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

A versatile design for resonant guided-wave parametric down-conversion sources for quantum repeaters

Quantum repeaters - fundamental building blocks for long-distance quantum communication - are based on the interaction between photons and quantum memories. The photons must fulfil stringent requirements on central frequency, spectral bandwidth and purity in order for this interaction to be efficient. We present a design scheme for monolithically integrated resonant photon-pair sources based on parametric down-conversion in nonlinear waveguides, which facilitate the generation of such photons. We investigate the impact of different design parameters on the performance of our source. The generated photon spectral bandwidths can be varied between several tens of MHz up to around $1\,$GHz, facilitating an efficient coupling to different memories. The central frequency of the generated photons can be coarsely tuned by adjusting the pump frequency, poling period and sample temperature and we identify stability requirements on the pump laser and sample temperature that can be readily fulfilled with off-the-shelve components. We find that our source is capable of generating high-purity photons over a wide range of photon bandwidths. Finally, the PDC emission can be frequency fine-tuned over several GHz by simultaneously adjusting the sample temperature and pump frequency. We conclude our study with demonstrating the adaptability of our source to different quantum memories.Comment: 10 pages, 8 figure

COMMUNICATION ANONYMIZERS: PERSONALITY, INTERNET PRIVACY LITERACY AND THEIR INFLUENCE ON TECHNOLOGY ACCEPTANCE

Despite the fact that many individuals are concerned about privacy issues on the Internet and know about the existence of communication anonymizers, very few individuals actually use them. This discrepancy can only partially be explained by evident factors such as a small degree of knowledge about Internet privacy issues, or the latency of the Internet connection caused by communication anonymizers. In this study, we determine factors that influence the acceptance of communication anonymizers: the role of personality traits of individuals, the actual knowledge about privacy issues on the Internet and how much individuals really know about them, as well as the time an individual is willing to wait when using a communication anonymizer. Our study shows that the personality traits ?Agreeableness,? ?Extroversion? and ?Conscientiousness? do not influence an individual?s acceptance of communication anonymizers. Further, we can show that individuals with a strong personality trait of neuroticism are more likely to have strong privacy concerns and that individuals that can be characterized as ?open? are more likely to use communication anonymizers. With regard to the knowledge about privacy issues on the Internet, we find that individuals generally possess a low knowledge. Surprisingly, we find a negative correlation between an individual?s ?stated? and his/her ?actual? knowledge of privacy issues. Last, we find that individuals are willing to wait slightly longer (3.5 seconds) when using communication anonymizers