Limits on the deterministic creation of pure single-photon states using parametric down-conversion

Parametric down-conversion (PDC) is one of the most widely used methods to create pure single-photon states for quantum information applications. However little attention has been paid to higher-order photon components in the PDC process, yet these ultimately limit the prospects of generating single-photons of high quality. In this paper we investigate the impacts of higher-order photon components and multiple frequency modes on the heralding rates and single-photon fidelities. This enables us to determine the limits of PDC sources for single-photon generation. Our results show that a perfectly single-mode PDC source in conjunction with a photon-number resolving detector is ultimately capable of creating single-photon Fock states with unit fidelity and a maximal state creation probability of 25%. Hence an array of 17 switched sources is required to build a deterministic (>99% emission probability) pure single-photon source.Comment: 7 pages, 6 figure

Theory of quantum frequency conversion and type-II parametric down-conversion in the high-gain regime

Frequency conversion (FC) and type-II parametric down-conversion (PDC) processes serve as basic building blocks for the implementation of quantum optical experiments: type-II PDC enables the efficient creation of quantum states such as photon-number states and Einstein-Podolsky-Rosen-states (EPR-states). FC gives rise to technologies enabling efficient atom-photon coupling, ultrafast pulse gates and enhanced detection schemes. However, despite their widespread deployment, their theoretical treatment remains challenging. Especially the multi-photon components in the high-gain regime as well as the explicit time-dependence of the involved Hamiltonians hamper an efficient theoretical description of these nonlinear optical processes. In this paper, we investigate these effects and put forward two models that enable a full description of FC and type-II PDC in the high-gain regime. We present a rigorous numerical model relying on the solution of coupled integro-differential equations that covers the complete dynamics of the process. As an alternative, we develop a simplified model that, at the expense of neglecting time-ordering effects, enables an analytical solution. While the simplified model approximates the correct solution with high fidelity in a broad parameter range, sufficient for many experimental situations, such as FC with low efficiency, entangled photon-pair generation and the heralding of single photons from type-II PDC, our investigations reveal that the rigorous model predicts a decreased performance for FC processes in quantum pulse gate applications and an enhanced EPR-state generation rate during type-II PDC, when EPR squeezing values above 12 dB are considered.Comment: 26 pages, 4 figure

Theory of filtered type-II PDC in the continuous-variable domain: Quantifying the impacts of filtering

Parametric down-conversion (PDC) forms one of the basic building blocks for quantum optical experiments. However, the intrinsic multimode spectral-temporal structure of pulsed PDC often poses a severe hindrance for the direct implementation of the heralding of pure single-photon states or, for example, continuous-variable entanglement distillation experiments. To get rid of multimode effects narrowband frequency filtering is frequently applied to achieve a single-mode behavior. A rigorous theoretical description to accurately describe the effects of filtering on PDC, however, is still missing. To date, the theoretical models of filtered PDC are rooted in the discrete-variable domain and only account for filtering in the low gain regime, where only a few photon pairs are emitted at any single point in time. In this paper we extend these theoretical descriptions and put forward a simple model, which is able to accurately describe the effects of filtering on PDC in the continuous-variable domain. This developed straightforward theoretical framework enables us to accurately quantify the trade-off between suppression of higher-order modes, reduced purity and lowered Einstein-Podolsky-Rosen (EPR) entanglement, when narrowband filters are applied to multimode type-II PDC.Comment: 15 pages, 13 figure

Erasmus von Rotterdam zwischen den Glaubensparteien

This paper concerns Erasmus’ role in the increased confessionalisation of the 16th century. It discusses Erasmus’ struggle to remain neutral in the Reformation debate and highlights the impact of his historical approach on the confessional debate. In 1520, Erasmus argued epistemologically by suggesting that because scholars’ verdicts on Luther differed they were unconvincing. In 1524 he turned his epistemological argument against Luther by introducing skepticism into the Christian discourse. Again, in 1529 he used his historical approach to argue against what he perceived as being a main concern of the Reformer’s, namely reinstating the early apostolic church. By emphasizing that the Apostles also quarreled amongst themselves and that, for better or for worse, time changes all things he was able to avoid demonizing the traditionalism as the Reformers did or to overvaluing it as did their Roman Catholic counterparts in his view. Thus by 1533 he could safely offer forward-looking advice in favour of restoring a unified church. The impact of his suggestions, which influenced the colloquy of Regensburg, was still felt in the ecumenical movement of the 20th century

Das Buch der Bücher popularisieren: Der Bibelübersetzer Leo Jud und sein biblisches Erbauungsbuch "Vom lyden Christi" (1534)

One of the main aims of the Reformers was to return to the pure word of God and to enable all people to read the Bible by themselves. That is why in 1531 the Zurich Reformers translated the Old Testament into German and edited it together with the Lutheran German translation of the New Testament in 1531. Yet, this relatively cheap print could not really succeed in popularising the “book of books” and the Zurich Reformer Leo Jud set to revising and translating a part of the Monotessaron, the gospel harmony of Jean Gerson from the first half of the 15th century, and editing it with edifying interpretations. Astonishingly, he not only used Gerson’s book  as his source text but also included many famous allegories and metaphors from the Church Fathers and from late medieval authors. Among these he included many questionable – from a modern standpoint – associations and traditions, as long as they were still in some way related to biblical terms and images. In contrast, Erasmus  avoided such allusions in his famous Paraphrases. Some years later, Jud translated and published all Erasmian Paraphrases as a meditative book which would replace his little harmony