Quantum Key Distribution Throughput Challenges Get Focus

Boosting the secret key rate in a shared quantum and classical fibre communication system

Introduction to the full study…

+  Our society is based on the continuous exchange of billions of data, and most of them travel in optical fibres. Nonetheless, most of the exchanged data are not protected against upcoming threats, i.e., new algorithms able to break current cyphers and the expected availability of quantum computers.

+  A quantum computer is a machine based on the laws of quantum physics, which will be able to crack some of the current cryptosystems, whose security relies on the limited computational power of an eavesdropper. As derived by Shannon, a way to achieve information theoretical secure communications is to use One-Time-Pad encryption, which requires a pre-shared key of the same size as the message to be sent.

+  However, other symmetric key algorithms based on computationally hard problems are also used, such as the Advanced Encryption Standard, since they require keys of constant length (e.g. 128 or 256 bits). The symmetric key used by these cryptosystems must be exchanged between the two parties, and this is usually achieved through public-key algorithms, two of the most widely used being the Rivest–Shamir–Adler and the elliptic curve cryptography.

+  A quantum computer can however break both algorithms, leaving the task of distributing keys to either post-quantum cryptography or to alternative methods such as quantum cryptography. Within the latter, quantum key distribution (QKD) addresses this challenge by relying on the laws of quantum physics to provide the required information-theoretic security. During the last 30 years, multiple demonstrations of free-space, underwater and fibre-based QKD systems have shown the feasibility of such a technology.

Nevertheless, multiple factors are limiting the global deployment of QKD systems: the low information rate, the short propagation distance and the compatibility with the existing network infrastructure. Indeed, most of QKD implementations have been realised in low noise environments (e.g. dark fibres), attesting to the difficulty of integration with the bright signals used in classical communications.

+  In [the full work at the source below], we show how to overcome the low rate and compatibility limitations by exploiting a 37-core multicore fibre (MCF) as a technology for quantum communications. This technology allows for efficient key generation, enabling the highest secret key rate presented to date. Moreover, we co-propagate in all the cores simultaneously a high-speed classical signal, showing that the quantum communication is only weakly perturbed by it, paving the way for a full-fleshed implementation in current communication infrastructures.

Source:  COMMUNICATIONS PHYSICS.  Davide Bacco, Beatrice Da Lio, Daniele Cozzolino, Francesco Da Ros, Xueshi Guo, Yunhong Ding, Yusuke Sasaki, Kazuhiko Aikawa, Shigehito Miki, Hirotaka Terai, Taro Yamashita, Jonas S. Neergaard-Nielsen, Michael Galili, Karsten Rottwitt, Ulrik L. Andersen, Toshio Morioka & Leif K. Oxenløwe,  Boosting the secret key rate in a shared quantum and classical fibre communication system…

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