Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - QINTERNET (Quantum communication networks)

Teaser

The objective of this project is to advance the real world realization of quantum communication networks. The vision of large interconnected quantum networks - a Quantum Internet - is to provide fundamentally new internet technology by ultimately enabling quantum communication...

Summary

The objective of this project is to advance the real world realization of quantum communication networks. The vision of large interconnected quantum networks - a Quantum Internet - is to provide fundamentally new internet technology by ultimately enabling quantum communication between any two points on earth. Such a Quantum Internet will – in synergy with the ‘classical’ internet that we have today - connect quantum processors in order to achieve unparalleled capabilities that are provably impossible using classical communication.
As with any radically new technology, it is hard to predict all uses of the future Quantum Internet, but several major applications have already been identified. One striking application of quantum communication is quantum key distribution(1) (QKD), which allows two remote network nodes to generate an encryption key, enabling the exchange of secret information between any users connected to the Quantum Internet. The security of QKD is guaranteed by the fundamental laws of nature, and thus fully future proof even against any attacker possessing a large-scale quantum computer. Other promising known applications are clock synchronization(2), extending the baseline of telescopes(3), secure identification(4), achieving efficient agreement on distributed data(5), exponential savings in communication(6), quantum sensor networks, as well as secure access to remote quantum computers in the cloud(7). Central to all these applications is the ability to send quantum bits (qubits). Qubits are fundamentally different from classical bits. While a classical bit can take only two values, ’0’ and ’1’, a qubit can be in a superposition of being ’0’ and ’1’ at the same time.
This project advanced quantum network technology in two crucial directions:
First, it develops new techniques and methods that show how quantum application protocols can be realized safely and correctly on real world quantum devices that are subject to imperfections and errors. These efforts enable to the real world implementation of such protocols, ultimately making them available to future end-users.
Second, it develops methods for routing quantum information to the right destination in the network. Quantum bits are very fragile and can presently not be stored for more than a few seconds. To design and scale future quantum networks it is therefore imperative to enable efficient routing decisions within the lifetime of the quantum bits.

(1) C. H. Bennett and G. Brassard. Int. Conf. Comp. Sys. Sig. Proc. pp. 175–179 (1984); A. K. Ekert, Phys. Rev. Lett. 67, 661 (1991).
(2) P. Komar, et al. Nat. Phys. 10, 582 (2014).
(3) D. Gottesman, T. Jennewein and S. Croke. Phys. Rev. Lett. 109, 070503 (2012).
(4) I. Damgaard, et al. Theo. Comp. Sci. 560, 12 (2014); F. Dupuis, O. Fawzi and S. Wehner. IEEE Trans. Inf. Theo. 61, 1093 (2014).
(5) M. Ben-Or and A. Hassidim. Symp Theo. Comp. (STOC) pp. 481–485 (2005).
(6) H. Buhrman, R. Cleve, S. Massar and R. de Wolf. Rev. Mod. Phys. 82, 665 (2010).
(7) A. Broadbent, J. Fitzsimons and E. Kashefi. Found. Comp. Sci. (FOCS) pp. 517–526 (2009).

Work performed

Highlights from the first period of this project include the identification of application driven stages of quantum network development, which provide a guideline to further development and aim to bridge communication gaps between experiment realizing quantum hardware, and protocol designers (Science, 2018). A good example is also the analysis of two-party quantum cryptographic protocols against imperfections in so-called continuous variable quantum systems, which enabled a real world implementation (Nature Communications, 2018). Furthermore, the world’s first application level simulator for quantum network has been realized to allow a tool for software development for quantum networks that is compatible with hardware efforts pursued by collaborators (SimulaQron, http://www.simulaqron.org)
In the domain of quantum network, we have also developed tools to asses the performance of a quantum link – specifically to measure its quantum capacity (Nature Communications, 2018).
To find useful routing algorithms and to understand their performance using real world devices, the world’s first discrete event simulator for quantum networks (NetSquid) was developed, which we will use to study such protocols in the second part of this project.

Final results

The project so far has significantly advanced the state of the art in enabling the implementation of quantum application protocols in the real world, and developed crucial tools for the analysis of routing protocols.
The second part of this project will focus strongly on developing routing protocols and understanding the scalability of large-scale quantum networks. The ambitious goal targeted by the end of this project is to understand several candidate routing algorithms on a large scale simulated quantum network, closely modelling real quantum hardware. Next to informing future routing strategies, it is also expected that this will inform the scalability of such networks.