Researchers take quantum encryption out of the lab

WASHINGTON – In a new study, researchers demonstrate an automated and easy-to-use quantum key distribution (QKD) system using the fiber-optic network in the city of Padua, Italy. The field test represents an important step towards the implementation of this highly secure quantum communication technology using the type of communication networks already in place in many parts of the world.

QKD offers impenetrable encryption for data communication because it uses the quantum properties of light to generate secure random keys for data encryption and decryption.

“QKD can be useful in any situation where security is paramount as it provides unconditional security for the key exchange process,” said Marco Avesani of the Università degli Studi di Padova in Italy, co-first author of the new study with Luca Calderaro and Giulio Foletto. . “It can be used to encrypt and authenticate health data sent between hospitals or money transfers between banks, for example.”

In the journal The Optical Society (OSA) Optical letters, researchers led by Paolo Villoresi and Giuseppe Vallone report that their simple system is stable over time and can generate quantum-secure cryptographic keys at sustained rates over standard telecommunications infrastructure.

“QKD systems generally require a complex stabilization system and additional dedicated synchronization hardware,” Avesani said. “We have developed a complete QKD system that can be directly interfaced with standard telecommunications equipment and does not require additional hardware for synchronization. The system fits easily into rack enclosures commonly found in server rooms.

Design an easy-to-use system

To produce the quantum states required by QKD, the researchers developed a new encoder to manipulate the polarization of single photons. The encoder, which researchers call iPOGNAC, provides a fixed, stable bias reference that does not require frequent recalibration. This feature is also beneficial for quantum free space and satellite communications, where recalibrations are difficult to perform.

“Because of the technology we developed, the source was ready to produce quantum states when we moved our system from the lab to the location of the field test,” Calderaro said. “We didn’t have to go through the slow and often fault-prone alignment procedure required for most QKD systems.”

The researchers also developed a new synchronization algorithm, which they call

Qubit4Sync, to synchronize the machines of the two QKD users. Rather than using additional dedicated hardware and an additional frequency channel for synchronization, the new system uses software and the same optical signals used for QKD. This makes the system smaller, cheaper and easier to integrate into an existing optical network.

To test the new system, the researchers moved their two QKD terminals to two university buildings about 3.4 km apart in different sections of Padua. They connected the systems to two underground optical fibers that are part of the university’s communication network. These fibers supported the quantum channel carrying the qubits and the classical channel necessary for the transfer of auxiliary information.

A quantum secure video call

“The field test was a success,” said Foletto. “We have shown that our simple system can produce secret keys at speeds of a few kilobits per second and that it works outside the lab with little human intervention. It is also easy and quick to set up.”

In a public demonstration, the researchers used their setup to enable a secure quantum video call between the rector of the University of Padua and the director of the mathematics department. The researchers note that the performance of the system is comparable to that of other commercial QKD systems in terms of secret key generation rate, while having fewer components and being easier to integrate into an existing fiber network.

They are working to reduce the size of the detection device and make the system more robust to noise from other lights traveling in the same fiber. The effort to develop a complete and self-contained QKD system has led to the creation of a spin-off company called ThinkQuantum srl, which is working to commercialize this technology.


Article: M Avesani, L. Calderaro, G. Foletto, C. Agnesi, F. Picciariello, F. Santagiustina, A. Scriminich, A. Stanco, F. Vedovato, M. Zahidy, G. Vallone, P. Villoresi, ” Resource-efficient quantum key distribution: a field test in downtown Padua “, Opt. Lett., 46, 12, 2848-2851 (2021). DOI: https: //do /ten.1364 /OL.422890.

About Optical letters

Optical letters offers rapid dissemination of new findings in all areas of optical science with short, original and peer-reviewed papers. Optical letters accepts articles which are remarkable for a substantial part of the optical community. Published by The Optical Society and edited by Editor-in-Chief Miguel Alonso, Institut Fresnel, École Centrale de Marseille and Aix-Marseille University, France, University of Rochester, United States. Optical letters is available online at OSA Publishing.

About the Optical Society

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