gesichtet und die Frauen zwecks Befragung kontaktiert. Von den 13 Patientinnen haben 10 an der Befragung, die in Interviewform unter Verwendung eines Fragebogens durchgeführt worden ist, teilgenommen. Zusammenfassend darf gesagt werden, dass nach der Neovagina-Bildung und nach einer etwas länger dauernden postoperativen Heilungsphase der Geschlechtsverkehr schmerzfrei möglich war und bei ungestörter Libido und ungestörter Orgasmusfähigkeit die Frauen eine insgesamt zufriedenstellende Vita sexualis leben konnten. Das alltägliche Leben hatte sich für die Frauen nicht verändert. Sie betonten aber, dass sie sich durch die Neovagina-Bildung vollkommener fühlten und unbeschwerter eine Beziehung eingehen konnten. Die Operationsmethode war für die befragten Frauen gut akzeptabel, wurde aber durchwegs als schmerzhaft erlebt, vor allem die Phase der langsamen postoperativen Scheidendehnung. 8 der befragten 10 Frauen waren der Überzeugung, dass sie den Eingriff erneut würden machen lassen, da sie das Endresultat als zufriedenstellend empfanden. Ein von allen Patientinnen geäussertes Anliegen war der Wunsch nach einer Selbsthilfegruppe für einen Austausch unter Betroffenen. Für die Gynäkologische Klinik ergab sich als Fazit aus dieser Arbeit die Erkenntnis, dass bei Frauen mit MRKH-Syndrom präoperativ noch mehr zu betonen ist, wie sehr die postoperative Phase von Schmerzen begleitet sein wird und dass insgesamt eine gute ambulante Begleitung der Frauen auch nach der Entlassung aus dem Spital angeboten werden muss, speziell für die Phase der Platzhalteranwendung. Im gesamten betrachtet kann aber der Eingriff bezüglich sexueller Zufriedenheit postoperativ empfohlen werden

Moving across scales: a quantitative assessment of X-ray CT to measure the porosity of rocks

We apply multidimensional X-ray CT to quantify the porosity of Berea Sandstone by using both medical- and synchrotron-based X-ray radiation, so as to produce images of the same sample with mm- and micron-resolution, respectively. Three different samples are used and the obtained tomograms are compared by considering the spatial distribution of porosity values for the range of voxel sizes 0.25-16 mm3. The agreement between the two independent techniques is assessed by means of the concordance correlation coefficient. Statistically significant correlations are found for each sample up to the maximum resolution of the medical CT scanner, i.e. for images with a voxel size of (0.5x0.5x1) mm3. The direct comparison of images obtained by medical- and synchrotron-based X-ray radiation has a dual benefit. First, it objectively informs the segmentation step required for the binarization of the high-resolution synchrotron images that is otherwise prone to operator bias; in this context, the applicability of the proposed workflow is demonstrated with two widely applied locally adaptive thresholding algorithms, namely the hysteresis and the watershed methods. Secondly, once this calibration has occurred, the coupling of the two techniques allows analyzing porosity heterogeneity across a range of length-scales that spans over more than eight orders of magnitudes. We anticipate that the ability to perform a true multi-scale experiment may represent the required point of departure for developing up-scaling approaches that capture the inherently complex heterogeneity of rocks

Capillary pressure heterogeneity and hysteresis for the supercritical CO2/water system in a sandstone

We report results from an experimental investigation on the hysteretic behaviour of the capillary pressure curve for the supercritical CO2-water system in a Berea Sandstone core. Previous observations have highlighted the importance of sub-core-scale capillary heterogeneity in developing local saturations during drainage; we show in this study that the same is true for the imbibition process. Spatially distributed drainage and imbibition scanning curves were obtained for mm-scale subsets of the rock sample non-invasively using X-ray CT imagery. Core- and sub-core scale measurements are well described using the Brooks-Corey formalism, which uses a linear trapping model to compute mobile saturations during imbibition. Capillary scaling yields two separate universal drainage and imbibition curves that are representative of the full sub-core scale data set. This enables accurate parameterisation of rock properties at the sub-core scale in terms of capillary scaling factors and permeability, which in turn serve as effective indicators of heterogeneity at the same scale even when hysteresis is a factor. As such, the proposed core-analysis workflow is quite general and provides the required information to populate numerical models that can be used to extend core-flooding experiments to conditions prevalent in the subsurface, which would be otherwise not attainable in the laboratory

Multidimensional Imaging of Density Driven Convection in a Porous Medium

Carbon dioxide (CO2) sequestration is a climate change mitigation technique which relies on residual and solubility trapping in injection locations with saline aquifers. The dissolution of CO2 into resident brines results in density-driven convection which further enhances the geological trapping potential. We report on the use of an analogue fluid pair to investigate density-driven convection in 3D in an unconsolidated bead pack. X-ray computed tomography (CT) is used to image density-driven convection in the opaque porous medium non-invasively. Two studies have been conducted that differ by the Rayleigh number (Ra) of the system, which in this study is changed by altering the maximum density difference of the fluid pair. We observe the same general mixing pattern in both studies. Initially, many high density fingers move downward through the bead pack and as time progresses these coalesce and form larger dominate flow paths. However, we also observe that a higher Rayleigh number leads to the denser plume moving faster towards the bottom of the system. Due to the finite size of the system, this in turn leads to early convective shut-down

Anisotropy effects on the magnetic excitations of a ferromagnetic monolayer below and above the Curie temperature

The field-driven reorientation transition of an anisotropic ferromagnetic monolayer is studied within the context of a finite-temperature Green's function theory. The equilibrium state and the field dependence of the magnon energy gap $E_0$ are calculated for static magnetic field $H$ applied in plane along an easy or a hard axis. In the latter case, the in-plane reorientation of the magnetization is shown to be continuous at T=0, in agreement with free spin wave theory, and discontinuous at finite temperature $T>0$, in contrast with the prediction of mean field theory. The discontinuity in the orientation angle creates a jump in the magnon energy gap, and it is the reason why, for $T>0$, the energy does not go to zero at the reorientation field. Above the Curie temperature $T_C$, the magnon energy gap $E_0(H)$ vanishes for H=0 both in the easy and in the hard case. As $H$ is increased, the gap is found to increase almost linearly with $H$, but with different slopes depending on the field orientation. In particular, the slope is smaller when $H$ is along the hard axis. Such a magnetic anisotropy of the spin-wave energies is shown to persist well above $T_C$ ($T \approx 1.2 T_C$).Comment: Final version accepted for publication in Physical Review B (with three figures