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

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

A model colloidal fluid with competing interactions: bulk and interfacial properties

Using a simple mean-field density functional theory theory (DFT), we investigate the structure and phase behaviour of a model colloidal fluid composed of particles interacting via a pair potential which has a hard core of diameter $\sigma$, is attractive Yukawa at intermediate separations and repulsive Yukawa at large separations. We analyse the form of the asymptotic decay of the bulk fluid correlation functions, comparing results from our DFT with those from the self consistent Ornstein-Zernike approximation (SCOZA). In both theories we find rich crossover behaviour, whereby the ultimate decay of correlation functions changes from monotonic to long-wavelength damped oscillatory decay on crossing certain lines in the phase diagram, or sometimes from oscillatory to oscillatory with a longer wavelength. For some choices of potential parameters we find, within the DFT, a $\lambda$-line at which the fluid becomes unstable with respect to periodic density fluctuations. SCOZA fails to yield solutions for state points near such a $\lambda$-line. The propensity to clustering of particles, which is reflected by the presence of a long wavelength $\gg \sigma$, slowly decaying oscillatory pair correlation function, and a structure factor that exhibits a very sharp maximum at small but non zero wavenumbers, is enhanced in states near the $\lambda$-line. We present density profiles for the planar liquid-gas interface and for fluids adsorbed at a planar hard wall. The presence of a nearby $\lambda$-transition gives rise to pronounced long-wavelength oscillations in the one-body densities at both types of interface.Comment: 14 pages, 11 figure

Effect of antiferromagnetic exchange interactions on the Glauber dynamics of one-dimensional Ising models

We study the effect of antiferromagnetic interactions on the single spin-flip Glauber dynamics of two different one-dimensional (1D) Ising models with spin $\pm 1$. The first model is an Ising chain with antiferromagnetic exchange interaction limited to nearest neighbors and subject to an oscillating magnetic field. The system of master equations describing the time evolution of sublattice magnetizations can easily be solved within a linear field approximation and a long time limit. Resonant behavior of the magnetization as a function of temperature (stochastic resonance) is found, at low frequency, only when spins on opposite sublattices are uncompensated owing to different gyromagnetic factors (i.e., in the presence of a ferrimagnetic short range order). The second model is the axial next-nearest neighbor Ising (ANNNI) chain, where an antiferromagnetic exchange between next-nearest neighbors (nnn) is assumed to compete with a nearest-neighbor (nn) exchange interaction of either sign. The long time response of the model to a weak, oscillating magnetic field is investigated in the framework of a decoupling approximation for three-spin correlation functions, which is required to close the system of master equations. The calculation, within such an approximate theoretical scheme, of the dynamic critical exponent z, defined as ${1/\tau} \approx ({1/ {\xi}})^z$ (where \tau is the longest relaxation time and \xi is the correlation length of the chain), suggests that the T=0 single spin-flip Glauber dynamics of the ANNNI chain is in a different universality class than that of the unfrustrated Ising chain.Comment: 5 figures. Phys. Rev. B (accepted July 12, 2007

Phase transitions in simple and not so simple binary fluids

Compared to pure fluids, binary mixtures display a very diverse phase behavior, which depends sensitively on the parameters of the microscopic potential. Here we investigate the phase diagrams of simple model mixtures by use of a microscopic implementation of the renormalization group technique. First, we consider a symmetric mixture with attractive interactions, possibly relevant for describing fluids of molecules with internal degrees of freedom. Despite the simplicity of the model, slightly tuning the strength of the interactions between unlike species drastically changes the topology of the phase boundary, forcing or inhibiting demixing, and brings about several interesting features such as double critical points, tricritical points, and coexistence domains enclosing `islands' of homogeneous, mixed fluid. Homogeneous phase separation in mixtures can be driven also by purely repulsive interactions. As an example, we consider a model of soft particles which has been adopted to describe binary polymer solutions. This is shown to display demixing (fluid-fluid) transition at sufficiently high density. The nature and the physical properties of the corresponding phase transition are investigated.Comment: 6 pages + 3 figures, presented at the 5th EPS Liquid Matter Conference, Konstanz, 14-18 September 200

Finite-size effects on the dynamic susceptibility of CoPhOMe single-chain molecular magnets in presence of a static magnetic field

The static and dynamic properties of the single-chain molecular magnet [Co(hfac)$_2$NITPhOMe] are investigated in the framework of the Ising model with Glauber dynamics, in order to take into account both the effect of an applied magnetic field and a finite size of the chains. For static fields of moderate intensity and short chain lengths, the approximation of a mono-exponential decay of the magnetization fluctuations is found to be valid at low temperatures; for strong fields and long chains, a multi-exponential decay should rather be assumed. The effect of an oscillating magnetic field, with intensity much smaller than that of the static one, is included in the theory in order to obtain the dynamic susceptibility $\chi(\omega)$. We find that, for an open chain with $N$ spins, $\chi(\omega)$ can be written as a weighted sum of $N$ frequency contributions, with a sum rule relating the frequency weights to the static susceptibility of the chain. Very good agreement is found between the theoretical dynamic susceptibility and the ac susceptibility measured in moderate static fields ($H_{\rm dc}\le 2$ kOe), where the approximation of a single dominating frequency turns out to be valid. For static fields in this range, new data for the relaxation time, $\tau$ versus $H_{\rm dc}$, of the magnetization of CoPhOMe at low temperature are also well reproduced by theory, provided that finite-size effects are included.Comment: 16 pages, 9 figure