The research group on Quantum Information and Computation, at the Universidad Politécnica de Madrid (UPM) is mainly formed by researchers skilled in the areas of applied mathematics, physics, networking and computational sciences, among others.
The group has experience in quantum key distribution (QKD), having installed the first point-to-point QKD link in the country in 2006 together with Telefonica R&D. Since 2009 they have built several network prototypes where research on quantum protocols and its integration within standard optical communication networks is being carried out. The first prototypes were installed in Telefónica Research and Development Future Labs and they evolved to demonstrate several test-beds and architectures overtime. Two of them were installed in the field, using production facilities of Telefónica. The last one (the fourth generation network) was also deployed in the field and contributes to European projects like CiViQ and OpenQKD, where IMDEA SW (RediMadrid) also participates.
A brief description of the different networks follows:
The fourth network prototype (2020-present), the current Madrid Quantum Network has 13 links. The network is a real world one in the sense that all the network is in production facilities, and that most of the nodes are being used simultaneously for classical communications, including the optical fiber. This is not an ad hoc network built for quantum purposes, but a conventional optical network enhanced for quantum communications. As a result, this presents the same challenges than a commercial deployment of QKD technologies would need to overcome, making for a realistic testbed. Distances and losses are also representative of a typical metropolitan area network, ranging from 2 to about 40 km and from 3 to 14 dB, respectively (when all losses, not only the fibre are taken into account). Distances and losses (only fiber) are quoted in the figure. The purple lines (connecting to UAH) are under comissioning. The red ring in the center is the old Madrid Quantum Network installed in Telefónica premises (see the third gen. network). It is interesting to note that some nodes host special installations that are of particular interest, like IMDEA Networks (IMDEA-NW) which hosts a Telefónica 5G lab.
More information here (link)
The third network prototype (2017-2019), initial integration research of QKD in novel network architectures, in particular using the Software Defined Networking and associated Network Function Virtualization paradigms. These new paradigms are designed for maximum flexibility by stepping away from proprietary appliances that work mainly as separated entities. Relying on as much common hardware as possible that is accessed through common interfaces, a logically centralized SW entity —the SDN controller— can manage the SDN network taking into account the peculiarities of all new hardware installed, as long as it exports the needed functionalities and the corresponding interfaces. In principle, this allows for a seamless integration and easy deployment of quantum communications over existing networks [Aguado et al., 2018.1 , Aguado et al., 2017.2 , Aguado et al., 2017.1 ].
This network has been implemented in the field in Madrid, with three nodes linking production facilities of Telefonica. A map is displayed below. More information here (link)
The team members are also skilled in QKD post-processing and secret-key distillation, having proposed novel methods for efficient and high speed information reconciliation (error correction) in QKD.
The second QKD network prototype (2012-2015) was less concerned with the coexistence of classical and quantum signals and sought to maximize the number of users in a quantum network. In this network, the classical signals were, at first, limited to those needed to keep the quantum channel stable and to distill the keys in the QKD link. Finally, this limitation was also raised. The result was a demonstrator were up to 32 QKD users could use simultaneously a fully addressable metropolitan area network (i.e., where any QKD device can decide with whom it wants to generate key) directly and without any trusted intermediate node. The network would, in an almost fully passive way, automatically direct the quantum and corresponding classical channels from the emitter to the receiver by using a mixture of CWDM and DWDM channels using standard components [Ciurana et al., 2014 ]. This network was also capable to distribute entanglement [Ciurana et al., 2015 ].
The first QKD network (2009-12) was unique in that it departed with previous thinking about QKD networks in not relying in intermediate trusted nodes connected through non-shared optical fibres. This was tantamount to have a separate, ad hoc network for the quantum signals alone. The network sought a full classical and quantum network integration by using the usual core and access architecture of a metropolitan area network. Standard, off-the-shelf, components were used to research the limits of quantum-classical coexistence in a CWDM metro area core network and using a GPON access network. The objective was to study the limits in stablishing a quantum link crossing a full metropolitan area network using standard components and sharing the already deployed optical infrastructure [Lancho et al., 2009 ] (see Video).
A. Aguado, D. R. López, A. Pastor, V. López, J. P. Brito, M. Peev, A. Poppe, and V. Martín “Quantum cryptography networks in support of path verification in service function chains” ; Accepted in Journal of Optical Communications and Networking Vol. 12, pp. B9-B19. (2020) DOI:10.1364/JOCN.379799
A. Aguado, V. López, D. López, M. Peev, A. Poppe, A. Pastor, J. Folgueira, V. Martín “The Engineering of Software-Defined Quantum Key Distribution Networks”; Accepted in IEEE Communications Magazine, vol. 57, no. 7, pp. 20-26. (2019) doi: 10.1109/MCOM.2019.1800763
A. Aguado, V. López, J. Martinez-Mateo, M. Peev, D. López and V. Martín, “Virtual Network Function Deployment and Service Automation to Provide End-to-End Quantum Encryption,” Accepted in Journal of Optical Communications and Networking, vol 10, No. 4, pp.421-430, 2018 (PDF ).
A. Aguado, V. Lopez, J. Martinez-Mateo, T. Szyrkowiec, A. Autenrieth, M. Peev, D. Lopez, and V. Martin, “ Hybrid conventional and quantum security for software defined and virtualized networks,” 2017, IEEE/OSA Journal of Optical Communications and Networking , vol. 9, no. 10, pp. 819-825, Oct. 2017. doi: 10.1364/JOCN.9.000819 (PDF ).
A. Aguado, V. Lopez, J. Martinez-Mateo, M. Peev, D. Lopez, and V. Martin, “GMPLS Network Control Plane Enabling Quantum Encryption in End-to-End Services,” in ONDM 2017, 21th International Conference on Optical Network Design and Modeling, Budapest, Hungary, May 15-18, 2017. Best Paper Award (PDF ).
A list of low-density parity-check codes and matrices particularly optimized for different coding rates and communication channels.