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Title

Photon-Pair Sources and Quantum Cryptography using Continuous Variables

Authors

Fabian Laudenbach (AIT Austrian Institute of Technology)

Abstract 

The counter-intuitive phenomena of quantum mechanics are currently leaping from their mere exploration to their deployment in real-life applications. Quantum superposition, the uncertainty principle, the no-cloning theorem and, most prominently, quantum entanglement are proven to allow for computing and cryptography algorithms, simulation of complex physical phenomena and sensing of physical quantities in new and beneficial ways which are unparalleled by classical devices. In particular, quantum technologies based on photons offer a straightforward way to protect quantum states from decoherence and, if necessary, transmit them from one place to another reliably. Most applications in the realm of optical quantum technology have successfully been demonstrated in proof-of-principle experiments. However, in order for quantum technologies to unleash their full potential and establish in the shape of wide-spread applications with a true advantage over their classical counterparts, they need to become scalable in size, quantity, performance and cost. This thesis is divided into two parts dealing with different aspects of quantum optics: The first part discusses ways to generate photon pairs with high brightness and, at the same time, high quality in terms of their performance in quantum experiments. The second part provides a theoretical discussion and experimental demonstration of quantum cryptography based on continuous variables — a promising concept to make the striking advantages of quantum communication compatible with off-the-shelf telecom hardware and fibre networks. As I hope, the research presented in both parts of this thesis will, in one way or another, make a contribution to the scalability of quantum technologies and thereby help to enforce the breakthrough of the so-called quantum revolution.

Title
Flexible entanglement distribution based on WDM and active switching technology

Authors
Hannes Hübel, Bernhard Schrenk, Sophie Zeiger, Fabian Laudenbach and Michael Hentschel.

Abstract
In future, the distribution of single or entangled photons inside optical networks will be a prerequisite for a general roll-out and adoption of quantum communication technologies. In particular, on-demand routing and active wavelength allocation will be needed to meet the demand of complex network architectures. In the last years several attempts have been made, based either on passive optical WDM technology or active switching of channels. Here we present a novel approach whereby we combine spectral slicing of the emission spectrum of SPDC sources together with space-switches to generate a reconfigurable distribution node for entanglement.  The increased switching complexity offered by our hybrid solution allows us to realise quantum ROADMs with up to three degrees.

Venue
21st International Conference on Transparent Optical Networks ICTON 2019 (http://www.icton2019.com/)

Place and Date
Angers, France, July 9-13, 2019

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Title
Modelling Weak-Coherent CV-QKD Systems Using a Classical Simulation Framework

Authors
Sören Kreinberg, Igor Koltchanov, Piotr Novik, Saleem Alreesh, Fabian Laudenbach, Christoph Pacher, Hannes Hübel, André Richter.

Abstract
Due to their compatibility to existing telecom technology, continuous variable (CV) weak coherent state protocols are promising candidates for a broad deployment of quantum key distribution (QKD) technology. We demonstrate how an existing simulation framework for modelling classical optical systems can be utilized for simulations of weak-coherent CV-QKD links. The quantum uncertainties for the measured characteristics of coherent signals are modelled in the electrical domain by shot noise, while a coherent signal in the optical domain is described by its quadrature components. We simulate various degradation effects such as attenuation, laser RIN, Raman noise (from classical channels in the same fibre), and device imperfections and compare the outcome with analytical theory. Having complemented the physical simulation layer by the post-processing layer (reconciliation and privacy amplification), we are able to estimate secure key rates from simulations, greatly boosting the development speed of practical CV-QKD schemes and implementations.

Venue
21st International Conference on Transparent Optical Networks ICTON 2019 (http://www.icton2019.com/)

Place and Date
Angers, France, July 9-13, 2019

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Title
Coexistence of discrete-variable QKD with WDM classical signals in the C-band for fiber access environments

Authors
D. Zavitsanos, G. Giannoulis, A. Raptakis, C. Papapanos, F. Setaki, E. Theodoropoulou, G. Lyberopoulos, Ch. Kouloumentas, and H. Avramopoulos.

Abstract
In this paper, a coexistence scheme between a Discrete-Variable Quantum Key Distribution (DV-QKD) and four bidirectional classical channels in a Passive Optical Network (PON) topology is theoretically investigated. The study aims to explore the imposed limitations considering the coexistence of weak quantum channels with realistic traffic flows of classical streams through shared fiber infrastructures. Based on a ‘plug and play’ phase coding DV-QKD implementation, we conducted numerical simulations of the QBER and the secure key rate for fiber distances up to 10km. The reported results suggest that in a fixed C-band grid, the spectral isolation between classical and quantum channels is essential at dense grids. By removing the leakage noise through stronger spectral isolation, the photons linked with the Raman scattering becomes the dominant noise source, since this mechanism covers an ultra-broadband window and gets stronger as the propagation distance increases.

Venue
21st International Conference on Transparent Optical Networks ICTON 2019 (http://www.icton2019.com/)

Place and Date
Angers, France, July 9-13, 2019

[Download]