Title

Differential Phase-Shift QKD in a 2:16-Split Lit PON with 19 Carrier-Grade Channels

Authors

N. Vokić, D. Milovančev, B. Schrenk, M. Hentschel, H. Hübel

Abstract

We investigate the practical network integration of differential phase shift quantum key distribution following a cost-optimized deployment scheme where complexity is offloaded to a centralized location. User terminal equipment for quantum state preparation at 1 GHz symbol rate is kept technologically lean through use of a directly-modulated laser as optical encoder. Integration in a passive optical network infrastructure is experimentally studied for legacy and modern optical access standards. We analyze the implications that result from Raman scattering arising from different spectral allocations of the classical channels in the O-, S-, C- and L-band, and prove that the quantum channel can co-exist with up to 19 classical channels of a fully-loaded modern access standard. Secure-key generation at a rate of 5.1×10^-7 bits/pulse at a quantum bit error ratio of 3.28% is obtained over a 13.5 km reach, 2:16 split passive network configuration. The high power difference of 93.8 dB between launched classical and quantum signals in the lit access network leads to a low penalty of 0.52% in terms of error ratio.

Venue

IEEE J. Sel. Topics in Quantum Electron., vol. 26, no. 3, p. 6400309, May 2020.

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Title

Analysis of the trusted-device scenario in continuous-variable quantum key distribution

Authors

Fabian Laudenbach, Christoph Pacher

Abstract 

The assumption that detection and/or state-preparation devices used for continuous-variable quantum key distribution (CV-QKD) are beyond influence of potential eavesdroppers leads to a significant performance enhancement in terms of achievable key rate and transmission distance. We provide a detailed and comprehensible derivation of the Holevo bound in this so-called trusted-device scenario. Modelling an entangling-cloner attack and using some basic algebraic matrix transformations, we show that the computation of the Holevo bound can be reduced to the solution of a quadratic equation. As an advantage of our derivation, the mathematical complexity of our solution does not increase with the number of trusted-noise sources. Finally, we provide a numerical evaluation of our results, illustrating the counter-intuitive fact that an appropriate amount of trusted receiver loss and noise can even be beneficial for the key rate.

Venue

Advanced Quantum Technologies, Vol 2. Issue 11, November 2019

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Title

Adding artificial noise for code rate matching in continuous-variable quantum key distribution

Authors

Sören Kreinberg, Igor Koltchanov, André Richter

Abstract

The reconciliation step of continuous-variable quantum key distribution protocols usually involves forward error correction codes. Matching the code rate and the signal-to-noise ratio (SNR) of the quantum channel is required to achieve the high reconciliation efficiencies that are crucial for long distance links. Puncturing and shortening is a way to adapt the code rate to the SNR at the cost of a slightly reduced reconciliation efficiencies. Instead of adapting the code rate to the SNR, we propose to add a controlled amount of artificial noise to the measured data, so that the resulting SNR could be reduced to match the given code rate. We show that our method can compete with puncturing and shortening and even outperform it in high-loss, high-excess noise scenarios.

Venue

ArXiv.org

Place and Date

https://arxiv.org/abs/1905.04925, Submitted on 13 May 2019

Title

Flexible User/Cloud-Centric Entanglement Distribution with Synthesizable Network Node

Authors

Fabian Laudenbach, Bernhard Schrenk, Martin Achleitner, Nemanja Vokic, Dinka Milovancev, Hannes Hübel

Abstract

The practical roll-out of quantum communication technologies in optical networks and the adoption of novel quantum applications demand the distribution of single or entangled photons. Flexibility and dynamicity is paramount for the provision of quantum resources, in order to scale with the number of users and to meet the demand of complex network architectures. We present a quantum network architecture that features this degree of reconfigurability, without being restricted to a rigid physical-layer network based on purely passive multiplexing componentry. We leverage spectral assets of photon-pair sources, from the short-wavelength band to the L-band, and agile spatial switching at a remote optical network node in order to realize a flexible distribution map that features different flavors, reaching from cloud-centric to user-centric quantum connectivity. Entanglement distribution is experimentally demonstrated at high visibility for five users in a 17-km reach, tree-shaped optical network. The delivered photon rate can be dynamically adjusted between the users by a factor of 2.5. Penalty-free operation is confirmed for integrating a co-existing classical control channel within the quantum.

Venue

Journal of Selected Topics in Quantum Electronics (JSTQE)

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