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European Quantum Electronics Conference (EQEC)

A novel concept of entanglement distribution in optical nNetworks

Andreas Poppe, Alex Ciurana Aguilar, Jesús Martínez-Mateo, José Luis Rosales, Bernhard Schrenk, Momtchil Peev, Vicente Martín Ayuso

Published Jan 1, 2015• 0 citations
OpenAlex

Abstract

A major road-block in bringing QKD to the market is the missing scalability of a single QKD-link connecting two users to a use-case with many users in the same metropolitan area network (MAN). The typical trusted node concept used for this, beyond requiring the trust on all intermediate nodes, is not able to distribute entanglement without the help of quantum manipulations that have yet to be demonstrated. Here we extend the concept of entanglement to many pairs of users by the introduction of novel structures. The goal of this work is the design of a MAN for quantum and co-propagating classical signals to allow an arbitrarily high number of users not bounded by e.g. the number of CWDM or DWDM channels in the ITU grid. The number of coexistent multiplexed links is clearly limited by this usable fibre bandwidth, but the network must be able to select the corresponding user out of a large pool of possible communication partners (as in mobile phone networks).

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•Sep 1, 2014•1 citation
A major road-block in bringing QKD to the market is the missing scalability of a single QKD-link connecting two users to a use-case with many users in the same metropolitan area network (MAN). The typical trusted node concept used for this, beyond requiring the trust on all intermediate nodes, is not able to distribute entanglement without the help of quantum manipulations that have yet to be demonstrated. Here we extend the concept of entanglement to many pairs of users by the introduction of novel structures. The goal of this work is the design of a MAN for quantum and co-propagating classical signals to allow an arbitrarily high number of users not bounded by e.g. the number of CWDM or DWDM channels in the ITU grid. The number of coexistent multiplexed links is clearly limited by this usable fibre bandwidth, but the network must be able to select the corresponding user out of a large pool of possible communication partners (as in mobile phone networks).
Abstract Quantum key distribution (QKD) would play an important role in future information technologies due to its theoretically proven security based on the laws of quantum mechanics. How to realize QKDs among multiple users in an effective and simple way is crucial for its real applications in communication networks. In this work, we propose and demonstrate a fully connected QKD network without trusted node for a large number of users. Using flexible wavelength division multiplexing/demultiplexing and space division multiplexing, entanglement resources generated by a broadband energy-time entangled quantum light source are distributed to 40 users. Any two users share a part of entanglement resources, by which QKD is established between them. As a result, it realizes a fully connected network with 40 users and 780 QKD links. The performance of this network architecture is also discussed theoretically, showing its potential on developing quantum communication networks with large user numbers owing to its simplicity, scalability, and high efficiency.
Quantum networks scale the advantages of quantum communication protocols to more than just two distant users. Here we present a fully connected quantum network architecture in which a single entangled photon source distributes quantum states to a multitude of users [1] and our work scaling the network to a complete end to end metropolitan quantum network with 8 users [2]. Our network architecture optimises the resources required by each user without sacrificing security or functionality. We established several long-distance loopback connections and demonstrated extended stable operation with high secure key rates. Unlike previous attempts at multi-user networks, which have been based on active components, and thus limited to some duty cycle, our implementation is fully passive. Further, we present our efforts towards coexistence of 100 Gbps classical communication and all quantum channels used in the network over the same deployed optical fibres. Most importantly, we have used our network to implement a wide variety of protocols. These protocols overcome major limitations of quantum networks and each of them represent the first implementation of that class of protocols on a large scale network.
Quantum networks have been shown to connect users with full-mesh topologies without trusted nodes. We present advancements on our scalable polarisation entanglement-based quantum network testbed, which has the ability to perform protocols beyond simple quantum key distribution. Our approach utilises wavelength multiplexing, which is ideal for quantum networks across local metropolitan areas due to the ease of connecting additional users to the network without increasing the resource requirements per user. We show a 10 user fully connected quantum network with metropolitan scale deployed fibre links, demonstrating polarisation stability and the ability to generate secret keys over a period of 10.8 days with a network wide average-effective secret key rate of 3.38 bps.
Quantum networks scale the advantages of quantum communication protocols to more than just two distant users. Here we present a fully connected quantum network architecture in which a single entangled photon source distributes quantum states to a multitude of users. Our network architecture thus minimizes the resources required of each user without sacrificing security or functionality. As no adaptations of the source are required to add users, the network can readily be scaled to a large number of clients, whereby no trust in the provider of the quantum source is required. Unlike previous attempts at multi-user networks, which have been based on active components, and thus limited to some duty cycle, our implementation is fully passive and thus provides the potential for unprecedented quantum communication speeds. We experimentally demonstrate the feasibility of our approach using a single source of bi-partite polarization entanglement which is multiplexed into 12 wavelength channels to distribute 6 states between 4 users in a fully connected graph using only 1 fiber and polarization analysis module per user. We then discuss practical usage scenarios to demonstrate the advantage of some of the salient features of our network topology. These include adaptations/hardware implementations that are more favorable for local area networks and those for long distance intercity links. Our implementation consisted of a single Type 0 MgO:PPLN crystal pumped bidirectionally in a Sagnac interferometer to produce polarization entangled photon pairs with an ≈ 60 nm bandwidth. These pair wise entangled photons were split into 12 different wavelength channels corresponding to 6 correlated wavelength pairs. Each of the 4 users in our demonstration received 3 wavelength channels multiplexed together via a solitary single mode fiber. Each user had just one detector unit that they used to simultaneously measure all input channels. We exploited small time delays between different channels to isolate the relevant signal from noise. We measured the quality of entanglement between each channel pair simultaneously and calculated the effective secure key rate using the E91 protocol. Our experiment showed the effectiveness of our network topology and its scalability against noise, number of users and losses. Further experiments are underway to increase the number of clients and improve the scalability of the topology. Also, we plan to demonstrate distributed computation tasks like secure auctions, Byzantine fault tolerance, and asynchronous reference frame agreement are feasible using our network architecture.
Current QKD designs try to keep the quantum channel as error free as possible by using a separate physical medium for this purpose. In the most common case, this means the exclusive use of an optical fiber for the quantum channel, precluding its use for any other purpose. In current optical networks, the fiber is the single most expensive element and this poses a major problem from a cost and availability point of view. Sharing the fiber is thus mandatory for the widespread adoption of QKD. The objective of this communication is to propose a general scheme and present some preliminary measurements of a metropolitan area network (MAN) designed to multiplex of the order of 64 addressable quantum channels and the associated QKD classical service signals on a single dark fibre. It uses as much existing components and infraestructure as possible in an attempt to simultaneously lower most of the practical barriers for the adoption of QKD.
The ability to generate entangled photon-pairs over a broad wavelength range opens the door to the simultaneous distribution of entanglement to multiple users of a network using a single source and wavelength-division multiplexing technologies. Here we show the design of a metropolitan optical network made of tree-type access networks where entangled photon-pairs are distributed to any pair of users, independently of their location. The resulting network improves the reach, number of users and capabilities of existing proposals. Moreover, it is made up of typical commercial components and uses the existing infrastructure, which allows for moderate deployment costs. Finally, we develop a channel plan and a network design that allow direct optical communications, quantum and classical, between any pair of users. Therefore, multiple quantum information technologies can make use of this network.