Bright Integrated Photon-Pair Source for Practical Passive Decoy-State Quantum Key Distribution

We report on a bright, nondegenerate type-I parametric down-conversion source, which is well suited for passive decoy-state quantum key distribution. We show the photon-number-resolved analysis over a broad range of pump powers and we prove heralded higher-order $n$-photon states up to $n=4$. The inferred photon click statistics exhibit excellent agreements to the theoretical predictions. From our measurement results we conclude that our source meets the requirements to avert photon-number-splitting attacks.Comment: 5 pages, 4 figure

Two-Photon Polarization Interference for Pulsed SPDC in a PPKTP Waveguide

We study the spectral properties of Spontaneous Parametric Down Conversion in a periodically poled waveguided structure of KTP crystal pumped by ultra-short pulses. Our theoretical analysis reveals a strongly multimode and asymmetric structure of the two-photon spectral amplitude for type-II SPDC. Experimental evidence, based on Hong-Ou-Mandel polarization interference with narrowband filtering, confirms this result.Comment: Submitted for publicatio

How Colors Influence Numbers: Photon Statistics of Parametric Downconversion

Parametric downconversion (PDC) is a technique of ubiquitous experimental significance in the production of non-classical, photon-number correlated twin beams. Standard theory of PDC as a two-mode squeezing process predicts and homodyne measurements observe a thermal photon number distribution per beam. Recent experiments have obtained conflicting distributions. In this paper, we explain the observation by an a-priori theoretical model solely based on directly accessible physical quantities. We compare our predictions with experimental data and find excellent agreement.Comment: 4 {pages, figures

Fiber-assisted single-photon spectrograph

We demonstrate the implementation of a fiber-integrated spectrograph utilizing chromatic group velocity dispersion (GVD) in a single mode fiber. By means of GVD we stretch an ultrafast pulse in time in order to spectrally resolve single photons in the time domain, detected by single photon counting modules with very accurate temporal resolution. As a result, the spectrum of a very weak pulse is recovered from a precise time measurement with high signal to noise ratio. We demonstrate the potential of our technique by applying our scheme to analyzing the joint spectral intensity distribution of a parametric downconversion source at telecommunication wavelength.Comment: 4 pages, 3 figure

Advances in the Spectral and Statistical Characterization of Quantum States of Light

Einzelne Photonen bilden die Grundlage der Quantenoptik und stellen Bausteine für spannende Anwendungsmöglichkeiten dar, wie der Quantenkommunikation oder der Simulation quantenmechanischer Prozesse. In diesem Zusammenhang hat die Entwicklung von Einzelphotonenquellen in den letzten Jahren große Bedeutung gewonnen, etwa mittels parametrischer Fluoreszenz. Als Umkehrprozess der zweiten Harmonischen durch nichtlineare Wechselwirkung werden stets Photonenpaare erzeugt. Die Eleganz liegt in der Möglichkeit, durch Nachweis eines Photons die Präsenz des weiteren, einzelnen Photons zu garantieren. Oft sind Photonenquellen dieser Art allerdings nur bedingt geeignet, reine Fockzustände zu erzeugen. Aus diesem Grund ist eine leistungsfähige und verlustarme Charakterisierung von optischen Zuständen essentiell für die Beurteilung einer Quelle. In dieser Arbeit werden experimentelle Methoden vorgestellt, gepulste Quellen anhand ihrer Photonenstatistik und spektralen Verteilungsfunktion zu analysieren. Mithilfe von Lichtwellenleiternetzwerken können die Photonen eines Pulses aufgeteilt und separat mit konventionellen Einzelphotondetektoren registriert werden. Dispersion in Lichtwellenleitern kann genutzt werden, die Wellenfunktion eines Photons gezielt zerfließen zu lassen, so dass die spektrale Zusammensetzung durch einfache Zeitmessung zugänglich wird. Ähnlich kann die spektrale Abhängigkeit zwischen Photonen durch Korrelationsmessungen bestimmt werden. Ein Experiment mit gezielt präparierten kohärent-stimulierenden Eingansmoden ermöglicht darüber hinaus eine amplitudensensitive Messung der parametrischen Fluoreszenz mit deutlich erhöhter spektraler Auflösung

Image processing device and method for producing in real-time a digital composite image from a sequence of digital images of an interior of a hollow structure

Image processing device for producing in real-time a digital composite image from a sequence of digital images of an interior of a hollow structure recorded by an endoscopic camera device so that the composite image has a wider field of view than the images of the sequence of images, the image processing device comprising: a selecting unit, a key point detection unit, a transforming unit and a joining unit, wherein the transforming unit comprises a key point matching unit configured for determining key point pairs, wherein the transforming unit comprises a transformation determination unit configured for determining a transformation for transforming a further image into a global coordinate system, wherein the transformation for transforming the further image into the global coordinate system is a concatenation of a perspective transformation, an isomorphic mapping and a Mobius transformation, wherein parameters of the transformation for transforming the further image into the global coordinate system are determined from at least some of the key point pairs, and wherein the transforming unit comprises a transforming execution unit configured for transforming the further image into the global coordinate system by using the transformation for transforming the further image into the global coordinate system in order to produce a transformed further image

Image processing device and method for producing in real-time a digital image from a sequence of digital images

Image processing device for producing in real-time a digital composite image from a sequence of digital images recorded by a camera device, in particular an endoscopic camera device, the image processing device comprising a selecting unit, a key point detection unit, a transforming unit and a joining unit, wherein the key point detection unit comprises a filter configured for producing a filter response for the reference image and for producing a filter response for the further image, wherein the key point detection unit comprises a maximum detection unit configured for executing following steps separately for the filter response for the reference image and for the filter response for the further image, wherein a variable threshold is used: i) creating blocks by dividing the respective filter response, ii) calculating the variable threshold for each of the blocks, iii) discarding those blocks of the blocks from further consideration, in which the respective filter response at a reference point of the respective block is less than the respective variable threshold