Quantum Networks: Towards a Quantum Internet

Within the world of communications there are many ways to encrypt messages [1]. As the field of Quantum Computation [2] develops the ability of classical method to keep data secure is decreased, if not
nullified [3]. To replace these systems city, and global, scale QKD (Quantum Key Distribution) system
are required [4, 5]. For city scale fibre based QKD, networks with a central source are the most scalable
systems that have been shown to date [6]. This project will investigate developing larger networks for
a wide variety of Quantum Protocols, along with testing long distance single links and interconnecting
multiple such networks.
The project will start with preparing an entangled photon pair source, centred at 1550.12 nm, that
distributes entangled states between individual users based on the wavelength. This forms the basis of
the planned quantum networks. The first experiment will be to test QKD over long distance connections.
The major challenges here are time synchronisation, dispersion, jitter and loss. The photon pair source
will then be connected to a system that allows for distribution across a 19-User network. An optical
switch will be used to control the distribution of wavelength channels to each user to create a quantum
ROADM (reconfigurable optical add-drop multiplexer). This will be the worlds first fully software defined large scale quantum network.
As the system develops what will be done may change. The current plan is to move on from the
19-User experiment to produce 2 concurrent quantum networks (one 16 user and one 8 user) that are
interconnected by a limited number of connections. This will be the first entanglement based interconnection of quantum networks - an essential step towards scaling up quantum networking to create the
quantum internet. This could also include research into Quantum Memories [7], Quantum Repeaters [8],
Quantum Frequency Conversion [8], control software, Machine Learning, and expanding to a network of
more users.
References
[1] Nidhi S. Kulkarni, Balasubramanian Raman, and Indra Gupta. Multimedia encryption: A brief
overview. Studies in Computational Intelligence, 231:417-449, 2009.
[2] Alexandru Gheorghiu, Theodoros Kapourniotis, and Elham Kashefi. Verification of Quantum Computation: An Overview of Existing Approaches. Theory of Computing Systems, 63(4):715-808, 5
2019.
[3] Artur Ekert and Richard Jozsa. Quantum computation and Shor's factoring algorithm. Reviews of
Modern Physics, 68(3):733-753, 7 1996.
[4] Nicolas Gisin and Rob Thew. Quantum Communication. Technical report, 2007.
1University of Bristol
2Head of the Photonics and Quantum Optics Labratory, Ruder Boskovic Institue (RBI), Zagreb, Croatia
1
[5] S. Pirandola, U. L. Andersen, L. Banchi, M. Berta, D. Bunandar, R. Colbeck, D. Englund, T. Gehring,
C. Lupo, C. Ottaviani, J. Pereira, M. Razavi, J. S. Shaari, M. Tomamichel, V. C. Usenko, G. Vallone,
P. Villoresi, and P. Wallden. Advances in Quantum Cryptography. arXiv, 6 2019.
[6] Siddarth Koduru Joshi, Djeylan Aktas, Soren Wengerowsky, Martin Loncaric, Sebastian Philipp
Neumann, Bo Liu, Thomas Scheidl, Zeljko Samec, Laurent Kling, Alex Qiu, Mario Stipcevic, John G.
Rarity, and Rupert Ursin. A trusted-node-free eight-user metropolitan quantum communication
network. 7 2019.
[7] Alexander I Lvovsky, Barry C Sanders, and Wolfgang Tittel. Optical quantum memory. nature.com,
2009.
[8] Farid Samara, Nicolas Maring, Anthony Martin, Arslan S. Raja, Tobias J. Kippenberg, Hugo Zbinden,
and Rob Thew. Entanglement swapping between independent and asynchronous integrated photonpair sources. 11 2020.