Title

Advances in quantum cryptography

Authors

S. Pirandola, U. L. Andersen, L. Banchi, M. Berta, D. Bunandar, R. Colbeck, D. Englund, T. Gehring, C. Lupo, C. Ottaviani, J. L. Pereira, M. Razavi, J. Shamsul Shaari, M. Tomamichel, V. C. Usenko, G. Vallone, P. Villoresi, and P. Wallden

Abstract

Quantum cryptography is arguably the fastest growing area in quantum information science. Novel theoretical protocols are designed on a regular basis, security proofs are constantly improving, and experiments are gradually moving from proof-of-principle lab demonstrations to in-field implementations and technological prototypes. In this paper, we provide both a general introduction and a state-of-the-art description of the recent advances in the field, both theoretical and experimental. We start by reviewing protocols of quantum key distribution based on discrete variable systems. Next we consider aspects of device independence, satellite challenges, and protocols based on continuous-variable systems. We will then discuss the ultimate limits of point-to-point private communications and how quantum repeaters and networks may overcome these restrictions. Finally, we will discuss some aspects of quantum cryptography beyond standard quantum key distribution, including quantum random number generators and quantum digital signatures.

Venue

OSA Publishing, Advances in Optics and Photonics, Vol. 12, Issue 4, pp. 1012-1236 (2020)

Title

Hybrid Polymer Integration for Communications, Sensing and Quantum Technologies from the Visible to the Infrared

Authors 

Moritz Kleinert, David de Felipe, Hauke Conradi, Martin Kesse, Lennart Jehle, Madleine Weigel, Tianwen Qian, Klara Mihov, Jakob Reck, Crispin Yawadyki, Norbert Keil, Martin Schell

Abstract

We present concepts for transferring PIC building blocks from classical implementations in the C band towards shorter wavelengths. Exemplary functionalities include hybrid tunable lasers for 785 nm and 1064 nm, on-chip free-space sections for non-linear optics, and dielectric thin-film filters with 68 dB suppression

Venue

ECOC 2021 (https://www.ecoc2021.org/)

Place and Date

Bordeaux –  France, 13-16 September 2021

Title

Integrated balanced homodyne photonic–electronic detector for beyond 20 GHz shot-noise-limited measurements

Authors

Cédric Bruynsteen, Michael Vanhoecke, Johan Bauwelinck, and Xin Yin

Abstract 

Optical homodyne detection is used in numerous quantum and classical applications that demand high levels of sensitivity. However, performance is typically limited due to the use of bulk optics and discrete receiver electronics. To address these performance issues, in this work we present a co-integrated balanced homodyne detector consisting of a silicon photonics optical front end and a custom integrated transimpedance amplifier designed in a 100 nm GaAs pHEMT technology. The high level of co-design and integration provides enhanced levels of stability, bandwidth, and noise performance. The presented detector shows a linear operation up to 28 dB quantum shot noise clearance and a high degree of common-mode rejection, at the same time achieving a shot-noise-limited bandwidth of more than 20 GHz. The high performance of the developed devices provide enhanced operation to many sensitive quantum applications such as continuous variable quantum key distribution, quantum random number generation, or high-speed quantum tomography.

Venue 

Optica 8, 1146-1152 (2021), OSA Publishing

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Title 

A Quantum Key Distribution simulator for BB84-type protocols with decoy states

Authors

Florian Prawits, Christoph Pacher and Hannes Hübel

Abstract

BB84-type DV-QKD protocols that implement weak coherent laser pulses as the carrier for the encoded information are severely limited in their maximally achievable transmission distance due to the inherent threat of photon number splitting (PNS) attacks. This potential weakness can be elegantly eliminated by the adaption of the protocol to include so-called decoy states (DS) in the transmission. These decoy states allow Alice and Bob to probe their transmission channel and statistically infer whether a PNS type attack is occurring, thus precluding Eve from successfully using this strategy. The added degrees of freedom of deciding how often to send decoy states and which intensities to use for them however further complicates the already complex task of predicting the impact on protocol performance and finding a set of suitable parameters to achieve optimal secret key rates (skr). In order to predict optimal performance, as a function of characteristics of the QKD setup like channel losses and device imperfections, state preparation fidelity, decoy state parameters and finite size effects, the software simulator pyDSsim has been developed. The tool is written in Python and implements the recent security proof framework introduced in [1,2]. The software can be scripted from the command line or used via a graphical user interface (GUI: QT5 framework) for easy exploration via parametrized x-y plots of over 40 different variables, allowing a comprehensive evaluation of their interdependencies. The main feature however is the option to numerically compute the set of protocol variables for a given QKD-setup which maximizes the secret key rate under constraints typical for practical implementations: fixed block sizes or fixed acquisition times for the raw key. To this end two different algorithms (differential-evolution [3] and L-BFGS-B [4]) are utilized, allowing for a cross-check of the acquired results and choice between speed and accuracy of the approach.

References [1] Rusca, D., Boaron, A., Grünenfelder, F., Martin, A. & Zbinden, H. Finite-key analysis on the 1-decoy state QKD protocol. Appl. Phys. Lett. 112, 171104 (2018) [2] Lim, C. C. W., Curty, M., Walenta, N., Xu, F. & Zbinden, H. Concise security bounds for practical decoy-state quantum key distribution. Phys. Rev. A 89, 022307 (2014) [3] R. H. Byrd, P. Lu and J. Nocedal. A Limited Memory Algorithm for Bound Constrained Optimization, (1995), SIAM Journal on Scientific and Statistical Computing, 16, 5, pp. 1190-1208. [4] Storn, R and Price, K, Differential Evolution – a Simple and Efficient Heuristic for Global Optimization over Continuous Spaces, Journal of Global Optimization, 1997, 11, 341 – 359.

Venue 

QCrypt 2021 (https://2021.qcrypt.net/)

Place and Date

Online, 23 – 27 August 2021

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Title

1.6 Tbps Classical Channel Coexistence With DV-QKD Over Hollow Core Nested Antiresonant Nodeless Fibre (HC-NANF)

Authors

O. Alia(1)*, R. S. Tessinari(1), T. D. Bradley(2), H. Sakr(2), K. Harrington(2), J. Hayes(2), Y. Chen(2),
P. Petropoulos(2), D. Richardson(2), F. Poletti(2) G. T. Kanellos(1), R. Nejabati(1), D. Simeonidou(1)
(1) High Performance Networks Group, University of Bristol, Woodland Road, Bristol, UK
(2) Optoelectronics Research Centre, University of Southampton, Southampton, SO17 1BJ, UK
*Corresponding author: obada.alia@bristol.ac.uk

Abstract

We demonstrate for the first time the coexistence of a quantum-channel and 8200 Gpbs 16-QAM
optical channels with launching powers as high as -9dBm/channel in a 2 km HC-NANF. Comparative
analysis with single-mode fibre reveals that the quantum-channel could not be sustained at such powerlevels.

Venue

ECOC 2021 (https://www.ecoc2021.org/)

Place and Date

Bordeaux –  France, 13-16 September 2021

Title 

Coexistence of a Quantum QKD Channel and 4×100 Gbps Classical Channels in Nested Antiresonant Nodeless Hollow Core Fibre

Authors

O. Alia*, R. S. Tessinari, T. D. Bradley, H. Sakr, K. Harrington, J. Hayes, Y. Chen, P. Petropoulos, D. Richardson, F. Poletti, G. T. Kanellos, R. Nejabati, D. Simeonidou

Abstract

We demonstrated for the first time a coexistence between a quantum QKD channel and 4×100 Gbps pm-qpsk carrier-grade classical optical channels in a 2 km Nested Antiresonant Nodeless Hollow Core fibre. Our results show a drop of less than 10% in the Secret Key Rate (SKR) when using a HCF compared to a significant drop of 97% in the SKR when quantum and classical signals coexist on a single core of a Multicore fibre (MCF) with equal losses, indicating that NANF type HCF significantly outperforms single-mode fibres (SMF) performance for quantum/classical coexistence. This significant difference in the SKR drop is due to the ultra-low nonlinear effects in HCF comparing to glass core fibres such as SMF and MCF.

Venue

Qcrypt 2021 (https://2021.qcrypt.net/)

Place and Date

Online, 23 – 27 August 2021