Quantum, which colour suits you best?

At OFC 2019 in San Diego we posed the question how a practical integration of quantum channels into passive optical access networks could look like. To do so, we should first pay attention to the FSAN roadmap. 5G is on the brink of being rolled out together with its optical fronthauling over cloud-radio limited reach of ~20 km, while access standards incorporate wavelength stacking towards 4 lanes of 10 Gb/s. The good news is: NG-PON2 with its WDM overlay is spectrally allocated at the C- and L-bands. This blanks out the O-band, and if we expect fiber deployment to dismiss legacy solutions, there is really much unoccupied space down there at 1310 nm.

Although quantum communication is not a resource-consuming technology with respect to the always precious optical spectrum, it is very picky when it comes to “contamination”. The high power difference of about 100 dB between classical and quantum channels can quickly become a showstopper when these channels are located too close to each other. Even the 100-nm far wings of stimulated Raman scattering are quickly imposing severe crosstalk to the quantum channel. Spectral displacement is therefore paramount, and the consolidation of down- and upstream channels of the next-generation PON standard in the C/L-band definitely helps.

The second big question concerns the loss budget. In optical telecommunications the signal-to-noise ratio worsens with an increasing loss introduced between transmitter and receiver. In the quantum world, however, we transmit single photons and loss is directly impacting the rate at which we are receiving them. Given the constant dark count rate of single-photon detectors, there is a hard limit at which no useful quantum signal can be received anymore. Unfortunately, PONs as the scene that we have set for our experimental deployment study, are known to be very lossy due to their broadcast-and-select methodology with concentrated 1:N branching loss. At ECOC’14 in sunny Cannes, Orange gave a hint on that loss figure by showing that their average optical budget in access networks is 22 dB. This is a good indicator for brown-field deployments and it is just compatible with GHz-rate quantum signals.

So, what is left is to put all together, and that’s what we show in our OFC paper. We exploit a conceptually simple laser-based quantum transmitter dedicated to the end-user premises. The complexity of the receiver, with its custom quantum detector, is centralised at the head-end where it can be cost-shared. With that, and by exploiting a dual-feeder scheme for the PON as well as the unidirectional nature of quantum channels, we obtain robustness to a high number of more than 50 downstream channels. However, we also notice that classical upstream channels are by far more detrimental for our fragile quantum signal. Emerging WDM standards in the O-band, such as LAN-WDM with smaller channel passbands than CWDM, promise a much better noise rejection feature – and after all, you can also include a custom narrowband filter if you already require an equally complex element such as a quantum receiver. For these reasons, we believe that 1310 nm is an attractive wavelength to dress our quantum channel.

See our technical paper for more information:

B. Schrenk, M. Hentschel, and H. Hübel, O-Band Differential Phase-Shift Quantum Key Distribution in 52-Channel C/L-Band Loaded Passive Optical Network,” in Proc. OFC’19, San Diego, USA, Mar. 2019, Th1J.5.

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Our 1st Technical Meeting in Berlin

On January 21 – 22, 2019 our 1st technical meeting took place in Berlin Germany hosted by Fraunhofer HHI.

The main topics discussed were the technologies, applications and demonstrators, which are going to be delivered in the project. Future actions and steps have been discussed and agreed among the project partners.

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UNIQORN at EU ICT 2018 Conference



On 5th of December, UNIQORN participated in the EU ICT 2018 Conference, which as open and participatory event discusses the future of the digital Europe and was hosted in Vienna in 2018.

Marie-Christine Röhsner from University of Vienna and Hannes Hübel from AIT delivered talks themed “Quantum computing – why should I care?” and “Building our digital society on the foundations of quantum physics”, followed by a lively discussion on the benefits and dangers that are to be unlocked in the upcoming years. We were also happy to join forces with our Quantum Flagship partner Stephanie Wehner from the QIA to promote the importance of quantum technology.

Furthermore, AIT conducted a public experiment to explain the guiding of optical signals to interested individuals not skilled in the art. The principle of waveguiding in optical fibers or photonic integrated circuits has been demonstrated in a hands-on experiment by streaming classic music carried by optical light through a water jet.

More than 6000 participants attended the EU ICT 2018 from all over Europe!

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EU QT Flagship kick-off event

© Quantum Flagship

As one of the funded Flagship projects, UNIQORN was actively participating in the festive launch of the European Quantum Flagship on 29th and 30th of November, 2018. Among the various application domains, quantum communication received prominent attention, resulting in an allocation of 4 of the 12 thematic projects to this important pillar. The complementary nature of these quantum communication projects promise cross-pollination among them, as it was also pointed out during the strategic discussions within the Science and Engineering Board.

The UNIQORN partners that participated in the kick-off event were actively engaged in the discussions on the strategic research agenda and the implementation of the Quantum Technology Flagship and could disseminate the objectives of UNIQORN through distribution of technical leaflets. AIT as the project leader presented UNIQORN during the poster session, which was positively recognised by the event participants.

We are looking forward to the next Flagship event in Grenoble in February 2019, co-located with the European Quantum Technologies Conference.

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UNIQORN Kick-off meeting

The UNIQORN project was kicked-off from 9th to 10th of October in the beautiful city of Athens, where the end of summer was blowing fresh wind in our sails – proudly being part of the fleet of the European Quantum Technology Flagship.

It was a pleasure to see two communities – quantum physics and photonics – fusing together in a joint undertaking towards cost-effective quantum technology that will pave the way for mass market applications. The partners presented their ideas and strategies to make this important step happening within the proposed timeframe.

UNIQORN is also proud to involve female scientists with strong motivation to conduct cutting-edge science. Several further job opportunities as post-doctoral researchers have been pointed out by the partners and we would like to encourage interested PhD students in their final year to get in touch with the UNIQORN partners.

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