University of Paderborn

About: University of Paderborn is a education organization based out in Paderborn, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Computer science & Context (language use). The organization has 6684 authors who have published 16929 publications receiving 323154 citations.

An efficient integrated two-color source for heralded single photons

Abstract: We present a pulsed and integrated, highly non-degenerate parametric down-conversion (PDC) source of heralded single photons at telecom wavelengths, paired with heralding photons around 800 nm. The active PDC section is combined with a passive, integrated wavelength division demultiplexer on-chip, which allows for the spatial separation of signal and idler photons with efficiencies of more than 96.5%, as well as with multi-band reflection and anti-reflection coatings which facilitate low incoupling losses and a pump suppression at the output of the device of more than 99%. Our device is capable of preparing single photons with efficiencies of 60% with a coincidences-to-accidentals ratio exceeding 7400. Likewise, it shows practically no significant background noise compared to continuous wave realizations. For low pump powers, we measure a conditioned second-order correlation function of g(2) = 3.8 × 10−3, which proves almost pure single-photon generation. In addition, our source can feature a high brightness of 〈npulse〉 = 0.24 generated photon pairs per pump pulse at pump power levels below 100 μW. The high quality of the pulsed PDC process in conjunction with the integration of highly efficient passive elements makes our device a promising candidate for future quantum networking applications, where an efficient miniaturization plays a crucial role.

Quantum-Limited Time-Frequency Estimation through Mode-Selective Photon Measurement.

Abstract: By projecting onto complex optical mode profiles, it is possible to estimate arbitrarily small separations between objects with quantum-limited precision, free of uncertainty arising from overlapping intensity profiles. Here we extend these techniques to the time-frequency domain using mode-selective sum-frequency generation with shaped ultrafast pulses. We experimentally resolve temporal and spectral separations between incoherent mixtures of single-photon level signals ten times smaller than their optical bandwidths with a tenfold improvement in precision over the intensity-only Cramer-Rao bound.

Photon temporal modes: a complete framework for quantum information science

Abstract: Field-orthogonal temporal modes of photonic quantum states provide a new framework for quantum information science (QIS). They intrinsically span a high-dimensional Hilbert space and lend themselves to integration into existing single-mode fiber communication networks. We show that the three main requirements to construct a valid framework for QIS -- the controlled generation of resource states, the targeted and highly efficient manipulation of temporal modes and their efficient detection -- can be fulfilled with current technology. We suggest implementations of diverse QIS applications based on this complete set of building blocks.

Online rank elicitation for Plackett-Luce: a dueling bandits approach

Abstract: We study the problem of online rank elicitation, assuming that rankings of a set of alternatives obey the Plackett-Luce distribution. Following the setting of the dueling bandits problem, the learner is allowed to query pairwise comparisons between alternatives, i.e., to sample pairwise marginals of the distribution in an online fashion. Using this information, the learner seeks to reliably predict the most probable ranking (or top-alternative). Our approach is based on constructing a surrogate probability distribution over rankings based on a sorting procedure, for which the pairwise marginals provably coincide with the marginals of the Plackett-Luce distribution. In addition to a formal performance and complexity analysis, we present first experimental studies.

LiNbO3 ground- and excited-state properties from first-principles calculations

Abstract: The atomic and electronic structure, zone center phonon frequencies, and optical absorption of $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ are calculated from first principles. The structural and vibrational properties predicted from density functional theory are in good agreement with experiment and earlier theoretical work. The electronic band-structure and optical properties are found to be very sensitive to quasiparticle and electron-hole attraction effects, which are included here using the $GW$ approach and by solving the Bethe-Salpeter equation, respectively. We predict the fundamental gap to be more than $1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ larger than the $3.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ frequently cited for ferrolectric $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ and calculate optical absorption spectra in good agreement with experiment.