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The race to conquer the quantum domain is among the most fiercely competitive in today’s world of technology. One important quantum technology is Quantum key distribution (QKD), that establishes highly secure keys between distant parties by using single photons to transmit each bit of the key. Quantum cryptography is unbreakable by any means — even with a quantum computer. QKD is suitable for use in any key distribution application that has high security requirements including financial transactions, electoral communications, law enforcement, government, and military applications.
The Chinese military and China’s defense industry have taken a keen interest in quantum technology. China is leading in Global Quantum communications race. The Chinese government has created a 1,240-mile QKD-protected link between Beijing and Shanghai. It’s also demonstrated the ability to use QKD to transmit and receive messages from a satellite. China launched the world’s first quantum communications satellite officially known as Quantum Experiments at Space Scale, or QUESS, satellite. This could potentially facilitate super-fast, long-range communications, as well as lead to the creation of unbreakable quantum communication networks.
US and Europe are trying to catch up China in Quantum Communications race. Europe’s economic activities and Europe’s single market is dependent on well-functioning underlying digital infrastructures, services and data integrity, not the least for critical infrastructures like energy, transport, health, finance, etc. Current security of the digital infrastructures and services will soon be under threat of no longer providing long-term security. Confidentiality of data and communications, authentication, as well as the long-term integrity of stored data have to be guaranteed, even in the advent of quantum computers. Introducing Quantum Key Distribution (QKD) in the underlying infrastructure has the potential to maintain end-to-end security in the long-term.
Quantum Communications
QC is about single photons. The information is stored in their quantum states. Generating them is rather easy—pairs of single photons, for example, are generated in nonlinear down-conversion processes where polarization or other properties carry the actual information. Missing a single photon due to losses means losing information. Amplification is not possible, as an individual photon cannot be made more powerful. Copying the photon would mean reading its information, destroying its single quantum state. Detecting single photons is also difficult, as this requires extremely low dark currents. Consequently, the transmission and detection of single photons is quite difficult.
Quantum testbed requirement
Quantum testbed is of the important system to develop and validate quantum communications concepts, software and hardware. The EU is already funding a pilot project on quantum communication infrastructure: OPENQKD, which aims to develop an experimental testbed using Quantum Key Distribution (QKD), an extremely secure form of encryption that has the potential to keep telecommunications, health care, electricity supplies and government services safe from cyber-attacks.
Testbed can demonstrate the feasibility of quantum communication networks. It can Validate quantum network technologies, architectures, protocols, including broader cryptographic services based on QKD infrastructure. It will also be used to test the Interoperability of quantum and classical networks, as well as multi-vendor interoperability. It will also lead to development of standards for QKD components, equipment and protocols.
US loop will serve as a testbed for researchers interested in leveraging the principles of quantum physics to send unhackable information across long distances. Researchers at Argonne and UChicago plan to use the testbed to explore science underlying quantum engineering systems and to harness the properties of quantum entanglement—a phenomenon Albert Einstein famously characterized as “spooky action at a distance.” Quantum entanglement links two (or more) particles so that they are in a shared state—such that whatever happens to one immediately affects the other, no matter how far they have traveled apart.
European OpenQKD testbed
Deutsche Telekom said it is participating in the research of quantum communication technologies via its involvement in OPENQKD consortium (Open European Quantum Key Distribution). The goal of the 38 partners of OPENQKD is to accelerate the development of quantum-safe data transmission. To this end, several test environments are being installed throughout Europe.
In September 2019 the EU launched the EUR 15 million Horizon 2020 project OPENQKD. The findings of this 3-year project will flow directly into the EuroQCI initiative. The AIT-led consortium comprises 38 partners from 9 EU Member States, as well as the UK, Switzerland, Bosnia and Herzegovina, and Israel, consisting of manufacturers, network operators, system integrators, SMEs, research institutions, universities, certification and standardisation bodies, as well as end users, and together covering a broad range of expertise.
Designed to establish a secure quantum communications network in Europe, as well as initiating a European ecosystem for quantum technology providers and application developers, the project will focus on developing a variety of demonstrators and future applications. They will include, amongst others, secure data transmission via telecommunication networks and appropriate storage in cloud infrastructures, the protection of sensitive medical information, official communication data, and the secure transmission of control signals used to operate critical infrastructure (telecommunication networks, energy supply). These activities are intended to protect Europe’s digital data economy against present and future threats, such as those from quantum computers, and to secure Europe’s strategic autonomy in the digital age
The project will create an open QKD testbed to promote network functionality and use-cases to potential end-users and relevant stakeholders from research and industry. Over 25 use-case trials have already been determined and will be complimented by open calls for funding third parties. OPENQKD will develop an innovation ecosystem and training ground as well as helping to grow the technology and solution supply chains for quantum communication technologies and services.
OPENQKD will deploy 40 QKD systems with standardized hardware and software interfaces for network devices and protocols on over 1000km of fiber links, as well as testing compatibility with satellite-based schemes. The OPENQKD network will be used to demonstrate the transparent integration of quantum-safe technologies and solutions broadly across the European digital landscape as well as advancing initiatives for the standardization and certification of QKD-enabled technologies. The work in the OPENQKD testbed should lay the foundations for rolling out a pan-European quantum-safe digital infrastructure, with a solid basis to educate and lead a quantum-aware workforce and with European industry leaders already engaged.
OPENQKD
Europe has called for proposals for Building an experimental platform to test and validate the concept of end-to-end security, providing quantum key distribution as a service. Proposals should develop an open, robust, reliable and fully monitored metropolitan area testbed network (ring or mesh configuration). The aim is to integrate equipment, components, protocols and network technologies with QKD systems and current digital security and communication networks.
The testbed should be modular, to test different components, configurations and approaches from multiple suppliers and benchmark the different approaches against overall performance. The proposed solutions should demonstrate resistance against known hacking techniques, including quantum hacking techniques. The testbed should make use as much as possible of existing network infrastructure (fibres and/or satellites), provide a quantum key exchange rate compatible with concrete application requirements over metropolitan distances (i.e. of at least 40km). The proposed testbed should demonstrate different applications and use cases of QKD (including for authentication), optimizing end-to-end security rather than the security of individual elements.
OPENQKD aims to raise awareness of quantum key distribution in security applications, attracting the end-user by showing them what the technology can do for their business. Other goals of OPENQKD include:
- Demonstrating seamless integration into current networks and security architectures: We want to show that quantum key distribution is a mature technology that can be integrated and installed in existing networks. We will also link the encryption application, so we can demonstrate the full security stack from key generation, to the final application that requires encryption.
- Standardised interfaces for vertical and horizontal interoperability: We will develop an interface so that devices from different manufacturers can work together, for example, the interface for the secure keys. The classical encryption that takes the keys will work with any quantum key distribution device, so the device can be changed without impacting the operation.
- Kick-start a competitive European quantum key distribution industry: We want to increase and build up a full supply chain for quantum communication in the European Union to encourage companies and SMEs to provide, components, software, electronics, and system integration know-how. The medium-term aim is to roll out a full QKD Network all over Europe with QKD devices manufactured in the EU.
- Operation of use-cases deriving from Secure Societies needs: We want to demonstrate that quantum technology can be used in many different industry sectors and ICT applications. In OPENQKD we have more than 30 use cases planned in 16 different locations around Europe. The use-case demonstrations include data centre communication, critical infrastructure protection (power grid and telecom network), e-government, e-health and protection of financial services.
- Quantum experimentation platform: The network installations are open, meaning the interested parties (beyond project partners) can visit them or even participate by bringing in new hardware and/or software.
There are many layers in a quantum key distribution ecosystem starting from research to components, systems, network integration, and up to applications. OPENQKD works more on the higher levels. We use technologically mature systems to demonstrate their security applications. Furthermore, we address the question of how many quantum key distribution links can form an integrated security network. For the lower levels dealing with components and systems, the EU has just launched the Quantum Communication Infrastructure (QCI) initiative.
The QCI has the aim to roll out a full quantum network over Europe in the next ten years. The first phase will be to create a quantum communication network linking Europe’s capitals. For this, many devices will be needed, and we are currently working out a supply chain of European producers to manufacture and assemble quantum key distribution devices. OPENQKD is a pilot project for QCI, concentrating on the deployment levels.
Proposals should include an assessment of the applications and parts of the infrastructure for which the integration of QKD is economically justified, as well as an assessment of the minimal acceptable key rate for each application and its total cost of ownership. Proposals should bring together relevant stakeholders such as telecommunication equipment manufacturers, users, network operators, QKD equipment providers, digital security professionals and scientists. This quantum communication infrastructure will be used for data transit and storage in a highly secure way. It will ultimately link sensitive public and private communication assets all over the EU, such as banks and administrations.
The AIT Austrian Institute of Technology, Austria’s largest applied research organisation, has been running the first European pilot project in the EuroQCI initiative – the Open European Quantum Key Distribution Testbed (OPENQKD) – since September 2019. The project is aimed at deploying quantum encryption to create a secure networked Europe. AIT expertise gained from many years of research will also play a key role in the first European QCI4EU study, which was launched in February 2020. This study aims to specify the user requirements and use cases which will drive development of the EuroQCI in close cooperation with the participating Member States. The findings will then be used to develop an overall system architecture for EuroQCI, composed of space-based and terrestrial solutions which are secure by design and will cover the entire European Union. The aim of EuroQCI is to facilitate the ultra-secure transmission and storage of information and data, and to link critical public communication assets throughout the entire European Union.
In Berlin, the researchers have access to an extensive fiber optic network with IT infrastructure. All types of QKD systems can be tested on it and limitations can be sounded out. At present, their range is limited to around 100 km, as no optical amplifiers can be used. The researchers are interested in how individual QKD systems can be interconnected to form a QKD network. The aim is to protect the management of communication networks and data transmission over them from possible attacks.
In addition to the basic research for the consortium, the scientists also investigate various telecommunication-specific applications. For example, the question is to be answered as to what extent a stable, secure and cost-saving operation of quantum optical communication links in the networks of the Deutsche Telekom is possible. The research also aims to encrypt connections up to the 5G mobile phone network. Finally, a target architecture for QKD key exchange in networks of telecommunication providers has to be developed and implemented.
A test system for quantum communication
In 2019, the German initiative QuNET started to explore and realize secure QC technologies. QuNET is an initiative of the Fraunhofer-Gesellschaft, the German Aerospace Center, and the Max Planck Society, and is funded by the German Federal Ministry of Education and Research (BMBF). The BMBF is currently funding the QuNET initiative with around 60 million euros. A total funding volume of 125 million euros is planned until 2026 as part of the German federal government’s cybersecurity research agenda. The funding targets technology development along the value chain in Germany to enable the industrial production of relevant components and systems, as well as the establishment of secure infrastructure in Germany and Europe.
The Fraunhofer Heinrich Hertz Institute (Fraunhofer HHI; Berlin, Germany) contributes several technologies to the project: photonic integrated circuits (PICs) for the quantum network, expertise in fiber-optic networks, and quantum key distribution. This includes the entire chain, from key functionalities via integrated optical components to real-time-capable systems for fiber-based quantum communication.
A complete quantum communication system has been set up for development and testing of all QC components. It has been built from of-the-shelf components at the Fraunhofer HHI as a test bed for software, protocols, and new components.
One goal within the QuNET project is to develop integrated components for QC based on established technology. The photon source is a strongly attenuated laser on a hybrid PIC . The two small white cubes on the left h the two lasers, being followed by integrated optics such as filter and waveguides for polarization coding on the hybrid PIC module.
It is based on the PolyBoard technology, using an on-chip micro-optical bench where ultrathin-film elements, nonlinear crystals, polymer interposers, and single-photon detectors can be combined on a photonic integrated chip. For QuNET, the systems employ the polarization coded BB84 protocol and other solutions such as time-bin coding using delayed photons.
The receiver part looks quite similar, but with one important difference: A typical source generates 1017 to 1018 photons per second, which are attenuated to single photons at a reasonable rate. Losses are actually created to achieve single-photon operation. On the receiver side, single photons simply arrive. Therefore, the loss budget is much lower than on the transmitter side. The actual receiver is a hybrid PIC receiving its signal through an optical fiber. The photons are sent through polarization filters on the PIC and, finally, counted in sensitive detectors.
The photodiode chips are based on mature indium phosphide (InP) technology and are fabricated in the wafer process line at Fraunhofer HHI, having Telcordia and space-qualified processes. InP components have been designed, produced, and characterized at this institute for more than 35 years.
Optical integration is a key technology that will enable QC to move from the research lab to real life. Researchers at Fraunhofer HHI prepare this transition by introducing established technologies from telecom and semiconductor manufacturing to QC systems. This way, it becomes feasible to apply large-scale industrial processes and develop high-performance components.
On the module level, the researchers use PICs that are based mainly on InP and PolyBoard technology (see Fig. 6). They have designed and manufactured modules for the generation of entangled photons, for the manipulation of QC signals, and for the reception of QC signals. Prototypes of these modules are currently in the test and characterization stages. By the end of 2021, these integrated optical modules will be introduced to the QC system, step by step on a plug-and-play basis.
Integration
The technology of hybrid integration of different photonic functionalities on a single chiplet has been developed in the PolyBoard project. As mentioned before, it uses an on-chip micro-optical bench where active and passive components can be combined on a photonic-integrated chip.
In the QuNET project, this technology will be used to design, manufacture, and characterize a number of different new modules. This includes hybrid integrated receivers for continuous value (CV) and discrete value (DV) quantum key distribution, as well as low-loss passive routing for the distribution of private keys across more than two participants. This hybrid integration approach allows for a combination of optimal material systems for the required functionality, especially with low-loss passive, on-chip waveguiding and efficient photon generation and detection.
Photodetector technologies
The detection of single photons is still difficult. The key to standard single-photon detector approaches is cooling to reduce noise. So far, most quantum detectors must be cooled down to below -200°C. The team at Fraunhofer HHI has set the goal of quasi-room-temperature operation from the very beginning. This is not only a condition for regular field operation—it also leads to much higher lifetimes of the components.
Within the QuNET project, two types of single-photon avalanche diodes (SPADs) are developed. One is the classical approach with top-illuminated SPADs. First preliminary results of the developed vertically illuminated SPAD are demonstrated in Figure 3 for room-temperature operation, showing a clear improvement from the initial design with further potential of improvement to be exploited in the next design iterations. The second SPAD type being developed in QuNET is a waveguide integrated photodiode. This approach has the potential to reduce noise due to smaller photodiode volumes. Furthermore, the waveguide-integrated SPADs allow monolithic integration with passive waveguide components for implementing further signal-processing functionalities.
New quantum loop provides ground testbed for quantum communication technology
Scientists from Argonne National Laboratory and the University of Chicago launched a new testbed for quantum communication experiments from Argonne last week. The quantum loop consists of a pair of connected 26-mile fiber-optic cables that wind circuitously between Argonne to the Illinois Tollway near suburban Bolingbrook and back. At 52 total miles, it is among the longest ground-based quantum communication channels in the country.
“Inaugurating this quantum loop is a significant step for Chicago and the nation in building a large-scale quantum network that can enable secure data transmissions over long distances,” said principal investigator David Awschalom, senior scientist in the Materials Science Division at Argonne, the Liew Family Professor in Molecular Engineering at the University of Chicago and director of the Chicago Quantum Exchange. “The loop will enable us to identify and address challenges in operating a quantum network and can be scaled to test and demonstrate communication across even greater distances to help lay the foundation for a quantum internet.”
Argonne scientists Joe Heremans, Alan Dibos and Gary Wolfowicz, who worked on the quantum loop project, demonstrated the operation of the testbed by generating and transmitting optical pulses through one and then both fiber loops. They witnessed a delay of 200 microseconds for the transit time of the laser pulse along one fiber loop, which is consistent with the speed of light in the glass fiber.
They also began to use the loop for a series of experiments, including transmitting signals from photons emitted from ensembles of ions. These ions can be used as a quantum memory for the network. A functional quantum memory, which entails the storage and retrieval of quantum states, is a key technological advance needed for quantum communication and a quantum internet.
“Quantum testbeds of similar scale exist around the world. But most of them rely on entangled photons – particles of light – to teleport information. Our testbed is unique in that, for the first time, we push towards an all solid-state architecture where trapped quantum particles in solids are used as information carriers,” said Tian Zhong, assistant professor of molecular engineering at University of Chicago and scientist at Argonne, who is a co-principal investigator of the project.
“We will need many of these quantum memories spaced out over about 100 kilometers to relay the quantum signal through a network. The quantum loop enables us to test and refine this quantum memory technology before deploying it in large scale,” said Tian Zhong, scientist in the Nanoscience and Technology Division at Argonne and assistant professor of molecular engineering at the University of Chicago.
“Research leading to science infrastructure such as the quantum loop will ensure that America remains a world leader in this pivotal, rapidly evolving field, which will open up important new avenues of investigation in areas like quantum data transfer and secure communications,” said Department of Energy Under Secretary of Science Paul Dabbar. “We look forward to continued increased support and accomplishment for this and other areas of quantum information science.”
“Performing information teleportation across real-world distances many miles apart allows us to identify practical problems involved in operating a quantum network – what are the technological challenges, how secure is the communication, and what are the limits to transporting information in this manner,” Awschalom said.
“This quantum loop is a significant capability for the scientific communities in quantum physics, communications and computing,” said Paul Kearns, Argonne National Laboratory director. “These experiments demonstrate how Argonne’s world-leading scientists and engineers help ensure U.S. leadership in essential quantum information science.” Argonne’s unique suite of world-class facilities, including the Center for Nanoscale Materials and the Advanced Photon Source—both U.S. Department of Energy Office of Science User Facilities—as well as the Quantum Factory, enable researchers to build and characterize materials and devices for quantum communication. In addition to the quantum loop, Argonne plans to develop a two-way quantum link network with Fermi National Accelerator Laboratory. When the two projects are connected, the quantum link, also supported by the Department of Energy, is expected to be among the longest links in the world to send secure information using quantum physics.
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